Too Much Lift??

[Anonymous]

If a cam is a .480 lift with a 1.5 ratio rocker arm what does it figure up to be with a 1.6 ratio rocker arm??

I had some rocker arm noise with my new cam and here is what I found...

You can see where the pushrod rubbed a groove in the rocker arm at the top of the threads! Too much lift!

Some work with the dremel solved the problem!

I went ahead and pulled the motor to install my stall converter and replaced a blown head gasket/rocker arms.....be carefull about trusting a NOS head gasket from 1969

It seems to lay down a bit halfway through 3rd gear but it still pulls 93 mph in the qtr. Per Bill's instructions, I'm going to install a Holley electric fuel pump...I predict mid 14's in the qtr...not bad for a "Turd" head 8) 8)

Even since I got the 7.25" "T-lock" rearend installed, I'm right back to having traction problems again. I'm just afraid that if I bolt on a set of Mickey Thompsons (or somthing similar) I'm going to smoke the rearend real quick...

Doug

 

[80broncoman]

lift with a 1.6 rocker will be .512

 

[LameHoof65]

Is that a result of how much has been milled off the head and/or deck? I thought the only clearance issues were with the valves hitting the pistons and maybe the stock rocker arms hitting retainers on springs. Bear with me here, I'm not that mechanically inclined, but was it the adjustment screw that was hitting, and if so wouldn't that mean there is the potential of the rocker arm breaking? :roll: Apparently it was the top of the pushrod that was pushing in and wearing the notch.

 

[addo]

I think that's actually an indication of the wrong length pushrod.

 

[DaGr8Tim]

I think that's actually an indication of the wrong length pushrod.

Oh....wise & wonderful addo
Not to change the subject or hijack this thread, but is there a forumla for finding the proper pushrod length?

 

[addo]

There are a couple of theories. I'll promulgate my fave.

The pushrod should be at 90° to the rocker arm cup, at the point of maximum cam acceleration (ie, where the cam is steepest). This is the where the greatest force is on the whole system and the chance of a pushrod distorting, is greatest. Keeping it square minimises this risk.

But - you need to temper this with the practical formula that makes sure it doesn't come close to interfering with the rocker arm or anything else during its motion.

I also believe it's a place where formulas can let you down. A dry run can assist in evaluating the requirements, but I'd only trust a full application-specific simulation otherwise. The final option would be measuring everything and doing it "old school" with a 1:1 scale engineering drawing. Good way to spend an afternoon!

Regards, Adam.

 

[Anonymous]

lift with a 1.6 rocker will be .512

.512 8) 8) 8)

Thanks!

The pushrods are the right length...I got the hardened pushrods from Mike and they are the exact same length as the Clifford pushrods I used to run. I'm opperating under the assumption that the lift was to much for the rockers in their "stock" form.

With the other cam their was no problem .450 lift, but with this one the lift is just high enough that the "cup" lip on the pushrod is what was rubbing on the rocker arm as shown.

I havent any problems with valve float shifting at 6,000 rpm's, (running Clifford dual valve springs) but by my calculations with a gasket that crushes to .050 I have right around .070 clearance left between my valve and piston.

Doug

 

[AzCoupe]

Doug, I agree with Addo, looks like the pushrods are to long. RAS makes the rockers assemblies and the pushrods, both for FSPP and Clifford. Thus the reason they are the same lenght (same lenght as stock).

If the geometry is correct, with the current lift & pushrod length, then the rockers need to be modified to correct the issue. But my guess is a shorter pushrod will be required to achieve the proper geometry. Evidently they didn't do their homework with high lift cams.

I'll give them a call on Tuesday to see what Gary has to say about it. I'm also going to call George at Clay Smith Cams for a second opinion.

Good catch. I'll need to contact all my other customers who purchased the rocker assemblies to make sure they are informed (in case they don't read this post).

On a side note, I'm just curious how many hours it takes you to R&R your motor? With the experience you have, you must be able to do it blindfolded by now.

 

[Anonymous]

Mike,

How much shorter could they be made?? I only have between 1-2 threads maximum protruding from the top of the rocker arm adjuster lock nut.

Later,

Doug

 

[wsa111]

Doug, You can try pushrods .060 shorter to get the adjuster ball further away from the rocker arm body, that will put the adjuster screw on the rocker arm darn near the top of the adjuster locknut, which should be ok. Does RAS make a adjuster screw .060-.125 longer than what you have, but you still need the shorter pushrod to get the adjuster further out of the rocker arm to prevent pushrod to rocker arm body clearance.
This is different than say a chevy where a higher lift camshaft has a smaller base circle & requires a longer pushrod to maintain proper valve train geometry. Each engine needs to be looked at differently. William

 

[addo]

That explains why it looks like the threads were damaged! Aren't you supposed to have a little over half the thread diameter as the engaged depth, minimum for a fastener (and preferably just over the diameter)?

 

[Anonymous]

Okay...I understand now! There is probably enough adjustment to go with a .060 shorter pushrod...wonder if this has anything to do with the rocker arm noise I've been chasing down too?

Just the very outer most thread was damaged..

Doug

 

[AzCoupe]

Doug,

I called and talked with Gary at RAS. Fisrt, you got one of the first sets he put together. Since then, they made some minor changes to the rocker body, which should eliminate the problem. IIRC, they also had to make corrections to the adjuster radiuses, which you also experinced problems with a couple years ago?

At any rate, Gary believes the pushrods are the correct lenght. And that its a problem with the old style rocker body. He had some questions, which I couldn't answer, so he said he would like to chat with you dirrectly. You may need to send him a few pics as well. Said he would look in his records for your phone number, but if you don't hear from him in a day or two, you might want to give him a call.

 

[Anonymous]

Doug,

I called and talked with Gary at RAS. Fisrt, you got one of the first sets he put together. Since then, they made some minor changes to the rocker body, which should eliminate the problem. IIRC, they also had to make corrections to the adjuster radiuses, which you also experinced problems with a couple years ago?

At any rate, Gary believes the pushrods are the correct lenght. And that its a problem with the old style rocker body. He had some questions, which I couldn't answer, so he said he would like to chat with you dirrectly. You may need to send him a few pics as well. Said he would look in his records for your phone number, but if you don't hear from him in a day or two, you might want to give him a call.

Thanks Mike!!

If I dont hear from him in a few days, I'll give him a call!! IIRC, it was last summer that he sent me the updated adjusters.

Later,

Doug