The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: KiwiGF on 06.09. 2012 07:55
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I thought I'd share a bit of information I've gathered done prior to putting my small journal A10 engine back together.
I'd heard that JP pistons and billet rods were heavier than the original BSA components, and consequently I might end up with an engine with abnormally bad vibration, due to the non OEM components altering the crankshaft balance factor significantly away from standard.
So I thought I'd have a crack at checking the balance factor "DIY style".
To start the job I needed some scales. I used cheap 0-5000 gram scales which I checked for accuracy using several different sizes of tins filled with water. I found the balance was consistently within 2% of the calculated weights of water (1 liter=1000 grams) which is good enough for what wanted.
Service sheet 712X gives useful information on cranks balancing, a copy is attached below.
The service sheet for my engine gives the standard counter balance weight as 2 x 18 oz 10 drams, which I reckon is 1056 grams. 712X also says there is no need to rebalance the crank unless the new big end assembly is different in weight by more than 1 to 1 3/4 oz (approx. 30 to 50 grams).
As 712X shows, without special equipment it's not easy to measure the counter weight (CW) of a crank, on the other hand I have no reason to think the crank I have is not counter weighted as standard e.g. been messed with.
For a rough check of CW I measured the weight required to make the cranks counter weights stay at horizantal using the method shown in the attached photo. The weight of the bottle of water and rod came out at 1050 grams, which is near enough to the BSA figure of 1056 grams for me to safely assume the crank is standard. I also turned the scale upside down and used a pencil to measure the upward force from the crank pin, again the "counter weight" came out near enough 1056 grams.
The next job was to weigh the piston components.I measured a few pistons to gauge whether the JP pistons I had bought were likely to be significantly heavier than the OEM.
The results of measuring are below.
Desc Weight (grams) Comment
======== ========= ===========
Bare Piston JP brand 7.25:1 256 Bare means no pin, rings, clips
JP Pin 78 Not tapered ID, 0.475' ID
JP set 3 rings 25
JP clips x 2 1.5
Bare BSA piston flat +060 bore 261 Its "partner" weighed 258 grams
Bare piston 8.5:1 std bore 241 Unknown brand
Bare hepolite 9:1 std bore 251
Pin, tapered ID 78
Pin unknown brand 89 Not tapered in ID, 0.43 ID, HEAVY!
Next up was to weigh the con rods, the weight of each con rod end needs to be measured separately, the method I used is shown in the photos below. I weighed the rods with both ends resting on nails placed under the middle of the small and big ends. Not having the nails exactly on centre did not affect the measurement too much so I reckon this gave an accurate enough measurement for my purposes. It would not be that hard to make some weighing fixtures to measure with the rods on edge and not horizantal, but I did not find that to be necessary. As another check, I also weighted the whole rod and this came out near enough the total of the 2 ends weighed separately (only 2g difference).
The results of measuring are below.
Desc Weight (grams) Comment
====== ========= ==========
OEM BSA SJ rod Big end 296 Rod has nuts/bolts/SE bush/-040 shells
Ditto small end 110 Ditto
Complete BSA rod 404 2g different to measuring ends separately
Thunder SJ rod Big End 298 Rod has nuts/bolts/SE bush/-040 shells
Ditto small end 122 12gr more than OEM rod
Complete thunder rod 422 2g different to measuring ends separately
-040 shells 41 2weight given is for half shells, for one rod
Now this is where it gets a bit tricky. I could have stopped here as i found the weights of the non OEM components I'm using are not much different in weight to the OEM parts....but I thought I'd look up how to calculate the balance factor to be sure a small increase in weight does not make too much difference.
The calculation of the reciprocating weight (RCW) using non OEM parts is as follows:
Desc Weight (grams)
======= ==========
2x JP Piston 512
2 sets JP rings 50
2 pairs JP clips 3
2 x JP Pin 156
2x Thunder Conrod 244 (measured at the small end)
=====
Total (RCW) 965g
Rotating Weight (ROW) = 2 x Thunder Conrod/nuts/bolts big end = 596g
Counterweight (CW) = 1056g (BSA standard)
BF = 100 x (CW - ROW)/RCW (this seems to be an accepted calculation for BF)
BF = 100 x ((1056 - 596)/965) = 47.7%
Using weights for OEM parts, BSA rods and pistons (at 261g ea)
BF = 100 x ((1056 - 592)/951) = 48.8%
I've not included for the weight of oil in the big end gallery in the above calculations. I reckon it would not make a big difference to a SJ crank, which holds very little oil. It would maybe add 1 or 2% to the BF.
