96 GTX 787 lower compression front cylinder

[ckk81]

96 GTX 787 lower compression front cylinder, 130 (vs 145 rear).

My real issue is the leakage show in the photo. Any immediate thoughts on a cause? Had the jugs bored to .25 over and used a wsm top end kit.

 

[Spider4real]

Looks like the oil might be blowing past the rave valve. I would check the bellow to make sure no holes and still attached properly.

 

[mikidymac]

On a fresh rebuild compression should be identical.
15 psi difference something isn't correct.

Agreed, looks like leaking RAVE valve for the spooge.

 

[ckk81]

On a fresh rebuild compression should be identical.
15 psi difference something isn't correct.

Agreed, looks like leaking RAVE valve for the spooge.

I agree on the compression difference. Any ideas? If the rave was trimmed too far would that harm compression? thanks.

 

[mikidymac]

No. It's cylinder, rings, and piston that control compression.

 

[ckk81]

No. It's cylinder, rings, and piston that control compression.

Thanks, any thoughts on a common issue for low compression on a fresh bore and rebuild? (AKA what did I screw up putting back together?)

 

[mikidymac]

Typically it is from the piston to cylinder clearance not being correct.
Did you take it to a shop that has 2-stroke experience?
Did the chamfer the ports?
Did you install the pistons with the arrow pointing towards the exhaust?
Did you install the rings with the stamp mark facing up?

 

[ckk81]

Typically it is from the piston to cylinder clearance not being correct.
Did you take it to a shop that has 2-stroke experience?
Did the chamfer the ports?
Did you install the pistons with the arrow pointing towards the exhaust?
Did you install the rings with the stamp mark facing up?

Yes, a lot
I don't know specifically, but I would bet yes. (I'll ask)
Yes
Pretty sure, but I guess it's possible.


Possible the rings rotated while sliding the jugs on, creating an issue?

 

[mikidymac]

Yes, a lot
I don't know specifically, but I would bet yes. (I'll ask)
Yes
Pretty sure, but I guess it's possible.


Possible the rings rotated while sliding the jugs on, creating an issue?

If the rings rotated the cylinder would have gotten stuck as the ring end locating pins won't let the ring get small enough to fit the bore.