rebore clearance

Information relating to the Matchless G11 or AJS Model 30 600cc twin
paulvk
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rebore clearance

Post by paulvk »

i have taken some pistons to be rebored and was asked what clearance is needed, i was told there are many veriations bpending on the material of the pistons, im using hepolite pistons regards paul
iandusud
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rebore clearance

Post by iandusud »

What bike?

Ian
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Malleon
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rebore clearance

Post by Malleon »

Presumably a 1953 Model 20 !
spindle
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rebore clearance

Post by spindle »

I Think you first need to establish the size of the Barrels to see if they are standard ? or have been rebored before (most likely) i think i am right in saying they can be rebored up to 3 times +20 +40 +60
once you have established which you already have you can then source the next size pistons and rings up and have the barrels bored and honed to suite
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paul knapp
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rebore clearance

Post by paul knapp »

I think paulvk already has the pistons, and the machinist who is going to do the boring is asking what running clearance he requires.
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wilko
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rebore clearance

Post by wilko »

Wirewound 1 thou, other pistons 4 thou, JP 20 thou!
willschub
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rebore clearance

Post by willschub »

Only 20 thou? Less trouble to run without them.
iandusud
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rebore clearance

Post by iandusud »

4 thou sounds a bit generous to me but I have no personal experience of the bike in question. I do have personal experience of Hepolite pistons on various British bikes and I would tend to aim for around 1.25 thou per inch of bore. If we're talking about a Model 20 I believe it has a 66mm bore (2.6"). 2.6 x 1.25 = 3.25 thou. Others may have personal experience of the bike and pistons in question. BTW lower clearances could probably be used with gentle running in, but I'm not convinced of the usefulness of this.

Ian
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cf160
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rebore clearance

Post by cf160 »

I believe this topic was discussed in connection to the fittment of Heplex pistons to the Model 18 which has a standard bore of 82.5mm or 3.25"
It was the opinion of the forum at the time that
clearance 2.5 -3.0 thou per inch of Piston diameter
was correct according to the old Heppolite paper on the subject (which can be found in Christian's Archives under "Heppolite Piston Fitment"http://archives.jampot.dk/Technical/Pis ... gs_Valves/
Just reading over the page, actual piston clearance is not mentioned ,but "ring Gap" is mentioned : For standard use (non racing) a ring gap of .003" per inch of bore is recommended. I still think we decided that 2,5 thou per inch of bore was reasonable .
Dave(cf160)
You might ask Don Madden as I believe he is the resident expert on these matters for G9 and G11 bikes.
David J.Potter
iandusud
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rebore clearance

Post by iandusud »

I'm sorry Dave but 2.5 thou per inch of bore is way too much for any piston.

Ian
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