Low Compression on 150

[brents]

I am looking at a 81 mariner v150. From what I can tell and the owner says the motor has had minimal use. However, it appears to be suffering from a bad rear exhaust gasket. The gasket can be seen, and is obviously blown. I checked compression and it indicated maybe bad head gaskets as well. Would the exhaust gasket drop compression as well. The low compression side was the same as the side of the exhaust gasket that was blown.

Compression was 105 on left 3 cylinders (looking from rear at plugs) and 95 on right 3 cylinders. The temp gage wire that goes into the right head was fried, only hanging by a couple strands.

Could it be this motor simply needs new head gaskets/temp gage and rear/maybe base exhaust gaskets replaced. Or do you think a rebuild is inevitable?

We started the motor, and it idled for a couple minutes. The tell tale picked up a bit with fast idle, but never really strong. It blew more air than water at lower idles. The motor never got hot though. It was also on muffs.

Thanks for your help. Also this is my second post, but nobody answered the questions in my other post.

 

[dwco5051]

Re: Low Compression on 150

I would buy only if the owner would pull the head and I could get a good look inside. If every thing but the gaskets look OK and the price is right I figure I would have had to buy the gaskets anyway. If he doesn't agree to this he probably will find someone who is willing to take a chance on a motor that would cost as much or more to rebuild than a good one is worth.

 

[brents]

Re: Low Compression on 150

I don't know if I am overthinking here or not.

It would seem the blown gasket being the same side as the low compression, and the compression being no lower than it is, and as even as it was, that the gaskets should cover it. If a cylinder was bad, or rings were bad I would have expected to see worse, or am I wrong in thought?

 

[dwco5051]

Re: Low Compression on 150

I agree with brents and that was my first thought. The burnt wire on the temp sensor made me wonder a little. He didn't mention if the paint on the heads appeared to have been affected by over heating or not so there isn't enough information for a complete guess as to the condition of the motor.

I am the eternal pessimist when it comes to spending my money on used equipment

 

[brents]

Re: Low Compression on 150

Re the paint on the block and heads, there is no indication of overheat aside from the frayed temp gage wire. Sorry if I am leaving information out.

The main question I need answered is, with the compression as it is, doesn't it sound more like a bad gasket rather than other potentially fatal diagnosis.

 

[Dukedog]

Re: Low Compression on 150

If the gasket your refering to is the exhaust divider gasket then no it won't. A bad head gasket has to be really, really, really bad for it to show on the entire side. Being fairly even on all three holes pretty much elliminates a bad gasket. Sounds like its just got low compression. But it could be tha comp guage. You need one that is KNOWN to be good or at least another one to compare it to if your not sure of your guage. One side being higher than the other is not unusal, not common, but not unusal. Usually if one side is noticably different the head has been trued, deck has been trued or possibly different head gasket. I've had a few motors over the years with this condition. Hope this helps..................D

 

[brents]

Re: Low Compression on 150

Duke,

Thanks for the great information. yes, that was the exhaust gasket I was referring to. I ended up not getting the motor, but the research done and iboats really helped me diagnose the motor, and determine the motor was not worth the investment.

Given what you have shared, and what I have learned, that leaves me to believe a rebuild will likely be needed in the near future for this motor, as the rings are likely giving way.

THANKS IBOATS YOU AND YOUR ARCHIVE ROCKS!!

 

[j_martin]

Re: Low Compression on 150

That was my first impression. I would bet overheat has taken the goodie out of the rings at a minimum, and spalled pistons likely. Running with exhaust gasses burning the wiring off indicates a pretty sloppy attitude on maintenance.

good choice
John