Mercruiser 4.3LH backfiring & weird timing

[dubs283]

Valve is tuliped. Most likely from water in the compression chamber

Might get by with a valve job but would be suspect of piston/cylinder issues as well

 

[stresspoint]

even although i can do heads myself ,i always find it best to send the heads out to have the valves and seats done . the head guys also set up the guides , inspect springs for tension and surface machine,
while they have them, get them to crack test and inspect the exhaust ports for soft spots as SBC boat motors have a common problem with rusting out the exhaust runner.
the cost is worth the bill if you ask me.

clean up the piston tops and check the piston heads for pitting around the edges , no pitting there and i would say you are good to go with having the heads done and stick it all back together.

check the bolts for length , run a thread chaser through all the threads and use the correct sealant on the bolts ( the head guys will recoment if you assk)

spend the extra and get OEM gaskets.

 

[Kzreelrods]

Ok… here’s the port side and a better look at the pistons after cleaning the crud off them a bit.

Clearly a tuliped valve in the middle port side as well. Looks like the valve on the left has some corrosion going on as well.

Here’s my options:
A. Bring the cylinder heads in to be redone and then put it all back together and hope there is nothing wrong with the pistons.

B. Tear the whole engine out and drop in a remanufactured long block.

Thoughts on the pistons? I can see the rings sparkling back at me when I shine a light in there and they don’t look as bad to me with he carbon/crud cleared away, but my eye is untrained in this area. Not sure how or whether it’s possible to confirm any issues there without pulling it out and breaking it down.

Thanks for the advice so far!

 

[Scott Danforth]

If the piston is 0.030, then it's a 0.030 oversized.

That valve is junk. Head needs a rebuild

 

[ROY WILLIAMS]

THE ENGINE IS 500HRS ... did the new engine or the fix the old engine ....did the water in the engine !
the new engine is very good !

 

[stresspoint]

for the cost of the heads to be done V the cost of a reman motor + the work to R&R the engine from the hull. i know the way i would go .

have the heads done and stick it back together .
if you are good with a hone you can get rid of most of the glaze that it appears to have on the bores (or just leave it , that's up to you) ,
i would say you should be good to go with just heads since you can obviously see the smoking gun.

 

[Kzreelrods]

Ok… I brought the cylinder heads in and will close this thread unless I learn anything new after it’s reassembled. Thanks all for the insights.