Pushrod Diameters and Lengths

The pushrods I removed from the engine as part of a top end rebuild have me a bit puzzled.
They are standard lengths: 7.3" exhaust and 8.15" intake.
The intakes are a tapered style, with a body diameter of .380".
The exhaust are a straigsht style, measuring .326" in diameter.

I have another set pushrods which have the same lengths, but both exhaust and intake are the tapered style at .380" diameter.
Is tapered preferred over straight? They certainly look more rigid.

This engine began life as a Combat, and still has the 2S cam in it. But it has the RH6S head. What are the right length pushrods for this "hybrid"?

The original pushrods on a combat engine were the same as all other Commando engines. These were tapered as you mention. Any straight pushrods are aftermarket. In my case I’m using .060” shorter chrome-moly straight ones to compensate on the rocker geometry for a shaved combat head. Something the factory neglected.

ILLF8ED said:

The original pushrods on a combat engine were the same as all other Commando engines. These were tapered as you mention. Any straight pushrods are aftermarket. In my case I’m using .060” shorter chrome-moly straight ones to compensate on the rocker geometry for a shaved combat head. Something the factory neglected.

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Are you sure the factory ones were stock length on a combat?
The ones I have come across have been shorter on a combat

Fitted at the factory were std pushrods as confirmed by NOC Commando Notes. They also recommended fitting shortened ones.

DYNO DAVE quote in a post of 2014
The combat had a .040 cut head yes....but also a high lift cam with .059 more lift.
I take 1/2 of the head cut and 1/2 of the cam change and you get about .050..... IMO that is how much a combat push rod should be reduced to be in a better ballpark than the later post 12???? to 75 push rods.

So if we follow his advise , in your particular case : combat cam say .60 more lift , RH6 only .020 shaved , so it should need only .040 and not .050 shorter rods ???

marinatlas said:

DYNO DAVE quote in a post of 2014
The combat had a .040 cut head yes....but also a high lift cam with .059 more lift.
I take 1/2 of the head cut and 1/2 of the cam change and you get about .050..... IMO that is how much a combat push rod should be reduced to be in a better ballpark than the later post 12???? to 75 push rods.

So if we follow his advise , in your particular case : combat cam say .60 more lift , RH6 only .020 shaved , so it should need only .040 and not .050 shorter rods ???

Click to expand...

Plus the 1.13 multiplier for the 1:1.13 rocker ratio = .0565”