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Jubilee piston to bore gap.

Submitted by gary_turner on Mon, 17/10/2022
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Light Twins

Hiya - I'm having a standard bore cyl taken out for a +0.020" piston. I can't find in any info what the gap should be between the cylinder bore and +0.020"piston. Any info would be appreciated thanks.

Regards

Gary

Submitted by david_cooper on Mon, 17/10/2022

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Normally the bore should be exactly as specified...nominal plus 20 thou in this case, and the clearance is provided by the piston manufacturer.  Hopefully someone will know what the clearance should be, but it should depend on the actual piston material.

Submitted by doug_ellis on Tue, 18/10/2022

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I would firstly warn against having the reborn done by a business that usually rebores water cooled engines and uses modern pistons. Old pistons and air cooled engines need more clearance.

What I have done successfully is to go to a reborn man who is used to classic air cooled enggines. Take the barrel and the pistons and ask him to reborn to a size to suit the piston.

Submitted by ian_soady on Wed, 19/10/2022

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.. of these Christian chappies myself and use a rebore specialist......

Submitted by gary_turner on Wed, 19/10/2022

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Thank you for the responses. I am replacing the right hand barrel as it had a lot of the top fin missing. I acquired a decent replacement that was on standard bore. I took the standard bore barrel and +0.020" piston to a local well respected engine specialist. He basically asked me what I wanted the clearance to be. I did some research and the recommendations were:- for road use 0.002" - 0.003" and for higher revving competition engines 0.004" - 0.005". As the Jubilee is a short stroke higher revving engine, I have opted for the latter piston to bore clearance.

 


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