I am rebuilding an A65L (1970) which has Ben all but destroyed! I've had many problems, but the one I'm currently trying to resolve has me stumped! The crank that came in the engine was, as well as being from an early engine, just about worn out; all journals on or close to minimum allowed. I bought another from Wrexham from a 1970+ engine, with all journals nominal, which I've had dynamically balanced. It wasn't in perfect condition, but well within tolerance. Previous owner had spun the TS bush (probably removing the cast boss that locates the thrust washer) wearing it to over three thou oversize. He then tried to remedy the situation by soldering the outside diameter of the bush with blobs of solder in an attempt to tighten it. He had the crank case machined with a slight slot in which to locate the bush radially, but with nowhere to locate the thrust washer and then put it all back together, including the thrust washer and ran it. I have no idea how badly it ran but I can imagine! The resulting loss of oil pressure was the probable cause of the worn out journals.
I wasn't fully aware of this when I had the engine worked on and much is based on guesswork. My previous, earlier, A65 didn't have a thrust washer and was a long time ago. I had the case bored, oversize, for a taylor-made, oversize bush, which was then line-bored to fit the new crank. Now that I'm re-assembling the engine, I realise there's nowhere to locate a thrust washer, and also, the total amount of end float with no washer or shims/shim cup, is 75 thou. The cup is 34 thou thick so even if I wanted to, I couldn't fit the washer, which is 62 thou.
I'm considering either of the following solutions:
A) try to pin the thrust washer in place and make my own cup out of very thin (12 thou) sheet steel
B) omit the thrust washer and take up the end float with a standard cup and shims
I will only try one of these and do not know the best choice. I really didn't want to have to convert to needle rollers, but I do acknowledge that if the first options don't work, I may be forced to go that way, but as with everyone right now, money is very tight. To pay for it I may have to sell another bike!
Hopefully, the pictures will explain matters. Pic 1 is the bush removed originally. 2 & 3 are how the bush should fit. 4 & 5 are how the case looks after having a new bush fitted.
there is a 3rd solution [ not my idea ] which is to make a housing bolted to the stator nuts with a ball bearing fitted to the housing and between the rotor and rotor nut. the housing is fixed to the crankcase and you would shim end float with the bearing also fixed. you will have to google for examples but a machine shop could make one up easily out of aluminium.
Is there any chance of providing pics 2-5?
It may be a bit too early in the morning (6:32) but I am struggling a little to understand what the problem is. I thought the original problem was that the TS bush had spun in the crankcase and, presumably, wore the crankcase hole oversize. What I didn't quite understand was how this happened given that the flats on the inner side of the bush normally locate in the slot provided in the crankcase?
The other bit I didn't understand was the problem with the thrust washer and why this can't be assembled on to the RHS of the crankshaft? Is the problem that the current TS bush installation now projects too far into the engine and therefore there is not enough space for the thrust washer anymore? If so, what is the reason for this?
I'm sure the missing pics would have made the problem clearer and it will therefore be interesting to see them!
I will try to post other pics and it should become self explanatory, when I get home later today.
These are the other images. My apologies as they were to large to post here. I had to put them on my PC to reduce the image sizes. The first one is the bush that was fitted when I got the bike. You can see the blobs of solder that have been applied to try to tighten it and which would have drastically reduced oil pressure.
The second shows the modification made following the damage caused by the spinning bush and you can see the remains of the bush housing boss.
The other two images show the way the fitted bush should look and how the thrust washer is fitted. Thrust washers were fitted from, I believe, 1966 on. I previously stripped and rebuilt a 1967 engine, but that was 40 plus years ago. I'm almost certain that that one didn't have a thrust washer, although I cannot remember to be honest. I'd be interested to see how the bush was located on models before the thrust washer, as I'm pretty sure it was something similar to the way mine now is, as when I first saw it I was not aware I had a problem! If you need any more info, please just post here.
Many thanks for the missing pics.
