This is more of a hypothetical question than a problem I am having. I just want to avoid any problems. I am running a 451 with a hydraulic roller cam and intend to push it to the edge of valve float. This should be about 6500 RPM.

I saw several posts here from the past that mentioned bending push rods in conjunction with floating valves. I am curious why this would happen? If a set of Hydraulic roller lifters were to float at high RPM then the engine would stutter and miss badly since the valves are not closing all the way. However for a push rod to bend something in the valve train would have to bind. The only thing I can think of that could cause that would be a valve hitting a piston. If that were to happen I would think a bent push rod would be the least of the problems. Is this an incorrect assumption?

To my way of thinking if the valves floated the engine would just stop accelerating and start to miss. Now if you held it at that RPM I could see where you might burn a valve since they are not going all the way closed.

Assuming the lifter is properly preloaded and does not collaps causing the pushrod to come off the rocker arm ball stud, what would be the harm is floating the valves for a short time? What else would cause a push rod to bend?

its when those valves arent closing fast enough that they hit pistons.

Come on. Someone must be able to explain this to me?

My new Scorpions just arrived. I get to put things back together this weekend. I can hardly wait.

I have another question. What torque do you tighten the rocker shaft hold down bolts to with Edelbrock aluminum heads? The shaft hold down kits appear to be Mopar Performance and I believe they are using grade 8 bolts. When I took them off they were at maybe 80 Ft. Lbs. It was about all I could do to break them loose with a socket wrench.

The valvetrain is complicated.. and it's similar to balancing the rotating assembly in that it has to deal with harmonics that are a natural part of it's operation. Bent pushrods can be from a bunch of things. Some possibilities: Mechanical contact... retainers to rocker, pushrod to head/gasket/guideplate, valve to piston, coil bind on the springs, loss of lifter plunger motion, guides too tight. Deflection of the pushrod itself. Harmonic issues from wrong springs, pushrod angles, rpm, or poor geometry. So there's no "it's always 'x'" here. If you are not sure, I would have someone who is sharp look at what you have, or post a bunch of pics of things like the threads left showing on the adjuster, the sweep pattern of a few cylinders, a side close up view of the rocker with the lifter on the cam base circle...
On the Edelbrock heads... They use a helicoil in the rocker support, but you want to make sure the bolts thread completely through it. I've found factory bolts are usually too short, so I replace them with simple grade 8s of the same diameter that are 3/8" longer. IIRC the rocker shaft torque spec is 20ftlbs. It's not too much.

I think rocker shafts are 35 LB.
the valves can float or bounce of the seats things don't like getting bounced around.
how big is the cam stock eddie springs are pretty good.

Thanks for the responses.

I was mainly wondering about some others here mentioning that floating the lifters will bend push rods. I don’t see how that could happen without the valve hitting the piston and if the valve hits the piston I would think there would be other more serious damage.

My cam is about .550 lift and 230 X 236 @.050. I have checked coil bind and I have anywhere from .050 to .080 remaining. I ordered Manton custom length push rods and the pattern on the tip of the valve is good. That also leaves about 3 threads of the rocker stud exposed below the rocker arm. It all looks good.

I plan on pushing the envelope for RPM and wanted to know the dangers of hitting the edge of valve float. Obviously I won’t be holding it at that RPM, but the valves will probably be floating a little bit before I am able to sense it.

Why do you want to spin it so high? Does that cam pull that high into the 6's? Did you check your installed spring height? Are you using the springs that cam on the E-Heads? If so will they handle the pressure of a roller cam?

I plan on a couple of 6500 RPM blasts. Right now I hit a brick wall at 6K. However it is pulling real hard when the brink wall shows up. The springs are the stock Edelbrock ones that came with the heads. I had them checked and they were very close to what the cam card called for. I think it was about 130 on seat and maybe 320 open.

262 @ .050, .630 gross lift solid roller,
451CI and E heads here. Makes max HP at 6300 rpm, has seen 6800 on chassis dyno and though it will go that high, the power falls off. I have the rev limiter at 7 grand and try to never hit it.

I'm not trying to be mean or mess up your thread, but honestly 6500 or 7 grand with a 230 degree camshaft is really not going to do anything...

whoops forgot you are running an RB, you might get away with 6200.

You know I am not really sure what the cam is. When I bought the car that used to have this engine in it there was paperwork that said the cam was a Crane and gave it’s specs. I didn’t take the short block apart beyond changing pans, water pump, head gaskets, intake, etc. I always thought it was kind of rough idling for such a short duration. It also winds up better than it should for the short duration. This weekend before I reassemble everything I am going to borrow some mics and see if I can tell more about it.

Hey Zippy, how much compression are you running and what kind of HP are you getting out of that combo?

I’m getting a little off topic. I’m still wondering if my push rods are in danger if I attempt 6500 RPM? I am guessing I will see float before that, but don’t want to bend anything if they do float briefly.

I used to spin a 11:1 383 iron headed dart w/ a 509 to 6800 using stock rockers, push rods and shafts. Never floated and never bent anything

why are you wanting to push your valvetrain to where you get valve float? that would be caused by the valve springs not being stiff enough, not your lifters. maybe you are thinking of lifter pump up . i agree that your cam will probably run out of steam before either happens. you will probably have no problem running it to 6500 rpm as long as your valvetrain has proper geometry. bent pushrods happen when something (usually a lifter) malfunctions. sounds like you got good pushrods so i think you will be fine. have fun but unless it's an all out race engine you probably don't need to wind it up super high.

If I remember right each time you float a valve you damage the springs enough that over time, the valves will float at a lower and lower RPM

"valve float" is really a misnomer. It's more like lifter jump. When the lifter leaves the lobe of the cam and there is clearance is what we usually call valve float. several issues can cause it, weak springs, weak pushrods, heavy lifter, too much rpm are the primary causes.

That all being said, you're running a heavy lifter at high rpms, not sure what pushrods you are using (are they thick wall ones?) and the valve springs on the Edelbrock head may not be up to controlling the valve train at the higher rpms you want to run. Hydraulic roller lifters generally call for a different spring spec than a similarly spec's hydraulic flat tappet cam (aggressive lobes tend to require stouter spring and aftermarket roller cams usually have more aggressive ramp profiles).

Good luck

some stuff
http://en.wikipedia.org/wiki/Valve_float
and

http://books.google.ca/books?id=GUC52-af...p;q&f=false

and
http://www.cartechbooks.com/vstore/showd...mp;chapter=6226

Thanks Dodgem,

I read the information in the links you provided. I thought the best one is the third one. I think I now have a good understanding of the answer to my question. It also tells me that I am going to need better / stiffer springs than what I have now.

Or not try to wind it way past it's power curve.

On a day to day basis I plan on shifting at 6K. Right now I have a slight miss through the RPM's as well. Also to shift at 6K means hitting float right at the shift point.

I don't want to go too far on the miss subject here since I already have a thread going on it at:
451 High RPM Miss