I need some input please. I have one engine that has two spark plugs, AC MR-43-T, that have lost the electode on separate occasions. The engine has not ever run correctly. It starts to pop out the exhaust, after anything over 3000 rpm, when it warms up, and has progressively gotten worse, missing while idling and dieing while docking. It finally would only run on about 5 cylinders (seemingly). I pulled the plugs and found the electode missing. Pulled the exhaust and valve covers. All the Crane roller rockers had lash except one. This is a Crane 134561 grind# H-296-2 Hydraulic. I am running stock Merc distributor and a V6-14° module.

I was expecting a valve hanging or too tight. (This motor was basically new, but assembled before I purchased it.)

It appears all the rockers except one are loose. It might be the one that is not loose that is loosing the electrode #4 cylinder.

Does this scenario turn on any light bulbs in someones closet of information?

I plan to adjust the valves 1/2 turn down from drag on the push rod and try it again.

I hope this makes sense to someone. I'm tired and want to get this fixed quickly.

Jim,
Is this a blower motor? What is your max timing? What carb? & jets are you running? What is the compression ratio?
Your motor is either too lean or has too much timing or bad gas. Colder plugs may help.
This is a serious problem, but not that hard to fix, however you may have more damage. Like burned valves or piston damage.
Run a compression test. If it's gone, you may have to fix the heads or worse.
Give us some more information.
JB

Were the burnt plugs tight --- A loose plug will do that. If not then you have a lean condition. Maybe from a valve hanging up. That valve with no lash-- loosen up the rocker and see if it is the same height as the other valves. Also see if you can push it down and then it returns all the way up freely. You can get a tool to compress the valve. Or put that cylinders piston at the top and just remove the valve spring and see if the valve will move freely in the guide. If you move the piston down slightly you will be able to open the valve all the way. Just don't let it drop below the point where you can pull it back up. DON'T USE THE PISTON TO PUSH THE VALVE BACK UP. A hanging open valve can cause a lean condition.

John,
Not blower motors,

They were originally 1987 Hawk 511's.
427 tall deck truck blocks .125 over
4.250 stoker crank
9.0:1 pistons
Max timing is 34° set at 4500+ rpm.
They've got 830 cfm Holley annular discharge.
Not sure on the jetting.
I did have some bad gas, but thought it was diluted enough. Maybe not.

Tinkerboater,
Most of the plugs were loose. I put the new plugs in myself. If I even thought that I forgot to tighten them I would have to sever my arms at the shoulders, but $hit happens. Ever heard of them loosening up on their own?

What kind of jetting should I have with this setup?

Are you certain the plug wires are not crossed on 2 cylinders?

I know it's a longshot...

LOOSE PLUGS WILL DO EXACTLY WHAT YOURS DID. THEY MUST BE SNUG. The motor will run like crap when that happens. Just try a new set of plugs and see what happens. Run it for 30 minutes ( if it runs good ) then pull the plugs and look at them. If the plugs are not tight they will overheat and burn out the center electrode. The threaded part looked like they got real hot don't they.

Detonation will cause the plugs to loosen. We used to run 84-86 jets in 850 Holleys with headers on 454ci. 420 mercs, which was 4 to 6 sizes over box stock.

The one valve may have tuliped. You may be able to back off the rocker arm and still have it seal.

You should check the fuel pressure above 3000 rpm to see if you have any. Four to five pounds minimum, all the way to full throttle.

It wouldn't hurt to back off the timing a couple of degrees, like 30-32 until you find the problem. Then set it for best top end later.

Also try a cooler plug, it can't hurt at this point!!

Good Luck JB

BTW, I burned down a 525 hp motor on an 89 Top Gun, because of a plugged fuel pick up in the fuel tank on one motor, very expensive. There was no electrode tip and the plug was loose too, #7.

I've got the good dual fuel system setup with a separate mechanical and electric fuel pumps. Gauges show a steady 5 all the way up.

I appreciate all the good advice. Alot I haven't thought of. I'm on the way out to do a compression check if I could only find the figging compression gauge. My father is sharing my shop with me now that I talked him into living on his boat, so he is getting even with me for losing all his tools. (i never did that)

I'll post my findings shortly.

I always like to keep my fuel pressure absolute minimum 6# and max 8.

In my opinion 5 is too low.

just a thought.

Along the lines of what Tinker said, if it is a valve is hanging up a valve spring is most likely the culprit.
If it is due to loose plugs, I've heard of holes in pistons also.
do a good check.
loose plugs let more air in causing lean conditions. (Just to back up what has already been said)

my .02
DAVE