Very odd compression problem

[88yfs]

Hey guys I just recently put a new wiseco piston and rings in my blaster. I used three heat cycles and rode it very easy for the first full tank of gas. It starts first kick cold or hot and has decent power, but I did a compression check just to see what the status is after two tanks of gas. It read 90psi! Um how could it run so strong and start first kick with that amount of comp on a new top end? Help please.

 

[motoman159]

My guess is your tester has a leak, it's it easy to kick over?

 

[scotj77]

so you just bought a piston and rings and put them in without getting it bored or honed? did you have the cylinder measured to insure it hadn't worn outside of specs? I'm sure this is your problem if you did not do these things

 

[88yfs]

No I honed it and it was in spec that's why I'm confused lol

 

[sicivicdude]

No I honed it and it was in spec that's why I'm confused lol

Just for giggles, what is spec?

 

[88yfs]

It's harder to kick over than the last top end but I also ride a crf250 so al two strokes seem easy to kick to me

 

[88yfs]

Spec is the tolerance measure that the cylinder must meet. If it exceeds this limit than you need a bore job.

 

[scotj77]

he meant the measurment for the tollerenaces on piston clearance

 

[sicivicdude]

Spec is the tolerance measure that the cylinder must meet. If it exceeds this limit than you need a bore job.

Not to be overly rude, buy no sh*t sherlock. I meant, what IS the specification and what is the current bore size?

You said it's in spec but you'd certainly need to know what that is before you can say it's in it.

 

[sporty982000]

No I honed it and it was in spec that's why I'm confused lol

you might want to check you're bolts, make sure they torqes or tight !

did you use new gaskets ?

you said you found that the cylinder was in spec, what size was it ? what size piston did you get ? what was the ring gap.

you pust the new piston ring in the cylinder by itself and see what the gap is and measure it.

Sporty

 

[88yfs]

Lol I honestly don't understand it. Because it runs flawlessly. But with that low of comp? .. And my comp tester is brand new and I kicked it over wide open throttle and gas off.

 

[scotj77]

I have seen blasters run fine at 90 psi. but it isn't something you want to do. you will develope piston slap. so what size piston and what size bore?

 

[88yfs]

New gaskets .. And sorry lol it's still on stock bore . My buddy measured the bore with his tool and he looked at the book and was still in spec. 66mm but I can't remember off the top of my head what the measurement was exactly

 

[88yfs]

With a 66mm wiseco pro lite piston kit and new wrist pin bearing

 

[blasterBruce]

With a 66mm wiseco pro lite piston kit and new wrist pin bearing

Just so you know , wiseco forged pistons use a different cylinder to bore clearance Vs a Cast stock wsm/art piston

 

[sporty982000]

Somethings not right, I dont see how that bore is still stock size after all those years !

Either dont worry about it and run it, or pull it and take it to a machine shop and have it checked right.

Sporty

 

[sporty982000]

Well did ya measure it after you honed it ? the spec would not be the same as before.

Sporty

 

[88yfs]

It's a 2002 motor sorry lol the 88 tranny went in 2001 . And I didn't know about the clearance difference. It fit very snug in the cylinder though just like it should? And I don't meen to aggravate anyone if I am. Im just very curious.

 

[blasterBruce]

It's a 2002 motor sorry lol the 88 tranny went in 2001 . And I didn't know about the clearance difference. It fit very snug in the cylinder though just like it should.

yeah more than likely too snug for comfort , that might be a problem !

 

[sporty982000]

try re torqing the bolts !

you did warm the engine up first, prior to compression check ? and had throttle full open, while kicking ? to check psi >>

Sporty