Compression.. Thoughts?

[Yesterday]

SO I finally rebuilt every other flippin part of this motor (Merc 850) and here is how the power head looks after running and then cooling down some:

130
145
140
145

I know the other 3 are fine, but how suspect is that #1 cylinder? Would you run it like that?

 

[1nebel0]

Re: Compression.. Thoughts?

Sounds like you didn't do the rings if I understand your post....Spray Sea Foam through each carbuerator and the numbers could come back in line...The 130 is on the edge as you don't want much less than 15% difference between the highest and the lowest...good luck

 

[Yesterday]

Re: Compression.. Thoughts?

Sounds like you didn't do the rings if I understand your post....Spray Sea Foam through each carbuerator and the numbers could come back in line...The 130 is on the edge as you don't want much less than 15% difference between the highest and the lowest...good luck

Nope I didn't touch the power head mechanics. Lower unit, mounts, hydraulics, wires etc.

Hmm seems I've read this before. Spray it in through while it's running if I'm right??

 

[Chris1956]

Re: Compression.. Thoughts?

There is a procedure where you mix 1 can of Seafoam with 1 gal of 50::1 fuel and run it through the motor, stopping the motor just before you run out of fuel. Let her sit a day and then run "normal fuel" at high RPM to clean out the junk in the motor.

 

[Yesterday]

Re: Compression.. Thoughts?

There is a procedure where you mix 1 can of Seafoam with 1 gal of 50::1 fuel and run it through the motor, stopping the motor just before you run out of fuel. Let her sit a day and then run "normal fuel" at high RPM to clean out the junk in the motor.

That is not what I had thought I had read, but it sounds quite interesting. Thanks for the suggestion! The idea is to break free any rings sticking into the pistons??

 

[kazek]

Re: Compression.. Thoughts?

Follow the procedure and you will be happy boater.yes,idea is to free and burn off any carbon build up that can cause damage to engine.think used/fauled spark plug to give you idea what that can do

 

[Yesterday]

Re: Compression.. Thoughts?

After a couple of hours running her and tinkering here and there, had this rig up to 40MPH. after the run and some cool down, a compression re-check (carbs closed) showed 140-150 across all 4. I think I will still run the de-carb procedure because I have the nasty mixed up already, but it was nice to see it come around on it's own. Thanks again to all!!

 

[wired247]

Re: Compression.. Thoughts?

The 15% thing is just a good general guideline. If you have 130 lbs compression you have a good ish enough bore and rings. If it improved thats great but I certainly wouldnt kick it out of bed for only having 130 lbs no matter what the rest of the cylinders show.