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RickR
11-05-2010, 09:33 AM
HP 500 Clone
9.1/1
MSD
Gil Offshore

Decided to spring for the Inconel Valves in the Dart Pro 1 heads I am having assembled BEFORE I discovered the failing stem on #8.:shocking:

OEM Retangular port Gen V (088) heads w/2 piece stainless valves.

I had a lean condition untill I upgraded fuel system.
What would this valve stem failure???????? Manufacturing defect? Lean condition? Reversion? All other valves look normal.

fogducker III
11-05-2010, 09:43 AM
I don't know squat but that does look like heat...? Just the one valve..? No other signs in the head? What did the plug on that cylinder look like...?

BUIZILLA
11-05-2010, 09:48 AM
stainless valves?

RickR
11-05-2010, 10:53 AM
Piston, Cylinder, Plug, Intake valve, Head all look normal. Most of the exhaust valves leaked during a leak down test.

GM 2 piece stainless valves, top half of stem is magnitic lower damaged half is not magnetic????? Damaged part was not flaking just looks eroded.

These heads have 1300 hours on them but all other valves look normal.

MOP
11-05-2010, 10:01 PM
Curious what the piston top looks like!

joseph m. hahnl
11-06-2010, 08:38 AM
HP 500 Clone
9.1/1
MSD
Gil Offshore

Decided to spring for the Inconel Valves in the Dart Pro 1 heads I am having assembled BEFORE I discovered the failing stem on #7.:shocking:

OEM Retangular port Gen V (088) heads w/2 piece stainless valves.

I had a lean condition untill I upgraded fuel system.
What would this valve stem failure???????? Manufacturing defect? Lean condition? Reversion? All other valves look normal.

Usually when a valve doesn't seat properly the blow bye from the exhaust will melt the seat of the valve away .The valve gets progressively worse until it is burnt away. In general an engine that pops through the exhaust most likely has a burnt valve. That said, I find it unlikely that the inner stem would have burnt before the leading edge's of the valve if it had been caused by blow bye. So it seems more likely that that is a result of the lean condition that you were experiencing.More mass will dissipate heat better than low mass As well as different metals conduct heat differently .As a result that damaged area and or the intersection of the dissimilar metals of the valve stem would retain greater heat than the rest of the stem causing it to out gas.

BUIZILLA
11-06-2010, 09:18 AM
does that valve guide go thru a water jacket? i'm not liking that discoloration above the degradation, and the binding marks on the stem above that

Pismo
11-06-2010, 01:26 PM
Exhaust or head coolant leak at #7?

Something unique to #7 only. Hmmm.

Cool picture, wish I could help.

RickR
11-06-2010, 08:40 PM
This is #8. I had my heads mixed up, DUH.

I am leaning toward a manufacturing defect.

Piston top looks fine.

No problem with the seat or valve face.

I assume all the valve guides go through the water jacket??? Discoloration is on all the exhaust valves below where the stem contacts the guide. Wear patterns from guides are normal and on all valves except for the scuff marks Buzz mentioned on the bottom of #8 .

No evidence of coolant leak in exhaust port.

A while back Buzz (and my local race motor guy) were questioning Mercs staggered jetting on the HP 500.
I have been running Merc's spec. Secondaries have 93 jet on starboard side(#8/damaged valve) and 89 jet on port side.
HMMMMM???????

Merc's early 502/465HP Blue engine secondaries had 96 on starboard and 86 on port side?????????

VetteLT193
11-08-2010, 01:09 PM
lose an impeller blade or anything? I wonder if there is blockage somewhere around that cylinder and it is running hotter.

with you saying the seat was good, was that per leakdown test?

mrfixxall
11-08-2010, 01:19 PM
#8 always runs lein..that could be the cause.

The Hedgehog
11-08-2010, 10:04 PM
Redo the heads and do some one piece valves. Manley severe duty on the exhaust.

RickR
11-10-2010, 08:31 AM
Vette
Engine has never overheated.

fixxall
Why would #8 run lean? Dart Intake?

Hedge
I'm going w/Inconels.