5.7 Mercruiser Hydrolocking

[JKlowry]

Re: 5.7 Mercruiser Hydrolocking

A1 is what they gave me and what the book shows but they are 6 1/8" long and my y pipe is only 4" long so it's not even close. The A3 is right size but doesn't mount correctly.......

 

[JKlowry]

Re: 5.7 Mercruiser Hydrolocking

I think I figured out shutter problem. The flaps never completely flatten out as I expected. But, I am still leary of my problem being fixed. New compression test on all cylinders was between 185-190 and timing was right on. Filled manifolds and risers with acetone and no leaks. All new mercruiser manifold and riser gaskets. I think I've covered everything but I haven't found anything wrong other than flappers gone. Any other ideas?

 

[Failproof]

Re: 5.7 Mercruiser Hydrolocking

Seems like youve covered your bases. Now run it and see what happens. Only way to know for sure.

 

[81 Checkmate]

Re: 5.7 Mercruiser Hydrolocking

Just asken.... you say you replaced manifold gaskets....

Does this mean you pulled them off the engine block? If so what did the old gaskets look like?

If it all looked good and you replaced with OEM gaskets and replaced your flappers you should be ok. If it is still happening i would do a pressure test to find the internal leak.

Could be the ever dreaded cracked block! Would'nt think that with the way your risers looked.

Also could be the way you are slowing down the boat..... a sudden stop with no flappers....is quite the rush of water towards the motor.

Hope you fixed your problem and good luck!

 

[JKlowry]

Re: 5.7 Mercruiser Hydrolocking

Yes I pulled them off of the block and they looked perfect. I did notice a crack in my exhaust bellows this evening so I dropped the lower unit to change it and found half of a flapper in there. As I stated earlier I am really hoping no cracked block and really don't think it is since I'm getting water on both sides of block. It's still possible but since I'm not getting water in oil it would be a long shot I hope. Thanks again for all the ideas.

 

[Scott Danforth]

Re: 5.7 Mercruiser Hydrolocking

pic #3 of post 19 shows some concern on the right side of the exhaust passage and the water jacket. did you run a file over the mating surfaces? I have even run a belt sander to true up the surface.

 

[JKlowry]

Re: 5.7 Mercruiser Hydrolocking

I have since run sander over the surface. That is how it initially looked. Trying it out today...

 

[JKlowry]

Re: 5.7 Mercruiser Hydrolocking

Well, I thought the situation was fixed. I had been out several times without issue until Sunday when it happened again..... I had tools on board so I pulled the plugs and cranked the cylinders dry and it started up fine. I am at a loss. I don't physically see how it is getting water on both sides of the engine.

 

[fasteddy3243]

Re: 5.7 Mercruiser Hydrolocking

It is not possible that there is "no" water in the oil. It will leak past the rings anytime there's water over the piston, especially if you try to crank it.

There are 3 possible sources for the water. (1) exhaust system, via backwash or leaking gaskets, (2) head gasket or cracked castings, i.e., head or block, or (3), the sneaky one, via the intake manifold gasket seal. I once bought a Cobalt 19BR for real cheap from a dealer with a diagnosed blown head gasket/water in the cylinder. It turned out to be a leaking intake mani gasket, a $25 fix.

Identify for me again which cylinders show water?

 

[JKlowry]

Re: 5.7 Mercruiser Hydrolocking

It's been a while since this all started. I know for a fact that the back two cylinders on both sides have had water. So, 6,8,5 and 7. It seems that I may have seen some coming out of 3 but not positive. All cyl have good compression and all exhaust and riser gaskets changed.