The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: BeezaDan on 21.10. 2020 22:47
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My SR (+060 bores, 9:1 pistons, SRM oil pump, SRM billet rods, etc) started to smoke (blue white) really badly.
Before stripping anything down, Checked all the things suggested on this and other forums.
Nothing serious found but did find that the tops of the pistons both sides went from looking normal matt black to wet black and both plugs furry black.
SRM sump plate with removable sump plug installed a while ago so removed plug and about a third of a pint of oil drained out. Fitted magneto cutoff type anti-wet sumping valve.
I have a toolbox mounted cartridge oil filter, also suspect that some oil is seeping back to the sump from that.
I suspected very rich running so moved jet needle down a notch and reduced main jet size.
Didn't help, it just produced weak mix so restored main jet, left needle in new position. Now plugs looking black shiny wet. (Small step forward?).
Still smoking like a steam engine. Decided to take head off, which confirmed piston tops wet with oil.
Checked bores, both showed vertical scoring front and back and also very shiny (like chrome).
Barrels off, both pistons also found to be scored plus signs of over heating around tops, rings looked ok but showing wear. Head gasket showing signs of some cross-cylinder leakage plus slight possible leakage cylinder to push rod tunnel.
Honed out bore scoring and restored both bores to correct honed surface (medium grit stones and oil wash during process), replaced pistons and rings with Gandinis at 8.5:1.
Always thought that 9:1s were perhaps a bit ott for a non-race bike, so 8.5:1s from Fecked seemed a reasonably sensible alternative.
Refurbished head, new valve springs, valves all ok and properly lapped in. Top oil feed banjo bolts looked to have slightly oversized oil holes so replaced with standard bolts.
Engine top end rebuilt (all new gaskets). Oil tank flushed out and filled to line with 'running in oil'.
Dry compression test showing 130psi both sides, repeat as a wet test (WD40 both bores) showing 165psi both sides. (Throttle and air valve both full open).
Noted that oil pressure gauge showing increasing and good pressure during pressure testing.
Good spark both plugs, timing checked and spot on.
Several days of careful work done and wallet empty, tomorrow's 'put some fuel in it and get it started' day.
I'll update you on results, wish me luck.
Hi Greybeard, thanks for the welcome and hello all, Part 2 -
Well, fuel in, started third kick, sounds great and running well, small oil leak from front rocker feed bolt, quick tighten and fixed. Oil pressure rapidly up to 55psi where the oil PRV cut in and dropped it to 50psi.
So far so good but (there it is Greybeard) Unfortunately that's about as good as it got.
Still smoking like a traction engine, - drat!
Had a think and decided to clamp the rocker feed pipe to see if there was any improvement to the smoke situation, Answer no.
Then decided to take the sump plate off add an extension to the sump oil pickup pipe stick the end of that into a jar of oil in a big drip tray and run it again. That showed a lot of combustion blowby (lots of combustion gasses coming out) also huge amounts of oil cascading out.
Conclusions - Clamping the rocker feed pipe probably means that the valve guides are ok.
Blowby and crankcase gasses probably indicating that the bores are now just that bit too big for the new pistons and rings. (Thought I would get away with slightly larger piston to bore clearence and ring gaps, not sure now that it was worth a try).
Volume of oil draining out could mean big end shells need replacement, (SRM oil pump able to push a high volume of oil out through the big ends?)
If crankcase pressure was forcing oil up the bores past the rings not sure why it was still smoking badly when running with the sump plate off, Unless it was residual oil in the combustion chambers.
Looks like another strip down (full this time), replace liners etc, check big ends, and double check everything else.
All very disappointing but lessons learnt and no doubt more to be learnt.
I had an A7 and then A10 GFs back in the 70s, lots of stripdowns in efforts to gain more power (as we did then) and of course as a result of pushing too hard. Never had a single moments problem with the oil systems. Hence this experience being an unwelcome surprise.
Now to start saving up.
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Hi, welcome.
I read all that expecting a BUT at the end. I'll keep fingers crossed for tomorrow. *good3*
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Dan,
My kneejerk reaction would be: "Who are you and where are you from." Nevertheless, welcome to the forum. *welcome* Try to get over to the intros page and, uuh, introduce yourself. Helps keep things friendly.
As for the smokong problem, while I'm not one of to sharpest mechanics on this here forum, I'm going to pose a couple of questions regarding the head rebuild. Whenever a bike is described as being so thoroughly rebuilt as yours, we end up left with little else than having to question that work when a big problem arises. Would we recognize the name of the shop? Is it a certainty that the intake valve guides are a perfect fit in their holes and around the valve stems?
