clearance pistons barrels A B

Ube

Hello;

I'm planning to rebuild a ducati engine, over time I have fortunately been able to find several special parts at an affordable price.
A couple of MP hc 94 pistons, carrillo rods, polished crankshaft, SP heads with ducts worked, flywheel, ergal pulley, etc, etc.

Near to moving in bringing the shaft, connecting rods and pistons to dynamically balance, i noted that the class of pistons (A) and cylinders (B) are different, I consulted the workshop manual and also the haynes where I found the maximum clearance values between the two (0,090mm), but not the values of the different classes of membership (0,A,B,C).

Not having a micrometer, I'm not sure to can use the new cylinders, or if I have to find a company that rectifies a pair of used.

I am aware about the fact that cylinders and pistons have to be of the same class to obtain a certain result, but the prospect of savings money captures me.

But just as I would like to understand and know how to read these classes, I did not understand also in what order of magnitude should be chosen and because the RS engines are all only of the class "B".

Thanks for the help from the most experienced, Ube.

brad black

it's kind of a moot point because you use what you can get. i think it'll make 3/8s of fuck all difference.

griff851

You kind of need to measure everything when you build an engine. They don't sort of just fit together. Get outside the operating tolerances and it will shit itself, possibly in a very expensive way.
The A's and B's etc are to do with machining tolerance runs during manufacture. Tool changes cost money and production time.
The operating clearances of components remain the same.

Mr.R

brad black wroteit's kind of a moot point because you use what you can get. i think it'll make 3/8s of fuck all difference.

I agree here, many years ago now I asked the same question of Steve Wynne of Sports Motorcycles fame and he replied...
"Use what you've got Steve It'll make Cock All difference!"
Ever since then I've mixed and matched A's and B's and nothing I've built doing this has blown up.
The difference between A's and B's are Microns/less than a thou.
To be fair though when building a new built motor I get the barrels coated to match the pistons that I'm using.

Steve R

brad black

yeah, if you don't have the stuff to measure it then get someone to do it - then you'll know. but if you can only get one size of piston then you run as is or get cylinders replated to suit.