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General => General Douglas Discussion => Topic started by: sidecar willy on 19 Dec 2007 at 18:49

Title: Advice on larger bore/pistons
Post by: sidecar willy on 19 Dec 2007 at 18:49

Hi...I am sure Doug will be able to help here.

I recently picked up a spare 250 cc Comet engine which looks as if its been well used with the inside of the timing cover and crankcase gummed up with thick black oil [indicating either high mileage or that the oil never got changed]The engine came complete with a magneto and pancake dynamo. Good spares.

I intend to have the engine overhauled with new bearings and pistons...but as I will have a rebore on the cylinders..just wondering how far I can go with larger pistons. There looks like a lot of meat on the bores...and assuming I can get larger pistons thought I could take the bore out as far as I can take it. Of course this puts a strain on the bottom end...but with new bearings this might be possible.

Any ideas from the forum would be handy!!!

cheers
Bill

Title: Re: Advice on larger bore/pistons
Post by: Edin on 19 Dec 2007 at 19:27

Quote from: sidecar willy on 19 Dec 2007 at 18:49

Any ideas from the forum would be handy!!!   cheers  Bill

Hej Bill
3 or 4 years ago I made 250 Comet from the bottom.  As right I remember, I found out at that time, the 250 and 350
cylinders are identical - with exception of cylinderdiameter. I have stil many parts from that project.
kind regards Edin DK


Edit:  Quote tags adjusted 20/12/2007.  A.