preventing inflow of water through inboard exhaust

[Erictodd]

I had an Inboard omc 351 in a 87 ski challenger that the engine was ruined by sucking in water from the exahust I have obtained a new pcm engine and I Would like to save $500 and reuse the exhaust manifolds. Is there a way to prevent a reoccurance of water ingestion or should I bite the bullet and get a new exhaust with risers

Thanks Eric

 

[Don S]

Re: preventing inflow of water through inboard exhaust

Are you sure how the water got into the engine? The only way for water to get "Sucked" into the engine is by leaky valves. or the engine dieseling when you shut it off.
Or does it leak in? After you shut it off. The manifold, or riser, or gasket between leaks and the water goes into the cylinder with an open valve.
Or, you shut the boat off while on plane and water shoshes up the exhaust into the engine when the wake hits the back of the boat.

What caused your watered engine?

 

[Erictodd]

Re: preventing inflow of water through inboard exhaust

most likely it was caused by coming to a hard stop after a skier fell and water shooshing up the exahust. I think some times I did turn of the engine which allows the water to enter the exhaust valves. on this moter the manifold and riser are one unit. The valves where good Im assuming it was an exshaust intrusion because there was water on top of the pistons not in the oil, and no means of water entering the carb. the engine ran well no misses and didnt diesal when I shut it off. I have heard of a marine power using a prevention device on applications that might be at risk for water intrussion I cant seem to find anything on it however

Thanks Eric

 

[Don S]

Re: preventing inflow of water through inboard exhaust

Two things that come to mind right off are,
1. When you pull it back to idle, let it idle and don't shut it off till the danger of the wake has passed.
2. Put some exhaust flappers on the outlet tubes on the back of the boat.

 

[Erictodd]

Re: preventing inflow of water through inboard exhaust

now that I think about it the rubber flappers on the exhaust where in bad shape one was missing good chance that could be the culpret. Ive read through other threads regarding risers and found that you and others have recommended replacement of manifolds and or risers after 5-12 yrs or based on condition. The manifold is aprox. 20 yrs old. I think I will take your advice re: rubber flappers / increase Idle speed and also throw in the extra 500-600 $ for new manifolds and risers

Thanks alot Eric

 

[Don S]

Re: preventing inflow of water through inboard exhaust

I think I will take your advice re: rubber flappers / increase Idle speed and also throw in the extra 500-600 $ for new manifolds and risers

Why increase idle speed. Do you have some desire to destroy your transmission?????

 

[Erictodd]

Re: preventing inflow of water through inboard exhaust

I combined 2 good thoughts to make one mistatement.

1. leave engine at Idle to prevent water intrusion after wake

2. I read that after running at very low speeds like through long no wake zones especialy at high operating temps you can prevent water intrussion by running in nuetral at higher rpms 1400-1800 for 45 seconds before shuting down engine