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primary chain needle roller bearings

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UKROBK7:
I spoke to a specialist reborer about a clean up hone and new rings which I have always had done.  He said that in his experience on most air cooled engines he found that because most bores went oval and tapered it was better to leave well alone so long as the rings met specification, he found that honing the bores usually worsened the problem of getting a good seal.  I haven't measured my rings yet so as the original compression was good (the variation across the cylinders I now put down to having worn valve faces on some valves, seats are OK) I may put the old rings back in if they are OK.  I think this is one of those things that there will be a difference of opinion on!

Ash, good point about the rubbers hardening, I never thought about that.  You are right, I won't be doing many miles after rebuilding this, I will have to live with the hardening of the rubbers unless something comes up before I get started an assembly

Rob

K2-K6:
It's interesting to get a perspective from somebody that is working on them all the time and certainly gives you more to make a decision on.

I guess when you're talking to someone using proper engineering equipment that they can see and measure to an accuracy beyond normally equiped mechanics workshops. He is correct in that the bores ultimately go oval in the plane of the con-rod as the piston really has no thrust imposed on the sides of the bore, also the effect of any unburnt fuel is to reduce cylinder wall lubriction more at the top of the barrel so giving a taper-type wear pattern.

I would assume that if you can see the hone marks evenly all round the cylinder wall then that proves you have low wear so far in it's life, which also adds up as the K7 has accelerator pumped carbs (I think) which allow them to run generally leaner and leave less unburnt fuel for washing the oil off the bores.

Sounds like it's in reasonable order.

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