I'm darn near certain others are about to chime in with other potential problems.
Richard L.
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Hi Richard,
Thanks for your comments. I'll do a bit on the intros section at some point, always friendly with those who are friendly back! I am still learning how to use this forum, my objective to share experience, learn from others of like mind and perhaps also to help someone else in the process.
Also agree with you ref always worth questioning the work.
You push the limits, - sometimes you win, sometimes you lose, that's life and learning.
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Hello Dan.
There will be plenty of help along soon enough!
I wouldn't have though there was much wrong with the bores if you're getting 160psi?...... Maybe an engine breather problem, but that's not my best area of knowledge others will know far more than I.
Anyway, off for a think while I eat my tea.
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Have you tried one of those nicotine patches? They're supposed to stop smoking.......
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keep out of low emission zones on your travels.
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hello and *welcome* beezadan have your bores become considerably oval, or you left a bit of lip in and broke new rings *dunno* Gandini rings usually sort everything except covid19 out *sarcastic*
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Hi berger,
From what I have read about the Gandinis you're right. I really thought that they would work their magic and the problem would be gone. Bores could be oval but were checked after honing and were round and consistent size tops to bottoms. Definitely no lip at top or bottom.
I had a thought, if SRM end crank direct oil feed has failed, might explain the amount of oil coming out of the bottom plate when I did the open crankcase running test earlier.
Can't explain why the smoking didn't reduce during that test as there would have been no pressure to force oil up the bores.
Similar question If its oil working down the valve guides, clamping the rocker oil feed pipe should have reduced the smoke.
This is a real puzzle. Going to talk to SRM to see if they have any ideas.
Thanks for the pointers, at this point any constructive ideas are welcome.
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what piston to bore clearance have you ended up with and did you run it long enough with the rocker feed clamped off, mind you it could be anything because mine ran with no oil pressure and no feed to rockers for an age and had loads of piston slap and scoring and deep scoring by a circlip and when I put the oil pipes on the correct way it didn't smoke but it had to be stripped and fully re-furbished [ flat cam and followers plus other horrors ] , except the valve gear which was all good
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After honing ended up with .018 thou piston to bore and ring end gap of .020 thou. Given that I got 165psi on the WD40 wet pressure test I figured that the pistons and rings were probably working fine.
If I had seen low pressure I would have called it a day at that point.
Thinking about possible end crank feed failure, if it has failed the SRM high capacity oil pump must be able to provide 55psi even with the failed end crank feed seal. I don't know if that is possible.
So many questions.............
I think that this is going to end up needing a full stripdown and investigation to find out what's going on, unless anyone else has gone through this and has a diagnosis/solution.
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After honing ended up with .018 thou piston to bore and ring end gap of .020 thou.
*eek* *eek* *eek* with that piston to bore clearance, its nearly out to the next over size *conf2* . might pay to re-check your mesurments. should be around 0.0045 / 0.006"
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Mine are out to almost 0.008" following new rings and still running strong after about 4,000 miles. Not recommending it, but at 0.060 pistons it was worth a shot. Goes through oil, but does not smoke significantly.
I'm shy about acting as if I know for sure the answer to any tricky or mysterious mechanical problem just by description. Nevertheless, I'm pretty sure the explanation here has to include a logic that gets oil into the combustion chamber while the compression is 165 PSI (or even 130). Is there such an explanation that could be attached to a quill feed failure and an empty sump. If there is, I don't know it (among billions of other things I don't know).
Hey, this just occurred to me, and may be completely useless. Are you running some kind of offbeat or specialized oil?
Richard L.
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wow 18thou *eek* were they slapping you in the face, mine were clanging away and hammering themselves at 8thou
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wow 18thou *eek* were they slapping you in the face, mine were clanging away and hammering themselves at 8thou
Bergs,
Not answering for Dan, but since you mention 8 thou and a lot of slapping, makes me wonder if mine are less or yours are more. I don't think mine are hammering.
Richard L.
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hi Richard mine were 8 when they were tinging away nicely but annoyingly , I finished them off on the cadwell run when I put the pipes on the wrong way. it didn't burn any oil when I put them on correctly , strange things happen
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Agree 18 thou skirt clearance is way over the top, and if that's with the new pistons and measured at 90° to the gudgeon (wrist) pin, not good news really. But if the smoke is and 'white and blue' still, and there's lots of it, it does suggest to me that there could be something on the inlet side. Not excluding any of the other possible causes, of course.
