'86 250 5.7 blown

[Oldsman]

I have been replacing my neighbors risers the past few days for they was leaking raw water into the cyl's. The risers appeared to be the issue with water leaking. The 3" snout was rusted off and just sitting in the elbow. Well I got it all finished up to day and replaced the starter(bendix broke in old starter) and before I put the plugs in I spun it over and all seemed well. Installed the plugs and started it up. It started up alot better and sounded better as well. Ran it for 10 min with no leaks and shut it off for 30 sec and started it back up with no issues. I did this a few times and I thought the risers was the issue so I shut it off. 15 min later went to start it back up and the mother &(^%(^ was hydro-locked once more. Needless to say I called it a few foul names. I started to pull the plugs on the port side and the was all full of water. I ran a compression test and # 1,3,7 was 150-160psi and #5 was 90 psi. Didnt do starboard side was too upset but know it spun over freely with plugs out on port side. Could this just be a head gasket and/or intake gasket? Or should we just pull it and rebuild it. Dont know the hours for there is no hour meter 'YET'. Any thoughts?

 

[Jimmy Buoy]

After testing compression, shoot some motor oil in the cylinder and test again (wet compression test). If the compression goes up it's piston rings - if it basically stays the same start looking at valves. That being said, if two neighbouring cylinders are low even after the wet test - it could be that the head gasket is blown out between them.

Just my humble opinion - I'm not an engine expert.

 

[OldSkool]

I must agree with Jimmy on this. If the exhaust manifolds are not leaking back into the head then it is most likely a head gasket. I think you can pretty much bank on pulling the heads. If you believe there is a piston issue you can further inspec them with the heads off. It is interesting that all the cylinders were full. Should only be one or two depending on the area the head gasket is blown. Might want to recheck the exhaust manifolds. Pull the plugs on the other side to see if it's full. Low compression might have been there before the water issue.

 

[Oldsman]

OK I did remove 2,4,6,8 plugs and there was no water. Comp test was all 150-160 on them. I an leading to say that it is the port side head for the one low comp on #5 cyl. We are going to take the heads off and have them rebuilt and replace the manifolds. We think it may be the the port side manifold that is letting the water drain back. It runs perfict and idles very smooth so it may not be a head gasket but we are going to replace the head gaskets anyway.