Hi All,

This is my first experience with reversion. I guess it's a process of elimination whether it's actually reversion or something else. First, by reversion I mean getting sucked in by the exhaust pulses not the stopping short water backing in type.

The engine is a Merc 350 mag stroked to 383 with blower pistons and 6" rods. The reversion began before the blower was put on and the boat has not been in the water with the blower on this engine. It's controlled by Accel DFI and an Innovate LC1.

The exhaust manifolds are Revolution Marine with the O2 sensor in the port elbow (cut through water jacket and welded in a sleeve to get to exhaust.)

The cam is from Comp, I think it's one of their custom grinds.Int lift 510, 230 dur @.050. Exhaust lift is .520, 236 dur @.050. The lobes seperation is 115 and the intake lobe CL is at 115.

The heads are the large port port Bowtie Vortec's with Inconel exhaust valves and nickel seats.

When I noticed drops of water on the O2 sensor here's what I did;
- Leak checked the manifold and elbow, twice. Found nothing.
- Check the starboard side, there were droplets of water there too.
- Ran the boat with the elbow bypassed, no droplets.
- Welded 6" extensions onto the elbows, no help.
- Played with timing and idle speed, no help.
- Put the sensor in a well to shield it, it didn't. Water still reached the sensor. It may even be worse becasue the water gets trapped in the well around the sensor.
- The port side always got more water than the starboard so I cut a valve in between the manifold and elbow. That helped but did not stop the droplets altogether.
- Finally ran a cylinder leakdown on #1. Around 20% leakage, sounded like the exhaust valve leaking. I hate doing this test by trying to hold the crank, it's an 18' Donzi. It's like working through the bonnet of an MG. Could not get an exact reading. I prefer to pull the rockers and let the piston go where it wants but I'm getting beat down.

From what I've read here and elsewhere the cam should not be the issue. There doesn't seem to be al eak. So i guess I'm left with the leaking exhaust valves. Somebody tell me I'm wrong and give me the hope I don't have to pull the heads again. They have been rebuilt 3 times. Each time stepping up in quality of parts. I run the boat real hard but try to keep the mixture no leaner than 12-12.5 from mid-range to WOT.

Others things to try with regard to the reversion would be appreciated along with some suggestions to keep the heads sealing.

Thanks

That cam should not have any reversion issues. However, 20% leakdown at an exhaus valve will cause quite a vacuum in the manifold, and is likely what is causing the reversion. I'd check them all for leakdown; I suspect you'll find more leaking. And then find out what is killng your exhaust valves.

Your exhaust valve issues may be a product of reversion. When cold water hits those hot valves, all sorts of things happen to them. The fact that the port side is getting more water than the starboard is unusual. It is most commonly opposite, due to the fact that the tail pipe or riser on the starboard side is shorter. In my opinion, that cam is not too big, especially on a 115* lobe seperation. I know you said you played with the idle. Is the engine idling too low? To low will suck water back up the pipes. I fought a simliar problem for a while. My answer was full dry tailpipes and mufflers to kill the sound a bit. Now, no more reversion to worry about. I'll never run wet exhaust again.

What kind of risers are you running?
Yes that cam can have reversion. I am in the same sittuation with a custom roller cam 228 @ .50 and 236 @ .050. The only solution is to get the water dumping further down stream. I don't have a choice, either pull both engines or have custom risers made. Risers are being made.

** I wanted to make a change to this. I made a big mistake, my reversion was casused by my misdiagnosis of reversion. I had a leaking gasket, then to make maders worse I losend the four bolts at the risers which caused reversion by exhaust exiting and vacuum sucking water back. 49 years old and still learning! ** At least I will have some new expensive BLING (risers)

What is the recommended ICL for that cam? A retareded cam will have the exhaust valve open longer during the down stroke of the piston. Sure fire way to get reversion right there. 115 seems way retarded for the ICL. I'd bet it should be more like 107-109*. If that is true and you have it in at 115, bingo. BTDT

BT

Thanks for the responses. The ICL on the cam card says put it at 115.
From piecing your responses together the scenario that makes some sense is;
- A low idle causes reversion. I've been idling around 600 rpm.
- Water gets to the valves and seats causing un-nice things.
- Loss of ex sealing worsens reversion more water gets to valves and O2.

Another couple of questions....I thought a faster idle would not help prevent reversion because when you shut the motor down you'll still get reversion? Or is it that this is such a short event that it doesn't bring in enough water to be serious as opposed to the low idle when you get reversion all the time?

A higher idle rpm will help with reversion.