GNJ

I have a question for the board. My motors had about 350 trouble free hrs on them before they were recently tore down. I had my motors rebuilt by a local machine shop. They also did magnaflux, mild port work (exhaust side) and a valve job on the heads.
The motors now have about 5 hrs on them. After noticing a slight drop in power during WOT, I ran a compression check and found that both #8 cylinders on both motors have 0 compression. I pulled the head off one of the motors and found the exhaust valve seat coming out of the head and dis-lodging the valve, not allowing it to close. Also the oil was milky and I think that is because the open exhaust valve is causig reversion, sucking water into the engine.
I'm going to pull the other motor apart today, but since the comp reading is the same on #8, I suspect the same as well.
The question is:
What causes a valve seat to come loose from the head?

Gary

gen 6 502's
Merlin single plane intakes
ZZ502 roller cams and rockers
Revolution Marine Exhaust

kennyo

Did the mechanic put new seats in the heads? If he did you need new heads. I've never seen replaced seats stay in a marine motor. I trashed a brand new engine over this same problem.

lilredboat

my exhaust seats started falling out due to stock manifold water reversion. Check for water in center manifold runners. hope this helps!

delsol

Are you using the zz502 roller cams? Are they not bad for reversion themselves? Might be getting water coming back on the seat and cooling the seat which helps to 'unseat' them.

Kidnova

Not to argue with delsol, but I ran a ZZ502/502 crate motor in my boat for 4 years, and no damaging issues with reversion. 1st season I ran the stock Merc exhaust, then switched to Revolution Marine exhaust. I had Imco Sound Advantage on all 4 seasons. I ran the engine hard in local poker runs and such. It was torn down this spring and my engine guy said all looked great. But, it only had about 140 hours so ......

That said, the LSA is 110* on the ZZ cam. As I understand it, the ZZ cam is very close to the hp500 cam. And I have read that the hp500s were prone to reversion.

GNJ ....... were the ZZ cams installed as part of the recent rebuilds ? If so, I can see where the cam might be suspect. But, I would also wonder if the valve seats were installed properly. Or if the tune was out of whack maybe causing #8 cyl's to run hot ?

I'm no gear head. Just shooting questions out there for the more qualified guys.

GNJ

OK here's more: The machine shop identified a crack in the head (#8 cyl) where the valve seat was. They also informed me that it appears extreme heat caused the crack.
After pulling off the other head on the other motor, I noticed (#8cyl) it still has the valve seat in place, but was warped so that the valve does not close completely. The spark plug electrode was destroyed from the first head and on the second head, it was completely white.
Therefore, I started looking at the carbs I put on, which were Holley 850's right out of the box. After reading about jetting, I think the issue is that I'm too lean from carburation. I pulled open the carb and there were 80's on the primaries and the secondaries. An over sight on my part. Going to try re-jetting the secondaries with 90's
Kidnova, Thats for the input. I selected the ZZ502 cam based on Dennis Moore's recomendation although he took some heat over the issue from other board members. They were installed during the rebuild.
When this first happened, I started second guessing in my mind the contraversy over 110* LSA in marine motors. Therefore, I'm glad you mentioned your positive experience with the ZZ502 cam. Once I get it back together, I will keep a closer eye on things especially the spark plugs.
Thanks for everyone's input. I appreciate it.
Gary

Kidnova

GNJ - This might help you some ..... I sent the Holley 850 from my ZZ502 to Nickersons to have it tweeked and marinized. It came back a whole different animal. A few changes Nickerson made to it included primaries 82 and secondaries were 88. Power valve was 4.5, primary pump size 50cc It was a vac carb. They re-worked the heck out of the carb. What I mentioned are just a few of the obvious things done to it. Hope it helps.

Not to be a whore or take advantage of a bad situation..... but I have a new set of AFR 305's advertised in the swap shop, if you need heads. If interested let me know.

Bill

H2Xmark

are you using the correct head gaskets for the gen6?? the wrong ones will make your enging run hot, mostly on the back cylinders, the problem with valve seats is most machine shops dont know how to install properly on a marine motor, they need a tighter fit than a pass. car to keep from falling out,

GNJ

H2Xmark: I'm using Felpro #17048 marine head gaskets
Kidnova: Thanks for the carb info. It helps. What intake manifold did you have on your motor?

Panic Button

Good thing you caught it, I trashed 2 motors last year due to dropping seats.