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Merc800 #2 way low compression

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TOPIC: Merc800 #2 way low compression

Merc800 #2 way low compression 13 years 4 months ago #36458

Matt Topic Author Offline Gold Boarder Posts: 586 Karma: 3 Thank you received: 0	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? Check this box to be notified of replies to this topic. Note: BBcode and smileys are still usable.
	Please Log in or Create an account to join the conversation. Matt in Illinois I ain't here for a long time, I'm here for a good time !

Re: Merc800 #2 way low compression 13 years 4 months ago #36472

dave bernard Offline Platinum Boarder Posts: 1471 Karma: 95 Thank you received: 30	pull the intake port cover off and look in.on #2 Check this box to be notified of replies to this topic. Note: BBcode and smileys are still usable.
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Re: Merc800 #2 way low compression 13 years 4 months ago #36480

Matt
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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

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Re: Merc800 #2 way low compression 13 years 4 months ago #36497

Chinewalker Offline Gold Boarder Posts: 548 Karma: 42 Thank you received: 10	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. Check this box to be notified of replies to this topic. Note: BBcode and smileys are still usable.
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Re: Merc800 #2 way low compression 13 years 4 months ago #36514

Matt Topic Author Offline Gold Boarder Posts: 586 Karma: 3 Thank you received: 0	thanks... Check this box to be notified of replies to this topic. Note: BBcode and smileys are still usable.
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Re: Merc800 #2 way low compression 13 years 4 months ago #36637

Matt Topic Author Offline Gold Boarder Posts: 586 Karma: 3 Thank you received: 0	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??? Attachments: Check this box to be notified of replies to this topic. Note: BBcode and smileys are still usable.
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Re: Merc800 #2 way low compression 13 years 4 months ago #36651

daveswaves Offline Expert Boarder Posts: 396 Karma: 36 Thank you received: 0	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. Check this box to be notified of replies to this topic. Note: BBcode and smileys are still usable.
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Re: Merc800 #2 way low compression 13 years 4 months ago #36661

professor Offline Gold Boarder Posts: 758 Karma: 87 Thank you received: 1	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 ???? Check this box to be notified of replies to this topic. Note: BBcode and smileys are still usable.
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Re: Merc800 #2 way low compression 13 years 4 months ago #36686

Matt
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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

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Re: Merc800 #2 way low compression 13 years 4 months ago #37170

Matt
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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

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Re: Merc800 #2 way low compression 13 years 4 months ago #37181

dave bernard Offline Platinum Boarder Posts: 1471 Karma: 95 Thank you received: 30	pull the powerhead as an assy. Check this box to be notified of replies to this topic. Note: BBcode and smileys are still usable.
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Re: Merc800 #2 way low compression 13 years 4 months ago #37185

Matt Topic Author Offline Gold Boarder Posts: 586 Karma: 3 Thank you received: 0	thanks...may look it over later tonight..see what damage I can do. Check this box to be notified of replies to this topic. Note: BBcode and smileys are still usable.
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Re:Merc800 #2 way low compression 13 years 4 months ago #37205

frog Offline Platinum Boarder Posts: 1431 Karma: 59 Thank you received: 3	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 Check this box to be notified of replies to this topic. Note: BBcode and smileys are still usable.
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Re:Merc800 #2 way low compression 13 years 4 months ago #37223

Matt Topic Author Offline Gold Boarder Posts: 586 Karma: 3 Thank you received: 0	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..... Check this box to be notified of replies to this topic. Note: BBcode and smileys are still usable.
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Re:Merc800 #2 way low compression 13 years 4 months ago #38022

Matt Topic Author Offline Gold Boarder Posts: 586 Karma: 3 Thank you received: 0	could a guy use used piston in this motor or should I replace the the bad one? and would the Compression be different? Check this box to be notified of replies to this topic. Note: BBcode and smileys are still usable.
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Re:Merc800 #2 way low compression 13 years 4 months ago #38245

Matt
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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?