Norton piston clearance

Based on the information gathered here I am going to specify a. Again, many thanks forall the assistance. Joined Jan 20, Messages 7, From what I have gleaned, the C2 crank bearings are the ones to use. I got C3 before I got all the info, but don't expect any issues, I'm not racing. Yes, Leo has my head and am awaiting his work on it too. Got a call tonight from MMW about his back. Dave 69S. A couple of cents that may save some bux. Ya might what to do some searches on clearance fudge factors.

The " is for moderately run long enduring moderate tune engines. Throw in extra fuel burn and hi rpm and bore clearances need to open up. A prior post explained the main issue is not so much the total expansion but the oval shaped bore distortion and effects on rings and piston bind. If this is a competition engine, where scoring is more important than interval between over hauls, might consider the " gap and knurl the pistons to take up slap and self burnish the ridges to best fit on its own, with some gain in oil film function.

Special device does this and lasts pretty well in street use but gets worn down if pressing limits much. I suspect the same for the crank bearings with extra temp and rpm than standard. Past Norton dragster racers preferred the thinner early and Combat cases flexible to tolerate better the hi rpm crank jump rope. Too tight may cancel the superblend forgiving geometry.

R Model Tony. Joined Dec 26, Messages IMHO from personal experience For the street with cast pistons Seizure at. I dry fit the barrel, gasket and cyl head and look UP through them for possible fouling. Piston top edge contacting a gasket or edge of a combustion chamber is not unheard of if piston height exceeds barrel top. Deleting the base gasket may cause this problem. Axtell showed me how he honed cylinders, and told me to use. I did that for 20 years with Powermax pistons and never had any seizures, scoring, etc.

Only problem I ever had with them was the oil ring grooves would eventually wear out. The forged pistons expand more with heat, and really do need the extra. Joined Nov 26, Messages 2, Great to see so many chiming in on this one. So I'll throw in something. I'm talking about JS forged pistons - not other designs which are close but not the same JS pistons are short and lightweight.

I then polished off the scuffing which was minor and lightly honed the cylinders to clean up scoring scratches, ending up with. See photo below. In the real world some people are going to twist the grip within the 1st hour because they can't help themselves. So I recommend. There is no objectionable piston slap because the forged pistons expand more than cast pistons and take up the slack.

On the down side I have heard from several people who purchased forged pistons on their own and ended up siezing them or severly scoring them when running inadequate clearances at. By the way - forged pistons are stronger and longer lasting than cast pistons and can be made with a lighter design structure. Photo below is after polishing the pistons to.

Note that I only drill pistons for my own bike. The pistons in photo have been drilled, undermilled, and chamfered down to grams and the pins taper bored.

This makes for a smooth running Atlas that cruises at 70 to 80mph with tall gearing see photo. The top can get much hotter. I would be concerned at less than 4 thou with the normal pistons. In reality the barrel will expand much less than the piston as the coefficient of expansion is likely to be higher plus it will get hotter. The Norton Owners Club Limited. Registered in England No. VAT Reg No Norton Owners Club. Search Search. User account menu Log in.

Recommended piston to bore clearance for new re-bore. If they have not got the… If they have not got the pistons and the manufacturers recommendation, they should not be boring anything. Log in to post comments. Japanese engines came in with half a thou clearances, and British clapped out machines could not do that. We used to do them on a very expensive Swiss jig-borer when the boss was not present.

George is right as to attitude. The Norton Owners Club Limited. Registered in England No. VAT Reg No Norton Owners Club. Search Search. User account menu Log in. Can any one advise me on the piston clearance on a commando. Usually the information… Usually the information comes with the piston. Log in to post comments. Bike purchase in boxes with… Bike purchase in boxes with 2 new piston with it. Who made the piston, the… Who made the piston, the clearance is determined by method of production ie forged or cast and the type of alloy.

Clearances In the Dominator Service Notes, the recommended clearance on a is 0. If all else fails The old 'rule' for aircooled engines of 1 thou per 1 inch of bore is as good a starting point as any, especially as you are in the dark as to the pistons origins.

However it is a lot easier to go bigger than smaller! Modern clearances On the general point about clearance, I have just had my Mk3 rebored. I don't know the specifics Bore Bashing Norman's posting reminded me of many years ago while attending a Norton celebration where I was able to talk with some of the original foundry workers who actually cast the Norton and other vehicle barrels.

Takes some interpreting and is only a guide. In the companies death throes, My thoughts: Anything that would run would be seen as ok.