Push rod lenghts


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By jcacciag - 13 Years Ago

What is the proper length supposed to be for push rods.
I have some out of a 292 (1959) that are 8.129 inch (new style rockers) I just checked the ones out of a 312 I am rebuilding with old style rockers and they measure 8.225 inch. I would like to use the push rods and rockers out of the 292 because I know they have less mileage on them. I cannot find any info on the longer rods. Can I still use then with newer style rockers. Also, Under the 312 rocker arm base are Diamondish shaped stampings not in the 292. Are they for oil direction and is that why there is a length difference. Do I need them?

By Ted - 13 Years Ago

There is a pushrod length difference depending upon the year.  For most instances, an effective pushrod length of 8.000” will get you in the ball park.  I’ve seen cases where the pushrod length did need to be shortened or lengthened 0.100” to get the adjuster in a more suitable position.

 

The oil deflectors under the rocker stands were dropped after 1956 but are worth putting under the rockers if you have a set.

By Doug T - 13 Years Ago
Ted What are the oil deflectors supposed to do? 

Also what is you opinion of the stock solid push rods used through at least '57?  I think they might be OK to line a garden path but should have no place in any engine!  IMHO I think they are the second weakest link in the stock Y blocks after the Load-O-matic dist.

By DryLakesRacer - 13 Years Ago
If you have the ability to have a set made and can control the height of the rocker stands, remember at 50% cam lift (or valve lift) the rocker should be parrellel to the base of the spring. You need the have the proper "wipe" of the rocker on the valve tip so you won't be pushing it sideways causing premature guide wear.

Everything we seem to do with rebuilding an engine changes these measuments. Head and block surface clean ups, cam grinding making it have a smaller base circle, grinding the valve tips, etc. I have even used lash caps to make the geometry correct when I can't resurface the rocker stands (you do remember your geometry class from HS?)

Hey maybe it doesn't matter to everyone but it's one of the things I want right.......So many things...so little time...

Good Luck

By Ted - 13 Years Ago
Doug T (5/4/2012)
Ted What are the oil deflectors supposed to do?
The oil deflectors simply kept the valve guides from being flooded with oil.  If you’re running the umbrella valve seals, the deflectors are a big help in this area.  Keep in mind that the deflectors are part of the valve train geometry if they are being used and depending upon how the heads are being set up in the rocker area, the deflectors become a part of that geometry.

Doug T (5/4/2012)
Also what is your opinion of the stock solid push rods used through at least '57?  I think they might be OK to line a garden path but should have no place in any engine!  IMHO I think they are the second weakest link in the stock Y blocks after the Load-O-matic dist.
While I’m not big on using those original ¼” diameter solid pushrods, they are limber enough that they provide a safety factor if something goes awry such as a stuck valve or seized rocker.  Considering how fragile the mushroom tappets are, it’s much easier to replace a bent ‘early style’ pushrod than tear the motor down to replace a camshaft and lifter set that wiped itself out due to a much stiffer pushrod being in place.  I ran into an instance awhile back where I was working with a set of angle milled Y heads and the ¼” solid pushrods saved the day as they would clear in the pushrod holes whereas the 5/16” tubular pushrods were rubbing in the heads.  Those small diameter pushrods made several 6000 rpm pulls with heavy valve springs without any issues.  I initially cringed at the thought of using them but have a new respect for them since doing that particular test.