1996 Force 75hp Compression

[dmlinal205]

Can anyone tell me what kind of compression should I be getting on a 75hp 1996 Force?

After running a test I am getting 93 on the top, 64 on the middle, and 91 on the lower. It is obvious the middle cylinder is losing compression somewhere, but I am not sure if the other two are low as well.

Thanks for your input.

Mike

 

[TwoFish]

Re: 1996 Force 75hp Compression

Hi Mike. Welcome to Iboats.

No more than 10% difference between cylinders and 100 psi and over. If your gauge is a bit sus, or a push in type, it may account for your low readings. Are you removing all the plugs & using a screw in type gauge?

It?s more the difference between cylinders that matters but if you compression is really 90 psi then it is a bit low.

I have a 1998 75 hp & it reads 120 ? 125 psi with my gauge. I?ve had it serviced a couple of times & the compression figures varied from shop to shop. (110psi at one shop & 135 at another).

How well is the motor running now? Are you checking the compression because you are having a problem?

Cheers
Dean

 

[jerryjerry05]

Re: 1996 Force 75hp Compression

Sounds like the middle cylinder is way low.Spray some oil in the cylinder and re-test.
I'd guess you need to remove the head and check for damage.
With a good Gauge 150# is about right.Different gauges will read differently.
Your looking for readings close to each other.within 5-10# J

 

[dmlinal205]

Re: 1996 Force 75hp Compression

Thanks guys,

I am going to pull the head off sometime this week and check for scoring on the walls and how much carbon build up is inside. Afterwords I'll re-torque the head bolts to spec and run another compression test. If it is still running rather low on all cylinders I will just replace the head gasket, it is 15 years old, and see how she runs.

 

[TwoFish]

Re: 1996 Force 75hp Compression

My understanding is the head gasket needs to be replaces each time the head is removed. Don?t run the motor if you retest it with the old gasket. You don?t want water from the water jackets leaking back into the cylinders and damaging the engine. At 15 years old it will need replacing.

Good luck. Hope it?s a simple fix.

 

[dmlinal205]

Re: 1996 Force 75hp Compression

After some time waiting for a new head gasket to arrive and trying to borrow a torque wrench I finally got everything put back. The middle cylinder is scorched with definite signs of water coming into the head. The piston is in rough shape, but a little oil cleaning and some seafoam soaking it is in better condition than before. So after a cleaning on all the cylinders and replacing the head gasket and bolting everything back on I got 128, 103, 123 on the compression test. I am going out for a ride this weekend to see how it performs, but after running for 10 minutes in the driveway with the muffs on she sounded better than before.

 

[jerryjerry05]

Re: 1996 Force 75hp Compression

It will run better when U improve the compression.BUT!!! if there is damage already started running it will just make worse.
U might get by with honing out the piston after a while ity will need boring and a new piston.
Post a few pics of the trouble.J

 

[jason32038]

Re: 1996 Force 75hp Compression

Usually when you start the scoring process not only does it score the cylinder but the piston wears unevenly. It will flop around like a fish in the cylinder causing severe damage rendering that cylinder unrepairable unless you want to spend an arm and a leg sleeving,boring and honing the cylinder...id take it in or take it apart yourself it's easy.