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B33 oversized question??

What is the largest bore that anyone has done with a B33 barrel? I assume I would have to put a larger liner in it. Just curious to know if 90mm is possible! If so any Ideas on a suitable piston?


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Re: B33 oversized question??

90mm isn't a problem...I have built numerous examples with a piston of that size...

When the barrel is bored out the spigot that locates it in the crankcase is lost but the barrel locates OK on the head bolts..Also the width of the head sealing seat is reduced...Again though, there are no issues with that...No liner is required unless you are planning to fit 112mm stroke M21 flywheels.

My own B33 had a 720cc engine to that spec. until recently...

Are you planning to 'stroke' it as well...? The M20 flywheels can be fitted (with suitable modification) for 598cc...The piston only will give you 559cc..

Avoid car pistons generally as the weight is excessive...Look for suitable motorcycle pistons bearing in mind the gudgeon pin to crown height, compression ratio and gudgeon pin diameter...

I have had batches of pistons made in the past but don't have any currently...

CP pistons (in America) will do 'one offs' to your pattern...Excessive compression ration doesn't do these engines any favours..8:1 to 8.5:1 will be ample to give you good performance when combined with suitable cams, port size, carb, crank weight etc...

You must lighten the crank if you want it to go well but even if you don't and only fit the piston you should have it rebalanced to a 60% balance factor..Ian

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Re: B33 oversized question??

Yes I will run 94mm stroke. So the barrel casting is good enough to bore? Thanks for the Info!


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