Valve Float

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Mar 27, 2006 | 12:22 PM

Mudman

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From: Minnesota

Valve Float

I have a project for my Vibration Engineering class that I have decided to do on high RPM valve float. I was wondering if any one has much experience on this topic and have any resources I could find for information.

Thanks,
Mudman

Apr 4, 2006 | 10:05 AM

mark a.

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There really isn't much to say about it. It can happen at high rpm's when the lifter can no longer follow the cam lobe profile, brought on by week valve springs.

Apr 5, 2006 | 02:27 AM

Torque1st

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You might want to check engineering references and magazines for articles on/from Competition Cams. I believe they have done a lot of work on the subject and have developed some unique testing machines. -At least if my old memory serves me correctly it was Comp Cams...

Apr 5, 2006 | 06:41 AM

tomw

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From: suburban atlanta

One thing to consider is the harmonics. A spring has a natural frequency that it likes to cycle at. If you happen to come into and out of that frequency, the spring will be like jello or feathers as far as actual spring work. Think of the spring getting exactly in synch with the valve and rocker arm. At one frequency, it is being compressed by the rocker and trying to push on the valve, but is cycling back and forth at its harmonic so that it exerts little pressure. I think. That's why you see those spiral flat 'springs' inside of the valve springs on a Bowtie engine. Haven't seen them on Fords, but you never know.
tom

Apr 5, 2006 | 09:57 PM

"Beemer Nut"

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From: "Islander"

I had flat dampers on 427 heads when I purchased them.
.....=o&o>.....

Apr 19, 2006 | 09:04 PM

krewat

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From: Long Island USA

The 390 I built has the flat inner dampers with double valve springs. Wolverine springs. I've seen many motors with the flat dampers.

Valve float is when the entire moving inertial mass of the lifter, pushrod, rocker, valve, spring and retainers overcomes the pressure pushing back from the valve spring. The lifter keeps moving away from the cam right after the tip of the lobe passes and when it comes back, it slams down into the flat side of the lobe.

The weakest link will break in the chain.

OK, so you bent a pushrod.
Get thicker pushrods.
You just LOWERED the RPM where you'll get valve float because you put MORE mass into the equation.
Which leaves the next weakest thing.
You get the idea.

Changing the cam profile can greatly alleviate some valve float, believe it or not.

Rollers can really lower valve float because you can put really stiff springs on it and the rollers will take the increased pressure without shredding, plus take care of the added friction.