Tech crap !

[Fathead Racing]

Jimminy Crickets ! You would think it would be a simple task to measure for pushrods using a pushrod length checker but noooooooooooo. There is the theoretical length the measured length and a gauge length. Then there is a method using a standard. I'm bout ready to pull my damn hair out. between the four methods there could be as much as .024" difference. I measured with a quality pushrod length checker 8.626" exhaust valve pushrod length, the checker has a flat on both ends to simulate an oil hole. That would be the measured length, but , some companys want the theoretical length as if there were no oil hole. I'll have to call Crane or Comp and show them how I measure. What a hassle.

 

[models916]

I used manley

Manley catalog spec is for actual measured length.

 

[Fathead Racing]

Got the chance to talk to a real tech guy at Comp Cams. He says to give him the real measurment from the pushrod length checker. My pushrod checker has flat ends that take account for the oil hole in a real push rod. A .100" oil hole in the end of the pushrod accounts for .017" off the radius. in other words, if you had a pushrod with a length of 8.800 that had .100" oil holes at both ends measured with a micrometer, the theoretical length would be 8.834. That is the measured length, as measured with a caliper plus the added material that was removed by drilling the end of the pushrod for the oil hole! I came up with a measurement of 8.626" for my exhaust pushrod. Comp Cams did not have an off the shelf 3/8" pushrod of this length. I asked the tech if .026 would make any difference in my valve train geometry. His answer was "probably not" this means I can order an off the shelf pushrod at 8.600 and save some money. I pushed him farther and asked, would a + or - .050" pushrod length make a difference? He said if you were not running the roller to the extreme out or inside of the valve tip you would be ok on a street engine. As you move up the scale to say a Bluescreemer you would want to dial in the geometry to a finer degree.

 

[raymar58409]

Ray, I like to install checker springs and use a length checker with oil holes, mount the heads on the engine as it is going to be run. In other words I mock it up with all machining done (heads shaved, block decked, head gaskets installed, etc.)and use the rockers I'm going to use. with the cam installed roll the cam from full closed valve to full open and watch the movement across the valve tip. Ifr you are going to err then err to the longer side, inother words I fell its better to be .024 longer than .026 too short. Just don't let it get too close to the outside edge. You can also check the posistion of the rocker over the valve at half lift and it should be over the middle of the valve stem. Hope this helps.
Ray

 

[bluescreamer]

Tech crap

Ray
Most push rod companys (Comp cam, Trick Flow, Crane, And Summit) make push rods in .050 increments. starting at 6.500 to 9.000 inches in lenght.
From your discussions with Comp Cam your should be in the ball park.
But it is time consuming and trial error to get the correct geometry so that the rocker arm roller crosses the middle of the valve stem.
Because I use a 11/32 valve stem this make it doubly important that you get it correct. I therefore use a lash cap on top of the valve stem, thereby increasing the contact area.
If you install a valve spring with a very light spring, ( such a small block) and use your test push rod on a intake and a exhaust, with rockers installed, place a business card between the roller tip and valve stem and rotate thru a cycle. this will leave a impression of the contact area. It should be centered in the middle on the valve stem. I don't think using a checking spring will create enough pressure, to get a impression.
I have many different sets of push rod that I have collected over the years just so I could get right.
Remember every time you change head gasket thickness, shave the heads, deck the block, do a valve seat, install new or longer valves. and change to a different rocker ratio, the contact changes on top of the stem.
It took me a couple of weeks on the motor in the Bluescreamer till I felt comfortable with the end result.
Allen

 

[Fathead Racing]

Allen I also use the 11/32" valve. Very good post on your experiance. I used the adjustable pushrod and found that 8.626 left a very good witness mark across the exhaust valve tip. Comp cams has a 8.6" pushrod. I adjusted the checker to 8.6 and ran the valve through two cycles. Shortening the pushrod by .026 did not change the witness mark enough to order a custom pushrod. I will use the 8.6 pushrod from Comp. I have just come in from the garage where I ran the intake through a few cycles and have a 8.84 length on my pushrod checker that leaves a good witness mark. I am now going into comps catalog and see what length they have to offer that is close to my checker length. After I find this length I will adjust the pushrod checker to it and run that length through a couple of cycles and check the witness mark again. I see the Comp cams has a 9.00 so I an going to run that through a couple of times, I'll bet that's what I end up with. 8.6" exhaust and 9.00 intake pushrods.

 

[models916]

solid roller?

Fatride, are you using a solid roller? If so you are on the correct path.

 

[Fathead Racing]

Fatride, are you using a solid roller? If so you are on the correct path.

Yes I am running a solid roller cam. My pushrods will be 8.6" and 9.0" .080" chrome mollys.