Conclusion
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The OEM BSA balance factor (small journal engine) seems to have been in the region of 50% using the above calculation method, and the actual balance factor using my non OEM components is not much different to that.
So...no need for me to drill extra holes in the crank :-)
If I've made errors in my calculations or methods of weighing - please let me know! (also if I've got it right would be good to know).
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Kiwi, you need a medal for all that !
Believe it or not I did read it all, Fairly much correlates to mine, except for LJ. I calculated about ~25 grm for the oil.
I used strips of lead(old flashing at the metal merchant $2 /kg x 4) as Musky suggested, but it was clumsy, so melted it down with a sleeve in a green bean tin-yuk & 1 pea tin(~72mm dia x ~24mm deep/wide), and halved it & strapped around journal with tape.
My pistons are 360grm ea x 2 = 720
Thunder Rods 440 (310/130) x 2 = 880 (620/260)
BSA rods (LJ) ~382 (280/102)
To cut it short, it 'balanced' with ~1166grm, calculated what I had as ~54% but had a new difference of about 90grm (1290-1199), which would've given me about 47%, so drilled a couple of holes, and I think I've ended up with about 58%.
These are figures of top of head, if need be can dig out the writings(after deciphering hieroglyphics) .
I've been endeavouring to take pictures, of bits of 'aids', too, hopefully that'll happen.
Gotta go now, more when I remember what I did, duTch
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Hi Kiwi!
Your calcs are spot on! I had posted my balancing efforts a while ago, and back then also found an original balance factor of 54% with the weight of original components (incl. the weight of BSA pistons at STD size) and a previously undrilled crank.
I have however altered the BF to 58% during my small-end-failure-conditioned rebuild, and I'm quite happy with the result. Next time I mgiht go a tad higher though, maybe 60-62% to move the sweet spot a bit further up the rev range. She's a bit rough above 70mph in fourth, but smooths out again above 85.
Cheers!
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Thanks Dutch and MG. I was not 100% sure about the arithmetic part so it's good to get confirmation and other evidence that's how it's done.
It sure was a long post! Probably TOO long for most!
Simon
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found it very interesting but totally outside my capabilities I'm afraid , I'll just have to splash the dough when I need anything like this done best of luck to you techno's BobH.
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Thanks, but just because we had similar maths, doesn't mean it's confirmation of correctness!!! 'specially if I'm involved, I was just going on what I read in the other end of the story, and made the rest up *smile*-as I went along-kind of?
Mind you MG sounds like he knows what's the g-o.though.
I made a doo-dad, with 4 bearings on it like one of those scissor wheels in the service sheet, and it was fun to play with, but found better results with the couple of bits of 25mm angle 'bout a foot long that I 'sharpened one edge of each to simulate 'knife edges', had to get them straight tho' or else the crank ran out of steam on the hill and ran away downhill....!! (if you get what I mean).
I also found it necessary to make a sleeve the same OD as the T/S main journal, to fit where the D/S roller fits, otherwise crank wanted to run in a curve.
I also realised today, that my crank has had a 'chamfer' (only about 5x8mm x130mm around the arc)on the outside edges of the fat side of the outrigger bob weights, probably doesn't affect my calculations, would've saved a bit of work if they weren't ground(as the other old crusty crank is)?
Another significant thing that Kel (my mate)stressed, is to check the 'Balance of Symmetry', where you sit the crank 'naked' on the knives (yes I did make them nice and level), and check that the line through the Big-end and shaft centre is vertical, B/e NOT leaning one way or t' other.
Have ta leave it there, for now -tell me if I got anything wrong??
Cheers, duTch
Ya shanghai'd me Bob, rounded me up
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I guess I'd summarise the post as highlighting that balance factors are as standard fairly low and that oversize pistons which are typically heavier reduce them further.
Whereas modern roads and their associated higher speeds are more suited to increased balance factors.
So if you're replacing pistons with heavier ones or fitting heavier rods its worth getting your crank balanced.
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72% works well at 8000 RPM *eek*
*bash*
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well its been a while since I posted this up and nice to see it gets read at least a bit!
I've now done over 3000 miles on the engine (JP pistons and billet rods and std crank and extra tooth on engine sprocket) and can report on the vibes albeit I've not ridden nother A10 as a comparison.