I don't know if it's even possible (just thinking on the keyboard really . . .) but could the head have a tiny crack from the inlet tract to the pushrod tunnel, just conceivably?
I pose the question because exactly that caused me months of head scratching on another bike, where there was loadsa smoke everywhere and no obvious cause. Having done all the things you have (with better bores mind you!), and not achieved any real improvement, it turned out oil was being drawn into the inlet tract (which had been ported and polished a bit by a PO), via a pinhole/ crack.
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Just a thunk from me. Might the petrol be the culprit?
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The more I read through this its like the Bermuda Triangle. The mystery is simply explained when all the relevant facts are presented.
We have scored pistons. Was it run without an air filter, scoring from road grit or dirty assembly is par for the course in this case.
Evidence of poor head gasket sealing, as Mr G relates, possible path for oil into unwanted places.
Bores smoothed and worn rings. A consequence of running too rich, the phenomenon of bore wash, more correctly fuel wash, almost neat fuel removing any lubricant from the bore. (Yes GB.)
Oil filter, is it plumbed in before or after the T to the rockers? After the T will send oil back to the motor in preference to the tank and overwhelm the scavenge system.
The result of the pipe in a pot test showed lots of oil coming into the crankcase, how did this compare with the ability to scavenge? An air leak on the pump or blocked/obstructed pipe and pick up valve are possibles. The capacity of the scavenge side should deal with like for like volume on the supply side.
With a piston/bore of almost the next oversize its remarkable it runs at all, the compression rings are working fine a kickstart speeds, but the remedy will be another block rebored correctly to suit your best pistons, certainly cheaper than a resleeve and more new pistons to suit.
I think its a complete tear down and an almost forensic examination of every component. I'm sure the answer will be simple but possibly elusive.
On a lighter note, this may be of use.
https://www.hastingspistonrings.com/tech_tip/fuel-wash-how-to-eliminate-this-potentially-serious-problem/#:~:text=There%20is%20a%20condition%20that,%2C%20pistons
Swarfy.
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greybeard I was thinking has someone sneaked up and poured oil in the petrol tank , it's nearly trick or treat time *evil*
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With a piston/bore of almost the next oversize its remarkable it runs at all, the compression rings are working fine at kickstart speeds...
That's a really interesting point and some next-level thinking (to me, at least).
Richard L.
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Hi All, thanks for your welcomes and useful comments.
Swarfy, thanks for the analysis. You are probably right, (Looks like I didn't get away with it).
It does run really well with not much piston tinging, probably because there's so much oil around in the lower bores. I'll investigate along the lines you highlighted ref oil filter and scavenging etc. Oil filter is in the line before the T. Pick up/scavenge pipe ball valve appears ok, ball is where it should be and free.
Previous owner did run it without an air filter so its possible that the bore & piston scoring I discovered was caused by that. He also had it running far too rich, biggest main jet I have ever seen in an A10! As you said, very effectively washing the bores!
Hoping not to have to reline but at already +.060 if I remember rightly going to +.080 is a probably not a good idea on an A10?
Groily, your idea ref a hidden head crack (expanding as it heats) could be an explaination for the increasing blue white fog. I'll look for cracks during the investigation.
Also changed fuel in case there could be contamination, that would have been a really easy solution, (why is it that life is never that easy!)
My gut feel right now is that this is going to end up being a perfect storm of contributing causes.
Yes, a full stripdown and investigation will be my next course of action.
Our friends in Wales are going into a full lockdown today so my conversation with SRM will probably have to wait. My engine problems are but a drop in the pond compared to what they are having to put up with.
Its great having access to some fresh perspectives, its like the old saying 'when you are up to your a...se in crocs, its easy to forget that your primary objective was to drain the swamp'.
Any more ideas that you can come up with are welcome, I will keep you all updated on any further progress as it happens and as I investigate your ideas on a cause.
Thanks guys,
Dan.
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Hi Dan and Welcome,
I would like to add one more potential issue which happened to me. My rebuilt engine smoked heavily on the LHS pot. After two strip downs, I discovered that the LHS piston was tilted 0.010" to the right. The small end bush had been reamed at an angle. A straight edge across the barrel and a feeler gauge found the problem. Check that both pistons are level within 2-3 thou. Unlikely but worth checking.
Col in Oz
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good lord Col, whatever made you look at something like that, thats a serious stuff up on a new piston....
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surely with those ring gaps and bore clearances, smoking would be inevitable, partic. as you have confirmed huge blowby too.....
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Hi Jules,
I think one of the Forum members suggested it, and to check everything measureable. I cannot find the reference.
