Measuring for pushrods.....how many cylinders do you check to get it right?

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Kern Dog

Kern Dog

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I'm working on a 5.9/408 build with a fellow FABO member and I got curious about this.

5.9 stroker build

When assembling a non stock engine, you often have to get custom parts to fit the application. We file fit the rings to each bore but does anyone actually measure for pushrod length on every cylinder?
I've only had to order pushrods a couple of times and I just measured off of #1 cylinder.
Come to think of it, when we degree a cam, we also only check the specs for the same #1 cylinder. Does anyone actually check specs on the other cylinders to see if they are consistent?
To this original point though...It didn't occur to us to measure pushrod length on cylinders 2-3-4-5-6-7 or 8.....
Until today.
Rich got inconsistent numbers despite verifying that the rocker shafts were snugged down, the cam was on it's base circle and that the pushrod checker was properly seated in the lifter.
The goal was to establish a zero lash measurement then add the suggested amount of preload to the number to arrive at a proper length. Three cylinders were checked and the numbers varied by around .030.
Now, that is well within the range of adjustment allowable in these rocker arms. It got me thinking though that since most of us have stock based engines with non adjustable shaft mounted rocker arms, how many of us are running a combination with either too much or not enough preload?
 

The subject of preload gets some debate too. I never even considered the amount of it given that most of my builds have been with the stock rocker arms and hydraulic lifters.
Rich was told that the Magnum series calls for .090 preload. My experience with stud mounted rocker arms is just with Chevrolets where it was advised to tighten to zero lash, then some amount of turns beyond that, often between half to one turn.
Today we found that with the rocker arms he has, Rich's setup takes 1 3/8 turns of the adjuster to reach .060. This was merely a test to see what results that a turn of the adjuster gives. This will make adjustments simpler than to put a dang dial indicator on every lifter.
 
On a basically stock engine with stamped arms I checked 2 per bank. There was a 0.020” diff bank to bank. If you have adjustable arms I don’t see the purpose but I am sure some will say check everything but what are you going to do about the differences?
 
On the 340 I assembled for my Duster and the 318 I assembled for my Dart I measured the length of every pushrod. That’s both pushrods for each cylinder.

Now, that being said, I was able to order 16 pushrods of the same length for both engines. But that single length was going off of all the measurements, so that each valve would be within the range of adjustability (not exactly just an average).

I have seen engines that have different length pushrods for the intake and exhaust valves. Not what I’d want, but they’re out there.

And to the point, what would I do about the differences in measured length for the pushrods? Clearly I’m not going to order 16 individual length pushrods. I’d consider ordering intake/exhaust pushrods. But if the pushrod lengths were different enough that they weren’t covered by the pre-load or the adjusters then the heads would go back to the machine shop. Because the valve lengths should at the very least be the same for intake and exhaust. If they’re not, it means the valve seats or the deck or cylinder head heights are all over the map, and that’s a problem at the machinists. So they’d get the heads back.

But in order to find that, you’d have to measure more than one cylinder.
 
Yep, I do the four corners as well. Run a straight edge across the tops of the valves to make sure there's no outliers. I forget Greg - didn't you have a valve job done on the heads?
 
I should have been clearer.
The engine that we are working on has new Trick Flow heads. That is the 5.9/408 build,
In regards to my 1990 360, I’m just reusing the pushrods and Hughes rocker arms that were on this engine. My machinist did a cursory valve job but said the heads were in great shape, they barely needed work besides milling them due to the blown head gaskets.

@RBConvert
 
Last edited:
Kern Dog said:
I should have been clearer.
The engine that we are working on has new Trick Flow heads.
I’m just reusing the pushrods and Hughes rocker arms that were on this engine. My machinist did a cursory valve job but said the heads were in great shape, they barely needed work besides milling them due to the blown head gaskets.
Click to expand...

If you're changing cylinder heads you definitely need to measure for pushrods. How many you measure I suppose depends on how much you trust your machinist.

But if you don't measure all of them, you have no way of knowing how close they all are. Measuring all 16 is probably overkill, only measuring 1 cylinder is putting a lot of trust in Trick Flow and your machinist.
 
There are two separate builds going on here.
Mine is the stock stroke 1990 360 that came to me with 2 blown head gaskets. It is an iron head mill with #308 heads, Hughes 1.6 rockers and roller cam and an Air gap intake.
The other engine was an original MP Crate 360/380 that Rich is building into a 4 inch stroke 408. It has Trick Flow heads, PRW rockers and a Hughes cam.
I appreciate the responses.
My main question was if it was customary to measure for pushrods on more than one cylinder. Rich has been reading a 408 build in old Mopar Action magazines and in one issue, Ehrenberg measured just one cylinder and ordered his pushrods based on that one reading of 2 rocker arms. That is what I have done too but Rich and I got curious about why people often just checked one cam lobe when degreeing a cam and just one cylinder when determining pushrod length. I'm glad to hear that others had this same curiosity.
 
Depends on who did your cylinder heads LOL you may need 16 custom push rods if they're old heads with various degrees of sunk seats.

You can do all four corners, or one int and one exhaust from each head.
 
I mean, really....... if adjustable rockers, ya need to measure all 1 of them. If your heads were done right with exact retainer height and the decks are proper, why would you need different length rods?

