97 model 80 hp yamaha trouble

**bulleteer** · 05-22-2015, 11:32 PM

97 model 80 hp yamaha (keeps blowing head gasket)

My dads 80 hp yamaha has blew the head gasket for the 2 nd time. Last spring dad did a comp check and #3 was about 30 psi lower than 1 &2. Changed head gasket and ran fine all last summer. Dad, like every spring, pulled a comp check the other day and #3 again was about 30 psi lower. Pulled head and gasket was blown again. Its happening below #3 cylinder at the big water dump. Its acting like there is way too much pressure and bulging the gasket back into the water cavity then over time breaking thru. Any thoughts? Poppit valve and thermostat looks good and do not see any blockage there.

Thanks, Gary

**CharlieN** · 05-23-2015, 04:16 AM

The V6 engines also bulge the gasket there, not a big deal to worry about.
I would make a generous size sanding block, use a 240 grit or so paper and after stuffing the transfer ports sand both the head and top of the block to find what it has for low spots. Make sure you plan a way to not get crap around the tops of the pistons.
The head is easy to send to a shop for surfacing and hopefully is where the issue is. The block should not be the issue since the gasket seats on the top of the liners. They should be true.
If it is going to clean up by sanding is go to a finer grit to finish off. Check the surface with straight edges as well.

**perfmarine1** · 05-23-2015, 09:30 AM

Many 3 cyl's have head gskt problems. Surface the head on a big piece of sand paper on a piece of glass or take to shop to have it surfaced. By hand works best as you can see where it is warped. At the end of sanding use a figure 8 motion to finish for best surface. Sand it long ways not side to side. The block can be surfaced with a new knife sharping stone and some light oil or parts cleaning fluid. High spots on the block are usually at the bolt holes. After installation re torque after warm up, then after first hour of operation, then after 10-20 hours. I use 120 grit.

**bulleteer** · 05-23-2015, 11:23 PM

Heres a couple of pics. Everyone keeps saying warped head but its not leaking water on the outside. It keeps bulging the gasket at the bottom of #3 where the water jacket is and then finally it blows thru.