I passed both Gudgeon pins through until they touched, and there was about 0.006" misalignment.
After repair, I checked with a length of 19mm bright rod, which was a surprisingly good fit for an 0.75" Gudgeon.
Very pleased to find it!!
Col
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G'day Dan.
With 18 thou in the bore and 20 on the rings *eek*
The WD test will seal for enough kicks to give good comp but not in a running motor. The hole in the left rod is squirting oil on the bore and splash from the right is getting past the piston & rings. Valve guides would also be suspect as it would take a fair while to exhaust all the oil up there after the feed is stopped.
Normally after stopping a motor there would be about 1 cup (250 -300ml) of oil in the sump.
Cheers
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G'day musky,
I think you could be right. Part of the perfect storm I am dealing with is highly likely to be the over bores.
I am getting the liners replaced bored and honed plus pistons fitted by a specialist machine shop.
On further advice from members I am also checking the pump + crank end feed and also the scavenge side of the oil system as well as the small end relative alignment. Big end shells will be checked as well.
If that lot doesn't fix the problem.............I'll think some more...............and set fire to it........
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Hi Dan,
Don't forget to clean the oil tank at least ten times *eek*
From your bikes symptoms it's likely that blasting grit was left inside it by the DPO
John
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CJ. On that basis Dan will have to take advantage of low rate finance and expect scored journals and a restricted flow crank as well.
One thing's for sure, there won't be many restful nights until the damn thing is down to the metaphorical molecules. Like I said, the Bermuda Triangle, but a good thought there that I had overlooked, we don't really know the full history and without that we can only speculate the causes of the problem.
From earlier comments the timing bush may have excessive radial clearance now, and too much oil is being dumped into the crankcase. Worth checking the lift of the crank in that bush. Like CJ I'm thinking possible abrasive destruction on a grand scale. Hope I'm wrong.
Swarfy.
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Good points Swarfy,
Will check absolutely everything. Now have your points on a list that's getting longer every day.
Cheers,
Dan,
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Hello All,
Hope you're all ok in these troubling times.
Well, Engine now stripped and forensic investigation (to date) completed.
Confirmed - A previous owner had had a full bottom end and barrels Rebuild done by SRM, new high capacity pump, SRM piston type PRV, end feed crank, s'trap cleaned and hex plugs fitted, dynamic crank balancing, SRM roller+ball timing side bearing conversion, billet rods, barrels blasted and stove enamelled, bores taken out to +.060, new SRM cam and followers etc, - lovely job.
Recap on earlier issue and actions - Engine smoking very badly so top end stripdown - Bores found badly scored so honed true and new pistons + rings fitted. Head cleaned and checked, valves re-seated, new SRM tappets.
Top end rebuilt. (Honing took bores to just beyond limit for +.060s and rings, my decision to try it).
Static test run confirmed still smoking, possible problem with oil scavenge/return side.
Latest Findings - Big end shells badly worn and scored with excessive clearence. Some debris in the sludge trap.
Detailed checks on:- Cam, cam bushes, followers, rods, bottom end bearings, crank bearing journals oil pump, PRV, - Show all are ok.
Crank big end journals showing some surface scoring.
Conclusion - Superb bottom end and barrels rebuild by SRM ruined, most likely by subsequent use of detergent 20w 50 or similar oil (guy I bought it from said that he was using modern 20/50 in it), and running it without first cleaning out the oil tank, that's the kicker.
Thank heavens previous owner didn't use it much and that I thoroughly cleaned out the oil tank when I got the bike, plus its fitted with a cartridge oil filter, which limited the damage.
Now to thoroughly clean out or replace the oil lines and all of the oil galleries. Replace valve guides, replace all oil seals, get the bores sorted properly, clean out the oil tank (again), re-check everthing and then rebuild.
Will take time to get all of this done, so next instalment will be a while away. Great how all of the old A10 experience has come back, helped a lot by your suggestions and ideas.
Thanks and stay safe guys,
Dan.
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I'm confused Dan, I thought the smoking issue was worked out to be due to the bore/piston sizing and scoring of the bores, is that the case? if so, then the teardown was to check everything else was ok because you had to fix the bores and piston issue anyway...is that right?
It sounds like whoever did the work previously wasted the effort by not thoroughly cleaning out after the machining, rather than "just" not cleaning out the oil tank, particularly if there is a cartridge oil filter in the supply side too, that should trap anything from the tank...
I'm also unsure why you would blame the oil for this, a good quality 20-50 with detergent scavenging in conjunction with the cartridge filter, should by all accounts be a very effective oil supply, I would have thought....