To me the engine is smoother than I expected at low rpm, in fact not much worse than my Suzuki 1400 v twin, at 60mph a tingle starts, at 70mph it's still ok is but the tingle is more of a buzz and is beginning to get uncomfortable for extended periods, and I cannot see the local NZ plod in the mirror.
I don't rev it much more than its going at 70 mph even through the gears (so muscrat I can't comment on what its like at 8000 rpm) *smiley4* but obviously the vibes would get worse at higher rpm.
If I spent more time at above 60mph it would be worth changing the balance factor to reduce the vibes I guess, but for me its fine as it is.
If I have to tear the engine down for any reason I might get the drill out though *smile*
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Hi all,
I have just completed my calculations using this fine posting by KiwiGF. I am unclear as to whether I should use the 1056 or 1113g standard weight factor to determine what my final balance factor actually is. I won't bore you all with all of my weights and math. I have run through them several times, re-weighed everything, and am satisfied with their accuracy.
What I do need is advice on raising my balance factor. It took 1310g to get my crank where it would stay put in any position I placed it. Unfortunately, as you all probably know, that took my balance factor to 49.6% using the 1113g Road Rocket standard weight, but only 43.3% using the A10 weight of 1056. It is a late model large journal crank, so I reckon the 1113g number is the one I should be using?
I mostly ride the bike at 55-60MPH with solo gearing. It doesn't have a tach, so I don't know what RPM I am running. I think 49.6% will be acceptable for my style, but 43.3% probably would not be! 60% might be best, but being inexperienced in drilling cranks, I'm a little chicken to dive in!
Opinions?
Thanks all,
Seabee
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Hi all,
I have just completed my calculations using this fine posting by KiwiGF. I am unclear as to whether I should use the 1056 or 1113g standard weight factor to determine what my final balance factor actually is. I won't bore you all with all of my weights and math. I have run through them several times, re-weighed everything, and am satisfied with their accuracy.
What I do need is advice on raising my balance factor. It took 1310g to get my crank where it would stay put in any position I placed it. Unfortunately, as you all probably know, that took my balance factor to 49.6% using the 1113g Road Rocket standard weight, but only 43.3% using the A10 weight of 1056. It is a late model large journal crank, so I reckon the 1113g number is the one I should be using?
I mostly ride the bike at 55-60MPH with solo gearing. It doesn't have a tach, so I don't know what RPM I am running. I think 49.6% will be acceptable for my style, but 43.3% probably would not be! 60% might be best, but being inexperienced in drilling cranks, I'm a little chicken to dive in!
Opinions?
Thanks all,
Seabee
According to the BSA service sheet a standard crank would require circa 1100 grams to achieve static balance, if yours requires 1310 grams it must be modified? any chance of a pic of it?
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do you think sludge trap contents will affect the balance factor over time ?
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Dont forget the oil which will be in the crank when engine running. Eddie Dow comments on this in his tips for tuning and assembly of the A10 included in his 1967 catalogue.
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Thanks for the feedback guys. I'll try to get some pictures later. Regardless, what would be the best approach to getting the BF higher?
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The A10 weight given in the table is for the small journal crank. The large journal weight on the service sheet is the same as Rocket. More thoughts on balancing from below Hap Alzina bulletin from 1960.
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Thanks for the feedback guys. I'll try to get some pictures later. Regardless, what would be the best approach to getting the BF higher?
If you use your figure of 1310g for “counterweight (CW) in the calculation for balance factor, what % balance factor do you get?
Note: I used the std counterweight of 1056g in my calcs on the basis that was more likely to be the correct figure than what I actually measured (1050g), but in your case you need to use 1310g.
EDIT: my calcs indicate that an A10 crank with a CW of 1310g with std weight BSA rods etc would have a balance factor in the region of 75%.
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Hi Kiwi,
I didn't use the figure of 1310 for CW. It is the actual weight the crank required to maintain position.
I used 1113 (RR large journal) as CW. Should I have used the 1310 actual instead of the 1113 standard as the CW?
My formula ended up looking like this:
RF = 100 (1113-665)/900 = 49.77%. 665 is my actual big end weights, including 25g for oil. 900 is my actual reciprocating weight totals. If I substitute 1310 for 1113, I get a BF of 71.66%! Yikes!
Here's the interesting part, my crank has 3 fairly deep 1/2" diameter drillings. The 3 holes total 2.34" in depth! I measured another large journal crank I have. It has 3 shallower 1/2" drillings totaling only 1.26" in depth. I'm guessing the crank I'm using has been played with before.
