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Howard Inough
Howard Inough
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My 71 engine has the 2 piece roller bearing. I have been told I can install a ball bearing and it is easer to set the crank side clearance. Do I have to change anything other than the bearing? Also my high gear bushing is a solid piece and I can only fine a split bushing. The split one has the same part number as the one in my parts book. Looks like the split one would leak. Any information is appreciated. Thanks Russ

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Both bearings require shimming. The roller bearing requires shimming to set end play. The ball bearing requires shimming to set running clearance.

It is also important to shim the primary to get primary chain running straight. Many overlook the primary shimming.


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yes you can fit a ball race. check the shimming to make sure the timing side thrust is not able to come away from it's housing
all the top gear bushings iv'e seen/used in the last 15 years have been split ones.

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Can anyone tell me the part number for the ball bearing?

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Russ,
JAF makes this bearing. It is an RMS-9 and most bearing suppliers should be able to get it. It is a fractional (non metric) bearing. Mine came from Buffalo Bearing....probably $75-$95. The nice thing about converting to the ball is the assembly is a little bit simpler. The running clearance in a non separable ball bearing is established in the manufacturing tolerances where with the roller you set clearance by shimming. The outer race of the ball is locked to the case and the inner race is locked against the crank so the crank assembly has virtually no lateral movement other than the tiny running clearance in the bearings, probably a couple ten thousandths. You probably want to install the shim cup and shims on a test assembly. This will ensure the rods are centralized under the cylinder bores and will give you an indication on whether the primary sprocket is aligned and ensure there is no bind. You probably won't have to shim the primary but check it.The thrust washer on the timing side does not have to be reinstalled but you can put it in and it won't hurt anything. If you plan to put it in (it doesn't really do anything), install it on your test assembly to make sure when you tighten the case bolts that a tolerance stack up doesn't put the crank in a bind (you might have mismatched cases). I put the washer back in to prevent the crank from shifting to the timing side in a ball bearing failure and subsequent catastrophic case damage. That is the only reason for reinstalling that I can think of.

Also note that the ball does not have the radial capacity of the roller but the earlier bikes used the ball bearing. When it is all reassembled the crank should be free tuning and there will be virtually no endplay as you typically detect in a roller bearing motor.

Hope this helps,
Mr Mike

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http://bearingsize.info/catalogue-o...rings/bearing-mj1.1-8-rhp-obj176777.html

Don't be tempted to use a 'budget' brand bearing here, well, not if you want it to do a few miles anyway.

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Classic British spares in California carries the higher end ball bearing.

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Thanks for the information. I have built a few Triumph motors many years ago but this is my first BSA. I am sure i will more question's. This forum is very helpful, Thanks Again

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Russ,
JAF is a Japanese firm that has made bearings since 1946. That ball bearing (RMS-9) is made in Japan. Most companies have taken their manufacturing to China. I don't know how JAF quality stacks up against known manufacturers like SKF,Fafnir, Torrington. Bearings Direct carries the bearing for $22.65 w/o shields/seals. Not sure who else makes these inch series bearings today. I believe my A65 is still running with this bearing. Richard Stone, who frequents this site, might know. I think he may still own the bike.

Mr Mike

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Is the ball bearing for the earlier engines the one i will need to order? CBS has 2 bearings listed with the same part # 70-1591. One is 68.95 and one is called the economy from Taiwan for 45.00.

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I recommend 70-1591 made by RHP (NSK) - England


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Russ,
I am not an expert on bearing grades and quality. This bearing is available thru many bearing houses. I would talk with your supplier regarding quality. The JAF I put in mine is dimensionally the same as the original inch series bearing and mine appeared (at least to me) to be high quality. As I said earlier it is made in Japan, not China....maybe that is worth something. I would install the best I can find. I am not sure the brand of the original bearing installed at the factory. The manufacturer may no longer make that bearing or for all I know they could be out of business. I will recommend the JAF from my single experience.

Mr Mike

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Originally, they would have been Hoffman which became RHP (Ransom Hoffman Pollard) which was then SKF


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