1996 40 hp mariner compression trouble

[logname]

hey guys,I did a compression test & found #1,#2 fine but #3 had a reading of 0 and #4 had a reading of 90.I was advised to put some oil in the spark plug hole & re-test to determine if it could be a stuck ring.After sguirting in the oil it almost imediately started dripping out from between the prop and the prop housing.Are these related issues?I'd appreciate your thoughts so when I take it in I don't get taken ,or is there anything else I could do? thanks.

 

[Nos4r2]

Re: 1996 40 hp mariner compression trouble

Err you wont want to hear this...<br /><br />It sound like you have a big gap where your pistons used to be-or at the best a big piece of scrap where your pistons used to be. Don't be surprised if this is gonna be expensive. Doesn't sound like they'd need to take you in on this one. The charges will be a lot in any case.

 

[Moody Blue]

Re: 1996 40 hp mariner compression trouble

Unless you made a mistake of some sort while testing compression me thinks you have a serious problem. Low compression is one thing but "0" PSI is a bad thing. Probably a hole in the piston or a melted piston. Ever overheated the motor or run it on straight gas ? How much oil did you inject into the cyls ? If you add enough oil it is possible for it to run down through the exhaust and out of the lower unit exhaust port.

 

[logname]

Re: 1996 40 hp mariner compression trouble

the motor has never been over heated that I know of and it's oil injected.when I look through the spark plug hole and turn the prop while in gear it looks like all the others.Is it possible to get a reading of 0 PSI from a bad or stuck ring?thanks for your input.

 

[AMD Rules]

Re: 1996 40 hp mariner compression trouble

My first thought if I was to see ZERO pressure would be a non-moving piston. When turning the flywheel slowly by hand, can you see the piston moving at all?<br /><br />Seems to me that a piston with a stuck or broken ring, or even a hole would generate some minimal pressure reading.<br /><br />Broken crank or connecting rod? Any unusual noise?

 

[logname]

Re: 1996 40 hp mariner compression trouble

when turning flywheel and looking though plug hole, piston moves like the rest of em.I can't seem to hear any odd noises.when putting my finger over the plug holes I can feel very very little pressure in this cylinder although it does'nt register on the compression gauge.

 

[Moody Blue]

Re: 1996 40 hp mariner compression trouble

Lets go back one step. What was the reason for the compression test in the first place ? Was/is the motor running before said tests ? These pistons have 3 rings. A stuck ring would result in low numbers not "0".

 

[Nos4r2]

Re: 1996 40 hp mariner compression trouble

What state were the spark plugs in? I'm wondering if you've blown a big hole in the head gasket thru to the water jacket rather than damaging pistons.

 

[logname]

Re: 1996 40 hp mariner compression trouble

The reason for the compression test was that the motor was getting increasingly difficult to start and the last time I had it out I was cruising along at 15-20 MPH and the motor just shut down,also I was told I should have more power.The motor was running but I was having a real hard time re-starting it so now she sits in the garage.The spark plugs are oily.Thanks for the help.

 

[Moody Blue]

Re: 1996 40 hp mariner compression trouble

Were you using the oil injection system or premixing the fuel ? Oil injection may have quit and possibly overheated the motor if it just shut down while under way. Did the warning horn go off prior to it shutting down ? If the plugs are oily/dirty, it would rule out the water jacket idea. If you were getting water in the cyls the plugs would look like they were steam cleaned. I'm still thinking a melted piston. Are the two cyls with bad compression the top two, bottom two, middle two or top and bottom ? What was compression on other cyls ?

 

[logname]

Re: 1996 40 hp mariner compression trouble

Iwas using the oil injection system and I've never heard a warning horn.The cylinders with bad compression are the bottom two.The top two cylinders both gave a reading of 120 psi.

 

[Moody Blue]

Re: 1996 40 hp mariner compression trouble

Could have been carb related. Each carb has its own idle mixture setting screw. If the lower carb was adjusted too lean this could have contributed to overheating by not supplying enough lubrication to the lower 2 cyls. This would also make it hard to start because the fuel mixture is very lean. Still have not determined though why compression is "0". Next step may be to pull the head off the motor and take a look inside.

 

[logname]

Re: 1996 40 hp mariner compression trouble

thanks for your suggestions and time.