Author Topic: a7 and a10 crank bearing conversion  (Read 4462 times)

Offline zedman

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a7 and a10 crank bearing conversion
« on: 14.01. 2009 10:56 »

can anyone send me any data on converting crank timing side bush to roller bearing. i have seen the SRM style, but I believe there is an easier way to do the conversion. ItII have already purchased the combo bearing for this, and I have talked to other BSA users and are sure that there is several methods to achieve the same result.
I have had this bike since I was an apprenticed motorcycle mechanic,and have waited all these years to get around to rebuilding. With the help of internet and computers to get info on this problem of premature wearing on bush bearing.
I have built the bike up to be a very quick bike, and would still give some modern bikes a run for it. It has high compression pistons, and used to run it on aviation 120 octane blend with super petrol. the results was a high speed very quick bike. but this dam bush needed replacing very regular to maintain sufficient oil pressure to live long enough, or break rods etc

Online RichardL

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Re: a7 and a10 crank bearing conversion
« Reply #1 on: 14.01. 2009 11:59 »
Zedman,

Welcome to the forum.

I don't know that it is easier, because nothing is as easy as spending money, but there is a detailed description of a roller bearing conversion at:

http://www.geocities.com/beezabill/mybsaa10rollerconversion.htm

I also don't know, to a certaintay, that this is good engineering, but it sure looks like it. Perhaps you've seen this and rejected it already as too difficult. If you have not seen it, it is, at least, interesting.

Richard L.
Plan on signing up for the world-wide 2017 DISTINGUISHED GENTLEMAN'S RIDE on September 30, 2018. Watch website at https://www.gentlemansride.com for details.

drog

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Re: a7 and a10 crank bearing conversion
« Reply #2 on: 30.01. 2009 09:44 »
I have just discovered/joined this forum, so I'm a bit of a newbie. I note with interest this thread on t/s brg conversions, because over the years I have converted 9 BSA A10/A65 engines to n/roller timing-side. The only engine I have close contact with is a 1952 A10 that has been hauling around a very heavy side-car for 12 yrs / 21,000 miles since conversion, with me as (81kg) passenger. We had to pull the engine apart at 18,000 miles because it spat the d/s bearing shim out. I have worked out why this happens, and re-arranged the shimming so it won't happen again (hopefully). At that stage I was able to inspect the conversion closely for any problems - it still looked like new. In fact I had to study the bearing track very closely to find any trace of roller contact. The bearing is pressure fed, which also ensures the t/s thrust face is also well lubricated, and all seems well for a long life. Two of the other engines are in classic racing side-car outfits that have given no trouble, and another engine is an extremely hard-ridden 750 cc converted A65 which gave considerable trouble until I converted it. No more trouble since then. The original A10 I converted has covered in excess of 20,000 miles, but I see the owner very infrequently, so I don't know it's recent history. This A10, incidentally, has a 12 volt dc generator which I  produced. I gave it to the owner to test, and he was so pleased with it he has forgotten to return it! That was 15 or more yrs ago. Cheers.

Offline zedman

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Re: a7 and a10 crank bearing conversion
« Reply #3 on: 30.01. 2009 11:20 »

 Hello there Drog,
 I have been keeping an eye on this for some time. And I am pleased some one has experienced this conversion. as I mentioned I have researched this subject, and have been looking for another way of feeding the mains, other than modifying to end feeding the oil to the crank and the rest of the oil circuit. I have already got the combo bearing that is recommended for the conversion, and i will also convert camshaft to needle rollers  which I have ready when I decide what way I can redirect the oil. My bike is 1952 plunger engine reinstated into a 1954 swing arm frame.I would call it a cafe racer in progress. My main concern with the end feed system is the detail on the drawings from SRM are a bit short of detail to the quill end that connects to the crank. And I think this type of conversion will only suit late A50 and A65 crankcases as they provide  a better casting area to hold the quill from being forced off under pressure. Is this right or am I on the wrong track of thinking the procedure and installation out. Your advise w2ould be appreciated.
Thans zedman

Offline Dynamo Regulators Mike

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Re: a7 and a10 crank bearing conversion
« Reply #4 on: 30.01. 2009 16:11 »
Hello Drog
It sounds like you experience will be of real value to bring to this excellent forum.
Very interested to hear your explanation of why the shims get chewed, and your cure. I have suffered this problem a couple of times, and it would be great to cure it for good next time.
thanks
Mike
Mike Hutchings
A10, B50, T800; 1,2,3 (& DVR2)
Director, DRL www.dynamoregulators.com

Online RichardL

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Re: a7 and a10 crank bearing conversion
« Reply #5 on: 30.01. 2009 17:42 »
Drog,

I add my welcome to the forum. It's great to have another deeply expereinced builder on the forum (I exclued myself from that, considering the depth of knowlege of many here, versus my own).

