Compression check with exhaust and air box already removed?

[Metal_man_Rob]

I pulled the exhaust and air ox off, drained the tank and pulled all of that then remembered I wanted to do a compression check. I did it with exhaust and airbox off and got 110 on both sides.

Did notice faint vertical lines on pistons through exhaust ports but rings look great. Intake side is clean. Exhaust ports a gnarly and coked up.

Should I pull the heads and clean the ports and replace the rings and maybe pistons or run these since the compression is good but exhaust ports are funky?

 

 

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[375hp banshees]

That's really a personal / budget decision. wiseco forged pistons will be a definite longevity upgrade but 99% you'll need it bored..., ..., ... first. Have you ran it yet?
Can you read the numbers on top of the piston?

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[Metal_man_Rob]

Oh I ran it a bit. I just bought it Monday. 
I usually go with Wiseco pistons any time the heads come off. Cast pistons make excellent ashtrays.

Never rebuilt or did any work on 2 strokes other than helping my dad’s friend rebuilt my top end on a CZ Fanta 400 about 30 years ago. Haha. 
No I can’t see numbers on the pistons. I didn’t remove the heads since the compression was good. I meant to check it before I pulled everything apart and remembered to do it right before I was about to pulled the carbs and reeds.

[ATV_hub]

Looks like some blow by in the last pic? Or a shadow?

I would rebuild it. If they are cast pistons, although they are fine and you can run a tighter wall clearance on them, they don’t like to go past service intervals or put up with as much abuse as forged pistons, last thing you want is a cracked skirt and wrecked motor.

If you don’t know what’s in it or how many hours it has done I would rebuild the top end and inspect everything else. At least then you know what you have and can have confidence in your machine.

While it’s open clean up that exhaust port, If you want to eliminate or at least greatly reduce that carbon buildup polish it and  use a good ester synthetic oil

[Metal_man_Rob]

Right on, man. Thanks! I'll pull the jugs off tomorrow and get a measurement.  

Edited January 17, 2021 by Metal_man_Rob