Low compression

[apeephere]

Hi guys .
Usually I just sit and read but since I developed this problem I decided to join and ask for help ,so here goes.I have a 1988 Maxum with a 88-Force 85 HP Outboard Motor.I have had a problem starting and idling once it warms up and usually dying as I put it into gear so I replaced the fuel pump,siphon / pump ball,and even disconnected from builtin tank and went to portable tank and installed an inline filter so I could see the gas going thru.Unfortuneately I did all this before doing a compression test.I have 125 HP in #1,& #3 and 85 in #2.This was done with engine cold(warm weather,engine not started for about 3 hrs)and not with WOC-which I realized was the wrong way of doing it after I had removed the head.But with a difference like that in one cyl. shouldnt it indicate the same? Head looks fine ,pistons and walls all look in great shape -no scoring or anything and no breaks in the gasket. I am thinking possibly rings but figured Id ask as I did so many things incorrectly. Should I reassemble head(can i use the same gasket?)and redo tests?Or do you think its rings also and I should just continue and replace the rings? I only have a Selock Manual but have ordered the Clymer and am awaiting its arrival.Any thoughts would be appreciated!

 

[Bifflefan]

Re: Low compression

If you dont see any other problems then its a good bet one of the rings is broken. If it has run for a while like this then you may be able to see a small scratch line in the cylinder, but maybe not.

if you grab the suspect piston, can you rattle it? That doesnt indecate a bad ring but just anouther test to see if the piston or bore is bad.

 

[apeephere]

Re: Low compression

I can move all 3 pistons the same amount-just slightly and it does seem to clean the walls as i turn the flywheel. Thereare no visible scratches or anything.

 

[Bifflefan]

Re: Low compression

I can move all 3 pistons the same amount-just slightly and it does seem to clean the walls as i turn the flywheel. Thereare no visible scratches or anything.

if they all move the same then i wouldnt worry about the pistons or bore. just sounds like a ring broke.
Ive never rebuilt a 2 stoker but the manual should give you good advise. Id go with a complete rering and gasket kit. also while you have it apart check the reeds and such. just to be safe.
no point in doing it, and then having to do it again.

 

[apeephere]

Re: Low compression

OK THANKS
was kinda hoping that it might be something else but we gotta do what we gotta do

 

[Jeremy90bay]

Re: Low compression

Before you pull the thing apart, it is possible there is a stuck ring. I would first put a NEW head gasket on and do a real good decarb. it is possible that you cant see the break in the head gasket, that is why I suggest you get a new one. a good decarb will loosen up the rings if they are stuck. chances are if you broke a ring it would have at least scratched you cyl wall a little. I would do this before you go tearing your motor apart.

 

[foodfisher]

Re: Low compression

Try a decarb. I gained 25#'s on my low cylinder after two proceedures. May save some work.

 

[apeephere]

Re: Low compression

Not sure what you mean by a decarb. Are there directions on doing this anywhere?

 

[Jeremy90bay]

Re: Low compression

There is a great thread on here on exactly how to do it. just search decarb and you will find it.

 

[apeephere]

Re: Low compression

Thanks

 

[jerryjerry05]

Re: Low compression

SEafoam or Engine tune by Mercury are two ways to decarb.Follow instructions.
Don't waste anymore $ on those manuals.Try to get a Force/Mercury manual.Go to the Mercury outboard site and look for the manual links.More expensive but the BEST way to go.
There is a reason your center cylinder carbon'd up. Make sure there is nothing in the carb and look past it and see if there is anything in the reeds.
I have found the sound deadning foam and a dragon fly in the reeds and leaves.That will affect the cylinder.
Set the air screws,all the way in and out 1 to 1- 1/8thturn out.This can make the cylinder go too! J

 

[walk-on]

Re: Low compression

I would put it back together and perform a wet compression test on the #2 cylinder. From the Seloc manual:

Using a can of fogging oil, fog the cylinder with a circular motion to distribute oil spray all around the perimeter of the piston. Retest the cylinder. If the compression rises noticeably, the piston rings are sticking. You may be able to cure the problem by decarboning the powerhead. If the dry compression was really low and no change is evident during the wet test, the cylinder is dead. The piston and/or rings are worn beyond specification and a powerhead overhaul or replacement is necessary.

FWIW - I did this test on my powerhead a couple weeks ago and the compression increased on the bad cylinder to nearly the same as on the two good ones. I removed the head and found a broken ring and scored cylinder so I am in the process of rebuilding now.

It sounds to me like you are lucky on this one. I would be inclined to replace the head gasket and spray some Seafoam into that cylinder and let it sit for a couple hours. I would then proceed with the decarb procedures found on this site.

Good luck!