OMC 235 crossflow keeps loosing head gaskets.

[perfmarine1]

A new knife sharpening stone works great for this when the block is on the motor. Use parts cleaning fluid on it.

[930turbo]

+1 Chris

[Fullthrottleguy]

Well i replaced the exhaust gasket with a new one a while ago and finally got a chance to take it for a run yesterday. It seemed to run better but was sill 700 RPM and 10 MPH slower than it should be; found some water in the cylinder after the run too. I came back to this site and saw a lot of posts that i missed. I removed the drivers side head and gently filed the block around the bolt holes - they were sticking up slightly; thanks chris. Not being content that the small amount of material removed could cause the issue, and seeing no signs of the head gasket leaking I removed the exhaust chest once again. I noticed that the bottom water passage in the line of small verticle slots down the center of the block was cracked. There was a lot of merky **** around the exhaust filler block on this side - while the other side was dry. I removed the exhaust filler block on that side and noticed that there is no gasket - just failing silicon. Is there suppose to be a gasket between the filler block and the engine block? (boats.net doesn't show one) I JB welded the crack yesterday; but today when i looked at it again with fresh eyes I realized that bottom passageway is a dead end and wouldn't have water flowing through it anyways - its more of just a support rib. PS i also took a straight edge to the heads and block paying close attention around the bolt holes - all look quite good after a bit of filing.

I'm going back outside to continue my investigation; looking for perrosity as was suggested - feel free to point out other things i should be checking.
Oh and someone asked if it was a salt water motor - it is not. (Toronto is very far from the ocean)

[DavidW]

Make sure the filler blocks are not sticking up above the surface of the block. I just took one apart that was freshly rebuilt. Someone put new filler blocks in and did not machine them flush with the block and it ruined the whole engine because salt water got in.

[levi ledet]

if any one is looking for any 235 stuff i just bought a boat that has a 235 on it with a extra gearcase and a fresh 30 over powerhead and a bounch of extra parts that i want to sell $2000 takes it all pm me if you want it i want that stuff out my shop i run mercury

[Forkin' Crazy]

if any one is looking for any 235 stuff i just bought a boat that has a 235 on it with a extra gearcase and a fresh 30 over powerhead and a bounch of extra parts that i want to sell $2000 takes it all pm me if you want it i want that stuff out my shop i run mercury

LOL! You may want to look into the buy and sell forum instead of posting it here. Or maybe you need to run it to see what it's about! LOL! I don't bleed white, black, blue, or grey... I like them all! The OMC crossflow is an excellent motor. They'll run forever if you take care of them. ALL of my mishaps have been self inflicted.

[levi ledet]

i will im offshore right now waiting till i can get home and take a few pics i bought a boat to run the old school class with dsra next year and thats what was on it i already run a xr 2001 in 1400 mod with a merc and have a lot of merc parts so im putting a merc on the old boat to

[Forkin' Crazy]

i will im offshore right now waiting till i can get home and take a few pics i bought a boat to run the old school class with dsra next year and thats what was on it i already run a xr 2001 in 1400 mod with a merc and have a lot of merc parts so im putting a merc on the old boat to

Very cool!!! So it is a modified motor? I think that DSRA class has a place for Xflows in it. I have a 350# bare hull... LOL!

[levi ledet]

The one on the boat looks like a mod motor to me what kind of boat u have

[aggiestckl]

My '81 235 Crossflow has been running great this summer. Its been pushing my hydrostream YT as fast as 89 MPH @ 6250 RPM.
The only issue I've been having is that this will be the second time that I'll have to change the head gaskets this season.

The first time around it started running a bit rough so i pulled the plugs and saw a bit of water; i had to drive it a bit more to get it to the trailer and by then it would pump water out of the cylinder with the spark plug out. This was the passanger's side bottom cylinder that did this and at the same time I also noticed water leaking from the gasket that seals the exhaust chest to the block. When I removed the heads everything looked good; I cleaned all the surfaces and installed new head gaskets being sure to torque to the OEM specs in the proper sequence. I also removed the exhaust chest and resealed the gasket in place with silicon; the gasket was in poor shape near the bottom but i was stuck without one and beautiful weather calling me back to the lake.

The boat has been running great over the past two months without issue. I did compression test after installing the new gaskets and the numbers were near perfect if not a bit better. Then last night it simotaniously blew the water pressure gauge off the t-fitting on the piss tube and buggered another head gasket. I stopped immediately when my water pressure when to 0; the engine its self still had plenty of water and never budget the temp gauge. After popping the gauge sender back on the boat seemed to have a miss; which is when i pulled the plugs and found water in the bottom cylinder - this time the driver's side.

My question is:
Could a faulty gasket between the block and exhaust chest put water into one cylinder? I can't believe that a head gasket would go again and honestly when i changed them the last time I didn't see any indications that the gasket had indeed failed when examining it.

Thanks for the advice,
Dave.

What kinda prop are you running?

[Fullthrottleguy]

Its a 28 pitch A5 Chopper II that has been ballanced, blueprinted and aggressively cupped. It bites hard, has the bow lift to air the boat out with 4 people aboard and runs like a 29 pitch with little slip. Its the only surface prop I've tried so far - i'm sure a looser prop would go faster but have some tradeoffs.

[Fullthrottleguy]

So i haven't been able to really find the source of the leak. I'm going to finish re-surfacing all the mating surfaces, put it back together and hope for the best. I thought about swapping my crappy heads currently on the motor for the shaved 638, 639 heads i picked up while i have everything apart - but maybe its best not to introduce another variable until this is sorted out.

[Fullthrottleguy]

The threaded brass bosses in the block were sticking up slightly and not allowing the head to seat properly. With everything flat and level she is back up and running strong!
Thanks guys.