Reversion?
 

454 420's and after idling i am getting some moisture on plug number 7. If i run with water flowing throu the manifold but not the elbow (dumping into the bilge) plug is dry. If i run water just through the elbow not the maniold i get a wet plug.
Pressure checked the exhaust elbow and cant find any leaks.
Why am i only getting it on one exhaust bank? Exaust is steamy on that bank also . Oil in valve covers is a bit milky.

Mercruiser Gil exhaust
No internal flappers
How do i fix this?

Re: Reversion?
 

What cam are you running? What is the centerline?

Re: Reversion?
 

ck.pressure test elbow again if all other banks are dry elbow must be cracked let us know if your result fairs differently

Re: Reversion?
 

Steamy exhaust means nothing; they can all look steamy, with wet exhaust.

Is the motor coming up to enough temp to vaporize the condensation that is inherant in boat motors?

If in saltwater, could be a corrosion hole in head, ex man or riser,(or are these the SS ones?).

Re: Reversion?
 

My vote is a leaky riser or manifold. Have them pressure checked.

Re: Reversion?
 

how or who can pressure check the elbow? I plugged them up and used a garden hose to pressure check them and saw no leaks (more pressure froma garden hose than the engine at idle)
I pretty much narrowed it down to the elbow. When i run with water running through the manifold only i get no wet plug. When i run water throu the elbow only i get a wet plug.

thanks

Re: Reversion?
 

I'm 99.9% sure its crack in your exhaust manifold. The stock merc Gil's are famous for this when they are 7-10 years old. Water passes through a hose from the manifold to the riser, so a riser gasket is not an issue.
The stock cam will not revert water. Here's the cam.
http://store.summitracing.com/partde...0&autoview=sku

Re: Reversion?
 

After rereading this I might have to second guess myself.

When you say elbow, do mean the SS riser?????

Is it doing this with the boat in the water???? Everything you said is about it running on a hose. Is the boat sitting at the same attitude/angle as if it was in the water???

If you want ot check the risers, simply switch them from one side to the other and see if the problem follows.

Re: Reversion?
 

when i say elbow i mean SS riser.
This is all while it is running on a garden hose, the attitude of the boat is pretty bow up. Not sure if it is sthe same as when the boat is in the water but pretty close. I am guessing the next step is to switch the risers around and see what happens

thanks

Re: Reversion?
 

A tiny exhaust leak can increase the chances of reversion on one side only.

Re: Reversion?
 

Didn't Mercruiser have a problem with reversion on the 454 and 502's with stock camshaft and thru-hull exhaust (there is a sevice bulletin on this)? Their recommended solution for this is the exhaust resonators.

Still do not know if these work.

Re: Reversion?
 

Do a leak test on number 7. You may have an exhaust valve problem as Brownie said.

BT :cool:

Re: Reversion?
 

Check the stainless tip that bolts to the cast iron riser. There should be a dam welded half way up. Iv' seen these rot out and cause the problem you are decribing