Author Topic: Setting push rod length  (Read 493 times)

Offline Mister_Fitz

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Setting push rod length
« on: April 19, 2017, 12:00:43 PM »
I have changed intake rockers and has started to measure push rod length on my SBC according to the "half lift" theory. They recommend to sett the length within 0.01". I use Comp cams 5/16" Hi Tech push rods and they are available with 0.05" increments.
I also noticed that my valves sits at different heights in the cylinder heads.
So if I would to measure and set all 16 push rod lengths individually I would most likely end up with a whole lot of different lengths. I would also have to keep track of which push rod that belongs to which valve.
This is of course doable, but how exact does it has to be?
What are your "tolerances" when setting push rod lengths?

I'm looking forward for some tips from the gurus!  :)

Offline coupemerc

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Re: Setting push rod length
« Reply #1 on: April 19, 2017, 05:07:49 PM »
Well I am not a guru but my B/ND SBC motor uses two different push rod lengths...one for the intakes, one for the exhausts. The lengths are set to .01". Use the strongest push rods (largest OD, thick wall) you can physically fit in the motor. Don't worry about their weight!

Offline dreracecar

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Re: Setting push rod length
« Reply #2 on: April 19, 2017, 07:34:31 PM »
If you use an adjustable push rod to measure with and the ends are full radius and no flats or oil holes, subtract .050 from the measurements. Push rods are measured from oil hole to oil hole which takes .025 off each end hi

Offline Mister_Fitz

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Re: Setting push rod length
« Reply #3 on: April 20, 2017, 12:21:16 PM »
I will also need one push rod length on the intake and one on the exhaust. But the valves in my cylinder head doesn't have the same height above the cylinder head. This is due to that for some reason the valve seats are at different heights in the combustion chamber. The difference is not big, perhaps within 0.05", ( I haven't measured it that exactly yet).
But there are a difference and if I would do it 100% correct I would have a variation of the push rod length between all 8 intake valves.
Should I measure each intake push rod individual? Should I take an average of all the intake push rod lengths and use that length on all intake valves?

How does everybody else handle this variation? Or is it just my old cylinder heads that has this problem?

Offline dreracecar

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Re: Setting push rod length
« Reply #4 on: April 20, 2017, 03:01:03 PM »
Mark and surface the end of the valve to equalize the assembled length as long as the rocker does not interfere  with the spring retainer,  only asking for trouble later on if you match pushrods to individual valves