Engines sleeves and pistons will always be distorted. They wear more in one axis than on the other, therefore when measured one side will be smaller than the other. In full size racing sometimes they make the pistons allready with the shape to whish they will wear.

UH OHHHHHHHHHHH!
 

If you did any serious grinding on the inside of the sleeve you better replace it!!!!!!!!!!!:eek:

It is very complecate process-grinding the sleeve and if you want to do only one-it will probably costs for you the same if you buy at list 3-4 for new sets. It can be done by hand laping, but it is realy time consumption process to and if it is totaly destorted-ther eis no way you will be able to fix it cheap way. All tooling to griding sleeve costs aproximately $ 5-7 K.
Just get another set out of realy good material and it will last double what you have expirienced.
We use grinding and final polishing, honning doesn't give very good surface and it is working as griding tool for piston when we are run in engines. So only grinding and polishing. People who saw my P/S sets can tell you how it looks. BTW, pistons are ground too, individualy fit.
Paul I need your adress urgent, can you please send it to me, I got something for you.

On my engine ( PS12) induction is 230 degree, open at 25 ABDC and close at 75 ATDC, but it will not work on conventional design due to the great crancase volume. The best opening so far I found for MR12 is 215-218 degree, but the is great chace that shaft will simply broken-not a realy good materials are used for mas production engines. I heard a lot of modfyers are faced this problem.

Does anybody know the stock port timings on a Novarossi NS12S3.

thanks for the reply about duration TG......

I know some of you guys modify carbs....has anyone ever enlarged the venturi(sp?) on the carb to like 7.5mm and just used carb inserts to adjust to different sizes like 6.5, 5.5, 5.4 and so on

just mod my first engine WOW i didnt know i could do that with a dermel. can anyone help me mod the carb, i herd of something about drilling, and polishing.

Man that was a long time ago when they interviewed me for that article.

An its still a great article ;)

Dennis, How was the new motor? When will it hit the shelves?

hey folks.....


do the piston surface finish have anything to do with exhaust gas flow????

IMO, it's a myth, but I'd like to get some fedback from the experts......


thanks!!!

Nope. I guess you are talking about top of piston-this is only one place where exhaust gases meeting the piston. We are talking in reasonable limits. Build up on top of piston makes difference, finish on walls makes big difference, but not in relation with exhaust gases
Edward.

yes, I referred to the top of piston....

i was told that polishing the top of piston (the part closer to the exhaus port), gives a better flow to the exhaust gases, but I didnt believe.......

thanks edward....

Polishing makes your engine easy to clean and build up resistance ( from fuel deposits ).

Head clearance
 

Hi all.

This is not really a modding question but it seems to be the right place to get a sensible answer.

I am helping someone to tune a Rossi 173R12 X3 and am having some difficulty.

So I started checking through the basics and discovered that the head clearance would not compress a piece of 1mm solder.

Removed all the shims and the clearance is 0.7mm.

Can this be right. If not, what should the clearance or compression ratio be for 16% nitro?

Thanks