If my math is correct, I think the 49.77% will be okay, but I'd like to raise it to 55-60%. Would the best course of action be to drill opposite the crank pins in the flywheel?
I have added some pics of the flywheel drillings.
Thanks for the help,
Seabee
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Well, it only let me attach one. Here's another:
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And one more
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Hi Seabee, yes I think you will have to use a measured value for CW as opposed to a stock value, given you have measured it at 1310g.
I don’t think the drillings in the pics would cause a 200g difference from stock but I have not calculated the weight removed. They might be stock drillings by BSA, might not.
Did you accurately measure the CW of your crank? Maybe using either of the (2) methods I used? Or even the BSA method in the service sheet?
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If my math is correct, I think the 49.77% will be okay, but I'd like to raise it to 55-60%. Would the best course of action be to drill opposite the crank pins in the flywheel?
I have added some pics of the flywheel drillings.
Thanks for the help,
Seabee
I'm no expert on this, but after getting involved in a couple of Dynamic crank balancings and asking lots of questions, here's what I think I know-
Raising the balance factor of any crank can't be done by drilling opposite the crankpin. Removing weight from that area lowers the bf. The only way to raise the bf by working on the Bob weight side is to drill the crank metal away and replace it with Mallory metal which is quite a lot heavier than the crank Bob weight steel.
Sometimes, at a later date and very high rpm, the Mallory metal flies out and destroys the engine.
I had a look at the remains of a racing V8 engine that had lost its Mallory metal and that really put me off that plan!
Glen
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Kiwi,
I used your method with the bottle of water. It worked very well.
Worntorn,
Logically thinking, I agree with you. I think drilling any more would make things worse.
I am building a bit of a "hot rod" version with this spare engine. It will have a 357 cam, aluminum A7 head with detachable intake manifold (dual carb?!) re-chambered to match a10 bores, and hi-comp pistons. I guess I could just accept it as a higher RPM engine and go run the snot out of it! I could build a Musky imitator, but I'm probably shy in the cahone dept!
I guess I'm going to just have to take a chance and see if I end up with a Tri-hard foot and hand number....
Thanks guys,
Seabee
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Kiwi,
I used your method with the bottle of water. It worked very well.
Worntorn,
Logically thinking, I agree with you. I think drilling any more would make things worse.
I am building a bit of a "hot rod" version with this spare engine. It will have a 357 cam, aluminum A7 head with detachable intake manifold (dual carb?!) re-chambered to match a10 bores, and hi-comp pistons. I guess I could just accept it as a higher RPM engine and go run the snot out of it! I could build a Musky imitator, but I'm probably shy in the cahone dept!
I guess I'm going to just have to take a chance and see if I end up with a Tri-hard foot and hand number....
Thanks guys,
Seabee
I think we would all be interested in knowing how the crank has been modified to have a CW of 1310g, steel weighs about 8g/cm3, so something like 25 cm3 of steel has been removed and/added? If mallory metal plugs were used they would be in the 2 counterweights I guess.
Maybe the “74” in the first pic of the crank is an indication of the % BF by the person who modified it? (Unlikely but you never know eh).
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G'day Seabee.
I'm flattered.
The only problem with using an A7 head is the valve size. I ended up with a bit of a mish mash. SR valves but had to marry the A7SS collars to the SR collets and use SS springs. Using the SR gear the springs will bind, especially with a 357 cam.
Cheers
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I think the 74 is a factory marking - similar seen on other cranks.
The photos show one with 79 stamped and one with 77 stamped both plus a scribed line. Timing side on the left both photos.
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Kiwi,
I used your method with the bottle of water. It worked very well.
Worntorn,
Logically thinking, I agree with you. I think drilling any more would make things worse.
I am building a bit of a "hot rod" version with this spare engine. It will have a 357 cam, aluminum A7 head with detachable intake I think the 74 is a factory marking - similar seen on other cranks.
The photos show one with 79 stamped and one with 77 stamped both plus a scribed line. Timing side on the left both photos.
manifold (dual carb?!) re-chambered to match a10 bores, and hi-comp pistons. I guess I could just accept it as a higher RPM engine and go run the snot out of it! I could build a Musky imitator, but I'm probably shy in the cahone dept!
I guess I'm going to just have to take a chance and see if I end up with a Tri-hard foot and hand number....
