JAP 600 cc Howard Gem Main Roller Bearing Question

[vhgmcbuddy]

Hello,

I was wondering if anyone could help me with this tricky rebuild?

I bought an unfinished project last year and am puzzled by the drive side main bearing.

It’s a crowded roller type (no cage) with 5.00 mm diameter rollers.

Most have flat ends but 4 are round (see pic).

Interestingly the round end rollers are slightly longer.

Is there a reason for this? Or has there been a mix-up?

Can I get away with mixing round and flat-ended rollers? Or do I need a new set?

Many thanks,

George

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[wristpin]

I’ve got a parts book for the JAP 600cc side valve Mark111 type 5 and the only place I can find a bearing with loose rollers is “timing side roller 15 “. You say drive side and your image shows 18 rollers! The driving side shows a normal ball bearing.
So I guess that either I’m looking in the wrong place or even the wrong version of the engine ?

[vhgmcbuddy]

Hi, I think this is an earlier version to the type 5. Looks like it was later revised to a ball bearing – not a good sign for my engine 🙂

[Author]

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