Pushrod measuring issue

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74Scamp

74Scamp

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I’ll try to keep this short winded as possible.

So I’m finishing up my 360 the other night and I went to adjust the valves only to find out the pushrods are too long as in the push rod will hit the rocker arm with the adjuster taken out too long. Back story is I’m using a set of heads from a buddy that haven’t changed since his build to mine. We both have nearly the identical build (same cam company and nearly identical profile even) so he figured the pushrods he used would work just fine with my engine. Guess that assumption was wrong and only thing we could figure out is my block got decked further than his did. Machine shop didn’t measure the before/after deck height so there’s no info on that.

I bought a Comp cams pushrod checker and the other night I checked the length. So I put a lifter on the base circle of the lobe, put 1.5 threads sticking below the rocker arm, snugged the rocker shaft down, and turned my checker pushrod until I had .020” valve lash. To my surprise my checker pushrod was only .020” shorter than the pushrods I was using. I double checked my work and checked the exhaust as well, same result. Solid flat tappet cam FYI.

From what I said can anyone help me out or point me in a different direction? The guys I talked to at Smith Bros Pushrods were in the same boat as me.

E3C29C1F-55C0-45F1-8D87-BC8B08FE401A.jpeg
 
Last edited:
Are you checking overall length or effective length. The two aren't the same.

Do you have ball and ball pushrods or ball and cup?
 
74Scamp said:
I’ll try to keep this short winded as possible.

So I’m finishing up my 360 the other night and I went to adjust the valves only to find out the pushrods are too long as in the push rod will hit the rocker arm with the adjuster taken out too long. Back story is I’m using a set of heads from a buddy that haven’t changed since his build to mine. We both have nearly the identical build (same cam company and nearly identical profile even) so he figured the pushrods he used would work just fine with my engine. Guess that assumption was wrong and only thing we could figure out is my block got decked further than his did. Machine shop didn’t measure the before/after deck height so there’s no info on that.

I bought a Comp cams pushrod checker and the other night I checked the length. So I put a lifter on the base circle of the lobe, put 1.5 threads sticking below the rocker arm, snugged the rocker shaft down, and turned my checker pushrod until I had .020” valve lash. To my surprise my checker pushrod was only .020” shorter than the pushrods I was using. I double checked my work and checked the exhaust as well, same result. Solid flat tappet cam FYI.

From what I said can anyone help me out or point me in a different direction? The guys I talked to at Smith Bros Pushrods were in the same boat as me.
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yellow rose said:
Are you checking overall length or effective length. The two aren't the same.

Do you have ball and ball pushrods or ball and cup?
Click to expand...
Cup and ball. You’re asking about checking length between the two push rods? If so I’m comparing overall length. Side by side. Push rod checker is a cup and ball, same dimension as my pushrods too. Maybe a little redneck but since I don’t have a caliper big enough I had both pushrods side by side and used a feeler gauge to fill the gap in until both pushrods were flush. .020” feeler gauge fit just right.
 
74Scamp said:
Cup and ball. You’re asking about checking length between the two push rods? If so I’m comparing overall length. Side by side. Push rod checker is a cup and ball, same dimension as my pushrods too. Maybe a little redneck but since I don’t have a caliper big enough I had both pushrods side by side and used a feeler gauge to fill the gap in until both pushrods were flush. .020” feeler gauge fit just right.
Click to expand...



You need to verify effective length, which is the length the pushrod is from the ball in the lifter to the cup in the pushrod, including the radius.

Using OAL length is a crap shoot at best.

The best length checker for what you are doing will measure effective length and instead of a cup on the rocker end it has a flat screw. That way you get the exact effective length which is what matters.
 
what lifters are you using?...as some brands have different seat distances...where the push rod cup is on the lifter
 
I just did the rocker arm geometry on my 340.
Harbor freight has a nice 8 inch dial caliper for about $25.00 or less. Its good enough.
You must use a 5/16 ball in the cup for measurement of push rods as each brand of cup is different. Total length does NOT work for this measurement! the ball is at most hardware stores in the nut and bolt dept. The 5/16 ball measures .3125
use 1/2 this measurement .1563 to get total length.
While checking this use zero valve lash to eliminate one more possible mistake.
Donnie
 
When you measure length with the 5/16" ball, you subtract the full .3125" from the length measurement (of pushrod + test ball) to get the effective length. The effective length is from the tip of the ball to the BOTTOM of the cup.
 
