The Stovebolt Site Forums The Shop Area Engine Shop Valve Adjustment screws too short

Hello everyone I've never posted a question before so forgive me if I'm doing it wrong. I use the information in this forum a lot to help me with problems. I'm rebuilding a 1948 chevy 2 ton truck with a 1959 261 6. I've had all the machine work done and new cam with new lifters and now I have an issue with two of the adjust men screws for cylinder 1. The issue is the adjustment screws appear to be too short. The locking nut just grabs a couple of treads with locking the screw. The rest of the cylinders are OK it is just number 1. This engine was locked up when I took it out so this is a complete rebuild. I also noticed when I was installing the push rods that one of them is bent so I've ordered a replacement. I installed one of the non bent rods into into the hole with the short adjustment screw and it is the same. The rocker arm doesn't look bent so I'm a little confused about this problem. I also compared the adjustment screw with the other ones and it is the same length.

Thank you in advance for any insight into this problem.
Randy

It sounds like you've gotten some mismatched pushrods. There are at least three lengths of stovebolt pushrods, depending on which engine they're in, and the design of the valve lifters. 216's have a different length pushrod (shorter) than 235's, and there are two different lengths of 235/261 pushrods, depending on the height of the valve lifters. Older 235's with "milk can" lifters have shorter pushrods than later models with more conventional-shaped lifters.

There's an old shade tree mechanic's trick of putting the adjusting screw lock nut UNDER the rocker arm instead of on top that I've seen done when short pushrods are used in an engine that needs long ones.
Jerry

Randy, Echoing HRLs thoughts on the pushrod lengths... The '68 Master Parts Catalog lists the pushrod (PN 3836260) length as 11-5/16" for all six cylinder engines (235 and 261), '56-'63. It also lists the rocker adjusting screw as 7/16-20 x 1-9/32". You may wish to check your parts against those dimensions.

Hope that helps.

Doug

Thanks for your input. I checked the measurements and the push rods I have are 11 1/4 inch long. I ordered some new push rods that I hope will work.

I will let you know if it works or not.

Thank you.

Randy

I got the new push rods in the mail and they are 11 1/4 inch long and they have the same problem as the ones I have. I just ordered a new set of push rods that are Melling and are Overall length: 11.262" That should make it work ok. I ordered a complete set so all the push rods are the same length and diameter.

I also noticed that the lifters on number one cylinder sites lower in the block that the other cylinders. I'm going to make sure the cam is not bent or the grind on the new cam is the same. I think it is ok because the adjustment screw had the same problem with the old cam. The machine shop fit the new cam with the cam bearings so I believe it might just be the way the block is cast.

Randy

Is the "short" pushrod problem on only one cylinder? If so, you have a bad cam, or a worse machinist. I can't imagine how a machine shop could make that kind of error, even if they used semi-finished cam bearings and messed up the line bore.
Jerry

If the lifters on only one cyl sit low , then it sounds like a lifter issue (assuming the cam hasn't had the bum ground out of it ).

11.262” length is only .012” longer than what you already have. That is less than 1/64” (about 4 thicknesses of paper). The push rods that HR was talking about are 11-5/16” which translates into 11.3125” a full 16th of an inch longer (.0625). Your new Melling push rods you ordered may have the same issue.

Flat cam lobe

Thank you for the information. You are correct the new push rods do have the same issue. I'm beginning to think I have more problems than just the push rods. I replaced the cam and lifters with new ones so I do not think that is the issue and I had the heads redone with new springs and valves and I checked all the valves and they look correct to me. The issue is the rocker arms are not centered on the valves (see attached picture). I looked at all the exhaust valves and they are the same.

Randy

Were the valve guides replaced? Either the guides have been installed at the wrong angle, or somebody has made some huge mistakes assembling the rockers on the shafts. Thee are four different rocker arms on a stovebolt engine, with different angles, and possibly different lengths for intake and exhaust. I'm going to guess somebody has made some fundamental errors when putting the rockers on the shafts.
Jerry

Where did the rocker set come from?

Thank you for all the help.
I think I found the problem with my rocker arms. I have some intake rocker arms from an older 235 and some are from the newer 261. The exhaust are all correct. The intakes rocker arms that are correct have a 7 and an 8. The rocker arms that are not correct have a 4 and a 5 on them indicating they are from an older 235 engine. I'm going to see if I can find the correct rocker arms for this engine.

The engine I have is a 1958-61 261. I think when they rebuilt this engine they mixed and matched rocker arms from the original 1948 235. I know the engine was rebuilt because the cylinders were bored 40 over. This engine was rebuilt before I got the truck and I do not think it ran much because the bearings all looks new when I took them out. also other than two of the pistons where seized in the cylinder they were fine and still showed the crosshatch from the honing.

One other interesting note is the rings that where in the engine where not 40 over and the ring gap was really large.

The truck I'm restoring is a 1948 two ton stake bed.

Thanks again for your help!
Randy

You’ve got to be careful because Chevy made a design change in the rockers for ‘59. They opened up the restrictor and pressurized the rocker arm by offsetting the oil groove in the bore of the rocker arm. Thanks to chev235guy, you can read about it here. Rocker Evolution

I went to a classic car wrecking yard here in Wendell and found a rocker arm assembly off a 1959 Chevy 261 and it is the correct rocker arms. I replaced the ones on my rocker arms that were not the correct numbers and now the valve alignment is better. Not perfect but better than what is was by a lot. The adjustment screws for the valve lash are correct now.

I'm going to finish assembling the engine and check the oil flow before I install it back in the truck.

Thanks to everyone for all your help.

Randy