Resurface block 90 two stroke

[mackwrench]

I'm a shop teacher for a high school. Had a 2003 yamaha that students took apart, one student used a wire brush grinder to clean gasket material form head and block, engine was reassembled and runs, but leaks water between head and block.
Removed head and can see that block is gouged up around edges. Cylinders look ok, engine has good compression and actually runs ok,....

If engine is disassembled can a machine shop surface block? I've got a oem service manual, but it doesn't show a spec for any material that could be cut from block.....

[TownsendsFJR1300]

I'm a shop teacher for a high school. Had a 2003 yamaha that students took apart, one student used a wire brush grinder to clean gasket material form head and block, engine was reassembled and runs, but leaks water between head and block.
Removed head and can see that block is gouged up around edges. Cylinders look ok, engine has good compression and actually runs ok,....

If engine is disassembled can a machine shop surface block? I've got a oem service manual, but it doesn't show a spec for any material that could be cut from block.....

Don't know why you couldn't. There's no belt, intake or exhaust manifold to be concerned about.

It'll bump your compression up some depending on how much take off but those gouges can't be more that .005", no?

[mackwrench]

I'd think .005 would clean it up, head will need it as well. The exhaust side cover leaks too, but perhaps that can be remedied with some sealant.....

[greasyshaft]

Sounds like something I'd do when I was at school 3 years ago....

[boscoe99]

People that are not familiar with what needs to be done can damage stuff. Hopefully, it will be a "lesson learned" for your students as to what not to do in the future. Think three times and then proceed with caution.

I suspect that we have all "been there" and "done that".

And speaking of scratches, a number of years ago a Boeing 737 was being prepped for a repaint by removing the existing paint and primer. It was not an old air plane. During the paint removal process the incorrect tools were used to scrape off the old paint, at which time the fuselage aluminum skin was lightly scratched in a number of places. Last I heard they were considering scrapping the airplane. There was no way to effectively remove the scratches without taking even a few thousands of metal from the skin without reducing its strength. It was going to be cost prohibitive to buy new fuselage skin panels, remove the old panels and install the new. You can bet someone was extremely embarrassed. Millions of dollars worth of an air plane thrown away. All because a job was not done correctly.