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TR4/4A Bent Valves

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KVH

KVH

Obi Wan
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I'm replacing a bad cam. Two bad lobes. Two bad lifters. But, now, my machine shop says 6 of my 8 valves are pounded and slightly bent. What would cause that? My pistons look good. Car ran great. My valve seats/guides were replaced 15,000 miles ago at most. thx
 
I would think he means "warped". Warped valves happen with use and age and is common. "Bent" valves are from mechanical damage, which it doesn't sound like you would have. Not sure what "pounded" is referring to. Either the tips are mushroomed from the rockers or the seats are worn down?? The more expensive valves have the hardened stelite tips, to prevent mushrooming over time. Many of the cheaper replacements do not.

What's the story on the last cam rebuild? What was done and for what reason?
 
Possible the engine overheated badly? If so, the valves could have seized in the guide, and that would cause the cam, follower and pushrod damage.After cooling, the valves would again move in the guides. I know because I had that on my 6.

Perry
 
I need help on this one. My shop is puzzled. Old receipts show a good, professional head job, new valves, including Stellite exhaust valves, new pushrods and the supposedly uprated lifters and new springs. The pistons don't look like they got hit. But 6 valves are bent, including all four exhaust valves. What happened?

My cam was "probably" a performance cam, but I can't find that receipt. The car overheated badly twice, but I just can't imagine that was the problem. I shut down quickly both times.

I've had pre-ignition in the past (not in the last year or so), but I always use the clutch to shut down and only rarely did a have "run-on" for more than two seconds at most.

Ideas?
 
Who installed the head?

I ask because the last time I bent a valve it's because I bumped into my fresh head that was standing up on edge on the floor. It looked great, but valve started sticking immediately on fire up. Only then did it occur to me that I cause the bend. Also curious why you pulled the head if it was running great?

The time before that I had piston contact. In that case the valve didn't just bend...it broke off the head after about 200 miels of driving. Ran great until it swallowed the valve!

I guess my point is...a bent valve is always mechanical damage. Something hit your valves to bend them.
 
Are the valve guides cast iron or bronze? If bronze they need just a touch more room than the cast iron guides when they are reamed or they can seize. This is pretty common in other LBCs as well.
Rut
 
I'd be suspicious of the newly installed performance cam; the excess lift on some cams can case all sorts of geometry problems with the valve gear (particularly if that is stock) and valve springs (coil bind) which "could" result in bent pushrods and/or valve stems.
 
Like CJD, I wonder what is meant by bent. Valves depend on contact with the seat for cooling. Too little lash or excessive degrees open will add to heat.
Bob
 
They are saying they don't want to grind the valves because they won't spin correctly. I'm no expert on how it's done, but they're saying the valve faces wobble like a crooked spinning top, mainly the exhaust valves. I suppose it all might relate to heat. What is "lash"? Is that the .010 tappet clearance, or something else?

PS It ran great, like a champ. But I was getting a clicking sound off Piston 3 and figured it was a bad tappet. It was actually a bad cam and tappet, and likely my fault since I never did a "cam breakin" after a rebuild with a new cam installed. That's why I pulled the head.
 
Lash is the adjustment clearance as you suggest. To me, the wobbly head suggest heat damage. Doesn't take much, these being thin wafers, and you said above you overheated significantly a couple of times. BTW, when you shut down a hot engine the temps of the iron go up for a while because the coolant is not dissipating the heat.
Bob
 
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