1.7RRs, Pushrod Length, and Valve Lift

[P72Ford]

I've been playing with my engine on the stand, lately. Measured and degreed the cam, finding true TDC, etc.

Anyways. GT40Ps, Crane/ Ford 1.7 RRs, and a stock SD HO cam. The lobe lift on the cam is .277, multiplied by the 1.7 rocker ratio should give me .471 lift at the valve. It would be .444 lift at the valve with the stock 1.6 rockers.

Anyways. I wanted to check that I had the correct PR length, so I bought the adjustable checker, converted one of my lifters to solid, etc. I set everything up. I was looking to center the witness mark on the valve stem (with the mark as narrow as possible), and also go for as much valve lift as possible, while varying PR length.

The most valve lift I could get with the 1.7s, was .450". Thats .021" less than theoretical. I was seeing .448"-.449" with the stock pushrods, and only a thousandth or two better with slightly longer, or slightly shorter rods.

Unless I varied the PR length radically, the witness marks were acceptably narrow, and centered on the valve stem. However, I am concerned that I should be seeing closer to .471" than the .450" I measured. I suppose with some PR flex, some measurement error, and the rocker tip arc, the 'tolerance' could add up.

Has any ever done this before? What were your results? I really wish I had a set of 1.6RRs, so I could compare. I have to admit, the fact that I am seeing little more than 1.6 lift numbers at the valves, using 1.7RRs, is a little disheartening.

I called the folks at Comp Cams, to see how they recommend checking PR length for these 'non-adjustable' rockers. They said to bring the lobe to the heel, slide in the totally collapsed adjustable PR, torque the rocker (should reach 20 ft*lbs in .25-1 turn from finger tight), and then adjust the PR to 0 lash. Add the desired pre load (.020-.060) and that is the PR length.

However, this method returns comparably short rods. When the length is tested with a solid lifter, the contact on the valve stem is good (like the stock rods), but the lift it the valve is as small as .435".

Today I am going to play some more, including with other cylinders, and see what I can see. I want to maximize valve lift while maintaining a narrow, centered contact. It looks like the stock rods return about the best result. Today I am going to check the witness marks, and valve lift with a solid lifter and the stock PR. Then I will check preload with a regular lifter. I'll do it on several cylinders, and record the results.

Then I'll do the same with Comp's method. See which delivers the best compromise.

But, I was wondering who else has done this? Does everyone just torque the rockers and go, or do you check rod lenbgth, contact pattern, and valve lift? Why might I be seeing significantly less lift at the valve, than I should? Is this something to worry about?

[gadget73]

I forget what was used on that motor. I want to say they are longer than stock length though. Keep in mind that you're seeing the lifter compressing since it has no oil pressure. It won't compress as much when its pumped up. I guess you could run the oil system with a priming tool and re-check the lift figures at the valves to verify it changed.

[1980c10]

He said he made the lifter solid. Seems a bit odd to me. Maybe measure with 1.6's like you said and see if it comes up 20 thous shy like the 1.7's

[gadget73]

missed that. Did you by chance verify the ratio on the rockers is what they claim it to be? I've never checked one, but its not impossible that the mfg's claims are BS.

[1980c10]

good point on the rocker ratio

[P72Ford]

I am sure there is some tolerance in the rocker, but probably not enough to account for the lost lift.

I was checking some things last night, and also had a little discussion with MustangEddie via PM.

I think it is figured out. These pushrods provide a little too much preload, which I will correct by shimming the rockers. The engine is in the rpocess of being painted now, but before I put the VCs on, I will measure each pushrod preload, and shim them. I am seeing .065-.070 pre load, whereas ideal is .020-.060.

Comparing the stock pushrod to my adjustable, I'd say these are stock pushrods. There are different ways to measure them, but going by Comp Cams method, they are 6.250, which is slisted as stock for a 302 HO.

[gadget73]

hm, maybe we didn't use different ones on that motor then. For some reason I thought we did though, but I may be thinking of something else. Stock ones look like they are made from 2 balls and a piece of tube, aftermarket ones don't look like that.

[P72Ford]

I confirmed that they are stock yesterday.

OPrdered some from Napa, and compared. I also measured the O.A.L. with a caliper. 6.250.

I will shim the rockers for correct pre-load.

If it is noisy, I will buy 6.200 pushrods, and re-check the pre-load.

[Mercracer]

Perfect is the enemy of good enough. Set your preload, bolt your valve covers on and consider the job done. 1/2 to 1 revolutions of the rocker hold down bolt from zero lash to snug is acceptable preload. 1/4 turn with 20ft lbs is simply not enough in my opinion. I went with shorter pushrods when I went to 1.7 rockers.
In order to blueprint your actual vs potential lift at the valve you would have to first verify lobe lift. There is a natural variance between factory cams and between lobes on the same cam. NMRA Factory Stock racers used to go through a mountain of used cams in order to find the most lift and duration and then bolt 1.7s on top of that.

[P72Ford]

Perfect is the enemy of good enough. Set your preload, bolt your valve covers on and consider the job done. 1/2 to 1 revolutions of the rocker hold down bolt from zero lash to snug is acceptable preload. 1/4 turn with 20ft lbs is simply not enough in my opinion. I went with shorter pushrods when I went to 1.7 rockers.
In order to blueprint your actual vs potential lift at the valve you would have to first verify lobe lift. There is a natural variance between factory cams and between lobes on the same cam. NMRA Factory Stock racers used to go through a mountain of used cams in order to find the most lift and duration and then bolt 1.7s on top of that.

I measured my camshaft. I know what I have, and I know what I should have at the valve, in theory. This obviously does not account for tolerancing, etc.

.277/.277 max lobe lift, I/E, 211/211 @.050", I/E.

With the stock pushrods, I had a little too much lifter preload (.070+ on some). 6.200 pushrods probably would have worked better. However, there is some variation across the board, and at times a 6.200 would not provide adequate preload. At the suggestion of a couple trusted sources, I will shim the rockers to fine tune lifter preload.