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Would be most surprised if just some crud in the oil tank would do that. I would look elsewhere.
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Hi Both,
Not blaming modern oils at all, they are excellent for engines designed with them in mind and having modern oil filters. They do the job slightly differently to 'mono' non-detergent oils (also excellent) where contaminant debris is concerned. Modern oils with detergent additives tend to break up and 'release' lumps of crud which would then be dispersed into the oil flow allowing a cartridge or other oil filter to catch it all.
In this case the crud in the oil tank may have been happily sitting there minding its own business until the addition of modern detergent additive oil did the job its designed to do and released it. That release would have been directly from the oil in the tank into the oil feed to the pump and then the main bearings and the inside of the crank case. (My cartridge oil filter sits on the return oil path to the tank, so would not have caught this debris before it got to the pump and mains).
Where max effect/damage would be inevitable. This would explain why the mains have been so badly affected. That accelerated wear then increased the clearence between the big end shells and the crank journals which then allowed the fantastic SRM high capacity pump to deliver masses of extra oil into the bottom end. That extra oil with its load of bits of crud scoring the bores and overwhelming the piston rings and causing the excessive smoking issue.
This is what I believe has occurred this time and if I am right it really reinforces the importance of cleaning out the oil tank thoroughly.
Anyone agree?
Cheers,
Dan.
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just my two penneth, I had some cases soda blasted a while ago and decided to use a syringe to blast petrol through the oil ways, then blast compressed air through them. this was done until the petrol was coming out clean. after that I remembered someone mention the crud that hides behind the plugs that are used to cap off the drillings so carefully drilled them out. the one above the prv was hiding loads of crap that run out on the drill bit and could be drawn out into the oil when the bike was in use. so I got some small diameter long cleaning brushes and found loads more crud removed from these oil ways. I didn't drill out the one below the timing gears with the little spray hole next to it because it is a bit difficult but the others were all drilled out , oil ways cleaned and new plugs made . I tapped the holes and made small threaded ally plugs which will be screwed in with Loctite . I am glad I found all the hidden crud!
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Dan - agree with your detergent / non detergent analysis. Something I've been banging on about for years. And it's not simply an opinion, I've seen old engines destroyed in a matter of hours by filling with modern oil. As you say, a high detergent oil keeps dirt (most of it abrasive) in suspension, where it then gets trapped by the oil filter before reaching the engine - in a modern engine. In our old engines, a high deteregent gives a double whammy - it also dislodges the crud lying around the oil tank and engine and, as you say, this abrasive mix is then circulated around the engine until something wears out. Old non-detergent oils were designed to let the crud sediment out, where it could be extracted at intervals (my old Riley car handbook recommends dropping the sump every 10,000m to clean out sludge).
The answer is to always use an oil the engine was designed for. The older ones (like ours) often have minimal or no filtration - certainly not pre-flow and are not suitable for modern oils. Nor are they suitable for the viscosity modern engines use - nowadays as low as 5.
Horses for courses as they say.
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Superb bottom end and barrels rebuild by SRM
How do you know?
Don’t let your assumption about “death by detergent” blind you to other possibilities.
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Hi TT,
Well, when you have taken everything apart, inspected it all thoroughly, looked at the history and the evidence, taken advice from others who know the subject and applied it, what's left is likely to be the answer.
Very interested in what you think the cause of the smoking is, What's your diagnosis?
Cheers,
Dan.
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Hi berger,
Yes, I have gone through the plugs as you did. I didn't find much crud behind them though. Probably because there wouldn't have been enough time for it to build up too much and I used a very good solvent pressure fed through the oil ways. I certainly found the worn off white metal from the big end shells, very sparkly solvent!
Thanks again for your input, I might not have thought of that one.
I will be continuing to inspect and clean until I am 100% sure that every part is crud free before I start the rebuild.
Cheers,
Dan.
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A couple of observations on this which readers may or may not agree with!
1. Having a main bearing and/or big ends with excessive clearance does not necessarily increase the flow of oil into the crankcase, the pump (in theory) will pretty much pump the same volume regardless of the resistance to flow, the scavenge side will ALWAYS be able to pump more than the supply side, so as long as a high percentage of the scavenge side oil gets returned to the tank then there will be build up of oil in the cases (so this means only a little return oil must go to the rockers, and the scavenge side pick up pipe must not have leaks).
2. Particles bigger than the bearing clearance won’t pass through bearings and cause scoring of the surfaces, so in the case of big ends particles bigger than (say) 0015” will stay in the sludge trap. This begs the question of how does scoring from dirty oil occur, and my guess on that is, after the clearance has increased for another reason, and then is big enough enough to let larger particles through. Scoring can also be caused by the break up of the bearing surface if course.
