Author Topic: Richard's 55 A10 Big End Problems  (Read 3129 times)

Online RichardL

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Richard's 55 A10 Big End Problems
« on: 13.11. 2007 18:48 »

What a great thread. Similar dad's and similar bikes! My old man mended aeroplanes in the navy most of his life - that's where my interest - but sadly with complete lack of his professional skills - comes from!

Re the cause of your lh big end prob Richard/Manosound, not sure about the diagnoses . . . the cush nut shouldn't control the crank end float should it? And nor ought a knackered piston. If the crank's wobbling around I think it's a matter of setting it up with the right shims and making sure the timing side bush is in good shape and the drive side bearing ditto. But even if it the crank moves a bit more than it should, the rod should stay in the same place relative to the journal it's on! (How far can it go walkies?) A wobbly piston might wobble in its 'ole, but it shouldn't make much happen down below, and certainly not cause the bearing shells to up sticks left or right. I would rather suspect the crankshaft oilways/sludge traps and the oil pump itself (plus look at the drilling from pump to the drive side main bush). The lh end is furthest away and will suffer first from any shortage of the slimy stuff. I very well remember having a left hand big end seize light years ago cos of a dodgy oil pump worm gear which went awol and caused a monumental catastrophe - in fact it was the thought of the cost, even then, of trying to fix it without any money (I'd used up all my stock of tired bottom ends) that made me give the bike away! Groily.

Groily,

I started a new topic, since we are now, clearly, off of the 9:1 vs. 8:1 issue.

I don't think I made it clear about my dad, he did, in fact, work on submarines, but from inside of them as a submariner (Electricians Mate 1st Class). Now that this topic is open, I can't help mentioning that he served on the ill-fated USS S-4 (check Google), but was not lost with the boat and all his friends, hence, I'm here.

Back to A10's --

The reason I mentioned the cush nut is because, before I separated the cases, I found what I thought was a sliver of shim in the oil sump. I was told by a respectable individual that a loose cush nut would result in the crank clanging back and forth and messing up the shims. Again, correct me if I'm wrong, but the cush mechanism does seem responsible for preventing movement toware the timing side. I am fairly certain that I had the end play less than or equal to 0.005 in, as prescribed. I think you are probabaly on it with the oil ways, though the sludge trap turned out to be quite empty. When assembling the engine I was rather careful to blow out the oilways. I need to check these again to be sure they did not clog-up in the mean time (but very few miles). The oil pump seems OK, but the only way I have to check is to watch oil returning to the tank. Is this enough indication? do you know a way I can check the output with the pump removed?

Thanks for your comments.

Regards,

Richard


Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020. This year it's a solo or pillion ride in dapper attire. Watch website at https://www.gentlemansride.com for details.


Offline a10gf

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Re: Richard's 55 A10 Big End Problems
« Reply #1 on: 13.11. 2007 18:59 »
moved the post to new topic as you requested.

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Online groily

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Re: Richard's 55 A10 Big End Problems
« Reply #2 on: 13.11. 2007 21:42 »
Hi Richard and well done your Dad for making it home in such terrible times.

Probably wise to start a new topic, however much we try to compress it!
I guess it's possible that a slack cush drive nut could make an end-float problem worse. I am just a makee-learnee born again A10 person - there are many here who really obviously do know stuff and i hope some of them will chime in. But the idea that crank end-float is controlled by the drive sprocket and cush drive nut - - sounds all wrong to me. Half a turn of a nut with say 18 or even 20 tpi is so much more than 5 thou, if you think about it . . . we'd be running around with mega- or minus- clearances were it true, and be none the wiser cos you can't measure it properly. No, the clearance is set, on the bench, using shims inside the cases, with a dial gauge to measure with, and often a fair bit of trial and error assembly and disassembly!

I really don't think the sliver of crankshaft shim you found in the sump plate came to be there just because the shock absorber nut wasn't done up fully. You shouldn't be able to move the crank more than the prescribed (small) amount whether the engine sprocket and associated parts are attached or not. If the nut was loose, it's possible I guess that any excess play present inside the crankcase would be magnified by the extra weight of moving parts thrashing in and out on the end of the drive side main-shaft like a slide-hammer, but I don't personally think anything outboard of the crankcase caused your big end to go. That was due to lack of oil - flow, pressure, or both. I don't believe (until it seized!) that the oil holes in the big end shells suddenly got blocked through mysterious misalignment. Maybe it's because I'm just too ignorant to know what I don't know, but I'd still suspect wear or some other defect in the timing side main bush for a lack of oil pressure. Or the pump. Or a blockage. I see that some people have reported that some types of main bush, constructed of an inner and outer sleeve of different materials pegged together, could possibly fail as a result of one part contra-rotating against the other and misaligning the oil feed holes between themselves and the timing side crankcase oil feed hole. I don't know. Others say that the two-part sort is better than a pure phosphor-bronze bush, which may wear the crank more quickly. I'm not a metallurgist and have no idea. Whichever sort is used, the holes feeding oil from the pump to the bush through the casting need to be aligned with the holes in the bush, obviously . . . if the bush turns in its housing cos it's a poor fit . . . result: oil flow reduced or cut off, and first casualty, lh big end.

