63 rocker arm configuration

[Steve D.]

63 convertible, small block

I just noticed that all of the rocker arms are not identical: there are twelve of one style and 4 of another. The difference is in the end that contacts the valve stem. One has a rather flat end and the other has sides that turn down a bit, apparently to keep the arm from slipping off of the stem. Is this a problem, as in there may be different lash setting specs?

Steve

[Joe L.]

Re: 63 rocker arm configuration

63 convertible, small block

I just noticed that all of the rocker arms are not identical: there are twelve of one style and 4 of another. The difference is in the end that contacts the valve stem. One has a rather flat end and the other has sides that turn down a bit, apparently to keep the arm from slipping off of the stem. Is this a problem, as in there may be different lash setting specs?

Steve

Steve------


What you are describing is the difference between original style rocker arms and later GUIDED rockers. The original rockers were of several part numbers, the first in 1955 being GM #3837175 (yes, that's the original 1955 part number) and the last being GM #3974290. Most of these will be seen with an "O" embossed on the valve end of the rocker arm.

For the 1987 model year, the rockers were changed to the GUIDED style. Guided rocker arms also eliminate the need for guide plates. These rockers are GM #10089648.

In July, 1989 the GM #3974290 rocker arms were discontinued from SERVICE and replaced by the GM #10089648 for SERVICE of all 1955+ small block applications (except 1996 LT4). From that time onward, you could not get the non-guided original style rockers from GM. However, for those that choose to use them, this type rocker arm is easily available in the aftermarket.

One of the things that GM did not make allowance for when it changed to the guided style rocker arms are those small block engines equipped with mechanical lifters. The use of the guided rockers makes valve adjustment much more difficult. However, I suppose for those engines in need of rocker arms, buying aftermarket, original style may be the way to go.

It is perfectly acceptable to have both original style and guided style rockers on an engine. However, the guided style rockers should not be used with engines with guide plates. If they are used on these engines, the guide plates should be removed and replaced with an equally thick, hardened washer. The guided rockers can also cause pushrod interference in older engines with heads with small push rod holes. Clearance throughout 360 degrees of camshaft rotation needs to be checked when using guided rockers on early engines.

For hydraulic lifter engines, I personally recommend the use of the guided rocker arms. Also, you don't think that GM went to the guided style because the original style worked just as well, do you?