I am running a set of EB Porting heads milled to a 52cc chambers, the .026" head gasket, stock lifters, stock bottom end, custom LE cam, and Harland Sharp rockers.

I am having a problem trying to determine the correct pushrod length for my engine. Using the method of centering the tip on the valve method, starting at 7.1" and working down to a 6.950" I still could not get the mark on the valve to center, it always ended up towards the exhaust side. Going shorter on the pushrod isn't an option either because at this point the rocker is nearly sitting on the bottom of the stud and any shorter and it ends up just sitting on the stud with play between the pushrod and valve tip.

I have double checked the rocker part# as being correct for SBC, so am I going about finding the correct pushrod length wrong? I have found another method that is based on trunion and roller tip centerline, should I use that method instead?

Also, I already have a set of Trickflow 7.1" pushrods, and if they are deemed to be a little too long, what is the consequence of TEMPORARILY running them until the correct size comes in?

 

It's always better to run a slighly longer pushrod (.05") than a slightly shorter pushrod.

What PR length checker are you using? Are you using a solid lifter?

 

Are you using tapered or flat rocker studs?

 

I am using a Trickflow adjustable pushrod and a stock lifter converted to solid. Since I can't get the sweep perfectly centered on the valve tip, should I then just try to simply get close as possible to center while also trying to get the most narrow sweep pattern?

 

Rocker studs are ARP 134-7103
Guideplates are Trickflow 30400623-8

 

I run the TF 7.100"...used a PR check tool after starting with stock 7.200" PR then setting the tool at 7.150" and then at 7.100".

ever motor combo will be slightly different. You can order any size 'custom" but unless you are building a $50k race only motor you should be fine with off the shelf sizes typically in .050" incriments.

 

I know I can get any pushrod size I want and that being within .050" length will work with off the shelf pushrods for my engine. My problem is that any .050" length i check from 7.150-6.950 is biased towards the exhaust side and not perfectly centered on the valve. A 6.90" length and the rocker just rests on the stud.

 

Make sure the guideplate is centered between the two rocker studs. Center the plate under one stud then clamp it down lightly, then do the same for the opposing stud, then torque both of them down.

 

Guideplates are centered. Went through again and tested pushrod lengths for 7.050-7.200 and checked both sweep position as well as measuring the width of the sweep, here is what I found:

Sweep Area Width
7.050 - .084"
7.100 - .063"
7.150 - .071"
7.200 - .069"

I checked all of these lengths 3 times and this is the average sweep area of each of these pushrod lengths, varying by no more than a few thousandths each time. With the 7.200" pushrod, the sweep area also only had about .068" from the end of the valve vs about .093" from the end with the 7.10" pushrod. Although the sweep of the 7.050" appeared to be more centered on the valve, it also had the greatest travel across the valve.

So based on these findings, would the 7.100" pushrods that I have be the best choice given they have the smallest sweep area?

 

without seeing the pics my $02 is 7.100". basically you want the most centered/narrow witness mark and confirm there is no interference with RR and stud anywhere during full motion cycle.

 

If you read CompCams explanation on rocker movement as the valve is opened and closed you'll find that the roller tip DOES NOT remain centered over the valve stem.

With the lifter riding on the base circle of the cam lobe, the roller should be positioned slightly OUT-BOARD (toward the exhaust) of the center of the centerline of the stem tip. At mid valve lift the roller should be centered over the valve and at full valve lift the roller should be slightly INBOARD (toward the intake manifold).

As reported in Circle Track mag, you must also factor in the amount of lifter preload since that amount has a direct effect on the working length of the pushrod.

I suspect you're moving in the wrong direction. Most often longer pushrods are needed, rather than shorter ones. In fact, an "Ole Racer's" axiom is that it's better to run a pushrod that's a little too long and one a little too short. An being a 65 year old "Ole Racer", I subscribe to that.

Jake

 

Jake

by 'centered" i mean when you test PR length by marking the top of the valve stem with a Sharpie, lash valve, rotate engine by hand 2 turns and then inspect "witness" mark left you want one that is centered on the valve stem tip vs favoring one side or the other. You don't want to side load the valve stem.. true the rocker tip does travel inboard/outboard of exact center but the point is you want that movement as centered on the valvestem as possible.

with heads that are 'worked" often they are milled/decked making the distance of head/block closer. The use of a head gasket about 1/2 the thickness of stock as OP is doing also reduces that distance. thus a shorter PR is often used.

He could probally go down the road just fine with stock 7.2" but 7.100" seems to bring him closer to center and he has them.

also congrats on your sons West Point graduation...we are all blessed in living in the shadow of Freedom our Military fights for.

 

Post a pic and what pushrod length you used to get that. We will let you know what to choose