Rocker Arm Geometry Question
 

Hopefully this is an easy question for you seasoned engine builders.
I’m in the process of setting up my rocker arm geometry on a small block 350 for my 65 C10 project.

I am using a stamped steel roller tip rocker from Summit (Picture) with a hyd. flat tappet lifter. AND, I am NOT using a light checking spring. (I bought the heads assembled)

I am also using a Comp Cam adjustable pushrod and the Pro Tool pushrod length checker tool (Picture) to measure pushrod length.

With the Pro Tool jig level/flat on the valve stem, I’m getting a pushrod length of 7.75”. BUT…when I paint the valve stem with a marker, install the rocker—with ½ turn preload—then manually turn the engine over two or three times…the roller tip wear pattern is slightly toward the back of the valve stem. Based on my research this is supposed to mean the pushrod is too short. Correct?

My question is whether or not I need to factor in the compression of the lifter since there is no oil pressure?

In my simple inexperienced mind, I imagine that the spring tension may be compressing the lifter enough to shift the valve stem wear pattern slightly toward the back. But with oil pressure, the rocker pivot will be slightly higher which will shift the valve stem wear pattern to the center where it should be.
Am I thinking about this the right way? Or do I just need a slightly longer pushrod?

Thanks for any advice!
http://static.summitracing.com/globa...89_90_w_ml.jpg
http://static.summitracing.com/globa...1506_cp_ml.jpg

Re: Rocker Arm Geometry Question
 

The roller tip rockers won't give you the precise measurement on the tip of the stem like a true roller rocker. The roller tip rocker doesn't have a true fulcrum on which it pivots like a true roller rocker.

The roller tip rockers aren't really all they are cracked up to be. If you insist on using them, just bolt them in with stock length push rods and adjust them as you would regular stock stamped rockers with a flat tappet cam.

EZPZ.

Gary

Re: Rocker Arm Geometry Question
 

While the roller tip rocker, wont be 'dead on" , like a full roller...it should be damn close? Every thing that you are thinking is pretty much "right on" ;) It looks like the pushrods are too short....but the lifters are not pumped yet, & that will toss the monkey in the mix? I would ask about your combo (heads/cam/ ect)....stock? mild? rowdy? Longhorn :ito:

Re: Rocker Arm Geometry Question
 

Thanks guys!

I think I'm going to send the roller "tip" rockers back and replace them with a set of Comp Cams full rollers. http://www.summitracing.com/parts/cc...1-16/overview/

Longhorn, I'm running a .060 block--so it's getting close to the end of its life--with a fairly mild cam. (Sealed Power 210/216 with 111 degree separation, I think. Sorry, going from memory)

Heads are Dart SHP 180cc intake / 72cc combustion chamber. (I just bought them new...so I don't want to trash the valve guides in the first 200 miles.

I'm also running a basic Edelbrock 600cfm carb (Item 1405) and an off the shelf Edelbrock Performer intake.

With that setup, I'm looking at a static compression ratio right around 9.3:1 with a dynamic CR around 7.5:1.

I'm looking for good idle, solid torque and decent top end HP. But nothing too crazy.

My local guys think this combo will work...and MarvD has given me some really good advice on the heads...so I'm feeling pretty confident.

But I'm getting the feeling I've just gone too cheap on the rocker arms.

Agree?

Re: Rocker Arm Geometry Question
 

It sounds like a good "torkey" little mill;) I would bet that you will do ok on the rockers, as a roller tip. Once the lifters pump up, they will probably show you what you need? If you can afford the full rollers, they will be a better deal, but I doubt that you need them? Longhorn

Re: Rocker Arm Geometry Question
 

Buy yourself a single solid lifter and use it when you check your pattern.
This eliminates the Hydro lift issue and gives a better reading.

Re: Rocker Arm Geometry Question
 

Ditto, that is the only way to get meaningfull data from the witness across the valve stem tip.
If you really want to be 'dead on' adjust your resulting pushrod length by 1/64" (0.015) to simulate the depth of pudhrod sunk into the hydraulics with a 1/2 turn of preload.

But just keep in mind, Pushrods are available in 0.050" increments for a reasonable price (~$120) I mean Smith Bros will custom make any exact length you want,, for a price!!
But unless your plaing Cmp Eliminator and spinning 12,000 rpm a $800 set of pushrods is sheer foolishness.

A Stock length SBC pushrod is 7.80"
If your getting 7.75" and add 0.015 for preload depth,, well.... A set of stock length pushrods is probably going to be just fine. I wouldn't sweat it too much.

KUDOS to you for checking tho. You wouldn't believe how few people even give valve train geometry a second thought (and wonder why their valve guides are wearing so quickly or breaks pushrods, and springs and... )