1994 Yamaha 7.4 L HydraDrive Hole in head from hydrolock

[ed.davis]

I Purchased a 1994 Chaparral 270 that had set for 8 years on a lift. I purchased it knowing it was going to have issues hence the name of the boat "THE HOT ISSUE" Amazingly it started with fresh batteries and was able to trailer it. My intent was to rebuild motor anyway. I was just checking the motor with muffs and started fine after shutdown tried to restart and hydolocked. Dismantled and found #1 cylinder had knocked a hole in the combustion chamber. Now to the question. The block casting number is 10114182 which comes back to a standard GM 7.4 GEN V and head casting 10114156 Which is also a standard head. The engine has some stainless bolts and some iron bolts throughout the engine. I understand some differences in the engine marine vs auto. All parts including gasket set is marine grade. Had to go with mercruiser gaskets no yamaha parts available.Can I replace the block and heads with a GEN V truck engine. The water passages are in bad shape. btw it only had 301 hours.

 

[Bondo]

Can I replace the block and heads with a GEN V truck engine.

Ayuh,.... Welcome Aboard,.... Yes, yer block is a plain ole Chevy part,....

 

[NHGuy]

Also make sure to do the homework and eliminate where the water came from that got in the combustion chamber.

 

[ed.davis]

Cracked manifold exhaust manifold close to #1 cylinder. Engine was a build anyway only had 80 -100 psi on compression check. The rotating assembly is probably a little different being a marine engine I would think but all of that looks in order and will reuse if you guys think that wise. I have a motor that I am pulling out of a suburban tomorrow castings are the same. As long as the mike comes out ok on the cylinders and doesn't need a bore job.

Would anyone know what oil would go in hydra Drive. I checked screen it had no debris in it thank goodness. By the way really strange drive compared to what i am used to.

Also I really appreciate all of the information on this forum from all of you. I have used it for info for the past year just never had reason to post. Massive amounts of info that has helped me and I am sure many others along the way.

 

[Bondo]

Would anyone know what oil would go in hydra Drive. I checked screen it had no debris in it thank goodness. By the way really strange drive compared to what i am used to.

Ayuh,.... They only imported 'em a couple of years,.... Parts are pretty much non-existent,....

I'd think a syn-oil in 75W-90 for oil like most other drives,...

 

[Scott Danforth]

Get a gen VI motor vs the gen V. Found in 96-2000 trucks Gen VI fixed all the issues with the Gen V

As far as exhaust manifolds, a few people have upgraded to mercruiser or aftermarket manifolds

 

[Capt Ken]

Do not use synthetic oil in a hydradrive. Causes the clutches to slip. Use regular marine hypo 90.