As to whats happened to this engine? Pretty clearly it smoked due to barrel wear, how many miles has it been since it was rebored? The big end wear sounds more likely to be oil starvation than dirty oil, so I would check the end feed is as it should be (and of course there is always the possibility the PO had a valve in the supply side to stop wet sumping and forgot to turn it on once *problem*).
Just my 2 cents worth!
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Hi KiwiGF,
Thanks for your ideas, appreciated.
The test I did by doing a quick engine run with the sump plate off (see earlier post) confirmed that a serious amount of oil was ending up in the crank case. Certainly more than was being pumped back to the tank. As you say the end feed has to be a suspect as well as the scavenge/return side. So I will be replacing the end feed seal and checking the return path carefully pre rebuild.
Its very evident that the SRM high capacity pump is capable of flowing as much oil as the clearences around the engine will allow.
Agree that debris bigger than clearences won't get through but as the clearences wear bigger more crud will find its way past, slowly increasing the clearances, - a vicious circle. Given my findings of debris during the parts cleaning process, it was definitely getting past the big end shells. (Yes, they are completely shot and were adding to the crud).
I did find some crud in the sludge trap but not much, probably the detergents in the oil carrying most of it onwards and back to the oil fiter on the return side.
Also agree that barrel wear is one of the main causes for the smoking, exacerbated by the abnormal amount of oil in the crank cases from end feed seal and/or the big ends.
As I said in an earlier post, this looks like a 'perfect storm' of several contributing factors.
One thing is for sure, as a direct result of this experience, I am going to know a heck of a lot more about the A10 engine, what does and doesn't suit it and how it really works than I thought I did.
Cheers,
Dan.
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I have said this before but here we go.
The last A65 and Triumph engines in the 70s were specified for 20/50 multigrade oils.
These engines are virtually the same as our older engines.
If everything is cleaned properly I see no issues with using these oils.
I have been using them for many years now with no problems.
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I love sawing into paper filters and having a look what's in there, very satisfying - nearly as good as plain chocolate biscuits quickly dipped in a cup of tea *whistle*
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Hi Dan,
Do not forget to dismantle the pressure relief valve, Any debris can jam them open and it's all downhill from there *eek*
John
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Hi KiwiGF,
Thanks for your ideas, appreciated.
The test I did by doing a quick engine run with the sump plate off (see earlier post) confirmed that a serious amount of oil was ending up in the crank case. Certainly more than was being pumped back to the tank. As you say the end feed has to be a suspect as well as the scavenge/return side. So I will be replacing the end feed seal and checking the return path carefully pre rebuild.
Its very evident that the SRM high capacity pump is capable of flowing as much oil as the clearences around the engine will allow.
Agree that debris bigger than clearences won't get through but as the clearences wear bigger more crud will find its way past, slowly increasing the clearances, - a vicious circle. Given my findings of debris during the parts cleaning process, it was definitely getting past the big end shells. (Yes, they are completely shot and were adding to the crud).
I did find some crud in the sludge trap but not much, probably the detergents in the oil carrying most of it onwards and back to the oil fiter on the return side.
Also agree that barrel wear is one of the main causes for the smoking, exacerbated by the abnormal amount of oil in the crank cases from end feed seal and/or the big ends.
As I said in an earlier post, this looks like a 'perfect storm' of several contributing factors.
One thing is for sure, as a direct result of this experience, I am going to know a heck of a lot more about the A10 engine, what does and doesn't suit it and how it really works than I thought I did.
Cheers,
Dan.
I did read the earlier post about the oil return test you did and I am still wondering if you MIGHT have drawn the wrong conclusion (probably not so please forgive me if so).
All the oil from the supply side of the pump ends up in the crankcase, either by passing through the big ends or pressure release valve. The volume of oil going into the sump CANNOT exceed the volume pumped through the supply side. “In theory” the geared pump is pretty much a constant volume pump at any given speed, in that the gears will drive a given volume at a given speed regardless of the pressure in the supply side, some oil will “bypass” or leak past the pumps gears but not much.
I very much doubt the volume of oil pumped through the supply side is affected much by the big end clearance, but I do not have facts to back that statement up. The oil pressure drops right down when the oil is hot and the PRV then has no job to do, it basically is a safety valve that only operates when the oil is cold (from what I have read elsewhere, I don’t have a gauge ).
The pump is if course in effect two pumps, one pair of gears for the supply and one pair for the scavenge, both driven at the same speed, the scavenge gears are wider than the supply gears so they pump more oil at a given speed.
