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Mushrooming valves

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dharri2

New member
"I put this boat together and

"I put this boat together and installed a used crusader chevy inboard 350 engine. After about 200 I mushroomed the exhaust valve.

We reworked the heads and reinstalled..problem recurred after about 2 weeks.

I installed a new long block, new carburetor, new risers, new distributor, different intake and problem recurred again.

It seems to happen above 3800 rpms.

My carburetor does not have a wedge...could this be causing the problem with running lean and overheating the valves?"
 
"Does this mean "tuliped&#

"Does this mean "tuliped". As in, the valve edge is warped, not sealing agains the head? Or, the valve stem is mushrooming due to impact from the rocker arm?
Or, are you burning a valve?
Anyway, I would suspect a lean burn, as evidenced by reading the plugs. Or, the shop did not grind the valves properly, leaving not enough contact area for valve cooling. Is it the same valve being affected?"
 
"Agree w/ Dave, a bit more det

"Agree w/ Dave, a bit more detail would help alot.

so, is it the head end of the valve or the tip?

Was it the same valve in the same head the first two times and same cylinder with the long block?

as far a causes, i found this post on another board. Copy and paste is much quicker:
http://www.wakesiderides.com/forums/lofiversion/index.php/t250.html
Assuming correct assembly and random location of the valves, I'd suspect a fuel restriction causing a lean out or a cooling system restriction causing a hot spot."
 
"It's tuliping the valve a

"It's tuliping the valve and then they won't seat. It's happened on the original motor, the long block and another new set of heads. We have ruled out overheating because the last set of heads did not melt the high temp indicators on the new heads and the engine never ran over 150 degrees.

It's not always the same valve"
 
"Wow, new carb and new heads..

"Wow, new carb and new heads.. My best guess is carb jetting. Maybe a vacuum leak. I'd try a vacuum gauge first. If normal, do some high speed runs, quick shutdown, read the plugs. Are you running a marine carb? Stock? YES, level that carb with a 12 deg spacer, if a straight inboard setup."
 
"is it raw water cooled?

I

"is it raw water cooled?

If yes, have you verified you have adequate cooling water flow?"
 
"That usually happens when the

"That usually happens when the motor is being lugged, as in over-propped boats, or in underpowered boats.

Jeff"
 
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