It's been a long time since I've had to mess with rocker arms. Quick background. 1956 316. The other day the engine start hammering. I pull the cover and easy I think, there is a loose rocker arm. I take it off and pull the pushrod. It's damaged on top. I went to get a set. The ones they had were about a 1/4 inch longer. Hmmmmmm. I went home and pulled another. It was the same length as the new one. It wasn't that the push rod was hammered down, it was simply the wrong pushrod. I have no idea how long it's been that way. So I pulled them all. All the rest are the correct size. Here is where it's likely an easy answer I just want to make sure (as I said, I haven't had to do this in a long time). I adjust the rockers to where there is no up and down movement of the pushrod but I can still just spin it. According to MOTORS, you then give it a full turn. I do that but the nuts back off after just a couple minutes. I do it again, only this time tighter. Runs great sitting there at idle. Go down the road and the nuts back off. I can't go tighter as it starts to stumble. Do I need to just get some lock nuts or is there something I'm missing? Another question specific to this engine since there was a wrong push rod, I'm just double checking a couple other things. I've really only done this before on Chevy stuff. Usually there is an oil hole in the rocker for the oil to come through. None on these rockers. Right? It also appears that the oil is only coming up through the last two rocker sets?
These old injuns oil the rockers through holes drilled in the rocker studs from passages in the heads, not through the pushrods like all '65 and later engines (a select few '64 and earlier engines did oil through the pushrods, 389 & 421 SD and HO/GTO engines would be the bulk of them). If the holes in the studs are clogged from the use of non-detergent oil 'back in the day' the rocker balls won't see oil. 99.999% of all Pontiacs have non-adjustable hydraulic lifter valvetrains from the factory, you just tighten the rocker nuts to 20-25 ft. lb. onto the tapered stop portion of the rocker stud. When changing to aftermarket cams this won't work in most cases, some type of self-locking nut (small-block Chevy) or polylock nuts are required to make the factory Pontiac non-adjustable valvetrain into an adjustable type. You can't use the stock Pontiac rocker nuts (they are NOT adjusting nuts) to adjust your valves, they can only be tightened down to the factory torque spec. The early engines used 8.715" pushrods up through '67 (1967 was a transition year where both long and short pushrods were used on different engines), most of the '67 and later engines used 9.145" pushrods.
Someone needs to help me here then. LOL Maybe the 1 pushrod is correct while the rest are not. I'll have to double check but I'm 99% sure the books show 9.1 as the correct size and that is what 7 out of 8 were. 8 out of 8 now. 99.999% of all Pontiacs have non-adjustable hydraulic lifter valvetrains from the factory, you just tighten the rocker nuts to 20-25 ft. lb. onto the tapered stop portion of the rocker stud. When I had them this tight, it wasn't going to run right.
The only years that used the shorter (8.684) pushrods are the 62-67 engines, all the rest are 9.146". Per shop manual, adjust one cylinder at a time, with #1 firing order, adjust to no axial movement on pushrod, than tighten 1 additional turn with nut, than so forth for each cylinder. There is a copy of the 56 Pontiac manual on Pontiacsafari.com with better directions. Maybe at least put some new locking nuts on the studs or threadlocker ( I would use the blue)
My reference shows all '61 - '67 engines (some '67) as using 8.715" pushods, I guess I can't make the assumption that the the shorter ones were used all the way back to '55. Interchange in another Pontiac engine book by the same authors (H-O Racing) shows '55 -'60 being different than '61 -'67 but unfortunately doesn't specify the pushrod length for the earliest engines. If your pushrods are too long, the factory torque specs will never work right for you. Same thing goes for most aftermarket cams, or heads that have been milled or had a valve job or two. These will all throw all of the factory distances between the cam base circle and the valve stems out of spec, requiring you go to the Chevy self-locking crimp nuts and start adjusting the valves like you would on a SBC engine. I'm foggy on exactly when Pontiac went to the non-adjustable valvetrain, it might have been after your '56 engine rolled off the line. Either way, if the Pontiac nuts are loosening right after a valve adjustment then you need to swap them for self-locking crimp nuts. After a number of adjustments even the crimp nuts will lose their ability to hold and they need to be replaced.
For the record, this is what I did. Ran great until the nuts backed off. They backed way off themselves in just a minute or two at 40-50 mph.
Even those year numbers sound off now I posted, 1960 MPC shows pushrods same from 55-60. 62-67 and lengths was from comp cams site. I believe the correct years with shorter pushrods should be more like 61-66? Because I know when I put my 67 (670) heads on the 66 389 I had to use the longer 400 pushrods.
Well, great then. LOL Unless someone tells me otherwise I'm going to do this one more time with threadlocker. If it still doesn't work, I'm going to get some lock nuts. Thanks
Just FYI for anyone who cares: I happen to have pulled a couple of my pushrods out of my 1955 287cu. today and the pushrods measured 9.300.(had a similar problem as WVENFIELD, but the pushrod end was damaged on mine). 1955 is not the same in many regards to the 56-later engines.
I cannot quote the height of the 1955 lifters, but If I am not mistaken we finally determined that the stock '55 the lifters were shorter and the pushrods longer, and '56 and later the lifters were longer and the pushrods shorter.
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