Following along here trying to learn, but wouldnt you take 1/2 of the dimension of 0.3125"= 0.15625 ? My thinking is the cup only "holds/houses" 1/2 the "ball" on the rocker?
nm9stheham said:
When you measure length with the 5/16" ball, you subtract the full .3125" from the length measurement (of pushrod + test ball) to get the effective length. The effective length is from the tip of the ball to the BOTTOM of the cup.
Click to expand...
 
You both are correct.
I just came back to finish and clarify my earlier post after I had my morning coffee and cleared my brain.
Donnie
 
I’m running a Bullet cam solid flat tappet cam and their solid lifters for that cam. I’m running 1.6 RR but I don’t know the brand. They came with the heads already. I’ll have to swing by HF and get a 8” dial caliper to measure the checker rod.
 
4spdragtop said:
Following along here trying to learn, but wouldnt you take 1/2 of the dimension of 0.3125"= 0.15625 ? My thinking is the cup only "holds/houses" 1/2 the "ball" on the rocker?
Click to expand...
Per Manton and Smith Brothers, the effective length is from the tip of the ball to the bottom of the cup. So subtract out the whole diameter of the 5/16" 'BB' to get the dimension to the bottom of the cup. It is a matter of getting to a standardized length spec, and the center of rotation (as in the center of the test 'BB') is not what is commonly used.

Determine Length – Manton Pushrods
 
I have a very foolish question about your build. Could your block & heads been surfaced before you got them & them cut more during your machine shop work? I ran into this problem when I built 2 engines & found through measuring that one of the block & heads had been cut to true them up. this lead to a custom set of push rods for the one build.
 
Well I know the heads weren’t being used for a while since my buddy had gotten a set of aluminum heads instead and my block was from a old farm truck so I doubt it would’ve had any machine work done in its life time. It is hard to tell since the machine shop didn’t take measurements of the deck height before/after. It would’ve been helpful had they done it just for the sake of info.
 
More information for ya. I also have the 1.6 rocker arms and that is where the push rod length problem started. Harland Sharp has a clear photo on there web site that shows the adjuster screw in the rocker arm as it should be. I had the same problem as you and found that a new set of push rods that were only .064 shorter were perfect.
Donnie
 
Just mail Smith Brothers your pushrod checker (that's what I did years ago). They will measure it, and make your 16 pushrods and send you the pushrod checker back with your order.
 
Donnie514 said:
More information for ya. I also have the 1.6 rocker arms and that is where the push rod length problem started. Harland Sharp has a clear photo on there web site that shows the adjuster screw in the rocker arm as it should be. I had the same problem as you and found that a new set of push rods that were only .064 shorter were perfect.
Donnie
Click to expand...
Although mine aren’t Harland Sharp rockers, I’ll have to take a peek at their website then. I got a big enough dial caliper and 5/16” ball to measure and I only got .022” shorter (effective length) than what Smith Bros made me and that’s not enough for a safe adjustment.
 
flyfish said:
Just mail Smith Brothers your pushrod checker (that's what I did years ago). They will measure it, and make your 16 pushrods and send you the pushrod checker back with your order.
Click to expand...
Even with talking to them over the phone we both didn’t feel comfortable doing that and i don’t trust the checker to stay accurate while keeping it in place for packaging and mailing. Until we get a big enough difference for a pair of pushrods to be made it’s still up in the air.
 
I cleaned off my comp cam checker, Adjusted it, and then used silicone to hold it in place. Takes a day to dry but it worked.
PS don't tell anyone that I be a hillbilly but as I said it worked.
 
74Scamp said:
Even with talking to them over the phone we both didn’t feel comfortable doing that and i don’t trust the checker to stay accurate while keeping it in place for packaging and mailing. Until we get a big enough difference for a pair of pushrods to be made it’s still up in the air.
Click to expand...
I wrapped my adjusting nuts on the checker with duct tape...looks ugly...works well.

Mine ended up being 7.312 effective length.
 
Wow, my motor is not like yours so I not comparing but mine ended up @ 7.278
How did you get a nut "on" that checker?
Didn't you say it was a comp cam checker?
 
I have custom Smith Brothers pushrods in my engine. I bought their checker, a ball X ball unit and checked several intake and exhaust using their instructions. Their website is a wealth of information. When I was confident I ordered their pushrods and my geometry was good. Note, 273 commando build with Lunati hydraulic lifter setup and stock rocker arms. I also ordered their rocker adjuster locking setup so the adjustment would stay where I put it and my problems (at least with this area) were over.
 
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