As to the pump, I'm not sure what to say. If oil returns when running , that's a good start and proves a) the pump turns at least some of the time and b) the anti-syphon valve isn't stuck shut. Oh, and c) there's oil down there. The only way I know to verify the thing is OK is to take it off, take it apart, look at it, and look very very carefully at the worm drive that turns it - the driving as well as the driven part. Are the teeth good on the internal gears in the pump, especially the feed side? Is the meshing of the  worm gears good - no tight or loose spots?  Are there chips round the edges of the 'teeth' cut in the worm? If in doubt, although expensive, a new pump and drive pinion is a helluva lot less than a(nother) rebuild! If you truly had far too much end-float on the crank, this is NOT a good thing for the worm gear which has to accommodate it somehow, as it doesn't have its own private cush drive built in.
 
Whatever, if you've cleaned everything, checked everything, replaced everything necessary, the good news is the thing will run fine and all this will just be history. Let's hope people who know more chip in with wiser words, which I'll look forward to reading. Groily

PS Also check and clean oil lines and oil tank pipework for clear delivery flow!
Bill

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Re: Richard's 55 A10 Big End Problems
« Reply #3 on: 13.11. 2007 22:08 »
Hi there
.005 is too much, recommended end float is .003 maximum, and this before you fit the cush drive which should have no bearing on the end float.
I have mine at practically .001 - as long as the crank spins freely that's fine.

All the best - Bill
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online RichardL

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Re: Richard's 55 A10 Big End Problems
« Reply #4 on: 13.11. 2007 22:23 »
Groily,

I think the point with the cush nut was that it would back out completely leaving the cush spring undercompressed. the gent who talked about this said it would probabaly be better to leave out the cotter key and have it make noise against the primary cover (alerting one to a problem) rather than have the crank uncontrolled. Anyway, I will soon take off the bearing and check the condition of the shims.

I think you may well have hit on the real point with regard to the timing-side bush. I will examine that carefully for the conditions you've pointed out. (I just got the engine disassembled and have not had much time to go into depth with looking at stuff.) Also, I will chek the pump for any signs of worm drive wear.

Your advice, and time in providing it in detail is greatly appreciated. Even though I've owned this motorcycle for 34 years, I guess I'm still a bit of a newbie with regard to working on it, considering it sat for 24 years before I decided to rebuild it.

Regards,

Richard

Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020. This year it's a solo or pillion ride in dapper attire. Watch website at https://www.gentlemansride.com for details.


Online RichardL

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Re: Richard's 55 A10 Big End Problems
« Reply #5 on: 14.11. 2007 03:41 »
Bill,

Regarding the 0.005" maximum end play number that I cited in a previous post, that is what's listed in Bacon's "BSA Twins and Triples" and in Chilton' "BSA Motorcycle Repair Guide." However, Haynes lists 0.003" maximum and that was the book I used to learn how to assemble the engine, so I must have had 0.003", or less. (Yes, I know that book has a colorful nickname.) Given your advice, I will target a closer fit this time. Thank you.

Richard 
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020. This year it's a solo or pillion ride in dapper attire. Watch website at https://www.gentlemansride.com for details.


Offline Brian

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Re: Richard's 55 A10 Big End Problems
« Reply #6 on: 14.11. 2007 06:50 »
I wonder if with this end float debate everbody is taking into account the different main bearings. With a roller main the crank must be shimmed for end float, the cush drive has no effect on end float. I have pulled a couple of A10's apart that have had a ball bearing main bearing, in this case the cush drive locks the crank to the left side. Both engines were out of very early A10's. I always use roller bearings and shim the cranks but maybe some early ones had a ball bearing as standard. Has anyone else come across a A10 fitted with a ball bearing main ?   Brian.