Manormike and Drog,

As often is the case, I am a bit confused. I don't read where Drog indicated the cure for smashed shims.  It seems unlikely Drog would place them between the d/s gear and the face of the race. But it soes sound a bit like that. Was it just a matter of moving them between bearing and crankshaft counterweight that cured the problem, or is it something more discreet, which I would definately need to learn? SRM attributes such distruction of properly located shims to end-wise hammering caused by a loose cush nut. Am I way off track here? All enlightenment is appreciated. ("Richard, go to the top of the mountain with a large candle, light the candle and watch it burn continuosly until it is out." I've heard that one.)

Richard L.
Plan on signing up for the world-wide 2017 DISTINGUISHED GENTLEMAN'S RIDE on September 30, 2018. Watch website at https://www.gentlemansride.com for details.

drog

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Re: a7 and a10 crank bearing conversion
« Reply #6 on: 30.01. 2009 19:25 »
Crikey, my post was perhaps useful. Ok then, let's deal with the shim issue first. If you erect all the parts of the drive side on to the crank, and leave the spring off, you can study the action. SRM are almost right, but the 'hammering' action is there even when the nut is fully tightened. The BSA system is flawed. My (hopeful) cure is thus: Firstly, the shim needs to be a single thick entity and not a lamination of several thin shims, and secondly, when mounting the bearing, the shaft and bearing and shim need to be SCRUPULOUSLY clean, the shim and the bearing is assembled to the crankshaft with a 'permanent mount' grade of loctite. The bearing is immediately clamped in position with a suitable tube spacer and the crankshaft nut fully tightened. I mean really tight - hammer blow tight. This is then left overnight at least. This is the first job I did when erecting the engine, and it is deliciously easy to get it right when the crankshaft is gripped in the vice, and not arguing with you. Sidecar outfits put enormous loads the shock absorber - I am happy to report no further problems, and I don't anticipate any. I still have my fingers crossed though...I have been too long in this game. :-).
My bearing conversion is a bit unusual, and a bit difficult to describe. I doubt it would ever be commercially viable because it involves some tricky machining, but it works very very well, and that is what matters as Einstein would say. It involves machining the cases to accept a substantial bronze bush, which in turn houses the needle bearing, and the tricky bit, a very narrow double piston-ring mechanical seal, the oil being fed into the crankshaft between the two piston rings. The whole seal is approx. 10mm wide. The leakage thru the tiny gaps in the piston rings lubricates the bearing/crank thrust face, and the timing-chest.
I wanted to retain the crank thrust face for several reasons - it is robust, it provides the extra length for the enclosed components, and (perhaps best of all) it can be fiddled with to ensure a decent thick shim on the drive-side. It might even be possible to arrange for no shim at all, but I have not explored this. I never will in fact, because the last conversion left my workshop some time ago - advancing years and a few little strokes have taken their toll. I hope this post will prove useful. Best wishes.

Offline a10gf

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Re: a7 and a10 crank bearing conversion
« Reply #7 on: 30.01. 2009 20:32 »
Drog, yourself and your experience are most welcome here. I hope you will find the forum to your liking.

erling
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"Success only gets you a ticket to a much more difficult task"

Online RichardL

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Re: a7 and a10 crank bearing conversion
« Reply #8 on: 30.01. 2009 22:25 »
Whew, Drog, that is a lot of engineering. How do you find a single shim of the exact needed thickness? My shim needs well exceeded the largest I know of, that is 0.010". Then, I'd be scared as hell with permanent Loctite, making any shim correction and future bearing changing, I would think, quite difficult. As for lubricating the roller bearing, I can't say I get it. Are you regrooving the pistons for additional compression rings (below the oil ring) such that the two new rings function as some kind of oil pump? The fact that I  am probably miles off in this understanding may be based on the fact that I only have two stock engine rebuilds under my belt.

Richard L.
Plan on signing up for the world-wide 2017 DISTINGUISHED GENTLEMAN'S RIDE on September 30, 2018. Watch website at https://www.gentlemansride.com for details.

drog

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Re: a7 and a10 crank bearing conversion
« Reply #9 on: 31.01. 2009 05:01 »
Hi Richard. Yes, you are wide of the mark. The mechanical 'piston-ring type' seal lives alongside, and outboard of, the needle bearing on the mainshaft. The seal is used to clamp the inner race of the bearing against the crankshaft web, and in turn acts as the distance piece for the timing pinion. Obviously it rotates with the crankshaft, and the 'piston-rings' rotate slowly inside, and seal against, the bronze bush. It sounds complicated, but in fact it is very straight-forward, and addresses (as far as I can see), all the pitfalls. It just needs very accurate machining, but that can be said of any bearing conversion. There is no welding involved. I loath welded motor-cycle crankcases - I have seen so many crankcases distorted and needing machining afterwards. One of the faults that was causing grief with the 750cc A65 I mentioned earlier was the distortion following welding.  I recognise that a picture is worth a thousand words, but I hope my explanation makes the situation a little clearer. Cheers.