Valve cupping? why? Anyone?

[rude50]

Stats: mercruiser 5.7l 4brl. Holy carb alpha sn: ol378057 about 2001 & 100 hours

It ran so perfect for 100 hours then started to run rough one day. so back to dock and home. Compression test: #6 dead, #3 weak. Heads off: #6 plug electrode melted, intake valve cupped in towards head by about 0.2 inches at center, #3 plug perfect but intake valve cupped in towards head about 0.055 inches.

WHAT THE HECK IS GOING ON?

More info; All other valves: fine, Timing: perfect, Carb mixture: as good as it gets, Plug type: ACMR43LTS, Plug condition and valve lash checked 30 hours prior to problem: perfect, Oil consuption: normal, Time running rough back to dock: 30 min., Water supply: adequate engine temp 170 deg. F. (home made exhaust temp alarms never sounded), Other cylinders: perfect compression, head and intake gaskets: nothing apparent, valve springs: all measure same unloaded dimension (no spring force data yet), WOT: less than 4200 rpm, All lifters, push rods, rocker, rocker studs, and valve stems appear to be visually fine.

There was no warning. No tapping, no back fires, perfect idle. One minute running at 3500 rmp and then a sharp tapping. Fearing a possible valve swallow I got it out off the water asap. I can fix the valves but I want to aviod the cause. Any thoughts?

 

[bomar76]

Re: Valve cupping? why? Anyone?

Tulipped valve......caused by the valve overheating.
Usual cause....a lean condition in that cylinder.
Fix the cause, not just the valve.

 

[WillyBWright]

Re: Valve cupping? why? Anyone?

It also happens to car motors used in boats, or car heads put on boat blocks. Car valvetrains don't stand up to boat use very well. Marine smallblock versions have stronger valvetrains used in heavy duty trucks, plus a whole lotta other stuff to allow it to run at redline for hours at a time. Try that with a car motor and it'll start sef-destructing in the first hour. Most car motors never come close to redline, let alone run there for long periods of time.

 

[rude50]

Re: Valve cupping? why? Anyone?

Thanks guys

Capt ken in another thread suggested that an exhaust gas recurculation restrictor could be the cause. I found no restriction in my head/intake manifold interface. I guess the proper gasket should somehow restrict these ports. My mercruiser factory engine gasket was wide open. Could this be the smoking gun?

 

[Bonus]

Re: Valve cupping? why? Anyone?

A lean condition can be caused by an significant vacume leak. In this case at the intake manifold. That would not be uncomon.

Bob in CO

 

[rodbolt]

Re: Valve cupping? why? Anyone?

the other reason I see quite often for swallowing an intake valve on a 5.7 is engine lugging due to over propping for the current hull loading.
we see it quite often with deck boats. the hull will get propped for one person and a half a tank of fuel. next thing ya know there is 4 coolers and 9 people onboard, poor engine dies.
I have a ski boat in the shop now that did it with 7 people towing a wake board. sucked two intakes.
I usually try to prop most 5.7 motors to turn 4800 or so when empty.
but a swallowed valve is a symtom not the problem.

 

[Haut Medoc]

Re: Valve cupping? why? Anyone?

Rodbolt, good to see ya back......​

 

[rude50]

Re: Valve cupping? why? Anyone?

Rodbolt thanks. i did have it propped for WOT 4500 rmp low load and the day of failure was fullup gas and a crew of five with accompanying accessories with hole shot hang time of about 10 to 15 seconds.

But the clue of #6 and #3 cyliders playing the victim seems to point in the direction of exhaust recirculation since they are such close neighbors.

Having never seen a intake manifold gasket from this species I would like to ask the more well informened of you ; Are the exhaust reciculation ports from the head to the intake manifold suppossed to be wide open or restricted? The gaskets I pulled off were wide open and the exterior paint on the intake manifold at these ports was burned off.

Keep the ideas comeing. I dont want to have to do the valve job more than once.

 

[Bondo]

Re: Valve cupping? why? Anyone?

4brl. Holy carb about 2001 & 100 hours WOT: less than 4200 rpm,

Ayuh,..........

The Holley isn't Stock,.... 4200rpm at WOT,+ a light load is Too Low,......
And a 2001 should have the Vortec Heads I thought,..... They don't have exhaust cross-overs.....

If it was at all Lean,...... Detonation would explain the present Damage.......
What Color were the rest of the Plugs,..??....

I dont want to have to do the valve job more than once.

Have your Machinest install Monel exhaust valves,+ Quality SSteel intake valves,.......
And,.........
I never liked a Holley,....... Bolt an Edlebrock on there,.... Much eaiser to Tune......

 

[rodbolt]

Re: Valve cupping? why? Anyone?

I cant remember if the carbed vortec heads used the crossover or not, EFI heads definatly dont have it.
I have never seen a marine engine with an EGR system,most dont even use a PVC system,some do but most dont.
most PVC and EGR systems dont work at or near WOT and marine stuff spends most its time at or near WOT so its just not used much.
but I am with Bondo, an experienced tech should have a look at the deposits on the plugs and valves.
usually that will tell the story.
but I am curious about why the valve lash got checked? very curious.

