Oil leak at head joint

[groily]

After a vigorous 120 miles today, the A10 displayed some uncharacteristic signs of disapproval . . . smears of oil all the way round the (iron) head/barrel joint, with a modest spattering of drops round the carb, mag, battery tray etc . . .
I suppose an on-the-way-out head gasket is the culprit. But for the life of me I fail to understand where oil can come from on a motor which has a separate oil feed to the rockers and no drillings - or am I wrong? - from barrel to head via the gasket. No loss of compression, no starting problems, no loss of performance, no smoke. Oil consumption is negligible and the engine is not breathing any more heavily than normal, which is not much. It's not from the rocker boxes - they're oil tight all round and the upper fins of the head are dry. It does seem to start from the front, or be an all-round thing, as no upper barrel fin or lower head fin or part thereof is oil-free. The accessible head nuts/bolts are tight but I'll have a better look tomorrow. Used as I am to oil leaks, and usually not too concerned as it's pretty obvious what's amiss and why, this one  is disconcerting because of where it is even though the quantities coming out are tiny. While entirely happy to pull it apart to have a good look-see and fix it,  would appreciate any war stories of a similar ilk! Groily

[RichardL]

Groily,

I'm just going to spew some thoughts, for what they're worth.

It's hard to imagine the oil eminating from the front of the head/barrell joint, as the gravity drain from the rockers is toward the rear. Assuming the oil is seeping out the rear, I think it not impossible for it to work its way around to the front. I think the air at the rear of the barrells would be turbulent and capable of goosing leakage toward the front. It could probabaly be helped to move by the heat of the top fin making the oil quite thin there. Other than the entrance to the exhaust pipe, I would guess that this is the hottest spot on the engine, certainly hotter than anywhere that oil is supposed to normally live. You say no loss of compression, that does take away the most obvious source for driving oil past the gasket. I wonder if there is some marginal loss of compression. Let's say there isn't, going back to the breather topic, the pressure could come from the downstroke of the pistons (with the breather being open midstroke on the downstroke, as I have observed). Another possibility might be pressure passed the exhuaust valve guides. Bad guides there would not bring on blue smoke at the exhaust (I am prettry sure). Another remnant of a thought from one of our previous threads relates to early head bolts breaking at the weak point at the junction of thread and shank. The correction being reduced shank diameter to take the stretching during tightening. Having tested the readily accessible head bolts, you still have three chances to find one that is loose or broken (assuming you have a one-piece rocker box), and all three of these surround your potential source of leaking oil.

Well, having said this much, I now have more possibilites that are likely to be wrong than right, even if one of them is actually  right.

Happy wrenching,

Richard
 

[groily]

Very thoughtful Richard and much appreciated. The idea that the turbulence makes the oil spread round sounds very right. There appears to be a tad more oil at the back left of the thing - adjacent to the big hole through which the pushrods run . . . ergo I hope to find something interesting later on this morning! I can't say there is NO marginal loss of compression because I haven't measured it and don't know what I started with anyway! Exhaust valve guides, I think probably not, but breathing trouble is always a possibility I guess. I shall report back! Groily

[bsa-bill]

Sorry guys but you are overlooking something here   
There is a drain at the front of the rockers, goes through the head at the base of the Ex valves then down through the barrels.
Look at an old gasket you will see the holes very near the central head bolt holes.
When I restored my first A10 I noticed these holes were almost completely blocked, I cleaned them out with a small round flexable file.
I have often wondered if these being blocked leads to people fitting breathers to their rockers, there is after all plenty room for pressure to get back to the crankcase if all is well.
Don't know if this has a bearing on your oil leak though

All the best - Bill

[groily]

Thanks both - and what Bill says is right and v useful to know - not my particular problem though . . .
Took rockers etc off this am to be able to get to all head bolts and get torque wrench on there to do proper checks after quick one with open-enders yesterday. . . found all bolts were slacker than I'd do 'em - probably 22-ish ft lbs, and that the ones you can't get to from the outside were about 15. Problem diagnosed therefore, but I thought before taking the head off I'd just test tighten the bolts to see whether they'd go up nicely as one one bolt just didn't feel good at all (and the long rocker cover bolts were horrible too - but with recoverable threads luckily in the head). Taking them all up 2 ft/lbs at a time, the said bolt failed at 26ft/lbs. Extracting all and looking at them was interesting. I thought all these were meant to be 3/8 BSF. Their heads - which surprised me yesterday, were all 9/16ths AF or maybe 14mm even, hard to say with some of them. But, weirdly and luckily, 3/8 by 20 and probably even 55 degrees. - all the way up to the heads (which I find very strange). Bad start. Most of them look like something you'd get from the local ironmonger to hang something on a garden fence . . .oh, and complete with hacksaw marks where they've been cut to length - except the one with the extra washers. Hell's Bells. Who puts these things together and then finds some fool to buy them I wonder! Just hope he didn't put the crank in too.

