Pushrod length confirmation

[JCJones]

Greetings-
I'm building a 1968 Chrysler 383 and need to purchase the correct length pushrods. I used one of Summit's adjustable, measuring pushrods to determine the length I need, and I'm just looking for some confirmation on my procedure and measurements.

I've had the block and heads milled for zero-deck piston clearance. I'm using a hydraulic flat tappet cam and hydraulic lifters. Prior to measuring, the heads were installed/tqd with a theoretical compressed gasket measurement of .039".

First of all... I made sure all of the rockers, shafts, and oil holes were in the correct orientation.... no small feat, since I had one of them put back together totally wrong.

Then I measured with the adjustable pushrod at the four corner cylinders (1,7 & 2,8), I soaked the lifters in oil, then installed them and rotated the engine until the intake/exhaust lifters were both on the base circle of the cam for each corner cylinder. Then I snugged down the stock, stamped steel (non-adjustable) rockers, before inserting the adjustable pushrod for measurements.

I then slid the adjustable pushrod between the lifter and the rocker and extended the pushrod into the rocker cup until I could feel resistance when spinning it with my fingers. I removed the rockers and measured and noted approximately how many revolutions the adjustable tip had extended.

Each revolution of extension = .050".

The Speed Shop near me said that when measuring for pushrod length,
in my setup, I should also add .050" for hydraulic lifter preload.

A summary of how I came to my pushrod length measurement is as follows:
Cyl #1
Intake: 13.0 Revolutions of pushrod extension
Exhaust 13.25

Cyl #2
Intake: 13.25
Exhaust: 13.4

Cyl #7
Intake: 13
Exhause: 13

Cyl #8
Intake: 13.5
Exhaust: 13.4

The closed length of the pushrod =7.800"

• Average Revolutions of extension = Total Revolutions/8 = 13.225 average revs/valve
• 13.225 * .050" = .6613" extension
• add .050" for lifter preload

So 7.800" + .6613" + .050" = 8.511" Pushrod Length to Order

I'm just wondering if anybody can confirm that this all looks correct, and makes sense. I'm assuming I can't order to 8.511" accuracy, so I guess I'd be ordering 8.5" pushrods by my calculations.

I'll be confirming with other sources wherever I order, but I value the opinions here more than I do Joe Blo on the phone.

Jason

 

[72Dart6pack]

Your math is correct.

 

[JCJones]

Thanks for the confirmations!

I used the "Revolutions" method because I don't have a caliper large enough to measure the fully extended pushrod tool, but... it may be large enough to measure to the meeting surface where the extendable tip screws together. I'd then have to measure from one end to the meeting surface, then measure and add separately, the extended portion. This might just give me another confirmation on the measurements.