Risers - think I caught this just in time?

[Superjetjim]

Just changing the risers out on the boat I bought a couple of weeks ago. It’s a 2005 dry joint system which looks original!

I can see what looks like the start of moisture running down the inside (tiny rust spots) in the soot - unless that’s normal from moisture in the exhaust?

My question is, would it hurt to smear a small amount of gasket seal on the mating surfaces when assembling (with new gaskets) as I understand you’re supposed to apply it to the water channel (orange bit) only?

Thanks!

 

[Lou C]

That could be condensation, because even if the outer water passages leaked I doubt it will find its way inside. I’d at least replace the elbows and see how the mating surface of the risers (spacers) & manifolds clean up. What I’ve done is to take off the manifolds and prop them up level & fill with Acetone & see if any dampness shows up in the exhaust ports that mate with the cyl heads. If so replace manifolds too. Look inside your exhaust ports on the cyl heads & see how the exhaust ports & valves look, shouldn’t be ANY rust there.

 

[Scott06]

Just changing the risers out on the boat I bought a couple of weeks ago. It’s a 2005 dry joint system which looks original!

I can see what looks like the start of moisture running down the inside (tiny rust spots) in the soot - unless that’s normal from moisture in the exhaust?

My question is, would it hurt to smear a small amount of gasket seal on the mating surfaces when assembling (with new gaskets) as I understand you’re supposed to apply it to the water channel (orange bit) only?

Thanks!

I dont think that is from cooling water more likely condensation. The dry joint manifold prevents the leakage potential by separating the water and exhaust passages.
also dont see any water streaks on them just rust and soot.

 

[Superjetjim]

Ok, so do we think these elbows are good to refit and run with new gaskets as is?

 

[Lou C]

Post up a pic of the water outlet area. They look good from what is showing in the pix. Fresh water or salt?
Is the rust just surface rust or do you see chunks coming off if you poke it with a screwdriver? If surface rust ok but if chunks are flaking off then replace.

 

[Superjetjim]

Post up a pic of the water outlet area. They look good from what is showing in the pix. Fresh water or salt?
Is the rust just surface rust or do you see chunks coming off if you poke it with a screwdriver? If surface rust ok but if chunks are flaking off then replace.

Hi Lou, here you go, few closer pics. I’ve not cleaned the elbows up yet, this is as removed.

 

[Lou C]

They don’t look bad to me, if you scrap em with a paint scraper see how much metal comes off. Surface flakes is ok but big chunks then replace

 

[sdowney717]

I concur, not too bad at all. There is hot exhaust and lots of salty water vapor, and that will condense on the inside of the manifolds, and it will rust like that, even further back inside like the first set of pics.

 

[sdowney717]

I have submerged rusty cast iron in regular white vinegar and after a week, it dissolves a lot of even thick rust. Helps too if the vinegar is hot. I cleaned up badly packed in rust on an Onan MCCK cylinder head, it got it all out of the passages with some time. I left them in a cooler of white vinegar for like a week, occasionally pulled them out and sprayed them off with a hose to get rid of the loosened rust and expose more rust to the vinegar. That kind of packed in rust will crack the cast iron.

 

[sdowney717]

There is something called exhaust reversion where engine exhaust sucks back into the motor while the engine is running. That temporary suction, reverse flow, always pulls some wet exhaust back towards the cylinders when the engine is running. That may seem like a myth to you, that exhaust gasses in very small amounts can do that. And every engine does this.

 

[Lou C]

True and both Merc & Volvo came up with ways to reduce that. Merc used a gasket designed to catch the water before it winds up at the bottom of the manifold exhaust passage and V/P used a vacuum relief valve to allow air into the exhaust to reduce the effect of vacuum created in the exhaust flow….

 

[Superjetjim]

Great info guys thanks!
Last night I took a wire wheel in the drill to the manifolds and cleaned them up / repainted. They look great now and hardly any corrosion as suggested by Lou C

 

[Superjetjim]

True and both Merc & Volvo came up with ways to reduce that. Merc used a gasket designed to catch the water before it winds up at the bottom of the manifold exhaust passage and V/P used a vacuum relief valve to allow air into the exhaust to reduce the effect of vacuum created in the exhaust flow….

Is that the middle gasket with the upflick on it? I wondered why they’d done that.

 

[Scott Danforth]

4.3's are always on the edge of reversion

 

[Lou C]

Great info guys thanks!
Last night I took a wire wheel in the drill to the manifolds and cleaned them up / repainted. They look great now and hardly any corrosion as suggested by Lou C

wow those look great good job!

 

[Lou C]

4.3's are always on the edge of reversion

Interesting I never had that problem with my pre Vortec. Did the camshaft profile change that much when they went the Vortec cyl heads?

 

[tank1949]

17 year old and you got that much usage? Must be fresh water used only. 5 years is about life expectancy of saltwater risers. Next time, you may want to invest in some muriatic acid to soak risers and then neutralize acid and soak in phosphoric acid (Ospho). Then acetone test them. This process has worked for me (so far).

 

[Scott Danforth]

Interesting I never had that problem with my pre Vortec. Did the camshaft profile change that much when they went the Vortec cyl heads?

the profile is a bit more aggressive with the later engines. However the 4.3 is just a bit closer to reversion than the V8's

 

[Lou C]

Not sure what Merc did when the Vortec V6 came out (they used that dreadful one piece system) but I know that V/P changed the shape of the alu down pipes to a sharper angle and installed one way check valves in the elbows to break the vacuum formed in the exhaust...they let air in under vacuum but don't let exhaust out. If I repowered with a Vortec I'd probably add those, I already have the later style down pipes.

 

[tpenfield]

As you probably know by now . . . the dry joint manifold/riser sets that you have are not likely to leak water into the exhaust chamber (thus the term 'dry joint').

Nice job in cleaning them up. The only other thing (chemical) I would recommend for cleaning up the rust is oxallic acid (wood bleach), but you'd still want to get the wire wheel and wire brushes in the water passages as much as you can before soaking them.

I usually use the 500˚F engine paint on the exhaust pieces.