Thanks guys,
Seabee
I think we would all be interested in knowing how the crank has been modified to have a CW of 1310g, steel weighs about 8g/cm3, so something like 25 cm3 of steel has been removed and/added? If mallory metal plugs were used they would be in the 2 counterweights I guess.
Maybe the “74” in the first pic of the crank is an indication of the % BF by the person who modified it? (Unlikely but you never know eh).
Kiwi,
I didn't find any mallory plugs. It's interesting that the total drillings are twice what my other crank has.........
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G'day Seabee.
I'm flattered.
The only problem with using an A7 head is the valve size. I ended up with a bit of a mish mash. SR valves but had to marry the A7SS collars to the SR collets and use SS springs. Using the SR gear the springs will bind, especially with a 357 cam.
Cheers
Thanks for that Musky! I'll have to take a very close look see!
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I think the 74 is a factory marking - similar seen on other cranks.
The photos show one with 79 stamped and one with 77 stamped both plus a scribed line. Timing side on the left both photos.
Wow Julian, that crank has been drilled to death! I wonder what the story is there?
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Static balancing by a company in Swanage, Dorset back in 1975 or 1976. Balanced to 65 %. Not convinced there was any noticsble improvement.
it grew some extra holes when dynamically ballanced by SRM 10 years ago. 54%. See photos below of the extra holes on the flywheel edge. That job did reduce the vibs.
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G'day Fellas.
I wish I had pics of my race crank. There wasn't much left of the flywheel. 1/4" off each side and drilled like swiss cheese. Can't remember how much lighter it was (around 1.5kg). Balanced to 72% she revved like a two stroke and would rattle my teeth out at anything under 6 grand but smooth as silk at 7.5 to 8 *eek*
Cheers
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For the very brave there is this rather brutal technique from a 1959 bulletin from Hap Alzina in California.
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Wow Julian, we Yanks are some crude creatures sometimes! Sadly though :!, it completely made sense to me!
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When the engine is apart, drill holes to make the crank over-balanced by a couple or so ounces. Then drill the opposite side until it is underbalanced by a similar amount. Tap that second batch of holes. You've then got a range of balance factors you can apply simply by fitting / removing screwed plugs from those latter holes. When you're working with experimental engines, where the balance factor is at best a guess, it's by far the easiest means of achieving a smooth engine. Been doing that for ages, though I think Richard too exception to the method when I mentioned it a while back. Maybe he misunderstood the expression 'window' that I used to describe access to those plugs. Of course, in most cases that 'window' already exists above the sump plate.
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Well, I couldn't just let it be. I decided that by adding a few more drillings, I could lower the amount of weight I had to add to balance the crank. I did 3 more drillings and got the rotating weight down to 1190. With my recip weight, I settled on 58.33%. I think that will work pretty well for my style.
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G'day Seabee.
I'm flattered.
The only problem with using an A7 head is the valve size. I ended up with a bit of a mish mash. SR valves but had to marry the A7SS collars to the SR collets and use SS springs. Using the SR gear the springs will bind, especially with a 357 cam.
Cheers
Howdy Musky,
I have completely restored the A7 (SS?) head with stock valves springs and keepers. What do I need to do to make it work with the 357 cam? I have a lot of time and $ invested in the head and really want to run the 357 cam. Is there a solution I can pursue?
Thanks in advance,
Seabee
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I have not used the A7SS head, however I used a 357 cam with an A10 iron head with standard A10 valves etc for many years and had no issues.
Currently using a 357 with A10 iron head, Road Rocket valves (not the big inlets), Road/Super Rocket spring seats and collets and Eddie Dow type top collars (from Ebor motorcycles) with WS type progressive springs. That works fine also. Why Road Rocket valves you may ask? Because I had a good set plus the bits to go with them from a wrecked (big crack) 67 1549 alloy head.
I assemble with a set of very weak springs first to makes sure of top collar to guide clearance and with proper springs check they are not coil bound.
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G'day Seabee.
The 357 will be fine with an SS head and valve gear. I wanted the bigger SR valves in the Cafe's twin port SS head which is where I had to do some creative fitting.
Even my 51 A7 plunger has a 357 (with a 57 SS top end).
Cheers
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Thanks Julian and Musky! What a relief..................
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A useful reference article from a book on A65 development
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had a lot of trouble with my A7ss and a 357 cam, it broke a pushrod, turns out the standard valve spring setup gets coil bound on full lift, had to get some machining done on the spring base and on the valves to get clearance, seems i am not the only one to have had this problem.
