1982 90HP Evinrude Compression Problem

[bo32792]

I'm working on a 1982 Evinrude v4 90 HP outboard that has been sitting at least 2 years (maybe longer). Initial compression readings were 100 psi on two cylinders (same side) and 60 psi on the other two. Got the engine running - started very easy and ran fine. The next compression check was done with readings of 60 psi on all four cylinders. The tstats were clogged (determined before engine got hot) Now in the process of replacing them. I don't know if the compression gauge is faulty, or if the engine needs a good decarb and then run for a longer period. I think that if the compression is going to stay at 60 psi then when the boat in in water the motor will bog down. I keep hearing "get rid of the motor" but it starts fast and sounds good. Hopefully someone can shed some light on potential problems and solutions. Thanks -Bo

 

[Docdoc]

Re: 1982 90HP Evinrude Compression Problem

Did you do the compression check both times after warming the motor up to operating temperature? If the engine had not been run for two years and you just checked compression cold, the two cylinders with higher compression may have had some corrosion old oil/fuel in them that made reading higher. The lower reading on second try (if done at normal operating temp) would be much more dependable for determining overall condition of the motor. I'm not sure how much good decarbing will do to increase compression. In fact you may see a slight drop in compression following decarb. 60 psi per cylinder doesn't sound very good to me. Have you gotten an estimate to see what a ring job would cost you?

 

[DHPMARINE]

Re: 1982 90HP Evinrude Compression Problem

Anytime you have reason to doubt any test equipment ....... STOP testing because you have.<br /><br />DHP

 

[ledgefinder]

Re: 1982 90HP Evinrude Compression Problem

Sounds like your gauge. It's pretty rare for all four cylinders to wear evenly like that. The other possibility is your starter solenoid.<br /><br />It's also rare (IMHO) for V4 thermostats to closed, particularly both of them. At least in my experience, they usually stick open. How did you determine that the thermos are stuck closed?

 

[Walker]

Re: 1982 90HP Evinrude Compression Problem

I believe a motor with only 60 psi would be very hard to start. Test again with a different guage.

 

[R.Johnson]

Re: 1982 90HP Evinrude Compression Problem

On the screw in side of your tester is a stem valve. It looks just like the screw in stem on a tire . You can use the same tool as used on a tire stem to remove it. Take it out, and clean, or replace it, Your auro store should have replacement valves. Tell them it is for your compression guage

 

[reeldutch]

Re: 1982 90HP Evinrude Compression Problem

yep i agree 60 psi on all cylinders is strange.<br />that does sound like something is going wrong with the test.<br />squirt some oil in the cylinders and try again with a fully charged battery.<br />and a other compression tester.<br /><br />i think you are gonna be fine.<br /><br />or may be your gaskets are blown???<br />retorque the heads before you do a other test.

 

[bo32792]

Re: 1982 90HP Evinrude Compression Problem

The initial compression check was done before the engine was fired up. The second reading was done after the engine was run for a few minutes. The water pump was working ok, but the outflow water was cold, then warm, then cold then hot, then back to cold, then steam – so the engine was shut down and tstats housing was removed. Both tstats was basically in pieces and the entire housing with pressure plugs were gunked up with sand and grit. All of this was cleaned, but now dealing with the middle ¼ bolt which broke off and now needs to be drilled out. I was concerned about a blown head gasket assuming prior cooling issues, but 60 psi all around seemed unusual. The compression gauge is a sears model. I will try another gauge, or replace the valve in the gauge. The starter solenoid was replaced prior to the compression tests being done. Thanks for all the help. - Bo