X30 Piston Clearance Fit

Is IAME overly conservative with their piston fits? I have had a used X30 in a box for a year and I am finally getting around to putting it together. The X30 overhaul manual calls for .11 mm clearance. Seems awfully loose.

I have always fit pistons tight on my own motors, but I am VERY careful with break in. Back in the day, for my best KT100 race motors, I would fit them at .0024"-.0026". In recent years, I have been working more on dirt bike motors, so may have lost my frame of reference…

For a 54mm bore water cooled iron liner motor, .085mm (.0033" +/-) seems more reasonable…

Assuming that it would be similar to the Parilla Leopard and with my experience with those engines clearance should be .005+. I know that goes against some of the principles on water cooling but the Leopard at least had to have that much clearance or it would stick before even broken in.

Thanks for the feedback. Now that I think about it…ALL the water cooled cylinders I have worked with have been motorcycles - NIKASIL. And all the iron liner engines I have worked with were air cooled. So I do not think I can draw any conclusions about IAME being “too conservative” in their fits. I will stick with the manual - .11mm.

I need to do my second engine. Don’t forget the size stamped on the piston isn’t the size of the piston it’s the size of your liner.

What do the 1^sel 2^sel 3^sel références equate to for the piston pin? I know it should be changed with the piston but I never know which one to order


Thanks…I am aware. Helpful for making sure you order the correct piston. I will say it is very annoying that IAME does not make any 54.07 and 54.17 pistons…

Isn’t a 54.27 Red 54.17 in size?



Green Dot means add .01mm to size marked
Red Dot means add .02mm to size marked

So, 54.10 Red means the finished cylinder bore should be ID 54.12. With a piston fit of .11mm, that means the actual piston skirt dimension of a 54.12 Red is 54.01mm!

It would be a heck of lot easier if they just put the actual size on the piston, and let us do the math. We are not going to trust what the piston mark says anyway. We are going to measure the skirt, and hone to our fit.

Crazy, I never knew that was the case. Would definitely be easier to just list the actual size. What is the intent of the red/green dot system?

Italian. They don’t do anything the easy way :rofl:


No. .11 is on the tight side for an X30. Iron bore TaG engines need loose pistons, as much as twice the clearance of a nikasil cylinder. A shifter builder I know stuck 2 X30’s in back to back sessions because he built them like he was building a shifter. As far as how Iame’s piston marking/sizing works:


1 Like

Good info… thanks.

Hi everyone, I currently have an X30 with a 54.05V piston which is due for a full rebuild but does not currently require honing (it was recently honed due to a seizure).

A lot of the other local competitors hone out the bore just so that they can fit the largest allowed pistons. Obviously, this will mean that honing any further will not be possible and a new cylinder will be required. Would the difference in performance (from the larger surface area/capacity) be noticeable enough to warrant such a risk, or would the difference be negligible?

Please don’t do that! Absolutely no difference and a total waste of money!


Why do the X30 and SSE 175 have an iron liner instead of a hard-coated linerless aluminum block?

That’s very good to know - thank you very much!

One of the main reasons is that with an iron liner you can fully and accurately machine the ports, and with modern cnc machines achieve very tight tolerances, which increases parity between engines.

1 Like