96 SPX and 97 GS compression readings

[brnr17]

Hey guys, i'm new to the site and tried doing a search but couldnt find exactly what i'm looking for. I'm looking at a package deal with the 2 pwc's above and a 2 place trailer for $2800. Seems like a decent enough deal to me (feel free to give me your thoughts) and i ran across a thread explaining what to check for when buying a pwc (great thread). I have a compression tester from working on my snowmobiles and i know they need to be within about 10psi of each other, but what kind of reading would be acceptable for these machines? 120,130,150?
Thanks in advance

 

[kustomkarl]

Ideally the compression should be 150 PSI.

Karl

 

[brnr17]

Ideally the compression should be 150 PSI.

Karl

okay, i know engine wear down and loose a little over time. at what psi does it have to drop to before it's in "engine rebuild" area

 

[kustomkarl]

Here is some basics on compression tests.

To test compression, remove the spark plugs. Place spark plug caps on the plug cap studs near the cylinder head to ground the empty caps. This completes the circuit of the ignition electrical system and prevents any electrical problems from the caps being un grounded. Using the correct adapter for the threaded end of the tester,( same length of the spark plug threads length)screw in the tester in one plug hole. Hold the throttle wide open. Push the start button. Watch the compression gauge, when it peaks out at the most compression, let go the start button. Read the psi number. I would do it 3 times to be sure it is accurate. Check all the cylinders the same way. The ideal compression is 150 psi per cylinder. If it is less, it's not a problem as long as they are close to being the same. If the psi is less than 90 it might need be time for a tear down and a rebuild. If the psi in 1 cylinder is say 140 psi and the other is 80 psi you need to tear down and repair. This difference is a lot then there is a problem. The ratio of difference is 10% difference between cylinder readings. I hope this helps you.

Karl

 

[brnr17]

Here is some basics on compression tests.

To test compression, remove the spark plugs. Place spark plug caps on the plug cap studs near the cylinder head to ground the empty caps. This completes the circuit of the ignition electrical system and prevents any electrical problems from the caps being un grounded. Using the correct adapter for the threaded end of the tester,( same length of the spark plug threads length)screw in the tester in one plug hole. Hold the throttle wide open. Push the start button. Watch the compression gauge, when it peaks out at the most compression, let go the start button. Read the psi number. I would do it 3 times to be sure it is accurate. Check all the cylinders the same way. The ideal compression is 150 psi per cylinder. If it is less, it's not a problem as long as they are close to being the same. If the psi is less than 90 it might need be time for a tear down and a rebuild. If the psi in 1 cylinder is say 140 psi and the other is 80 psi you need to tear down and repair. This difference is a lot then there is a problem. The ratio of difference is 10% difference between cylinder readings. I hope this helps you.

Karl

yes it does thank you ... so would optimum psi in both pwc's be 150 then? if i remember correctly they're different motors

 

[kustomkarl]

It doesn't matter on which engine...they should be at 150 psi.

Karl

 

[voodoo]

I have a 97 single engine boat and it started and ran with 140-80, you could tell something was not good and I quit before it locked from overheating, when I opened the cyl head the top of one piston had started the meltdown and you could see about 40 degrees of the ring, the ring land had melted away - based on this and what happened to Snipe with the same boat and motor I am thinking below 100 is the end. When you do the test open the throttle a little and then pour in a coffe shop spoon of oil to see if any marked improvement indicating the piston/rings zone is shot.