Super Jet 125psi??? youve gotta be kidding me

superjetguy

superjetguy

It's hard to speak without a tongue.
Location
lake hogan
hey guys i have my 96 superjet 61x/62t and i have a r&d head with what the seller said were 760 32cc domes, i put pistons in the ski less than 8 months ago and have probably 20 hours on it, i never checked my compression with this head, or with another head on this rebuild. i checked my compression with a $30 guage from pep boys. what do you think is is? crappy rebuild, head, or guage?
 
superjetguy

superjetguy

It's hard to speak without a tongue.
Location
lake hogan
the ski runs god for now but i dont know what i should start with when winter comes, tested with friends gauge is 130-130. i live locally to the ski clinic and had them mic my ski, i asked them to bore it and port the motor and they said its already ported and stock 701 pistons would work, so i dont think it could be that but i wont rule that out. oh and typo first post, ski has 30 hours maybe a little more
 
Matt_E

Matt_E

steals hub caps from cars
Site Supporter
Location
at peace
Hmmm it's ported and you were told to use stock 701 pistons?
I'd be measuring that bore and ring gap, ASAP.

A few years ago I bought a ported BB topend with new pistons from a board member. It ran okay but had low compression (120ish) even though I was using domes that should have gotten me nearly 200 psi. Turns out that the bore was big enough to actually need 85.00mm pistons, not the 84.00mm that were shipped with it.
 
Bobert540

Bobert540

Site Supporter
Location
Rockford,MI
I'm no engine builder but wouldn't you just take the diameter of the cylinder wall subtract the diameter of the piston and that will give you ring gap... I could be way off.
 
Matt_E

Matt_E

steals hub caps from cars
Site Supporter
Location
at peace
Bobert540 said:
I'm no engine builder but wouldn't you just take the diameter of the cylinder wall subtract the diameter of the piston and that will give you ring gap... I could be way off.
Click to expand...

That would be piston to wall clearance. Ring gap is the gap between ring ends, in the piston and in the bore.
 
superjetguy

superjetguy

It's hard to speak without a tongue.
Location
lake hogan
so i measured 81.2mm and my piston is worn out its a wiseco forged piston, with ~31 hours on it what couldve went wrong? now should i go 81.5mm or just go bigger while i have the chance? i was thinking 83mm or is it just not that big of a difference
 
550/440

550/440

Maybe I'll get it all the way around NEXT time....
Location
Arizona!
The easiest way I've found to measure ring gap is to insert the ring into the cylinder (without the piston), then use the piston to set the ring in the bore - slide the piston into the bore and level out the ring, and place it at a depth that would be easy to measure. Then, using a :):):):):):) gauge, measure the gap between the ring ends. You can also detect some (poorly) differences in your bore diameter from top to bottom by moving the ring further down the bore and measuring ring gap at intervals. It's the poor man's bore gauge...
 
ProSouth

ProSouth

Seriously, Don't be a dick.
Location
kawasakis suck
125 is too low I think for rings. I have worn rings and 35cc domes. Used to be 195, now it's 165. That entire topend needs to come apart. Measure end gap JUST like js/SJ said, measure bore with a gauge then piston with a dial caliper, not vernier caliper.
 
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ProSouth

ProSouth

Seriously, Don't be a dick.
Location
kawasakis suck
Wow, did you clean those pistons? Or we're they like that when you pulled the head? No need to measure, replace your topend and inspect your crank
 
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