DORaymond

It is genarally understood that reversion is a function of cam design and valve overlap, why does it seem to happen on stock engines as well. Can minor valve train issues caused by wear overtime (normal wear and tare) begin to cause reversion? If stock setups are not prone to reversion, why did Merc issue a Service Bulletin on the subject and recommend installing resonators in the exhaust hoses (thru hull only) on the 454 and 502?

Alot of us seem to wrestle with this problem.

ghittner

I think that most so-called reversion issues are ones of worn gaskets and risers or riser to manifold surfaces being worn and corroded. As far as the Merc resonators? Extra insurance as cams got larger and closer to a reversion subject grind. I have personally never had a reversion problem even with cam grinds that were on the edge and with stock elbows, however I have had parts wear issues one might mistake for reversion....

Donzi502

You can always use your boat as if it does have a reversion problem even if it doesn't. Goose the gas when you shut down. Drain the exhaust with a tap on shut down and and then fire for a couple of seconds. I do it with a pretty big cam and have no problems. I actually have a feed from the water logs out the back with a 1/4 hole. 5 mins after shut down, the the headers are empty, a quick fire while opening the second beer dries the exhaust.
Just my thoughts, Seems to work for me.
Jason

DORaymond

The resonator I am speaking of is in the photo below. Mercruiser recommended it in a Service Bulletin (2003?) on the stock 454 and 502's. One gets installed in each rubber exhaust hose 11" downstream of the elbow. Say it breaks up exhaust pulses to reduce reversion. Not designed to help with the riser to manifold gasket and seal.

bcarpman

Jason, Can you elaborate on this? What do you have attached to the exhaust? Is it a check valve or do you manually switch them open. Doesn't the last quick fir just fill them again? thanks

brian41

iTrader: (1)

I had 2 bad valves causing reversion on my starboard engine when checked they were at 20 percent bleed down.I replaced valves in both motors and no more problems.

DORaymond

Brian41 - So valve trouble in a stock engine can cause reversion? When I see evidence of water on valve stems I always wonder, was there a reversion problem that caused the damage, or did valve trouble cause the reversion which caused the damage.

Big Block Billy

Yes, this will make it suck water on an intake stroke.
Believe it or not put the wrong rotation starter in and it will suck water. Also when overheated the hot motor will cause a vacuum affect and pull the cool water up the exhaust like sucking on a straw ! Having the water exit the elbow farther away keeps it from mixing with the exhaust and being pulled back in during scavenging. Also an absolute must at least 1/2" of dead rise per foot of exhaust system from manifolds to back of boat. Don't trust the manufacturer. Spacer blocks will definitely help. I had a special set of risers made from copper to solve this problem once. Also stainless marine sells shutter valves for about $65 pr that you slice the hose and install inside the hose with 2 clamps, they work well to correct these problems.
Many times there are small light boats with Big Blocks in them and because of lets say a built in swim platform or some other obstruction, we end up being very limited in our exhaust choices.
Before doing anything make sure the manifolds and elbows are good. Also there was a load of aftermarket sierra elbow gaskets that are known to fail, their the black paper ones, Avoid them at all cost. Hope this helps, BBB

DORaymond

Billy - Yea I had bad exhaust that I believe leaked in causing valve trouble. Later I replaced the exhaust with dry-joint style (Revolution Marine) but I pulled the riser off recently and I still see signs of water. But, this may be because I know I need valve work.

Also, I have been trying to get someone to comment on the resonators that Merc. recommends - any thoughts?

ghittner

Hmmmm.