Low compression one cylinder

[Dbroadbe]

I have a 90 hp Merc optimax dfi engine top cylinder reads 30 psi removed injector rail inside of cylinder looks normal, could an injector not delivering proper amount of air from pump be a cause for low compression

 

[racerone]

Doubt that.---.

 

[Dbroadbe]

No head to take off, I is a solid piece only splits at crankshaft

 

[flyingscott]

Look to see if you have access covers on the side of the block.

 

[Dbroadbe]

Look to see if you have access covers on the side of the block.

None

 

[Dbroadbe]

None, I think I will try swapping the air injectors between one and two to see if the problem moves with the injector

 

[flyingscott]

That is not how that works. Bet you have access covers on the right side of the motor. You have a dead hole no injector is going to fix that.

 

[racerone]

It is a different block from the conventional 3 / 4 cylinder.----Perhaps time to look for another motor.

 

[Dbroadbe]

It is a different block from the conventional 3 / 4 cylinder.----Perhaps time to look for another motor.

This is a 2009 with low hours, I'd rather try to fix it this is a direct fuel and air injection does not use mixed gas oil is injected into the main bearing not into the fuel mixture, burns straight gas so it meets CARB requirements

 

[racerone]

You might have to fix it yourself.-----Very few shops will entertain rebuilding these.----Rebuilt powerhead is an option.

 

[Dbroadbe]

You might have to fix it yourself.-----Very few shops will entertain rebuilding these.----Rebuilt powerhead is an option.

Having a real problem getting the flywheel off have a puller on it and tightened it as much as my ir impact will torque about 450 ftlbs don't want to heat it but may have to

 

[racerone]

I suggest you refrain from using heat.----Run to a Mercury dealer and have them pull it for you.

 

[flyingscott]

Get a bore scope

 

[Dbroadbe]

I got the motor all apart, burn piston in top hole

 

[stresspoint]

someone did not clean / replace the air pump filter and it caused it to burn up.

as posted not many people like to work with these motors (including me back in the day) because owners neglected to do "basic maintenance" , one thing leads to another and they suddenly stop in a cloud of smoke.

i have seen someone clean up the melted aluminum (melted piston) from the cylinder walls , stick a new piston in one of those motors and it run for many more hours afterward ,its probably still going strong because the owner understood that it needs regular maintenance.

 

[Dbroadbe]

I bought the boat from a novice boater, got it for a decent price because it wasn't running right, I'll get the cylinder bored and replace rings and bearings on all pistons put new filters in and clean everything up and should have a good running boat fuel pump was full of sludge so bad water drain was blocked filter looked like charcoal

 

[stresspoint]

I bought the boat from a novice boater, got it for a decent price because it wasn't running right, I'll get the cylinder bored and replace rings and bearings on all pistons put new filters in and clean everything up and should have a good running boat fuel pump was full of sludge so bad water drain was blocked filter looked like charcoal

if you keep those motors maintained you will get many hours out of them,
they are a good solid powerful motor when they are kept healthy .
enjoy your project and try to use OEM parts if available , cost may be a little more than aftermarket , but the extra cost will save you in the long term.

on a side note :although frowned upon in some circles . it is ok to bore 1 cylinder oversize and leave the others standard, just be sure to stamp the piston top as to what overbore you have done that cylinder.

 

[flyingscott]

You might want to find out why it failed in the first place.
Give the compressor a very thorough look over. Extremely expensive parts on that motor.

 

[racerone]

You have to be sure/ repair why it failed.----Or it will fail again.-----??---Computer read out might be helpful.----Must check cooling system and computer controlled oiling too.

 

[stresspoint]

You have to be sure/ repair why it failed.----Or it will fail again.-----??---Computer read out might be helpful.----Must check cooling system and computer controlled oiling too.

agreed : hence the reason not many will work on an opti when they have failed .
Op just to be on the safe side , grab yourself a shop manual and study up.
i also recommend to take it and have it checked and set up on a diagnostic tool before taking it for a first run sea trial after assembly..

not trying to scare you , just trying to save you the let down of the motor having a hissy fit the first time out .