96 GTX Compression Test

[Bflauto]

I just got around to testing compression on a 96 GTX that Im fixing up for next year. The original owner said it was tested at 155psi.

I just recently finished doing the oil lines, fuel lines, and a bunch of random fixes. I finally got a compression tester today and attempted to test compression.

I got 73 psi on both cylinders. I am aware that this is insanely low.

I have a nearly dead battery that Im using to turn over the engine. It cranks pretty slow. My question for the smart people... Could a dead battery be the cause for low compression?

The ski starts up and seems to run fine. I've run it on the hose and able to rev it. Would it even be able to run at 73 psi?

I bought a really cheap compression gauge from Amazon. Could it be a faulty gauge, especially since both cylinders read the exact same value?

Any other thoughts?

 

[etemplet]

Lots of times low compression is from cheap gauges. Recharge the battery.

 

[mikidymac]

Yes, have a good strong battery, no jump packs! Hold the throttle wide open and crank until the gauge stops climbing.

 

[Grnbeano]

Agree with Mac on this one

 

[Web]

Just went through the same thing. Get a good tester. I read 90 on each and really had 155#

 

[Brewey]

I just got around to testing compression on a 96 GTX that Im fixing up for next year. The original owner said it was tested at 155psi.

I just recently finished doing the oil lines, fuel lines, and a bunch of random fixes. I finally got a compression tester today and attempted to test compression.

I got 73 psi on both cylinders. I am aware that this is insanely low.

I have a nearly dead battery that Im using to turn over the engine. It cranks pretty slow. My question for the smart people... Could a dead battery be the cause for low compression?

The ski starts up and seems to run fine. I've run it on the hose and able to rev it. Would it even be able to run at 73 psi?

I bought a really cheap compression gauge from Amazon. Could it be a faulty gauge, especially since both cylinders read the exact same value?

Any other thoughts?

155 on a 96 ski ummmm really , I have a 99 951 GTX and I have about 110 psi on both and with my son riding it because he’s lighter than I am he is saying 45 miles an hour out of it, I would suggest you run it up get it warm and Then test the psi but it will run on 73 the warmer it gets the better of me

 

[Web]

I will say mine was a 97 gtx

 

[etemplet]

I've had skis read in the 155psi range and I consider my gauge pretty accurate. Most engines 150psi is all you get. Compression readings are just a measurement and gives one a reasonable expectation of the condition of the engine top end and performance. I have had a couple of engines read 130 and 135psi that had scoured pistons and broken top rings with pieces missing. If compression is down there is a reason and for a two stroke it generally isn't worn rings only.

On a 787 or 951 you can remove the rave valves and get a look at the side and top of the pistons. You can see if the rings are stuck or if any metal has moved around. With the way people treat these engines, many times they don't last as long as they should. I shake my head a lot. Good Luck !!

 

[mikidymac]

155 on a 96 ski ummmm really , I have a 99 951 GTX and I have about 110 psi on both and with my son riding it because he’s lighter than I am he is saying 45 miles an hour out of it, I would suggest you run it up get it warm and Then test the psi but it will run on 73 the warmer it gets the better of me

The 951's run lower compression than the smaller Seadoo engines.

130 psi is perfect on a 951 and 110 is about the bottom. Cold or hot really doesn't make a noticeable difference on the compression numbers on these.

 

[nsoley]

Hello!

Sort of in line with the convo….

Picked up a ‘94 Seadoo SPI this weekend with the 587 engine.

I compression tested the jet ski and both cylinders were at 155. (Yay!)

HOWEVER, there was a very very very slight decay in pressure over time. (~ 3 minutes later the pressure reading for both cylinders was about 90 psi)

Is this normal? Is a decay in pressure after getting an initial pressure reading normal

 

[mikidymac]

No, that is not normal. Are you sure the cylinders were not full of oil causing a false high number?

 

[nsoley]

Hi @mikidymac The engine was pulled and almost all the oil came out of the block into the hull.

I also took a flash light into the cylinder head and it looked "dry" -> If the cylinders were full of oil, i think i would be able to see it. I also compression tested it twice with the same results.

If the upper end (or even bottom end for that matter) was bad, i don't even think the ski would be able to get up to 155psi, correct?