bad manifold test

[jg700]

OK, in short: 1987 Mercruiser 3.0. Starts fine, after warm. RPMS drop, runs sluggish with noticeable knocking sound from lower part of engine.Found water in #4 and oil pan (white milkshake). I removed the engine for tear down. Tested manifold by removing it from engine. Poured water into hose intake until it filled water jacket and I could see it in water ports on other end. After 20 minutes or so, water down considerably, and exhaust ports filled. Am I correct in deducing that the manifold is cracked internally? I assume that water should never be seen in the intake or exhaust ports, yes? Finally, would this cause my engine problems? Thanks!

 

[Bt Doctur]

All answers are Yes

 

[jg700]

How would the cracked manifold cause the knocking sound?

 

[carrier82]

If it has hydrolocked at speed, the force of the camshaft pushing bends the piston rods, which are folded under the piston above them. While the crankcase or the heads can be ruined in the process and the crankshaft bearings destroyed. Piston rod, pin or crankshaft bearing damage?

 

[pureinsanity]

I would say a good possibility of the bearings being bad causing the knocking.

 

[jg700]

I've removed the bearings -they look great! No marks or wear patterns. Good compression in all cylinders. Not quite sure what to do now. Reaasemble with a new manifold, or rebuild. Any ideas?

 

[carrier82]

That was a quick one. Any slack in the piston pins? I suppose the crankshaft bearings turn as easy as a bearing should?

 

[jg700]

How can I tell if the piston pins have slack in them? Do I need to remove them from the block to check? Thanks!

 

[carrier82]

Never been there but i know a case in which the pins were damaged and caused a knocking sound. I suppose if you can move the piston while the piston rod is stationary, the pin may be damaged.

 

[flipbro]

So you tore it down and inspected just the beaings? Did you mic the crank or use plastigage to check Clearances? How about piston skirt to cylinder clearance.

 

[jg700]

uhh, no. Not even sure what those are.