As said, pre-1966, there was no thrust washer fitted. I don't know the ins and outs of why the change was made but my guess would be that it was fitted because it was easier to replace the washer than the bush when it wore down because of the side thrust forces from the crankshaft. It may also have been that it may have allowed a slightly different spec'ed material to be used for the bush and the thrust washer.
I am sure that you can live without the thrust washer on the basis of what is said above. However, it sounds as though the bush does not project far enough towards the crankshaft to take up the end float that the thrust washer would have taken up. The solution may therefore to either fit a modified bush to take up the end float or to fit a plain shim of similar material to do this.
When BSA changed the primary bearing from a ball race to a roller bearing, the end float had to be controlled by the timing side thrust washer and primary side shims and cup. HTH
The inclusion of a thrust washer certainly coincided with the replacement of the original drive side ball bearing with a roller bearing. In the original design, the ball bearing took all the side thrust and so none was transferred to the shoulder on the timing side bush. I haven't looked closely but the thrust washer could simply have provided a larger surface area to take the side thrust or it might have been made from a slightly different bronze material compared with the bush to better able to take the resulting wear or they might have thought it was easier to replace a worn thrust washer rather than the bush.
In principle, it might be possible to revert back to the pre-1966 bearing layout and use a drive side ball bearing in which case the thrust washer is no longer needed - the end float, as said, is then controlled by the drive side shimming. Unless you are going to give the engine a hard long life, I would personally be tempted just to shim the timing side with a steel or bronze shim or washer.
Having just read an article on the subject, the conclusion seems to be that for 1966 and later engines, it is possible to fit whichever bearing type you want (roller or ball bearing) providing everything is properly centred and shimmed afterwards. Unless you are after using max power from the engine, I would have thought a drive side ball bearing would be perfectly adequate for normal use and would definitely eliminate the need for the thrust washer and the problems associated with it!
Thanks everyone for your extremely helpful comments. This has been very useful and I'm gonna opt for the ball bearing route. But if I still have the bike when it next needs the bush replacing, I'll probably go for a needle roller conversion, but not with SRM! Theyre far too expensive for my meagre means. I don't intend thrashing it; I'm nearly 70 now, so it should be good for many years yet. I had my first one for over 15 years and it was still going strong when I had to part with it, although it was a 7.5:1 compression version.
Again, thank you all.
Bit late I know but I came across this article a few years ago.....
https://www.classicbritishspares.com/blogs/news/early-vs-late-cranks
Hi, go with the ball main bearing and leave out the thrust washer. I have done this on my 1972 Lightning following advice from the following book "Building Budget Brits, a practical guide to refurbishing BSA & Triumph unit twins" by Mike Brown published by Whitehorse Press in the USA. The best book by far on building an A65 to use, there's a whole chapter on the A65 bottom end and a reasoned discussion about reverting back to the ball bearing, how to do it and things to consider. The article mentioned above in the thread explains the differences between early and late cranks and that some combinations won't work ie a late crank in early cases. In the case of an early crank in later cases there will be excessive end float as the cases are wider (the article above explains this) so a way round it is to use a ball bearing to control the end float using shims to centralise the crank and leave out the thrust washer as everything is pulled over to the drive side when the alternator nut is tightened up, exactly as in early A65 motors. The specified end float is in the ball bearing itself so don't skimp on this, these days its probably RHP or a new old stock Hoffman or SKF if you can find one. I have just completed 1000 trouble free miles on mine having rebuilt the bottom end like this. I also replaced the rods with a pair from Thunder Engineering and had a solid bush line bored properly and rebuilt my cast iron pump. I agree about the SRM conversion being expensive for what it is (I've had Devimead & SRM ones through the years) and really don't think it's worth the cash layout these days unless its for a racing engine or say constant motorway work. Best of luck in figuring it out, the catalogue number for the book I mentioned is ISBN 978-1-884313-62-2 and was published in 2009.
Very good book, well worth buying.
In my opinion, the easiest solution would be to make up some new originally cast in bosses and get them welded on to the RH crank case half (the positions, sizes and shape is obvious)and machined off to original spec. including space for the thrust washer.