If Ma Mopar ever put diff rods from the factory, I'd be SHOCKED.
 
I agree to a point but some experts advise to have an X amount of threads showing on their adjusters. One turn may equal .050.
I may be splitting hairs but I was just curious if I was out of the loop on this.
 
You can figure out how many turns of the adjuster gives you X amount of preload by the thread pitch.

IMG_1198.png
 
Kern Dog said:
I'm working on a 5.9/408 build with a fellow FABO member and I got curious about this.

5.9 stroker build

When assembling a non stock engine, you often have to get custom parts to fit the application. We file fit the rings to each bore but does anyone actually measure for pushrod length on every cylinder?
I've only had to order pushrods a couple of times and I just measured off of #1 cylinder.
Come to think of it, when we degree a cam, we also only check the specs for the same #1 cylinder. Does anyone actually check specs on the other cylinders to see if they are consistent?
To this original point though...It didn't occur to us to measure pushrod length on cylinders 2-3-4-5-6-7 or 8.....
Until today.
Rich got inconsistent numbers despite verifying that the rocker shafts were snugged down, the cam was on it's base circle and that the pushrod checker was properly seated in the lifter.
The goal was to establish a zero lash measurement then add the suggested amount of preload to the number to arrive at a proper length. Three cylinders were checked and the numbers varied by around .030.
Now, that is well within the range of adjustment allowable in these rocker arms. It got me thinking though that since most of us have stock based engines with non adjustable shaft mounted rocker arms, how many of us are running a combination with either too much or not enough preload?
Click to expand...
Well I always check all of them all 16. Usually you should only have no more than 2 threads showing on the adjustment nut on the rocker arm itself if they are adjustable rockers. Since its a stroker engine I am assuming you had it decked and squared up etc.. the heads? Were they milled any all these things affect the push rod length. Check EVERYTHING then check it again. Those push rods should all be the same length unless your running w'2s or something like that. The reason why Im carrying on about this a bit is one time I had 2 cam lobes new cam out of the box that were 0.20 less lift than the rest of the cam! Valve height check that as well.
 
No, you are not out of the loop. Retainer height? It's stem height. There's alot more to a valve job than what it looks like.
The valve seat, grinding the valve, retainer height, spring pressure, coil bind and stem height. Plus the valve guide. The whole thing is an art, and it takes practice.
 
I ran a straight edge across the valve stems. In each cylinder, the exhaust valve stem was below the intake by almost .010.
Again, these are Trick Flow heads. He did not resurface them. A machinist could have ground the seats to get an even stem height across the board but neither of us have experienced this before.
This is his first engine build ever. He has done plenty of mechanical stuff but not to this extent. I've never worked with aluminum heads on anything but big blocks.
 
OK I see now. Well being aluminum heads and a hydraulic cam check a few cylinders if ok adj the rockers to where they have zero lash then give them all another 1 full turn in or even one and 1/2 turns in to preload the lifters's and you should be fine. Those head's will expand after it's warmed up which will loosen up the lash a little which will be fine as long as they are not ticking. Here's the fun part after you have run it a while and this goes for all makes of v8 engines with aluminum headed engines you really should re torque the heads again just check them to make sure they retained their torque on each head bolt. I know they say if you use the right head gaskets you will not have to do that. Simple ask yourself a question would you rather check it now or wait till you start having a head gasket leaking 200 miles down the road? Hugh's Engines machine shop is now shut down so they send everything out to be done now was on the phone with them yesterday in fact for other things. But I'm sure the work that was done is fine they would not send them to somewhere that did not know what they were doing.
 
I leave nothing to chance, I too check all of them along with valve height and possible rocker are bind. There is not a more disheartened feeling, as soon as you newly modified engine makes strange noises the first time you crank it up.
 
I
Kern Dog said:
I ran a straight edge across the valve stems. In each cylinder, the exhaust valve stem was below the intake by almost .010.
Again, these are Trick Flow heads. He did not resurface them. A machinist could have ground the seats to get an even stem height across the board but neither of us have experienced this before.
This is his first engine build ever. He has done plenty of mechanical stuff but not to this extent. I've never worked with aluminum heads on anything but big blocks.
Click to expand...
I am going to insert this here as you are the OP for this thread. One thing not mentioned at all through this thread is "Rocker Arm Geometry" all rocker arm type engines regardless of pivot and or push rod or not has to have the rocker geometry set first before calculating the push rod length.
This is done on setting up the valves, spring height, etc. It is a visual method with springs off. Determine what the gross lift of the valve will be insert valve make a mark on the stem ant the half lift of the valve , then instell the rocker for that valve open the valve with the rocker to the mark and look at the rocker tip location on the valve it should be at 90* and in the center of the stem. Adjustments are made depending on location inside or outside of center and angle. Another words valve stem height and or rocker shaft "pivot location" needs to be altered.
This affects two things valve guide wear and actual valve actuation from the rocker as designed into the cam, correct lift and duration, if geometry is wrong lift and duration at valve will be wrong.
 
Well, since the man said that ONE turn of the adjuster equals .050 of movement, I'd think that it would need more preload than 3/4 turn.
 
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