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Hi again KiwiGF and All,
Yes, agree with your statement KiwiGF that the whole flow from the oil pump ends up in the crank case.
Following my forensic investigation of the stripped engine and thoughts from knowledgeable forum members, it might help general understanding on why my engine (and maybe others) is smoking badly if try to put my thoughts another way.
For a crank end feed oil system on an engine operating perfectly and fed with whatever type/ grade oil you choose to use -
The initial high pressure flow from the oil pump goes only to the crank, which means that the crank end feed oil seal has to deal with a potential momentary pressure of up to 100psi.
(Just for info - The SRM crank end feed seal is rated at 100psi, any pressure above this risks popping the seal. Reference article in Classic Motorcycle Mechanics mag by Brian Woolley of CMM and Steve McFarlane of SRM).
There is a little back pressure on the pump at that point so the oil flow won't be to the full capability of the oil pump.
So lets call that initial full high pressure oil flow 'X'.
Then very quickly the PRV operates to reduce pressure going to the crank end feed and then to the big end shell bearings, it opens to take part of the oil flow from the pump through a bypass route that feeds the timing gears and ends up delivering the excess oil to the camshaft trough where it is thrown around the crank and timing cases by the cam shaft and the timing gears.
Lets call that flow 'X2'.
The main flow from the oil pump runs through the crankshaft end feed route to the big end shell bearings. That oil is thrown vigorously around in the crank case and into the lower cylinder bores. (No problem if the piston and piston ring clearances are to specification and operating correctly).
Lets call that flow 'X1'.
So flows X1 + X2 = X (the whole output from the pump less a small amount of back pressure caused by keeping the PRV open and the main bearing shell clearances). All of the oil flow ends up in the crank case as you rightly said.
Now lets consider the same scenario in an engine suffering worn cylinder bores, excessive main bearing wear resulting in large main bearing shell clearances, and a possibly a part blocked return line back to the oil tank -
Total oil pump output of high pressure oil flow 'X' happens as above.
The PRV operates to reduce pressure via flow X2 as above.
Flow X1 to the crank end feed and then the big end shell bearings operates as above.
Now the X1 flow is dramatically increased due to the excessively worn big end shell bearing clearances, (which in respect of oil flow are not operating correctly due to excessive wear).
The X1 flow ends up venting out of the big end shell bearings at an increased rate dictated by the capability of the oil pump, and in the case of a high capacity SRM pump at a significantly higher rate. The big end shell bearings are being rotated at high speed, throwing a much increased volume of oil around the crank case and into the bottom of the worn cylinder bores,
The X2 flow is decreased proportionally and still ends up in the crank case and being thrown around by the cam shaft and timing gears.
So we still have oil pump total flow 'X' as before but subject to modified conditions.
If the oil scavenge return to the oil tank is also part blocked the amount of oil ending up in the crank case and being thrown up into the worn bores would very quickly overwhelm the ability of the pistons and piston rings to control it from ending up in the combustion chambers resulting in a badly smoking engine.
So in my view, fixing the worn big end bearing shells and checking the scavenge/return oil flow path to the oil tank are the two main objectives for sorting the problem. Of course, if the bores, pistons and piston rings are excessively worn the engine will still smoke a bit but a lot less oil being thrown into the lower bores means potentially a lot less oil getting past the piston rings and into the combustion chambers.
Oils thinner by grade or made thinner by heating would also exacerbate the problem.
I am fixing it all, so unless I have missed something I expect to achieve a smokeless A10 once its rebuilt and run-in.
Sorry for the novel but it might help someone else with a badly smoking A10 to stay sane, or even prevent them from setting fire to the thing.
Of course, if I end up with a still smoking A10 I'll be cremating it for posterity as soon as
I get out of the funny farm.
Cheers All,
Dan.
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If pistons / bores are in good nick, extra oil flung to the bores from the big ends shouldn't make much difference.
A certain model of engine I used to frequently work on in the 70's / 80's had three variants as regards this issue. Early ones had no con-rod drilling to lubricate the cylinder walls. Later models did, whilst the high-horsepower ones had a 2nd oil pump delivering 10galls / min at 60psi to the piston undersides via a spray rail. None smoked more than the other in this regard. Some did, but for other reasons - eg .005" over-bore to prevent seizure on uprated engines, white smoke when idling due to low compression ratio, etc.