So, as ever, a new set of issues to amuse this afternoon . . . how to recover the thread(s) in the cylinder barrel. Can't do usual dodge and make stepped studs to screw into one-size-bigger threads in the cylinder, and use nuts on top, cos the head won't go over them without taking the darn engine out (probably anyway). Last resort maybe, but what a pain. Don't want to enlarge the hole(s) through the head much, to take bigger, say 7/16th, bolt(s), but could if I have to for just one or two I suppose. And I worry about making serious beyond-helicoil thread inserts cos of the lack of meat on the barrels . . . Hmmm. All grist to the mill! Memo to self: kill all bodgers on sight. This'll be the same bloke who so assembled the gearbox that the top gear dogs barely engaged because he'd hammered the sleeve gear bushes through from the clutch side because he couldn't get THAT to go together properly. Lord spare us from all such folk. Ah well, there'll be a happy ending . . .Groily.

[RichardL]

Bill,

Thanks for the correction. Before I wrote Groily, I went right for the picture of the barrels and failed to observe the two holes that are obvioulsy not head-bolt holes. Adding to my embarassment of missing the obvious, there needs to be a way for oil to drain from the exhaust side without turning the guides into submariners. So, in a pure case of rationalization, I guess I got so caught-up in my idea about how oil gets from the rear to the front (at the joint) that the front holes became invisible.

Groily,

Regardless of my folly, it seems reasonable to think that the oil was, indeed, getting out from the backside, considering the looseness and problems with bolts under the rocker covers. Though, eminating from the front, or both, does not seem to be ruled out. At this point, it probabaly doesn't matter, because the head is going to come off, if it is not already.

I didn't quite understand why original-thread helicoil is not the answer. Also, assuming there is meat, could double helicoils be used? I am curious to know if this is workable. I have thought of doing it myself (for other purposes), but havent heard from anyone with experience.

Richard

 

[bsa-bill]

I think I would go for helicoil, three mates had Shooting Stars in the sixties , all of them had helicoiled spark plug holes in there alloyheads so you would think if they can stand the pressure in that position in alloy they should work well in cast.
Right back to the shed, putting the gearbox together, biggest problem is this project is taking so long I keep forgetting where I put stuff
(like the screw that holds the inner cover on ) - did I keep the old one or did I buy new one - can't remember

All the best - Bill

[groily]

Hi Richard,
Yes those holes are there and there for a reason, as Bill and you say. The suboleagine valve would be a messy thing! Yup, the head's off, the bolts are all rubbish (bar one - the short one at the rear above the inlet manifold - which is as maker intended) but the bores are very good, the valves look new, the rockers are in good shape apart from a lot of wear on the tappet adjuster screws which I'll replace while I'm here, and the only prob was going to be the thread in the barrels . . . however, have spent a happy hour since lunch picking out the stripped bits of bolt with a scribe and cleaning things up to see what the true state of affairs is, and I'm pleased to say that after running a bottom tap down a few times it's passable. Not like new, but no worse than 2 or 3 of the other threads in what is a 50 year old object. It easily took 30 ft/lbs on test with a decent bolt from the box, so I am spared having to be too inventive. As to helicoils, I don't know either. Engineer friends of mine have told me in the past that for these sorts of applications they are too marginal and one needs a more substantial sort of insert - but frankly I just don't know and maybe they didn't either. Helicoils may be more than up to the job, as Bill says in his latest, but have to say there's a lot more thread area in a plug thread, to take rather less torque. What I had decided to do as the least of the evils if I absolutely had to was to take the thread out to the smallest size up in whatever thread form, yes even metric if it would save me some metal, and ease out that one hole through the head enough to take the oversize. Didn't want to as it would have meant lifting the barrels to get them on the miller to be sure of a vertical hole and thread, as well as weakening the castings - and now am not going to have to. Did this a year or too ago on an old car's cylinder head using a turned down Jaguar big end bolt, and it works a treat. Downside is you get one weird fastener, but at least I know why it's there!
As to where the oil was coming from, hard to be specific. Back left adjacent to the pushrod hole - your theory - for sure, and from front centre too, between Bill's oil holes, I think, but it's academic now. With any luck I'll have a new gasket set, some proper bolts and some new tappet adjusters by the end of the week and all will be back to normal in no time. BTW, are the bolt heads meant to be as per standard 3/8 BSF or did BSA for some reason use a hybrid AF head on a BSF threaded bolt? And where on earth did the bloke that put this together get the weird bolts he used? I've never seen such a thing barring a few hybrids I've had to make from time to time for reasons not dissimilar to today's problem. Anyway, ta v much to self and Bill for your advice and thoughts, much appreciated. Just hope the loony hasn't done something even more horrible further down the engine! Time will tell. Groily

