# Low Compression



## Robert Hunt (May 28, 2018)

My 2002 25hp.Merc ran great last summer then sat most of the fall . I had regular fuel in it with ethanol when started before winter I suspected water contamination and discarded it. The motor was put away without fogging it and now has 70 & 100 psi compression . Thinking rings must be stuck I have mixed 50 % acetone and ATF and poured in plug holes . Any ideas other than shooting myself for being lazy and stupid .


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## Weldorthemagnificent (May 28, 2018)

Seafoam has been known to work on stuck rings. 


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## richg99 (May 28, 2018)

I know far less than many about engines,...but....if you have stuck rings, would the engine even turn over?


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## KMixson (May 29, 2018)

richg99 said:


> I know far less than many about engines,...but....if you have stuck rings, would the engine even turn over?




The engine will turn over. The problem with "stuck rings" is that they don't expand as the piston moves up and down in the cylinder causing low compression. They are stuck in the grooves by carbon deposits and gummed up fuel.


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## richg99 (May 29, 2018)

Thanks. Now I understand.


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## Robert Hunt (May 29, 2018)

KMixson said:


> richg99 said:
> 
> 
> > I know far less than many about engines,...but....if you have stuck rings, would the engine even turn over?
> ...


 That is exactly what I believe has happened. It will start but very difficult and won't stay running . It has soaked for 15 hrs with 50% acetone and ATF . I'm going to move piston up and down 1/2 inch this morning then go kill things at the gym in attempt to keep my sanity . I be hoping for the WIN .


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## GYPSY400 (May 29, 2018)

Chances are the rings are stuck.. that's a fairly new motor to be worn out already.

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## DaleH (May 29, 2018)

I'd drain that out well and would then give that OB the 'Dunk decarb method' _shock treatment_ using Seafoam and the 1-gallon mix, but double the oil as Pappy suggests. And I suggest taking it easy on her ... I do it at a high idel speed and don't throttle the snot out of her. Always best done in the water, for adequate back pressure. 

See post: https://www.forum.tinboats.net/viewtopic.php?f=4&t=39239


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## nccatfisher (May 29, 2018)

richg99 said:


> I know far less than many about engines,...but....if you have stuck rings, would the engine even turn over?


Stuck as in stuck to the piston grooves, not stuck to the bore.


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## onthewater102 (May 29, 2018)

What type of merc (HP rating)??


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## Robert Hunt (May 29, 2018)

^ 25 Hp. ^ As of 1300 hr. I pulled cord till a vapor disappeared and did compression test got 100 top cylinder and 120 bottom. Trying some Sea Foam deep creep now . I still be a hoping :roll: ..................


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## onthewater102 (May 29, 2018)

I have an older one of these motors, if you check the parts diagram on your block based on your serial number and find the same image as I've got below then you've got a motor with a sealant between the two halves of the block (two parts marked number 1 in the diagram with no gasket between them). A leak there is another possibility for your problem beyond the stuck rings. I haven't personally had this issue (knock on wood) but I learned about it from another post somewhere on TinBoats.


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## GYPSY400 (May 29, 2018)

Nothing wrong with 120.. that Motor should run now. The other cylinder should come closer to 120 once it frees up


Robert Hunt said:


> ^ 25 Hp. ^ As of 1300 hr. I pulled cord till a vapor disappeared and did compression test got 100 top cylinder and 120 bottom. Trying some Sea Foam deep creep now . I still be a hoping :roll: ..................



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## Robert Hunt (May 29, 2018)

GYPSY400 said:


> Nothing wrong with 120.. that Motor should run now. The other cylinder should come closer to 120 once it frees up
> 
> 
> Robert Hunt said:
> ...


 =D> I be liking your post very much .


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## Robert Hunt (May 30, 2018)

First couple pulls it tried to start then flooded lower spark plug . With both plugs out and having ample time to dry out and several rotations of motor bottom cylinder went to 123 lbs. and top went back to 75 lbs. Thinking that there's no winning ............... But wife did make chicken dinner


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## muddywaders (May 31, 2018)

Robert you may be ok but running a motor with a stuck ring usually results in damage.Inspect the cylinders using a bore scope/inspection camera or you can remove the transfer port and exhaust covers.
Bent or broken reeds will result in low compression as will bad seals.Not familiar with mercosil blocks but the older mercs could be over-heated piston and rings fried but the hard chrome lining would be easily cleaned up with a scotch-brite pad or a quick hone new piston and rings and last another few thousand hours. These blind-bore motors are expensive to rebuild if needing oversize pistons and your money is better spent on another motor.mw


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