'87 Inline 6 115 -- Low Compression on #6

[codertimt]

Hey guys. I just bought a fixer upper with a 115 Mariner on it...with a bad lower unit. Well before putting down the cash for a used lower unit, I decided it would be prudent to check compression and it all looked pretty good until #6. 1-4 all ~120 and #5 was 115. But #6 was only around 30.

I poured some oil in and retested and it jumped up to 80, so it's looking like stuck rings...or a melted ring/piston mess.

I bought it with the lower unit removed, so obviously these test are with the motor stone cold. So should I try to get some water to it, warm it up and Seafoam it before losing all hope...or is #6 most likely toast?

Thanks for any feedback... I know the answer is probably, "don't know...all you can do is try", but I thought I'd ask for opinions anyway. If nothing else, this let's me share my disappointment with a group of like-minded folks.

Thanks,
Tim

 

[AMD Rules]

Re: '87 Inline 6 115 -- Low Compression on #6

A value that low is usually a sign of damage above and beyond stuck rings, but ya never know. I'd probably opt to pull the lower inspection cover on the intake side and have a look. You can evaluate the condition of the cylinder, piston, and ring when looking in through the intake ports. Check the rings for free movement. If you push on one and it doesn't spring back, it is likely busted. I'd usually recommend you look through the spark plug hole as well, but #6 is near impossible to access without pulling the powerhead. Sometime you can get to it by lowering the rear of the cower cowl.

No real harm trying to use Seafoam, and running it, but I think its "toast", as you say.

Good luck.

 

[codertimt]

Re: '87 Inline 6 115 -- Low Compression on #6

Thanks for the reply.

Yeah, I think I'm ready to call it. I left it sitting with oil in #6 last night with the cylinders vertical...then ran it this morning a little to warm it up. Found metal on the plug... Re-tested compression warm and it was less than 30.

At this point, I don't think theres any real point to waste my seafoam on it. Since it also needs a lower unit, my original plan was to replace the motor with my old 85HP Johnson anyway, so I guess I'll go back to that plan...and the Mariner will get sold for parts.

Oh well, time to head over to the JohnnyRude section.

 

[AMD Rules]

Re: '87 Inline 6 115 -- Low Compression on #6

Good luck with your project.

I saw your signature.... are you a member here as welll?
What boat do you have?

http://www.readylens.com/messageboard/default.asp

 

[codertimt]

Re: '87 Inline 6 115 -- Low Compression on #6

Thanks.

My Glastron doesn't qualify as Classic. It's a 2007 GT 185, thus I was trying to start up a "regular old glastron" owners club. Not going so well so far.

The project with the Mariner is a 1986 Challenger Fish and Ski. Obviously I plan for it to be used for the former and will use the Glastron for the ski...

 

[quebec#1]

Re: '87 Inline 6 115 -- Low Compression on #6

I tried to become a member of your site but when i try to register it says my email address is invalid