1997 Mercury Sport Jet head gasket advice.

[fierodough]

The engine is a 175HP XR2 from a Doral jet boat.

I have low compression on the 3 cylinders on the starboard side.

Port side is 130psi, 130psi, 130psi
Starboard is 20pse, 90psi, 20psi.

I took the head off and this is what the head gasket looks like:

Top cylinder 20psi

Middle cylinder 90psi

Lower cylinder 20psi:

I'm concerned because the compression ring portion of the head gasket looks intact. I can't really tell where it was leaking.

I have some scoring in the cylinders but nothing that seems critical..

Here is the head after cleaning and resurfacing. (it was slightly warped, probably still within spec but made it perfect)

I ordered the new head gasket and hope that will solve the problem. Would there be anything else that would only affect the 3 cylinders on the starboard side and leave the port side cylinders intact?

How many reeds on this type of engine? Is there separate reeds for port and starboard? and do the reeds affect compression readings?

Thanks guys! I'm very familiar with automotive engines but when it comes to marine, I'm a fish out of water..

Cheers!

 

[wired247]

I think you are barking up the wrong tree. 20 PSI is almost hole in the piston territory. I'd be looking at bore and ring condition. Your heads look fine.

FWIW those are torque to yield fasteners on the heads 30 lb/ft plus 90 degrees. Some people will reuse them at 37 lb/ft. I won't.

Each cylinder has its own bank of reeds.

 

[fierodough]

Do the reeds affect compression? While looking in the cylinders, I don't see any obvious broken rings and surely no holes in the pistons.

 

[wired247]

They can but not that much. Once you get the heads back on do the reed check test and hook a low pressure ( under 10 lbs ) gauge to the bleed fittings and start it up . You should have 5 lbs of pressure in the crankcase at the bleed valves. Remember that each cylinder basically has an individual crankcase with its own sealed air path from the carb to the exhaust. Reeds are unique to that cylinder.and there are sealing rings on the crank to isolate cylinders from each other.

I'd look for stuck rings if it has sat for a while. Do a good decarb with solvent to free the rings up.

 

[fierodough]

They can but not that much. Once you get the heads back on do the reed check test and hook a low pressure ( under 10 lbs ) gauge to the bleed fittings and start it up . You should have 5 lbs of pressure in the crankcase at the bleed valves. Remember that each cylinder basically has an individual crankcase with its own sealed air path from the carb to the exhaust. Reeds are unique to that cylinder.and there are sealing rings on the crank to isolate cylinders from each other.

I'd look for stuck rings if it has sat for a while. Do a good decarb with solvent to free the rings up.

Thank you for the info!

I will check the bleed valves. Once I took the heads off, I've been spraying the cylinders / pistons on the starboard side (the bad side) with Sea Foam. I hope this helps free up the rings.

 

[Faztbullet]

Lets see a picture of this non critical scuffing...

 

[fierodough]

Lets see a picture of this non critical scuffing...

This is the bottom one (20psi) the cylinder wall is actually very shiny... The piston itself is nasty and there are light ridges on the cylinder wall.

This is the middle 60psi cylinder

And this is the worse one, the top cylinder also 20psi. The lines are not as bad as they seem, I sprayed tons of seafoam in there and moved the piston in and out to spread it.

 

[fierodough]

Well sucks to be me.... Put the new head gasket on and my compression is the same 20,90, 20... Looks like I have stuck or broken rings... To make things worse, while on the flushing hose my port head gasket blew because the bottom cylinder filled with water... Good grief...

What should I expect to pay to get he block re-sleeved and new pistons / rings installed?? Or could I get away with a hone and new rings??

I'm regretting taking on this project now....

 

[wired247]

You could probably get by with a light hone and new rings as long as you dont have any actual deep gouges. Sleeves are typically $300 a pop installed..

 

[Dukedog]

With those numbers an tha looks of it ya might as well bite tha bullet. Its gotta come apart ta be fixed................Your lucky with it runnin' with any water in tha cylinder. Usually ends up with a "ventilated block"..........Oh yeah one other thing. Any resurfacing on block parts (ie: heads or deck) ya need ta do tha same amount ta "both" sides........

 

[fierodough]

Any advice or shortcuts to get to the crank and diconnect the rods to the pistons can come out? I hope to do a quick and dirty honing, new rings, slap it back together while disturbing as little as possible on the engine.


Thanks for all the help so far!

 

[Dukedog]

I got nothin' for ya........and good luck!

 

[racerone]

???----There are no short cuts to this job.----The powerhead needs to come off and total dis-assembly is required.

 

[wired247]

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