GOODT

Man you are right small ray of hope, wishfull thinking...with plugs that look like that there was transferance ( went from one cyl to another ) which means enough damage for worst case, but there is always hope

LAKESIDE RESTORATIONS

No doubt, but its good to be an optimist.. Jamie

gofastlvr

I hear you guys but the engines were rebuilt about 200 hours ago before I bought the boat. The guy I bought it from is a hot rod car kind of guy and my guess is that it is cheap valves. I am pulling it out over the weekend and gonna see what's up. I am pretty sure that the cylinders are gonna be trashed - so what does everybody feel about sleeving the two and leavin' the rest alone. I don't really know how I feel about that with the harsh enviro that marine engines live in.

The motors say 400hp on the valve covers but the cam in there isn't stock by any means so who knows about the rest.

wieland77

iTrader: (1)

I did do a compression test on my #7 cylinder and it was just about at 140lbs. I Then checked #5 and that was around 150lbs. Do I have a broken valve with 140lbs compression? I figured that I would be way under 100lbs if the valve was shot. I am going to pull the head anyway just to be sure.

Also, what heat range or number NGK or Delco should I be running with a carbed early 90's 502?

PatriYacht

Merc used Manley inconel exhaust valves in those engines. They're abour 45.00 apiece. Some people cheap out with stainless when they rebuild. Not a good idea. The cam doesn't really matter as long as there is no reversion. You can check that by idling for a while and then pulling an exhaust riser and checking for water. Prolonged reversion will make even an inconel valve brittle and break.

kennyo

I had a similar problem. The boat I had someone had put hardened seats in the exhaust side. One of the seats dropped out and did the same thing. It sucked it thru the egr to the other side. Good news it spit it out the exhaust ond didn't hurt the cylinders. Put a set of merlins on it and was out the next week.

1BIGJIM

iTrader: (1)

Do I have a broken valve with 140lbs compression?
Probably not, but something is wrong.
You can have the head off in a couple of hours and look at the cylinders to give you a better idea of what is going on.
The cylinder walls could still be messed up and you could get a 140 reading.

Wobble

I run NGK v-power stock number 6468, they are R5674-9, I think this is a good all around plug for an iron headed 502.

be sure and check out the spark plug wires, cap and rotor, if in doubt replace them, also check for vacuum leaks around the carb and intake.

You may have gotten lucky, there is probably some small damage, but if it runs and doesn't burn oil, you may be ok.

wieland77

iTrader: (1)

Thanks for the info. I think I will pull head just to be sure cylinder is ok and head is not damaged. The last thing I want to do is run it and make more damage that could have been prevented. Thanks again, MIKE