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There's a lot more to fitting a performance cam than many realise. Apart from matters such as inlet and exhaust pipe design, there's valve gear acceleration, valve gear clearances, valve spring and cotter / collar to valve guide clearance, valve to piston clearance and even valve to valve clearance to take account of. Ain't just a bung-in and whizz off in a cloud of tyre smoke ..........
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There's a lot more to fitting a performance cam than many realise. Apart from matters such as inlet and exhaust pipe design, there's valve gear acceleration, valve gear clearances, valve spring and cotter / collar to valve guide clearance, valve to piston clearance and even valve to valve clearance to take account of. Ain't just a bung-in and whizz off in a cloud of tyre smoke ..........
G'day RD.
Hit the nail on the head there.
Even more work to fit SR valves in A7SS twin port head! Everything has to work in unison.
Cheers
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had a lot of trouble with my A7ss and a 357 cam, it broke a pushrod, turns out the standard valve spring setup gets coil bound on full lift, had to get some machining done on the spring base and on the valves to get clearance, seems i am not the only one to have had this problem.
Also worth considering use case. the 357 is a great cam and works really well above 5000, but the 356 is no slouch and very strong to the low 6's and better mid range than the 357. Don't get me wrong, I've seen my sidecar light up out of corners to 7500 on the 357 but on a road engine would choose the softer 356 for the mid range between 3-5k. The extra couple of ponies claimed were at revs the average preunit twin owner will never dare use. Appreciate we do have some here who do use ALL the throttle available and for them the 357 delivers a wee bit more up the very top. The 7500 I've seen is not the engines limit either, it needs watching up there as I think it would happily go higher, I just expect it would go bang. Musky will no doubt know but expect 8k with a 357 in a 500 is on the cards. I have broken engine mounts off the cases, cracked frames and head steadies due to balance issues, but then I've also broken hubs
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many moons ago i built an A10 that was very modified, needle roller bearing everywhere, 9:1 pistons, large valve alloy head that was ported, using a gardener carb, it had a polydyne cam which is very like a 358 cam, it was all balanced and went like the clappers, it was a bit of an animal on the road, good fun though, it was loud , never had any problem with the springs getting coil bound, but it did have goldstar springs in it. it revved well,
had to fit an electronic rev counter as it kept braking the normal smiths one. a lot of fun but not really suitable for todays roads.
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Interesting read as I am looking at balancing my SR crank. Not having any "knife edges" I am considering mounting the crank between live/rotating centres on my lathe. Has anyone tried this? Just concerned about the amount of resistance in the bearings in the centres. I've tried two centres and the difference in how free they run is considerable.
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Interesting read as I am looking at balancing my SR crank. Not having any "knife edges" I am considering mounting the crank between live/rotating centres on my lathe. Has anyone tried this? Just concerned about the amount of resistance in the bearings in the centres. I've tried two centres and the difference in how free they run is considerable.
For knife edges I just used some nails on a portable work bench, a pic of the set up is on the first page of this thread.
I think trying to use a lathe whilst more elegant will not work as well as the nails *eek*
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Interesting read as I am looking at balancing my SR crank. Not having any "knife edges" I am considering mounting the crank between live/rotating centres on my lathe. Has anyone tried this? Just concerned about the amount of resistance in the bearings in the centres. I've tried two centres and the difference in how free they run is considerable.
For knife edges I just used some nails on a portable work bench, a pic of the set up is on the first page of this thread.
I think trying to use a lathe whilst more elegant will not work as well as the nails *eek*
Thanks, will try a variation on a nail solution.
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a friend passed me this, thought of relevance
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G'day RR.
That's exactly (only taller) that I use. I made an adjustable one for height and width mainly for balancing wheels. Used the little rollers for sliding doors. As little as 1/2 gram will make it spin.
Which ever method you use they must be level and true both sides.
The lathe method with the crank between two live centers isn't good enough as the clamping force (as little as it needs to be) will create drag.
Cheers
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Hi All,
I modified a wheel balancing jig by replacing the crappy bearings with skateboard low friction bearings
I was balancing an Indian Chief crank that was made up from bits and I needed to balance it
Their method is to hang one complete piston from a rod as the weight required
I tested the method on a BSA V twin crank as well and found it good with the same method
One of the days I will check the crank SRM balanced for the MAP rods and Wisco pistons to see what factor they used ?
John