Mercruiser MIE 340 454 won't turn over when hot

[JeffT65]

I have an old 1984 searay ec390 with twin 454 mercruisers. When cold the engines fire right up and run perfectly. Once the motors are warm/hot, if I shut them off I can barely turn them over. It acts like the timing is way off but it's fine and set at 8 degrees btdc. I recently replaced my exhaust manifolds because there was no water flow and they were packed with scale. I did not replace the risers and extensions. I cleaned up the risers and did not see any cracks. The only thing I can think is that maybe I could be leaking some water somehow back into the exhaust portion of the manifold and hydro locking the motors that way??? I'm really not sure. Oil is fine no "chocolate milkshake" so I don't think it is a head. Any help is really appreciated.

 

[alldodge]

Do they just crank slowly and is there any place where they stop, or almost stop and then continue to crank?

How are the batteries?
Has cables been cleaned on both ends to shinny metal?

 

[JeffT65]

Do they just crank slowly and is there any place where they stop, or almost stop and then continue to crank?

How are the batteries?
Has cables been cleaned on both ends to shinny metal?

alldodge,
thanks for the advice. I went over all of the electrical connections first hoping that was the case, but unfortunately I have bad exhaust risers and water is leaking back into the cylinders through the exhaust valve creating a hydro-lock situation. I will be putting back together tomorrow and hoping the engine is not damaged. So far so good but I won't know for sure if I spun a bearing or something until I get it running with the new exhaust components.

 

[JeffT65]

Do they just crank slowly and is there any place where they stop, or almost stop and then continue to crank?

How are the batteries?
Has cables been cleaned on both ends to shinny metal?

I am new to this site and actually posted this in the wrong forum. Should have been inboard engines. I didn't know how to delete or change it. Sorry about that.

 

[alldodge]

All good, and the easy way to have it moved is select the "Report" link in any post. A box will open up and just enter "should be in Merc inboard". All the admins will see and one will move it. Use the same link to report things no good

 

[alldodge]

Never mind, just saw your other thread. Lets let this one die