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valve float

Post  Larry Williams on November 12th 2012, 12:29 am

how many causes are there for valve float besides weak springs?

what damage can be caused by float?
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Re: valve float

Post  c.evans on November 12th 2012, 1:31 am

Larry Williams wrote:how many causes are there for valve float besides weak springs?

what damage can be caused by float?

Larry,
Causes for valve float can be any number of things.

1. How radical the cam lobe profile is. You can sometimes determine this by studying the master lobe catalog and comparing the difference between the .050" lift to .200" lift, on one set of lobes, verses another set of lobes.

2. The weight of the valves and the retainers.

3. The rpm zone that you are operating the engine in. All springs have a fussy zone where they exhibit bad harmonics, and if you operate the engine either above or below that rpm point, things will clear up.

4. We have found that operating the spring closer to coil bind, actually about .060" away from coil bind helps. No need to have a 2.100" installed height,,, coil bind of 1.200",,, and just use a .700" lift cam.

5. Flexible thin wall pushrods, are kinda' like a fiberglass pole that a pole vaulter uses in track and field events.

As for the damage that is caused.

1. The valves can actually hit the pistons and be bent.

2. Then bent valves can hang up in the guides and cause catastrophic engine damage.

3. Accelerated wear and tear on the locks, cups, retainers, roller rocker arm tips, roller lifters and the list goes on.

4. Also, the engine will not rev to it's potential, and nose over early.

5. The valve seat contact area in the head will actually wear out quicker, and instead of let's say being .045" wide like it was when you cut it, it becomes .060 -.070" wide in a short time.

Hope this helps,

Charlie Evans

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Re: valve float

Post  bruno on November 12th 2012, 10:14 am

in this in reguards to the video that was posted on fb ????? ...if so that doesnt seem like valve float .......
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Re: valve float

Post  rmcomprandy on November 12th 2012, 11:26 am

Larry Williams wrote:how many causes are there for valve float besides weak springs?

what damage can be caused by float?

As Charlie has eluded to: Whether or not a valve spring is considered to be to weak in pressure depends upon the weight of the valve train, its stability, RPM wanted, the flank rates of the camshaft and how abruptly it closes the valve ... among some other things.

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Re: valve float

Post  Larry Williams on November 12th 2012, 11:43 am

bruno wrote:in this in reguards to the video that was posted on fb ????? ...if so that doesnt seem like valve float .......

nothing to do with the video that surge was caused by a fuel return line that was too small
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Re: valve float

Post  Larry Williams on November 12th 2012, 11:54 am

the reason i am asking is that my small block developed valve float after I replaced the retainers with titanium ones and replaced the push rods with a larger diameter one. anything after 7000 it was like it was on the rev limiter. it wore out a keeper. the valve hit the piston and bent taking out the piston and cracking the guide. I will get the guide replaced but it seems like it could be used like it is, no excessive clearance. I had checked the opening spring pressure on the car (330) and before I reinstalled the heads I checked open and closed pressures with a bench tester. all springs seemed ok. assembled height was where they should be. this time I will replace the springs and need recomendations. the motor has to be good for 7500+ with out float.

would the retainers weigh more and the added weight of the larger dia pushrod have caused the float?





c.evans wrote:
Larry Williams wrote:how many causes are there for valve float besides weak springs?

what damage can be caused by float?

Larry,
Causes for valve float can be any number of things.

1. How radical the cam lobe profile is. You can sometimes determine this by studying the master lobe catalog and comparing the difference between the .050" lift to .200" lift, on one set of lobes, verses another set of lobes.

2. The weight of the valves and the retainers.

3. The rpm zone that you are operating the engine in. All springs have a fussy zone where they exhibit bad harmonics, and if you operate the engine either above or below that rpm point, things will clear up.

4. We have found that operating the spring closer to coil bind, actually about .060" away from coil bind helps. No need to have a 2.100" installed height,,, coil bind of 1.200",,, and just use a .700" lift cam.

5. Flexible thin wall pushrods, are kinda' like a fiberglass pole that a pole vaulter uses in track and field events.

As for the damage that is caused.

1. The valves can actually hit the pistons and be bent.

2. Then bent valves can hang up in the guides and cause catastrophic engine damage.

3. Accelerated wear and tear on the locks, cups, retainers, roller rocker arm tips, roller lifters and the list goes on.

4. Also, the engine will not rev to it's potential, and nose over early.

5. The valve seat contact area in the head will actually wear out quicker, and instead of let's say being .045" wide like it was when you cut it, it becomes .060 -.070" wide in a short time.

Hope this helps,

Charlie Evans
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