Pistons is demolished...

Found this when I pulled my jug off...Intake side skirt broke. Only debris I found were a few small flakes setting forward of my reed cage.Bottom end isnt siezed. Should I just flush oil a few times before My new piston goes in?


There won't be anything in your oil since the crankcase on a 2 stroke is separate from the transmission where the oil is. If you haven't already shine a very bright light into the crankcase, if you don't see any debris down there you may be ok. IMO, you would be wise to split your case and make sure your main bearings are OK, plus that would give you complete access to clean your crank case and make sure it is going to be solid.

always best to split the cases and inspect!

piston got loose in the bore (lack of maintenance) is the most common reason for your issue.

+1 lack of maintenance on the piston. Too much clearance lead the skirt to slap and desintegrate. How many hours was the piston ? How is the clearance ?

Far better to split the cases to clean every debris and check the bottom end because the debris could have or will (very common) :

-damaged crankshaft bearings

-damaged rod bearings

-deformed or damaged the inner case leading to future leaks

The bad news is you can't do it yourself if you have no idea how the engine works.

Anyway If splitted, take the opportunity to replace at least crank bearings.

And what contition is the cylinder ? Maybe it needs to be rebuilt aswell. Make it controlled and the ovalisation measured by a shop.

Agreed, best to split the cases. Make sure you measure your cylinder as well, if your cylinder is worn then this will end up happening again with the new piston.

Not sure on the hours. I bought the bike and the kid who previously owned it said the piston was new. Him being from southern maine I did not trust him..pulled jug off and found the piston as is. The cylinder is in good shape but not sure its within spec. Ill measure it tonight and go from there..I know he didnt take care of it because when I bought it there was no air filter. The clutch perch and lever looked like it came of his daughters huffy. Thanks alot guys

Another vote for splitting the bottom end. Cheap ins. & you'll have that piece of mind which is priceless in my book. As mentioned have the cyl. checked before installing a new piston.

Case is being split and cylinder being inspected today

Wellllllllllll.......I have an 81 YZ465 that was locked up, I pulled all the pieces out, flushed it with diesel and and compressed air. I spent a good 30 minutes doing this. I now have a good 8 hours on it. You would not go wrong splitting the cases, it's really pretty simple, but I got away with not splitting.

Edited by SMarquez

Since it was ridden without an air filter, I would install new mains and rod/bearings.

Edited by CamP

He said it wasnt run without one but, you are right..I will do that.

seem to have it coverd,

dont waste your time on cast pistons again, this has tobe at least the 10th cracked 2 stroke cast piston i have seen between all the different forums i frequent.



Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now