Hydrolocked 420
 

1988 Formula 311 420's B/W Trs about 500 hrs. Gil manifolds

I opened up my boat yesterday to find one motor fine and the other was locked up. I took all the belts off to make sure it wasn't an accessory locked up and put a wrench on the crank and could move it a little. I pulled all the plugs and #5 was wet. Cranked it over and out came a bunch of water. I did a compression check and #5 had 225 psi, just like all the other cylinders except #7 and #3 which only had 160.

I know water didn't sit in there all winter because it cranked for a little bit and then locked up, so it was obviously in the exhaust and as soon as that valve opened it just filled the cylinder

I pulled the manifold on that side and pressure tested it and found a pin hole right in the #5 vane. I know it didnt freeze because when I drained that manifold it was full of antifreeze. (I meant to drain it when I winterized it but I guess I missed one)

My question is why do you think those other two cylinders have lower compression, and what should I do next? Im gonna replace all four manifolds.

Also I'm looking for 4 Gil manifolds in good shape, preferably fresh water, or headers for reasonable money

Thanks
Chris

Chris,
I think you should pull the other two manifolds off,if they pressure check ok,put them on the other motor,change the oil,and fire it up. Let it run up to temp and check the oil for moisture(milky).By the sounds of it I think you may be ok with the motor and just need exhaust. Your dad gave me the merc part #'s for your manifolds.I may be able to save you quite a bit of money.Just need a few days. Good luck,Jeff

ttt