Compression Help!

SurfCrazed

SurfCrazed

Location
Southern Virginia
Im currently building a 701 for my ski and I have torqued all the bolts down properly and everything in the cylinder is new bore (2mm over), rings, pistons (sudco), and gaskets! I only get 90 psi for compression!! what could be wrong?!?! Also both cylinders are at 90 psi. Also I have no idea if the compression guage is working right or not i barrowed it from a guy at work it uses an o-ring to seal it could that be a problem?? I was told that the piston to cylinder wall clearence was suppose to be .005 in but i can go all around the piston with a .006 filler guage but nothing any higher could that also be the problem?? I did lube everything before installing with some Yamalube i had from last season
 
Last edited:
meatball

meatball

User Title Unavailable
Location
Maryland
test a ski that works fine and see what numbers that puts out. Might try putting a teaspoon of motor oil in the plug hole. Not sure what you meant by you lubing it all.
 
vomitspot

vomitspot

Location
mobile alabama
you have the arrow pointing to the exhaust port right! hope so
what king of head are you useing?could be a bad gasket/orings
also open the throttle when checking comp
 
SurfCrazed

SurfCrazed

Location
Southern Virginia
meatball said:
test a ski that works fine and see what numbers that puts out. Might try putting a teaspoon of motor oil in the plug hole. Not sure what you meant by you lubing it all.
Click to expand...
I dont have another ski with me at the moment its 2 hours away at another house.. I basically did what you said but with the head removed.. Also YES i have the F to the front of the cylinder and the -> to the exhaust ports! I havent had a carb even on the motor while testing... and tested with one no change!
 
SurfCrazed

SurfCrazed

Location
Southern Virginia
vomitspot said:
you have the arrow pointing to the exhaust port right! hope so
what king of head are you useing?could be a bad gasket/orings
also open the throttle when checking comp
Click to expand...
Hey I bought the pistons from you would know where i could get some rings for these since they have the little pins for the rings in them or does any ring for 2mm over work?
 
Speedfreak

Speedfreak

Location
So. IL
You said stock head so check you squich clearance to see how far that head is from the piston.

I am just drawing at straws trying to find somethign that you missed.

And all pistons should have alignment pins to keep the rings from moving around the piston.

And another thing get a couple of adapters and hook your compression gage to your air compressor. That is what I do to check my compression gage. Doing it that way then you can use the schrader valve on the side of the compression gage to even check thoes gages with tire gages. I have 9 pressure gages in the shop and they only vary about 8 to 10 psi one extreem to the other and my compression gage is right in the middle.
 
SurfCrazed

SurfCrazed

Location
Southern Virginia
Speedfreak said:
You said stock head so check you squich clearance to see how far that head is from the piston.

I am just drawing at straws trying to find somethign that you missed.

And all pistons should have alignment pins to keep the rings from moving around the piston.

And another thing get a couple of adapters and hook your compression gage to your air compressor. That is what I do to check my compression gage. Doing it that way then you can use the schrader valve on the side of the compression gage to even check thoes gages with tire gages. I have 9 pressure gages in the shop and they only vary about 8 to 10 psi one extreem to the other and my compression gage is right in the middle.
Click to expand...
What could i use around the house to measure squich? i know some use solder but i have none around! is there something else?
 
Speedfreak

Speedfreak

Location
So. IL
Umm I don't know of anythign else. It has to be soft enough to compress but you can't hvae it so soft that it changes while you pull it out of the cylinder.

I have heard of putty but that would stick to other things and cause a big mess.

Just get some solder tomorrow. Se if anyone has a roll that you can borrow or just run to Lowes and pick up a small roll. You can get the bigger stuff in small amounts over in the pluming section.
 
SurfCrazed

SurfCrazed

Location
Southern Virginia
I ordered the headgasket from AlanticJetSports. I have a 62T(701) Cylinder(im a cheapo!)and a 61x Head but didnt think it would matter and on AJS they had 2 different gaskets one for 61x and other for 62T(701) Cylinder but all i heard was the only the port timing was different could this have anything to do with it?? should have i gotten a 61x gasket?
 
Waste Land

Waste Land

Non Multa Sed Multum
Location
Florence, AL
90sJ said:
I ordered the headgasket from AlanticJetSports. I have a 62T(701) Cylinder(im a cheapo!)and a 61x Head but didnt think it would matter and on AJS they had 2 different gaskets one for 61x and other for 62T(701) Cylinder but all i heard was the only the port timing was different could this have anything to do with it?? should have i gotten a 61x gasket?
Click to expand...

62T as in from another jetski? Or Still stock cylinder. Roundnoses too use 61X cylinders just 62t cases
 
SurfCrazed

SurfCrazed

Location
Southern Virginia
Waste Land said:
Correct me if I'm wrong....but dont 62t and 61x cyclinders use diffrent heads? I know ADA sells a kit for both...is your domes the correct diameter for that cylinder and bore?
Click to expand...
yes every fit prefect all bolts go in perfect and line up. I have no idea what the difference in heads is so.. :dunno:
Edit: i just looked on ebay at a raider motor to check the head out and it doesnt look any different from a 61x and the gasket fits perfect on the 61x head with no over hang or covering up part of the dome
 
Last edited:
ski4

ski4

gonzo
Location
cleveland
you are doing a lot of things and really i am betting that guage is not any good.
get a new guage if you don't have another ski to verify it on. or go rent one at autozone
 
Air Gramps

Air Gramps

Air Gramps
Location
Virginia Beach
Pretty sure it's the compression gauge..... swing by my place this weekend.


All this reading, you did align the rings with the piston pins ? and what was your ring cap at?
 
ski4

ski4

gonzo
Location
cleveland
really think you need to 86 that guage and try again
i have an old one i had to stop using cuz it would just peg at 120 didn't matter how much higher it should read , always 120 and nothing more
just check with another gauge before you start pulling heads and checking ring gaps and all the other bummer stuff
 
You must log in or register to reply here.
Top Bottom