New here, did some searching and didnt find much. Picked up a blaster recently with a 240 kit in it, (bore measures 72mm at the "ring groove"). It has 115# of compression and runs like a top, but the piston can be moved around a bit in the cylinder. This movement seems excessive to me. Is there a way to measure clearance without pulling it apart? Should i even be worried yet?
How loose is too loose?
- Thread starter Uhoh0573
- Start date
With that compression reading, it's time for a new top end. Stop running it before you break a skirt off and screw up your cases.
4 stroke or 2 stroke, if the bore is out of specs, a machine job will be needed to fit an oversize piston.
You cannot just slap a new piston in a worn bore.
Measure the bore and proceed from there.
You cannot just slap a new piston in a worn bore.
Measure the bore and proceed from there.
If it all measures up good run it! I don't hone jugs unless new rings are used, the pins in the ring groove keeps them in place and they are broke in to the jug.ur compression is an indicator of a worn topend or leak of some
kind. Better Yank it and investigate!
kind. Better Yank it and investigate!
Only once have I put a new piston in an existing bore. Discovered a crack and it was less than half the service limit. A quasi restoration I knew wouldn't be ridden much or hard.
If it's within acceptable limits of wear you could do hone and rings. Did you compression test before teardown? Results?
If it's within acceptable limits of wear you could do hone and rings. Did you compression test before teardown? Results?
With 4 strokes one does have to hone the bore as the rings seldom will go back excatly in the same place as they are free to roam.
With a 2 stroke where the rings are pegged so that they cannot move it is not nessesary to hone if one is putting the same ring in its original groove.
Although it it is not nessesary to hone, I always diagonally deglaze the bore, and after leak testing, heat cycling to condition the gaskets, and re tensioning , take it easy for a while before I fang it.
But why, when you have it apart do you not put a fresh set of rings in.
With a 2 stroke where the rings are pegged so that they cannot move it is not nessesary to hone if one is putting the same ring in its original groove.
Although it it is not nessesary to hone, I always diagonally deglaze the bore, and after leak testing, heat cycling to condition the gaskets, and re tensioning , take it easy for a while before I fang it.
But why, when you have it apart do you not put a fresh set of rings in.
My blaster budget grew a little this week so looking like im just going to put a new piston in and be done with it. The current piston is forged and has the cutout on the top exhaust side, that is a vito's im assuming?
Picked up a bbk vitos gasket set with an extra base, going to pressure test one more time before i put the new piston on. I figure its worth wasting one base gasket to be sure...
Picked up a bbk vitos gasket set with an extra base, going to pressure test one more time before i put the new piston on. I figure its worth wasting one base gasket to be sure...
yea your def. gonna need at least a set of rings. my stock bore cyl. comp. is 125-128PSI so a 240bbk has to be higher at least 160-175psi i think dont quote me on that.
Don't forget to add 3.4% for every 1000ft in altitude above sea level to your readings to get "sea level" readings. EVERY manual is based upon "Sea Level" readings.
Where are you located? What altitude are you at?
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