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#877549 04/13/22 5:39 pm
Joined: Apr 2022
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Long time lurker but first time poster on the Forum. I have rebuilt several Unit twin engines over the years but this one is a little different and I'd like to find some information regarding it. # is A65D5216. The lower end arrived here a month ago after it's chassis had been through a cosmetic restoration of some kind. Unfortunately the perpetrators hadn't thought it necessary to read the manual especially the page regarding the oil lines. The bottom end gave out after about 3 miles. I was surprised it went that far. Upon stripping it down I was surprised to find a Hoffman roller bearing on the drive side. Everything else is as I would have expected for an early A65 except for the T/S bush. It is the early type but has the little pin in it to prevent rotation of the inner part. I can only remember seeing those on the later bushes in the past. I couldn't find a specific parts book mention for an A65D but assume that "L/R" refers to it. In any event this engine has done very few miles from new and if it has ever been apart before it was done very gracefully. My questions are as follows :- Is it even remotely possible that it came with the roller bearing from the factory?, Are the Kibblewhite bushes a quality item?, Does anyone have any experience of the current production "Wassell" oil pumps as to performance? I've installed several SRM ones and been very pleased with them but they are currently unavailable anywhere.
I'm pretty sure that the proper course of action is to retrofit a T/S ball bearing and grind, shim and fit the crankshaft as necessary.
Comments, anyone????
Many thanks.

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The engine number on your bike suggests its a 1965 A65L LIGHTNING ROCKET and interestingly if you compare the parts lists between 1965 and 1966, the D/S roller bearing part no 68-625 is used in 1966 whereas in 1965 the D/S ball bearing was used as part no 67-1240. Both bearings appear to use the shim cup arrangement to take up end float. So it may be that your bike was an early user of the roller bearing during the crossover period.

No idea about the T/S bearing pin or Kibblewhite bushes, but suggest you find a suitable NOS bush suitable for the crankcases and have it line reamed.

The SRM pumps are certainly the best you can get, there doesn't seem to be much info on the Hepolite pump but I don't see why they shouldn't work well. Having said that, there's not much of a price difference, so I would probably go for SRM.

I'm not sure I would retrofit a D/S ball bearing if a roller bearing is fitted, a lot would depend on how much end float there is and how the bike will be used in future. It seems possible that the D/S roller bearing is original so I would keep it that way.

Last edited by gunner; 04/13/22 7:04 pm.

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The two bearings share the same dimension and are interchangeable. The ball on 65 and earlier does not need the thrust washer as the ball locates the crank to the drive side and there is no lateral movement other than the miniscule running clearance of the balls in the race. The roller bearing however requires the thrust washer and proper shimming to limit float (lateral movement) of the crank. The roller has considerably more radial load and that is likely why BSA went this way. These bikes were hot rods of their time and were ridden hard. Setting up a roller to get the end float to specs really requires a dry assembly so the float can be measured and then selecting the shims on final assembly to get it within specs (.015-.003). Target your final float to the low end of the specs as the thrust washer wears over time increasing float.

Not sure which manufacturer's produce the best bush. I had my machinist make one for me. Align bore to get a true final clearance on the crank journal.

Mr Mike

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If the t/s bush is an early one it will have a thicker flange on the inner side.
As to the anti-rotation dowel, that was used 64-65 onwards.
The crank dimension across the webs changed when they went to roller
so you'll have to fiddle around with shimming if it's an early one.
Basically, any of the cranks will fit any of the cases with any of the bearings
but the degree of messing about changes.
Kibblewhite make a one piece t/s bush, their gear is high quality. I prefer the
original lined steel type but that's just me. If you have a lathe you can reline the
original, 660 is fine.


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