Major need of help!!!
 

OK so i have a GM mercrusier 468 in a boat that last year dropped a valve on #5 cylinder. So i went through the motor and had it dynoed and all was well. When I put it in the boat it ran great. I have stainless marine exhaust with short risers. I was concerned with reversion so after running it for a bit I noticed that I had alittle water leaking from the band clamp that holds the riser to the manifold. I pulled the manifold and one side looked good and dry. The other side looked like it had water beads in the #5 cyliner exhaist runner. I pulled the manifold and made a pressure testing rig from a automotive pressure tester. I dunked the manifold in a big tub of water and presssured it up to 30 psi. No bubbles or leakage. Could the riser leaking be a sign? If so why would it leak into only one cylinder? Have asked to many so called professionals and am at a loss. Need some input.

did you reuse the old heads?

yes I had them worked over. Pressure tested and installed econell valves. They are racing head service heads.

im not saying it,s the problem,but maybe you have a leak around the exhaust guide on #5 that might not leak until it gets hot so it did not leak when pressure checked.also,keep in mind that an engine on a dyno has no water pressure so it would not leak on the dyno.

Yea I wish I could remember if I put that head back on the same side as before.

If your riser gaskets are leaking it will cause a vacuum and suck water back down. Don't use those cheap green rubber gaskets, use the nice thick carbon fiber ones

Thats the kind of things I want to hear.Man I ready to put this thing in the water but dread having to open the motor back up. It just seems weird to me that it is on the same cylinder that had the problem before. With the exhaust off it looks like that side had some traces of water but # 5 looked like it had been exposed to more that the rest. This was the side that looked like the exhaust riser was leaking the worst. And looking at the riser gasket you can tell it wasn't sealed.

corey,what part of the country do you live in,what state?

Kentucky, we boat on the ohio river

if you were closer you could put your engine on my run stand and get the water temp up to 200 deg and build some pressure in the system,might be easy to find a leak that way.get it hot,remove the header and look in the exhaust port #5.

fixx
 

if your engine compaetment is wide open and make sure you have no gas fumes i have started the engines in the boat with the manifolds off to see if the exhaust guides are leaking..it will make like a steam effect when it gets hot...just extend the hose that comes off the thermostat housing and dump it over board..

the problem with that is it wont make any pressure and very little heat on the garden hose.

I saw you said you pressure tested the manifold, but did you also pressure test the tailpipe/riser? Cold water dripping on a hot exhaust valve will take it out. Ive seen the stainless marine tails have pinholes at the welds near the bend where they turn to go towards the transom.

I think today i will swap sides with the manifolds and risers to seee if the leak will follow the riser and manifold. That may confirm if the head head a problem.

Just swap the risers if you can.

Have you tried running the water for a while, and NOT starting the engine? Then remove riser, and look for water traces dribbing down. If the engine isn't running, water should not get near the riser joint if the head is leaking. If you can, try to rig the garden hose directly to a freshwater flush if you have one, or directly to the 1 1/4 line feeding the engine. So it can build a little more pressure than the muff's will allow. You may have to remove the water stat(so water flows thru block) and just let the hose run for a while and see what happens.

call dave at imco get new set of power flows no more water

Well I think it was water reversion due to to big of camshaft and riser gaskets leaking. I cleaned up the gaskets and put some silicone on them and lengthened my pipes on the risers. Ran it for a while took the riser off and all was good. Where can I get good riser gaskets for the stainless marine exhaust? They are like a flat gasket that gets tightened into place with the v-band clamps.

Im confused. Can you post a pic of your exhaust manifolds? Stainless marine manifolds should be a dry joint between the riser and manifold. Meaning that water doesn't flow thru the joint, just exhaust. The water is bypassed from manifold to riser. If water was leaking from the riser/manifold joint, somethings wrong.

What camshaft are you running in this engine??

You are correct but with the short riser it must have givin the ablity to pull some water back into the manifold. Also I was told that if the riser wasn't sealed it would create a vacuum and cause reversion. So I lenghtened my pipes closer to the tips and sealed up the riser with some silicone on both sides of the gaskets. Ran it for a while pulled the riser and no reversion. Some told me that the overlap on cylinder #5 could have be alittle greater than the others on that side. It seems to be cured but I want to get some good riser gaskets and check it again so if its good I can just put on the good gaskets and be done.

Corey, my heads were tired on my 468's almost dropped a valve. I chose to go to Dart Iron Eagle heads. The Chevy castings are basically unchanged from 30 years ago and don't fix the issues they have. I would strongly suggest looking at new heads.

Wannabe

Not sure I can agree with #5 having more overlap, or a exhaust leak at the riser joint causing reversion, but hey, if its fixed, its fixed. Extending the riser pipes is a good idea when running anything hotter than a stock cam.

I think these are the gaskets you need?

http://www.cpperformance.com/p-14432...er-gasket.aspx

I like those Iron Eagle heads. Great replacement for the old GM rect ports imo.

You can get reversion due to leaks at either the head or riser gasket. If you have a leak at the riser put a straight edge on both the riser and manifold surface, you may have a low spot because the gasket is not the problem. Also if you are bottoming out the nut on the clamp band, get new bands, they are stretched.