[RichardL]

Groily,

I learn more about my A10 from trying to answer questions on this forum (not always correctly) than I would any other way. 

First, in two or three previous posts, I failed to point out that the diameter of the shank on headbolts was reduced when alloy heads were adopted, due to the greater coefficient of expansion for aluminum vs. cast iron. I have attached, below, part of the story that led me to this (from Roland Pike).

Regarding the Whitworth size for the head bolts, according to the link at the bottom of this post. Whitworth heads are not to be greater than 1.75 x shank diameter. As I measure it, the reduced shank diameter is 0.311", leading to an allowable across-the flats of 0.544". The across-the-flats of my head bolts is 0.525", for use with the 1/4W socket. How this works out for actual 1/4" bolts, I don't understand (yet), though the article says it's nearly spot on.

Assuming the offending bolt is actully BSF, and not something forced into the hole, it looks like such a thing could be bought at britishfasteners.com.

Richard



The follwoing (about head-bolt shank diameter) is quoted from Roland Pike as found at http://www.restorenik.com/daytona/RP_chp_22.htm:

After a year we had improved the port configuration and it ran so much better with one big carb that the twin carb option was dropped. We had found it useful to measure the capacity of the inlet ports and check on performance, about 142 to 150cc's gave optimum results. If an engine was down for power we often found the ports undersize.  Like all aluminium cylinder heads, these expanded a lot with heads and at the outset we experienced stretched or broken head bolts. These bolts went downwards through the head into the iron cylinder block and would usually break at the root of the last thread, which was the weakest point because it took all the stretching. To overcome this we quite simply put the bolts in a lathe and reducing the diameter of the pIain portion to 10% less than the diameter of the root of the thread. This meant that the thread was no longer the weakest point and that the plain portion could stretch without exceeding its elastic limit.

This was completely successful on the first attempt and no more trouble was experienced with the bolts. They could stretch when the head expanded and return to their original length as the head cooled own. When the new twins were going into production however, Alan Jones who was Works Manager at that time phoned me to say they were unable to make the head bolt as needed, despite my pointing out that we bad found them necessary, he just continued to say they were unable to make them. I went on with my work and forgot about the matter, but I did not have to wait long, within a few hours the motor cycle test shop foreman was on the phone to me complaining the head bolts of the new twins were breaking right and left, so I referred him to Alan Jones.  Mr Jones reiterated they were unable to make the bolts we had designed. Prior to this last call I had taken the precaution of calling the drawing office to say that Jones would not follow their drawings of the bolt thus securing an ally. Alan Jones got no sympathy when he had to pull all the bikes concerned back, dismantle the engines and use the bolt we had specified.

The following is copied from: http://www.enginehistory.org/british_fasteners.htm

Bill Allan adds "It should also be stated that some of the early nuts would have been machined from round stock, with an integral washer, so round bar stock sizes would have been involved in calculations. One other problem is that the original Whitworth heads (AF) were too large relative to the actual bolt shank, (that's why spanners/wrenches are the length/size they are: so you can't apply to much torque. In the first part of the 20th Century, the head sizes were reduced to the size one below. (British Standards specify that the AF measurement of any bolt not be greater than 1.75 that of the shank: 1/4 inch Whitworth is almost bang on the button) This causes even more problems when you need replacement Whitworth fasteners, for machinery over a 100 years old. It's also the reason why some old spanners/wrenches have two Whitworth numbers on them."

