Dropping Valve Seats?

[Cobra75]

Last fall, CSX4100 was running on 7 cylinders...it turned out the intake valve seat on #1 cylinder had dropped and the intake valve was stuck open.

Well after last month's SAAC event in Nashville, a similar "missing" started to occur again. It got worse on the return from Cobra Revolution, and two miles from home, a pronounced clatter began. I immediately shut the engine down and trailered the heap home. This time the noise appeared to be coming from the other side. Upon removal of the driver's side valve cover, I discovered #5 intake valve in the open position. This time the valve spring had broken, and the keeper & retainer of course were loose on the top of the head.

The similarities are striking:
Both times it was the front cylinder.
Both times it was the intake valve.

What could be causing this? These are Edelbrock Performer RPM aluminum heads, complete with Edelbrock valves, springs, dampers, retainers etc. They have been installed since 1998. No porting work was done to the heads. The engine never runs hot, I have a rev limiter set at about 6000, and typically short shift at track events. So I don't think I abuse the engine.

I have never heard of a valve seat dropping out, much less two of them. Pulling the heads requires the removal of the engine due to clearance issues. The last repair cost a fortune due to the labor-the machine work and parts were cheap.

This time, I am thinking of pulling the engine myself and taking it to a shop and having it torn down & checked from top to bottom and dyno tuned.

Any ideas and/or advice?

[map]

I think Edelbrock has a over due Phone call !!
I have a set on a 429SCJ and haven't had any problems yet!
Mike/Map

[Steve R]

As I understand it, that is caused by not enough "interference fit" of the seat to the head. Sounds like Edelbrock dropped the
ball on that run.
Steve

[427sharpe]

SteveR is pretty well right on....A valve seat like this is a simple ring that is pressed into the head so that you can run unleaded gas (a hardened seat). These seats SHOULD be a very tight interference fit, as is a cylinder sleeve. Done correctly, they should last as long as a stock head. If you have had 2 come out, I would really press Edelbrock on their warranty policy as this is a workmanship failure of some sort.

[Excaliber]

Now wait a minute, sounds like TWO different problems.

One, dropped a valve seat.

Two, broke a valve spring (but seat was OK?).

That they happen to be both front cylinders doesn't say that much to me.

More investigation is required. Weak spring and stuff happens? Bad machine shop work on the seat (no doughnut for the machinist) or bad head and the seat won't stay put?

Cam lift causing the springs to bind? First spring breaks, followed shortly by another one?

Ernie

[Cobra75]

Originally posted by Excaliber


Now wait a minute, sounds like TWO different problems.

One, dropped a valve seat.

Two, broke a valve spring (but seat was OK?).

That they happen to be both front cylinders doesn't say that much to me.

More investigation is required. Weak spring and stuff happens? Bad machine shop work on the seat (no doughnut for the machinist) or bad head and the seat won't stay put?

Cam lift causing the springs to bind? First spring breaks, followed shortly by another one?

Ernie

Have not pulled the head yet, but the I believe the seat dropped and some time later the valve spring broke.

[Steve R]

Ernie,
You're right. I made the assumption that the 2nd failure involved a seat. I guess we'll find out when he pops the head off.
Steve