Bb Rocker Arm Slot Length

[Jeff M.]

What is the slot length of the long slot rocker arms that have either the L or H stamped on them? I have a set that have an M stamped on them, and another set with nothing on them. My M stamped ones are around .690 long. What does the M mean? With the stock LS6/L72 cam, do you need the long slot?

[Wayne M.]

Re: Bb Rocker Arm Slot Length

What is the slot length of the long slot rocker arms that have either the L or H stamped on them? I have a set that have an M stamped on them, and another set with nothing on them. My M stamped ones are around .690 long. What does the M mean? With the stock LS6/L72 cam, do you need the long slot?

I can't definitively answer your slot "length" question, but here's what I have [a set, probably off a '68 with oval port "215" heads, and the slot is 0.69", as you have measured, but my set has NO letter stampings].

From the Chev parts catalogs, seems these short slot arms are part # 3860305. Next step up is the "L" stamp, for solid lifter engines L78, L72, L71, L88 (to 1st design '69), etc. Don't have a slot length. Part # 3860308; these might also be stamped "Z", or even "X" in the earlier '66 timeframe.

Finally is the longest slot with "H" marking (no length mentioned, but is longer than the "L", per How-to-Hotrod BB Chev's book) for 2nd design 1969 L88's and ZL1's. Part # 3959182.

[Jeff M.]

Re: Bb Rocker Arm Slot Length

can somebody measure an H or L for me

[Clem Z.]

Re: Bb Rocker Arm Slot Length

can somebody measure an H or L for me

the "H" ones are good for .600 lift but to prevent the sharp stamped edges from cutting into the sides of the studs they should be deburred with a small diameter stone in a die grinder

[Jeff M.]

Re: Bb Rocker Arm Slot Length

clem, I have heard that, thank you. But can you tell me how long the actual slot is

[Clem Z.]

Re: Bb Rocker Arm Slot Length

clem, I have heard that, thank you. But can you tell me how long the actual slot is

sorry none laying around here. if you are thinking about grinding a std one for a long slot for a higher lift cam they are not the same heat treat as the "H" rockers and could cause a problem with a heavier spring pressure. i rockwell tested the differnt rockers back in the day but i don't remember the numbers

[Joe L.]

Re: Bb Rocker Arm Slot Length

clem, I have heard that, thank you. But can you tell me how long the actual slot is

Jeff------



The slot in the GM #3959182, "H"-marked arm is 0.723" long. The slot in the GM #10112680, "L"-marked arm is 0.705" long.

I have NOS examples of all the others(3860308-"L", 6258611-"M", 3860305) too, but I can't find them right now.

The 3959182 and 10112680 are pictured below.