 

[groily]

It's all great stuff Richard. A life without torque wrenches and trying to make the bolt-heads just the right size for the sort of length of tool that's going to be applied to it! But it was like that, my old Dad used to regale us kids with it all the time. Not to mention trying to achieve reasonable economy of stock in making all these things - imagine using round bar and having to make hexes (I do it all the time, but not for a living thanks be!). Anyway, on an A10 there are limitations beyond the straightforward engineering ones - look at the lack of room to get a spanner on some of these fasteners! I had to use 3/8th drive tools to get the head off this morning - when I last had one of these bikes in the early 70s it was box spanners . . . often with an open ender applied badly to the 'other' end when the tommy bars bent! Something to be said for progress after all. Whatever, certainly shan't be going to the web link for more of the same sorts of weirdo non-bolts! Time for wine and dead animals, the metal bits can wait till tomorrow . . . Groily

[groily]

I do live there Richard and the appetit was tres bon, merci! Shame that the dogs launched a canine version of the Tet offensive over a few scraps of Sunday roast which interrupted proceedings momentarily (until I stole the scraps back and ate them myself). I'll get back to the more metallic scraps in the morning, but shall rest comfortably in the knowledge that matters are under control. With luck, I'll get all the right bits, including a set of proper bolts from SRM, for not too much money, to be here by mid-week and I'll be on the road again next weekend, when I've got an old mate coming to ride the thing for a local club day out while I take an AJS twin I've had for ever (or vice versa - he sold me the AJ in 1976!) Groily.

[groily]

 . . . and checked with an old mate who's a proper working mechanical engineer (and previous owner of my AJS) this morning to get his view on helicoils for things like head bolts and he said they are "generally regarded as definitely good enough" in his answer, ie same as Bill's advice, with the obvious proviso about there being enough meat for the outsize hole. Which is pleasing if I ever have to go that way and shows me up for the old woman I must be turning into, worrying about it.
Oh, and parts all in the post this a.m. too. SRM may not be the cheapest people on earth but they are downright efficient and what I have had from them has worked as advertised and been very nicely made, mostly in the UK, and not down to a price. Groily

[RichardL]

Groily,

It would be very interesting to hear your friend's (or others') opinion(s) about using helicoil-in-helicoil to correct for a hole that has been bodged or damaged beyond the O.D. for the desired I.D. of a single helicoil.

Richard

Erling, I don't know if it's time to take off into a new tech topic, "Helicoils," so I leave that to you.

[groily]

I'll ask him Richard. I'm seeing him in a week or so, so shall save the Q till then. I suspect he'll say that's pushing things, and that it would be better to settle for a stepped stud or some of the other options we've been musing about. There might also be a question about the engagement of the threads. Are the thread forms on the outside of a helicoil, with its special taps etc, a match for the inners in whatever thread onee selects? . . . whatdoiknow cos I've never used one. If you've ever seen the sort of inserts that get you from say an 18mm hard-to-find sparking plug to a smaller one, that may be a better sort of thing for a very messed up hole - a friend of mine made one here for his Ydral (?spelling) 2 stroke engine so he could buy plugs of a suitable heat-range more easily. Seems to work just fine. And was what i was thinking about making, if there was enough metal, for my cylinder barrel. Groily

[dpaddock]

Whew! This has been an interesting thread, to say the least.

1) The iron barrel IS capable of taking a helicoil. In 1986, I had to do just that on my 1957 Spitfire for head bolts #8 and #9 (the two behind the pushrod tunnel). I replaced the stripped BSF bolts there w/ 3/8-16 UNC Grade 8 HoloKrome socket head cap screws. (Don't inquire re why these bolts stripped; it's embarrassing.)

2) I am currently torquing to 40 ft lbs, using hard flat washers under the bolt heads to spread the load over the alloy head. The washer dimensions are 3/4" OD X 25/64" ID X 1/8" thick. I lightly lubricate the bolt threads before tightening.

3) I find that the composite head gasket does a much better job of preventing oil leaks than the solid copper gasket (which is darn near impossible to get soft enough to seal for oil), and I have had no combustion pressure failures.

4) As for the root causes of oil leakage in the A10 engine, much has been written (most of it well-meaning but speculative). Make certain the oil-cavity faying surfaces are pristine and torqued evenly. Make certain the engine is otherwise air tight and is breather-timed properly. And note that the crankcase has very little capacity to absorb piston blow-by pressures in an even moderately-worn engine i.e., get used to puddles.

Tally ho!