Ace 90 piston size identification

[jaybird]

I've torn down my Ace 90's engine for rebuild, and I'm trying to find out what size piston it has. The bore is no longer round, the ring end-gap is about a quarter of an inch, and the piston is scuffed up and grooved, so I'll have to rebore and go oversize on the piston. Trouble is, I can't tell what size this original piston is so that I can order a larger one.

I don't have a micrometer big enough to measure the piston diameter, but I was hoping that I could tell just by the markings on the piston whether it is stock or oversize.

Alas, there is no simple number on the piston such as 00, +10, +20, etc. What is stamped into the top of the piston is the number 75. Does that mean anything to anyone?

Tom

[rlkarren]

I had a similar problem. I solved it first, by determining standard size bore, and what over-size pistons were available. Then I took the cylinder to the machine shop and told them that the standard bore size is 48mm and which over-sizes you can get parts for and ask them to bore it to the smallest oversize possible according to available pistons kits..

Meaning I told him that the standard size was 48mm, and that I can get 10, 20, 30, and 40 over pistons. It was obvious I needed at least .020, but ended up with +.030.

[jaybird]

Thanks for the info. I guess I should let a machine shop tell me what size piston I need too. I just thought that there might be some mark on this piston to tell me whether it's the original (factory-stock) size or not.

Tom

[admin]

Tom 75 is a standard bore stamping on the crown of the piston. Remember though that Hodaka did not make odd size piston kits for the 90's. They were Std, +.20 and +.40. Rocky prior to becoming Tucker Rocky did make +.30 sizes which might still be available.
I hope this helps
Thank you
Paul

[jaybird]

That's the information I needed, Paul. Thanks very much. I'll take the cylinder to a machine shop now and see what size piston it will need after it's bored out enough to clean it up.

Tom