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Valve Adjustment screws too short
#1377079 Tue Sep 15 2020 01:22 AM
Joined: Jul 2020
Posts: 6
R
New Guy
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

Re: Valve Adjustment screws too short
rkworman #1377145 Tue Sep 15 2020 03:24 PM
Joined: Feb 2004
Posts: 21,021
H
Boltergeist
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


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Valve Adjustment screws too short
rkworman #1377161 Tue Sep 15 2020 05:28 PM
Joined: Aug 2018
Posts: 261
D
Shop Shark
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

Re: Valve Adjustment screws too short
rkworman #1377186 Tue Sep 15 2020 09:57 PM
Joined: Jul 2020
Posts: 6
R
New Guy
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

Re: Valve Adjustment screws too short
rkworman #1377587 Fri Sep 18 2020 10:58 PM
Joined: Jul 2020
Posts: 6
R
New Guy
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

Re: Valve Adjustment screws too short
rkworman #1377627 Sat Sep 19 2020 01:27 PM
Joined: Feb 2004
Posts: 21,021
H
Boltergeist
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


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Valve Adjustment screws too short
rkworman #1377741 Sun Sep 20 2020 06:40 AM
Joined: Feb 2001
Posts: 1,134
D
Shop Shark
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 ).

Re: Valve Adjustment screws too short
rkworman #1377745 Sun Sep 20 2020 11:59 AM
Joined: Feb 2019
Posts: 839
P
AD Addict
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.


Phil

1952 Chevrolet 3100
Project Journals
‘59 235 & hydraulic lifters
“Three on the Tree” & 4:11 torque tube
12v w/ Alternator
Re: Valve Adjustment screws too short
rkworman #1377814 Sun Sep 20 2020 10:49 PM
Joined: Dec 2008
Posts: 1,484
P
Shop Shark
Flat cam lobe

Re: Valve Adjustment screws too short
rkworman #1378253 Wed Sep 23 2020 09:52 PM
Joined: Jul 2020
Posts: 6
R
New Guy
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

Attached Files
Exhaust Valve rocker arm.jpg (34.38 KB, 70 downloads)
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