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well i'll just have another gulp of gravy and a big drag of me fag. when you say you had 18thou piston to bore clearance and 20thou ring gap it wouldn't matter if you only had drip feed or shell and BP were pumping oil in off a rig. those bores are gunna smoke like an ageing hippy. I know I am one *grins*
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Unless the PRV is totally seized shut, the crank seal will never see 100 psi momentarily or otherwise.
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No discussion (yet) about the cartridge oil filter, I agree that the scavenge side needs a good hard look, particularly as you mentioned that the filter is on the return (low pressure) side - with the amount of crud that you talk about its quite possible that the filter was blocked and quite quickly too, I'm sure its capacity is quite small....
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Anyone remember the original BMC Mini? A gearbox full of engine oil directly under a longstroke engine. Can't remember a baffle plate above the gears, but when new I never remember constantly topping the oil or much blue smoke until the valve guides wore.
interesting thoughts there by Dan, in essence a difference of where the majority of the oil ends up, but as RD notes, the bore and rings in good condition would cope with this liberal volume, as in the Mini.
My guess is it's a combination of almost all the lubrication and wear problems these engines can suffer all mixed, jumbled and stirred, but I can see Sherlock Dan is very firmly on the case. Once cleaned out, I'd ditch the filter short term as like Jules I reckon the scavenge side is a major factor in this problem.
Swarfy.
Additional. Nice to see Bergs sticking to a healthy lifestyle........
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I have not bought an SRM pump but from what I have been told is that the gears are 35% wider so it pumps 35% more oil, so, at a given resistance to flow, the pressure will be a bit higher.
The A65 pumps also have the 35% wider gears, and I have one fitted to my A10.
Just my opinion but I don’t see how having a greater flow from a pump could make an engine smoke, and I don’t see it having worn big ends causing it to smoke either, the oil flow past the shells won’t change much with larger than service limit clearances. The big ends will knock when they have just a few thou clearance. From memory the big end ovality service limit is 002”?
A leak in the scavenge system could cause a build up of oil level in the cases, but I have heard of engines missing the scavenge pipe, that worked perfectly ok *dunno* (the oil just rises to to the hole where the scavenge pipe fits, maybe a safety feature).
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Shows the SRM pump internals below. Also has dowled body and O ring seal between the worm and body.
With the end feed it is very important that the seal and quil are not damaged. My experience with a (unknown at the time) damaged seal was that after draining the sump and within a short time of starting a lot oil was blown from the breather then a few miles after that the blow stopped. Careful examination of the seal revealed a split. Replaced the seal and the blow from breather had stopped and things back to normal. So it seems that the scavemge side was temporarily overwhelmed due to seal damage.
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Hi Julian and All,
Recently myself and another member on here were chasing round and round for a reason why his newly built engine was blowing oil out the breather *????*
Eventually I discovered that oil was leaking at the crank end feed in the timing cover
I reasoned that it's the gear train up to the breather is carrying the oil up to the top hat and then out the breather outlet
We had gone through everything else several times including bypassing the return filter and removing the sump magnet to no avail, I had an endfeed cover from a project to hand, fitted that and problem solved *smile*
John
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before I re seated the little ball in the crankcase and fitted the srm pump mine wet itself to the point where it ended up all over the floor and blew past the mag seal, while it was doing this it never chucked any smoke out {an example of swarfy's mini mention } and pretty quickly there were bubbles in the return flow, that with a 60 year old bsa pump. I still say dans problem was the pistons , rings and bores.
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before I re seated the little ball in the crankcase and fitted the srm pump mine wet itself to the point where it ended up all over the floor and blew past the mag seal, while it was doing this it never chucked any smoke out {an example of swarfy's mini mention } and pretty quickly there were bubbles in the return flow, that with a 60 year old bsa pump. I still say dans problem was the pistons , rings and bores.
Yep, I don’t use my GF that often, after a month of non-use the level in the tank will have gone down 2”, maybe 4”, I don’t get smoke, or oil leaking from the breather on starting. It’s done 9000 miles since the bores were honed to remove scores and new JP pistons and rings fitted so you can’t say the bores are new!
The big ends being worn on Beezerdan’s bike is a concern if it has not done many miles (do we know how many?), and if the big ends are worn but it’s got good oil pressure when hot that would be a puzzle.
A mate took down his GF engine at 30k miles after a rebuild with std main bearing bush, no discernible wear anywhere except the cams and followers which he hadn’t replaced during the rebuild.
Another mate has an A65 hornet with roller conversion, might not be by SRM he bought it like that, he stripped it down after he had done 100k miles and is replacing shells and mains and rings as a precaution, no discernible wear seen in the bottom end. He is not gentle with the hornets engine either!