Super Jet ADA Head 35cc domes compression problem. base gasket changed

Papnschmilees

Papnschmilees

Berinnn dinn dinn
Location
Seneca Creek, MD
I am finally ready to ride my ski after shortening the pole and installing the new head.

compression with stock head 155 front 150 back

installed head 185 front 180 back

put it in the water started it and thanks to the fogging oil I easily noticed that the base gasket was leaking badly. took it out of the water and tested it again
still 185 and 180

purchased new gasket from yamaha compared thickness with the blown one and it "looked" to be the same. Dropped the jugs back on without doing anything to the rings or cylinders.

now my comp is 160 front and 160 back. Tried the leak test and it held 8psi for 15 min then I stopped.


Is it safe to ride? any idea why im seeing the drop?
I sprayed more fogging oil and checked the comp again immediately and it was still 160

Do the rings reseat? or is the gasket really the culprit for 20PSI lost

thanks in advance.
 
tor*p*do

tor*p*do

Squarenose FTW
Site Supporter
Location
NW NC
if they are equal and passed leak test it should be safe to run
the new base gasket may be thicker reducing compression
 
Papnschmilees

Papnschmilees

Berinnn dinn dinn
Location
Seneca Creek, MD
I will take it out on Monday and check it again after riding it for a bit. I can see the base gasket changing the comp but 20psi seems excessive.

Sent from my ADR6300 using Tapatalk
 
Waternut

Waternut

Customizing addict
Location
Macon, GA
Cranking compression is very dependant on battery charge as well. So if you've been cranking a lot and haven't charged the battery, that may be the reason for the drop. The 5psi difference between cylinders isn't enough to worry about.
 
Papnschmilees

Papnschmilees

Berinnn dinn dinn
Location
Seneca Creek, MD
The battery was back on the charger while the head was back off. And its not the difference between cylinders I'm worried about.

Its the drop of 20 paid across the board after changing a blown base gasket with a new one.

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Waternut

Waternut

Customizing addict
Location
Macon, GA
If the battery is charged, the only real thought is the new base gasket is thicker than the old one. There is no way you could eyeball the difference between them. Even side by side, it's tough to see 0.010"-0.020" difference. Even if you checked the two with calipers, one could crush more than the other.
 
Waternut

Waternut

Customizing addict
Location
Macon, GA
Superjet-113 sells them. My recommendation is measure the old one if you still have a scrap of it and replace it with similar thickness. In general, 0.010" will give or take 10 psi on the motor.
 
Papnschmilees

Papnschmilees

Berinnn dinn dinn
Location
Seneca Creek, MD
Took it for a decent ride today still 160 -160 . I purchased two OEM base gaskets so I measured the extra OEM .025 and the one that was blown was .020 at its thinnest spot

So I'm baffled

Sent from my ADR6300 using Tapatalk
 
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