Pushrod oiling - do I need it?

rmchrgr said
For my own edification and to clear up any confusion, here are some pics comparing a stock head bolt to an ARP head stud. OMM used the word 'taper' to describe this situation but I would say it's more of a step. Normally I'd think of a taper being like the conical area underneath the wider part. Either way, you get the idea.

Here's the stock bolt. Note the step in the shank under the head. I admit I had never noticed that before. I always knew the one bolt was a different length but never noticed the step or what it might be there for.
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Top of the shank diameter measurement.
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Diamter decreases .050" below the step.
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ARP head stud shank diameter. There is no step as with the OE bolt.
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Diamater of the bolt hole in a stock, '70's cast iron cylinder head.
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Diamater of the same bolt hole on an Edelbrock aluminum head.
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Even though the step is clear as day now, I'm still not understanding the point of it and it's affect on oiling. There are two holes off the rocker stand oil passageway on the intake side of the hole; one is above the other by about 3/8" or so. In my mind, pressurized oil comes out the bottom hole, fills the area around the bottom of the bolt shank, goes back into the top hole and then out the rocker stand orifice. Again, my best guess for doing this is that the oil flowing around that bolt shank creates a dampneing or swiriling affect on the pressure feed so it does not just spray everywhere.

Regardless, since the bolt holes in both the stock and aftermakret heads look to be about .0025" larger than the ARP stud shank, some amount of oil is definitely flowing around the stud shank. Machining a recess in the shank will obviously add more volume but again, it does not seem necessary since there is no step in the stud like with the bolt. Without that step down in diamater, the airspace volume around the stud shank would probably end up being about the same as with the stock bolt. There's no need for the step anyway because there is no bolt head.

So yeah, I'm just gonna stay with the studs as-is. Never been a problem before and now that I verified things with hard numbers, I really can't see how a straight-shank stud could create any sort of restriction since the inner diamater of that bolt hole provides enough volume for that little bit of oil to flow into.

We have seen the bolt holes as small as .502 on some heads . But what I think was the game changer for the shop was when reinstalling the Indy heads on a race engine where the rockers were starving for oil we noticed the stud was tight against the hole in the head.

Most know when installing or removing a head with the studs in place they are tight going on and off. Also there is no insurance that when tightening that nut on that stud the the stud stays center. If you pull the torque wrench toward the one side it may stay against that side. A hole that is .502 with a stud thats .499 doesn't leave much room for error on 10 holes in the head.

14-1 compression on a alcohol engine and never did we have a cut stud that was compromised .

The Taper/step in the bolt guarantees the hole to be open. There is no step cut in the stud at all and no room for error and no way to check it once its assembled and torqued. So its either buy a tapered/stepped stud set which they do sell. Or take the chance on the oil getting to the top. We have not gulled any push rods or destroyed and needle bearings in the rockers since we have been doing this.

If your building your own engine and you can afford the possible damage from lack of oil then take the chance. Because we have seen the carnage from lack of oil to the heads from straight cut studs. We found the groove cut in the stud is the best way rather then cutting the whole stud shank to a smaller diameter. Or just use bolts. Drilling the head does not prevent the stud from the possibility of the stud covering the hole in the head. What we do works for sure and never a stud failure.

Take this info for what its worth I am only trying to inform you on what we have found to help members. If I was building a street engine I would use bolts. Very high compression engines or engines with boost need studs. High boost he will o-ring the block or heads .