How can I tell if I’ve had a piston wash out?

(Darrin Stuckwisch ) #1

How can I tell if a piston washed out on a bench break in? I have a rotax Max evo that is sealed so I can’t just pop off the cylinder. Is there any other way to tell?

(James McMahon) #2

What do you mean when you say “washed out” piston? I understand piston wash patterns, but looking to see exactly what you mean here.

You could peer into the cylinder with a scope like this. You can even record with it, which is nifty.

(Darrin Stuckwisch ) #3

I meant, when you are breaking it in not letting it stay at one rpm as to not get piston scuff in the cylinder?

(James McMahon) #4

Gotya, naturally the only thing you can do without breaking the seal is inspect the cylinder wall. Scopes like the one I linked often come with attachable mirrors that make it easier to see out the side.

Piston wash is a pattern you’ll find on the crown of a piston that gives an indication of how even the flow is between the ports as well as an indicator of where your jetting is at.

Here’s an example of piston wash pattern:

(Marin Vujcich) #5

Pull off exhaust and look at piston skirt and cylinder wall.
If all good then get into it😉