Replacing 95 merc 4.3 with 87 OMC 4.3

[markhodges78]

Just got off the phone with Michigan Motors and it was verified that there was only one 14 inch flywheel for the 4.3 from 87 and up 1 piece seal

 

[Lou C]

I thought that looking at their parts section but it’s good to know for sure…

 

[markhodges78]

Ok quick question on manifolds.. so I looked them over and did not see any reason why they would be faulty . So I have pressure tested them at 25 psi and I'm getting no leak down. It does however look like the Riser gasket was leaking to the inside and the outside .. could the gasket have been what took the old engine out?

 

[Scott06]

Ok quick question on manifolds.. so I looked them over and did not see any reason why they would be faulty . So I have pressure tested them at 25 psi and I'm getting no leak down. It does however look like the Riser gasket was leaking to the inside and the outside .. could the gasket have been what took the old engine out?

Absolutely that is a common cause of hydrolock. The surfaces between the exhaust and water passages have to be flat so gasket can seal. Big issue especially in salt water. Post a pic of them and the elbow folks here can probably steer you wether dressing them with a file, belt sander, or having them milled can work.

 

[Lou C]

Agreed those gaskets can be a problem on any wet exhaust design especially in salt water. When I installed my Barr exhaust conversion 6 years ago I coated all of the sealing surfaces with Permatex Aviation & that & good gaskets seems to have helped it seal well. So far no leaks but I’ll probably replace the elbows this fall.

 

[markhodges78]

Absolutely that is a common cause of hydrolock. The surfaces between the exhaust and water passages have to be flat so gasket can seal. Big issue especially in salt water. Post a pic of them and the elbow folks here can probably steer you wether dressing them with a file, belt sander, or having them milled can work.

Her are a few pictures from one of the manifolds and riser

 

[Lou C]

The manifolds look ok, but the sealing surfaces of the elbows look a little questionable. If I was replacing an engine I’d replace the elbows to be on the safe side.

 

[Lou C]

On second thought I might want to go over those elbows with a file or belt sander and then check em

 

[markhodges78]

Lol I already ordered new elbows ... but that doesn't mean I have to use them now ....

also the surface on the manifold's should be pretty good since I was able to seal them with a 1/4 inch peace of aluminum an put 40 psi to them right?

 

[Lou C]

They might be fine; the “official” way to check these is to lay a straight edge over them and see if you can fit a .003” in anywhere it should not fit, if they are really good a .001” won’t fit.

 

[Lou C]

.003" feeler gauge I meant. Yesterday the forum was acting wacky lol. Volvo Penta published a document indicating how to check the sealing surfaces and how to re-surface properly.

 

[markhodges78]

.003" feeler gauge I meant. Yesterday the forum was acting wacky lol. Volvo Penta published a document indicating how to check the sealing surfaces and how to re-surface properly.

Wow thanks for this ... and yes the forum was defiantly acting weird yesterday

 

[Scott Danforth]

I use a section of glass with stick-on DA paper for cleanup after surfacing with a big file or my airboard

 

[Lou C]

When I bought new Barr Marine manifolds and elbows to replace the one piece OMC V6 units, after I removed the paint they were perfect, couldn't even get a .001" feeler blade in under the straight edge anywhere. Here's what a new manifold looks like...


one more tip, if re-using the old manifolds, before installing the elbows make sure the bolts will thread all the way in, so you get good & even clamping force, if not clean out the threads with a thread chaser. Follow the manufacturer of the gaskets instructions on sealer/no sealer and torque. As you can see I used a pair of longer bolts with the heads cut off to make it easier to install the manifolds, much easier that way. After cutting the heads off the bolts, I cut a slot in the stub to make it easy to remove with a screwdriver. You thread in the 2 headless bolts, slide on your gasket, slide on the manifold, install the other bolts, then remove the 2 headless bolts and install the last 2 bolts then torque all to spec.

 

[markhodges78]

Thanks for all the tips ...