Small Block Rocker Arms

[Clem Z.]

Re: Small Block Rocker Arms

Joe,

Just to be clear, can you use the guided type rocker arm on a stock small block head with or without pushrod guides?

if the head has the double "D" shaped push rod guide hole you have to enlarge it so you do not get a bind because you are trying to align 3 points,the push rod guide hole in the head,the stud and the groove on the rocker tip on the valve stem. also you have to remove the bolt on guides if the head has them

[Tracy C.]

Re: Small Block Rocker Arms

Tracy------


There were 5 different rocker arms used on Chevrolet small blocks over the 1955-95 period. Each was also supercessive to the former for SERVICE. These are as follows:

1955-57----GM #3837175----I don't know what was stamped on these;(does anyone know for my edification?)

1958-63-----GM #3746241-----I don't know what was stamped on these; (does anyone know for my edification?)

1964-69-----GM #3843359-----These were usually stamped "O" but some late 60's examples were stamped with a "triangle";

1970-86-----GM #3974290-----Stamped with a "V"

1987-95-----GM #10089648-----Guided type rocker


The GM #3974290 were the best of the non-guided type rockers. However, these were discontinued from SERVICE in July, 1989 and replaced by the GM #10089648 guided-type rockers. The 10089648 are the only stamped steel rocker arms currently available from GM for Gen I and Gen II small blocks.

Thank you very much Joe!

For the record, I've also seen new in the box GM #3974290 with a small "o" on the tip. They have a factory polished surface on the bottom of the valve tip. I figured they must be special to have that kind of finish treatment right out of the box.

tc

[Robert K.]

Re: Small Block Rocker Arms

In about 1969 I collapsed a rocker arm and damn near lost a pushrod through the valve cover. I bellied up to the Chevy parts counter and asked for the best rocket arms they had. It was the rocker with the O. The broken one may have had a triangle, but not sure, too many Buds since. I know I trust the Os.

[Keith L.]

Re: Small Block Rocker Arms

Os on my early 70 LT-1

[Domenic T.]

Re: Small Block Rocker Arms

Thanks, One advantage (other than oil splash control on the valve stem) that I can see is they also help keep the spring retainer centered on the valve spring. Without them, the retainer fit on the top of the spring seems sloppy.

tc

In my day they were called umbrella's.
They kept the oil from sucking down the intake guide when the intake valve was open. They had a simple but good O-ring seal. Then they used a seal that wiped the valve stems dry and they did just that. As a mechanic we machined many valve guides that wore out because of lack of oil ( new type seals).
And today they still use the same seals but are trying to improve the guides, no let the guides suck a qt of oil every thousand miles and keep the guides and valve stems oiled.
Never mind, Who checks oil any more? It is healthy for the engine to ingest 1 qt of oil per thousand miles.
ALL of my vintage engines use the old O ring seals with umbrella's, Oh yeah it costs me $3.79 every thousand miles but I know I won't have to pull the heads every 100K.

DOM

There were some

[Tracy C.]

Re: Small Block Rocker Arms

.....

I have a used set that is a mixed bag. Some have an "v", some a triangle, and some an "o" on the inside of the valve tip end of the rocker. What are the differences in these if any? I didn't find much in the archives.
....

thanks,
tc

Here is one for the "For what it's worth department"

After I cleaned up my used set of rockers, I discovered they were all the "triangle" configuration. Because I had access to a few NOS "o" rockers, I decided to take them to a nearby metalurgical lab and let them tell me if there were any differences in the two configurations.

Bottom line is there is a significant difference!

The Rockwell Scale A average value for the GM # 3843359" "triangle" tips was 36.7 where as Rockwell Scale A average value for the GM # 3974290 "o" tips was 70.7. For those in the know here, that is just north of 180 ksi. This territory is considered "ultra good stuff" by structural engineers. This supports the comments above from others regarding the "o" tip rockers.

The "290" rockers also have a polished tip right out of the box. I'll presume the polished tips reduce friction on the valve stem tip and make valve lash settings a little easiler. Regardless, I suspected they were special and now I know why...

tc

[Joe L.]

Re: Small Block Rocker Arms

Here is one for the "For what it's worth department"

After I cleaned up my used set of rockers, I discovered they were all the "triangle" configuration. Because I had access to a few NOS "o" rockers, I decided to take them to a nearby metalurgical lab and let them tell me if there were any differences in the two configurations.

Bottom line is there is a significant difference!

The Rockwell Scale A average value for the GM # 3843359" "triangle" tips was 36.7 where as Rockwell Scale A average value for the GM # 3974290 "o" tips was 70.7. For those in the know here, that is just north of 180 ksi. This territory is considered "ultra good stuff" by structural engineers. This supports the comments above from others regarding the "o" tip rockers.

The "290" rockers also have a polished tip right out of the box. I'll presume the polished tips reduce friction on the valve stem tip and make valve lash settings a little easiler. Regardless, I suspected they were special and now I know why...

tc

Tracy------


GM says that the 3843359 had an "o" and the 3974290 had a "v". It may be that those symbols were actually unrelated to the rocker part number and were related to the actual manufacturer.

I have some NOS examples of the 3974290 and they do have a "v" and they have no "polished" area.

[Joe L.]

Re: Small Block Rocker Arms

Well, thanks to some wonderful assistance from another member I think I have some more of this puzzle figured out.

First of all, I now am virtually certain that the stamping on the end of the rocker arm is Chevrolet-assigned, specific to the rocker arm part number and has nothing to do with identification of the manufacturer.

Next is the fact there's something we have been missing here which we never figured out before even though we should have been able to do so from P&A Catalog information. I'm ashamed of myself. However, the 64-68 rocker arm, GM #3843359, is described simply as "arm, valve rocker". The GM #3974290 is described as arm, valve rocker (with ball)". So, that represents an obvious difference between the 3843359 and the 3974290 and, possibly, the ONLY difference between the two.

As a matter of fact and as it turns out, that was the only difference between the two parts from 1970 until 1974. The 3974290 was a UNIT which consisted of the 3843359 rocker arm + rocker ball and nut. Of course, the 3843359 rocker was apparently the one with the "o" embossment, so 3974290 available until 1974 had the "o" embossment.

In 1974 the components of the 3974290 UNIT changed per revision to the specifications for the unit. The 3843359 rocker was dropped and replaced by rocker arm GM #355940 which was not available separately. The 355940 rocker arm was specified to include the stamped letter "V" for identification. So, 3974290 during and after 1974 should have included a rocker arm with the "V" embossment.

[Tracy C.]

Re: Small Block Rocker Arms

Good stuff Joe.... the "290" boxes I have do contain the rocker ball and nuts, I just didn't show them. Now all that is left to clear this up is to determine what part number the "triangle" rockers are.

They came off a pair of "462" heads from a 1966 hyd lifter 327.

tc