 

[John_S]

Re: Valve cupping? why? Anyone?

Can you take some pictures of your engine and carb and post them? A couple of things are not fitting. One, I'd like to know if you truely have vortec heads or not. The year and serial number would let me believe that it does. No vortec head has exhaust crossover passages. Just a small hole and filled casting. The Holley and possibly the intake had to be added. Merc did not sell any vortec 4brls carbs. Only 2brl carbs, TBI, and MPI.

 

[rude50]

Re: Valve cupping? why? Anyone?

Bondo & rodbolt thanks.

Bondo: All of the plugs were a nice mocha brown except for #6 which had a burnt electrode and the worst cuppinig. The two effected cyliders, 6 & 3, were remarkably clean. No soot or carbon at all. I thought over heating, lean mixture or small ammouts of water would acount for that. But there were no sign of water intrusion.

Rodbolt: I took the engine out of a friends boat and gave it the once over before I put it in my boat. I checked and changed the plugs and checked the valve lash, timing and mixture. I was, at the time, convinced I was on a first name basis with the engine, having know the owner and the boat. Me and the engine are now in counseling. It's time for honesty

There is an exhaust port in the heads that leads to the intake manifold. No EGC control like on a car, just an open port. I've tryed to find accurate pictures of the correct intake manifold gasket and the best I can tell is that, indeed, those ports should be restricted by the gasket. I guess when I buy a new gasket I'll know for sure.

So for now the plan:
1) new valve job with the best valves money can waste / buy
2) correct gaskets
3) reprop for better than 4500 rpm WOT, say 4501 rpm
4) pray to the gods
5) enjoy it while it lasts.

 

[John_S]

Re: Valve cupping? why? Anyone?

"There is an exhaust port in the heads that leads to the intake manifold. "

Then you do not have vortec heads. Standard heads would not have this restricted on a stock Merc. The crossover is used to heat the cast-iron intake for quick warm-ups and driveability.

How many intake manifold bolts do you have? 8 or 12?

 

[MikDee]

Re: Valve cupping? why? Anyone?

On a point, we used to use the Mr. Gasket intake manifold heat riser blocking gaskets on performance car engines, just to keep the carburetor cool for denser fuel mixture, not necessarily keep the engine cooler. I would think you'd want to keep those ports fully open to circulate the hot air more, instead of trapping it at each head, this may be better IMO.

 

[rude50]

Re: Valve cupping? why? Anyone?

OK the numbers are in;

Head casting: 14101081 1987 to 1995 305cu non vortec
Block casting: 10241880 1995 to 2000 5.7l vortec truck with roller cam ( I haven't looked at cam for # nor have I pulled a lifter to check for roller but I do believe they are rollers.

Intake casting: 14096244 unknow but it fits the 12 bolt non vortec head set.

Could a cam / head mismatch be a problem?

should I scrap the heads and intake and go back to vortec?

Boy, just when you think you know your engine! I was almost sure the whole thing was a 2000. My vortec ignorance is showing. All the mercruiser #'s indicate such a vintage.

OK, now what? Thinking caps on?

 

[John_S]

Re: Valve cupping? why? Anyone?

You are running 305 heads on a 350, which is probably giving you too much compression for a boat engine. They would also restrict the airflow compared to a 350 head. That may be part of the problem. I'd still like to see some pictures of everything before recommending which way to go. If it is what the numbers say, then would recommend vortec heads/intake.

"I haven't looked at cam for # nor have I pulled a lifter to check for roller but I do believe they are rollers."

Was there a metal pan in the lifter valley? It is called a "spider" and holds the lifter aligners down. No pan, no stock roller cam.

See picture below for spider. Note: the head is a vortec.

 

[MikDee]

Re: Valve cupping? why? Anyone?

I agree with John, If they're 305 heads, they won't work on a 350, plus the valves are smaller then a 350 head, probably the ports too, I would think the valves are smaller with combined overall measurements then the 305 approx. 3.5" bore, IMO so they don't hit the sides of the block when they open.

 

[rude50]

Re: Valve cupping? why? Anyone?

Thanks Inported john s

The head #'s are what they are. The on line source I used said '87 to '95 305 heads. All those having pitty on me about now could double check the #'s definitions for me.

Compression tests on the good cylinders (cold) were all about the same, three beats as follows 150, 170, 180 lbs/sq in.

If I do make the switch to votec is there anthing I need to look out for exept for a hole in my wallet? Like push rods, valve spring force, themostat housing. I can already see a choke actuator difference.

 

[rude50]

Re: Valve cupping? why? Anyone?

Import john s & MikDee:

"spider" and keeper plates are there thats what led me to think they are roller.

I was looking online at Marinecylinderheads.com and new 350 vortec heads with standard grade merc valves are $235.00 each. (seems to good to be true)blanks are $175.00 each. Anyone have suggestions on where to get heads and intake?

 

[rude50]

Re: Valve cupping? why? Anyone?

More on heads: the intake valves measure 1.839 dia. So it is indeed 305 setup.