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Re: Richard's 55 A10 Big End Problems
« Reply #7 on: 14.11. 2007 07:58 »
Very interesting point indeed Brian and if we're talking a ball - I've only in my ignorance seen drive side rollers - then there's maybe something here. Fascinating stuff and looking forward to learning more! Groily
Bill

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Re: Richard's 55 A10 Big End Problems
« Reply #8 on: 14.11. 2007 14:58 »
Hi, have had some end float problems over time to investigate, and this is what I experienced, for my a10 plunger.

This engine uses a ball bearing. The end float set by shims on the drive side, one can buy sets with different thicknesses. Went for o.oo1, = barely turning freely in a very (freezing actually) cold cranckase, as measurements made after heating the crankcase showed an increased clearance of some thou's when very hot. I believe in absolute min. endfloat with a cold engine, as I do not think the endfloat will minimize over time, on the contrary. The cush has nothing to do with clearance, but a defective cush may put quite some stress on the whole system.

My problems where due to the drive side bearing inner race slipping on the crank shaft itself, thus not always following the revolutions of the shaft and shims = the shims where grind down (ending up with pieces of disintegrated blue heated shims to be found in the bottom of the crank *conf* ). If several diff. thick. shims are needed to get the correct clearance, I use the thickest at the bearing side. Think best would be to use one shim only if poss.

Regards
e.

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Online RichardL

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Re: Richard's 55 A10 Big End Problems
« Reply #9 on: 14.11. 2007 18:02 »
Hello Folks,

Everyone has been quite helpful and I thought I should share the advice that led me to think the problem was the cush drive. Unfortunately (in terms of wasting some your helpful time), I misinterpreted the first sentence wherein this advisor descirbes the cush drive itself as causing the noise, not the crank clanking, as I initially interpreted it. Apologies for the confusion. The metal referred to was a sliver of apparent shim material found in the sump. I had forwarded a video to this fellow and he generously attempted to diagnose from the video (I think some of you may have seen it, but I have since removed it from YouTube.) With respect to this individual, he was only going by the sound on the video. As it turned out, it is big end trouble, likely caused by oil starvation that resulted from blocked passages or pressure release at the timing-side bush (as has been suggested in this forum).

As another revealtion in all this, I finally figured out that the tiny oil hole in the left con rod is there to release pressure so oil will flow. (I say this with appreciation of no audible "duhs".)

Regards,

Richard

The metal is more than likely shim material, common problem caused by the non tightening of the cush drive nut in the clutch side, clanking is cush drive assembly loose on the crankspline, and possibly loose crank bearing on the crankshaft .
The cush drive nut is critical, must be 65 foot lbs torque tightened, this holds the cush drive assenbly tight against the oil seal spacer, which in turn holds the crank bearing , which in turn hold the shims against the crankshaft; if this is all loose , crank splines wear badly, crank bearing wears crankshaft so it is loose fit on shaft , and shims break up and fall inside engine. Usually if the split pin has been fitted above the cush drive nut , when nut comes loose, it goes against pin, and you dont know it loose, happily riding and causing engine damage, best to leave this pin out, so nut touches primary cover and makes a noise , so it is investigated before the serious damage is done. But this is not the casue of the engine noise !
 
Possible causes :-
Small end bush failed - spun in conrod , or loose slack fit to pin
Wrist pin clip dislodged/ missing- and wrist pin is thrusting into side of cylinder bore.
Camshaft lobe / cam follower failed- pattern quality cam and followers badly worn, or valve springs too compressed due the valve seats being replaced and not machined to correct height.
 
It does not sound like bottom end bush or big end trouble, but the quality of Youtube video is not good.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020. This year it's a solo or pillion ride in dapper attire. Watch website at https://www.gentlemansride.com for details.


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Re: Richard's 55 A10 Big End Problems
« Reply #10 on: 14.11. 2007 20:31 »
I have to agree with e that when shimming crank go for zero end float also use the thickest shims needed. I always bolt up crankcases with no shims fitted & fit cush drive done up tight.Make sure crank spins freely then tap both ends of crank with copper mallet to settle crank in cases (dont belt it hard) then fix dial gauge to crankcases & dial in crank end float to establish what shims are needed.Once   this is done you just need to strip & fit necessary shim/s once bottom end is built up check that crank spins smoothly if a bit tight tap crank end again & re-check.Also I only fit shims on driveside I have seen them fitted to both timing & driveside shafts but I would not risk it .This is the way I now build all my A10 motors & have had no problems with end float.My latest engine is nice & smooth hardly any vibes thru footrests & seem to run better the more I use it.Hope this is of help to someone out there ??  Dave..