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TOPIC: Merc800 #2 way low compression
Merc800 #2 way low compression 12 years 11 months ago #36458
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I tested compression in a one of my other mercs thats hanging out in the shop...125,30,125,124...
any tips i could try to see if its a stuck ring? Skegs is messed up on the lower...but trying to figure if i want to mess with to get running or perhaps be my first part out? |
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Matt in Illinois
I ain't here for a long time, I'm here for a good time ! |
Re: Merc800 #2 way low compression 12 years 11 months ago #36472
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pull the intake port cover off and look in.on #2
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Re: Merc800 #2 way low compression 12 years 11 months ago #36480
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dave;
what will I be looking for? missing rings? scortched walls? weird that this is the only bad one? is the intake cover one gasket? i looked n my shop manual not very helpful..hoping maybe its just a stuck ring. i 'm assuming i can do this w/o pulling powerhead? is there a way to pull lower cowl to give me working room? |
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Matt in Illinois
I ain't here for a long time, I'm here for a good time ! |
Re: Merc800 #2 way low compression 12 years 11 months ago #36497
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The intake covers are on the starboard side of the motor. I wouldn't worry about the gaskets - with only 30psi, I doubt it's just a stuck ring. It is not uncommon for a motor to lose compression in one cylinder - it's actually how they usually happen.
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Re: Merc800 #2 way low compression 12 years 11 months ago #36514
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thanks...
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Matt in Illinois
I ain't here for a long time, I'm here for a good time ! |
Re: Merc800 #2 way low compression 12 years 11 months ago #36637
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well did as asked....an I'm quite certain I know what the problem is...now have to decide to do a tear down or perhaps...start pulling parts and do a little parting out???
 
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Matt in Illinois
I ain't here for a long time, I'm here for a good time ! |
Re: Merc800 #2 way low compression 12 years 11 months ago #36651
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Yup, you found the problem. Not an unusual problem. The rest of the engine is likely fine. It could be put back in use by replacing the piston and cleaning the aluminum deposits from the cyl walls with acid. Light hone and re assemble. Or part out if you wish.
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Remember, my opinion in no way diminishes your opinion, nor yours mine. Collectively, there is a middle ground that is \\\"correct\\\" for the reader balancing all the input.
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Re: Merc800 #2 way low compression 12 years 11 months ago #36661
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If you repair / replace the piston , you must determine / find / corect the cause of the damage.
If not you will just be doing this again. Bleed insert still in that wee hole ???? |
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Re: Merc800 #2 way low compression 12 years 11 months ago #36686
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I noticed up on #1 oil residue while #2 really have any..
I have wanted to to do a tear down on a motor...this one cost me the gas I burned to bring it home...so I guess I'm out nothing. I guess will this it over...it is complete, owner ran it for several years on his pontoon....the skeg is shot and I didn't run it before pulling the cover. thanks for the input.... |
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Matt in Illinois
I ain't here for a long time, I'm here for a good time ! |
Re: Merc800 #2 way low compression 12 years 11 months ago #37170
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if i attempt to tear into this motor
will i have to pull off carbs,starter...etc... prior to pulling the powerhead or pull it with thes on it? i will read through my shop manual to see what it tells me... also i did see piston kits on east coast marine..but wondering if I put new piston and rings in won't compression be higher and throw off the the motor if the other 3 are only 125 and the new one has 150? |
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Matt in Illinois
I ain't here for a long time, I'm here for a good time ! |
Re: Merc800 #2 way low compression 12 years 11 months ago #37181
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pull the powerhead as an assy.
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Re: Merc800 #2 way low compression 12 years 11 months ago #37185
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thanks...may look it over later tonight..see what damage I can do.
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Matt in Illinois
I ain't here for a long time, I'm here for a good time ! |
Re:Merc800 #2 way low compression 12 years 11 months ago #37205
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matt, frog here. i have a 1970 merc 800 with a good power head, if you need any parts let me know. should have stated that this motor is a parts motor, bad starter and ign system, and broken skeg also, have a 2 and 3 blade props for it. frog
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Re:Merc800 #2 way low compression 12 years 11 months ago #37223
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thanks frog...
this one I got bad skeg too.. but only one bad cyclinder...so thinking of tearing it down, and repair it...looks like i'd be a couple hundo deap into it. i will keep you in mind..... |
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Matt in Illinois
I ain't here for a long time, I'm here for a good time ! |
Re:Merc800 #2 way low compression 12 years 11 months ago #38022
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could a guy use used piston in this motor or should I replace the the bad one?
and would the Compression be different? |
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Matt in Illinois
I ain't here for a long time, I'm here for a good time ! |
Re:Merc800 #2 way low compression 12 years 11 months ago #38245
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so i pulled it apart tonight...got crank assem. out and 2&4 are bad...2 the worse 4 not sure how it held compresssion..bad lower ring..
no contimplating what avenue do I go? look for used pistons or buy 2 new and re-ring others? #2 cyclinder wasn;t scored but piston show some seird marring wondering if i can't see the bad on the cyclinder? |
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Matt in Illinois
I ain't here for a long time, I'm here for a good time ! |
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