Question on replacement Rocker Arms

[Dennis H.]

In the very near future I'm going to pull and rebuild the L82 in my 73 Vette and remove some pass misdeeds (hot rod parts) being the engine back to OEM L82 Specs.

I have the original rocker arms and they all look good except 3 that have some minor gouging or galling (not sure what you call it).

Picture 1 is an example of 13 and has the O stamped in the arm and look good.
Picture 2 is the 3 in question that I think need replaced.

If I understand what I'm researching the GM replacement is the Rocker Arm Kit (Arm+Ball+Nut) Grp. 0.333, PN 3974290 or the new PN 10089648. The original bare rocker arm with the stamped O is PN 3843359 which I'm guessing is no longer available.

Does the above PN research sound correct and what do you think of the 3 rocker arms in question?

Thank
Dennis

[Joe L.]

Re: Question on replacement Rocker Arms

In the very near future I'm going to pull and rebuild the L82 in my 73 Vette and remove some pass misdeeds (hot rod parts) being the engine back to OEM L82 Specs.

I have the original rocker arms and they all look good except 3 that have some minor gouging or galling (not sure what you call it).

Picture 1 is an example of 13 and has the O stamped in the arm and look good.
Picture 2 is the 3 in question that I think need replaced.

If I understand what I'm researching the GM replacement is the Rocker Arm Kit (Arm+Ball+Nut) Grp. 0.333, PN 3974290 or the new PN 10089648. The original bare rocker arm with the stamped O is PN 3843359 which I'm guessing is no longer available.

Does the above PN research sound correct and what do you think of the 3 rocker arms in question?

Thank
Dennis

Dennis-------


Those 3 rocker arms need to be replaced.

The rocker arms originally installed on your engine were GM #3974290 and those are what you have pictured. The GM #3974290 was discontinued in July, 1989 and replaced by the GM #10089648 which remain available. The latter are a guided type rocker arm with impressed rails on the valve end which prevent lateral movement of the rocker, effectively centering it on the valve stem. However, these should not be used on engines with guide plates GM #3973418 which your L-82 should have. Actually, the guided rockers eliminate the need for guideplates. 1988-92 Corvettes used the 10089648 in PRODUCTION in combination with guide plates GM #10111771 which were mainly an assembly aid. These were eliminated after 1992.

By the way, the GM #10089648 are extremely high quality rocker arms but they are quite expensive with a current GM list price of about $35/each.

You can look for NOS GM #3974290 or you can obtain aftermarket rockers. Most of these are the non-guided type and virtually identical to your originals save for the "O" embossment. Sealed Power P865R is such a rocker arm.

[Mark E.]

Re: Question on replacement Rocker Arms

You'll have a new camshaft and lifters as part of the engine rebuild. Instead of guessing about condition, make it a thorough job by also installing a new set of pushrods, rockers, balls, nuts, and valve springs. These are high wear parts. Ditto with valve guides.

[Duke W.]

Re: Question on replacement Rocker Arms

You may find it tough to find OE and OE equivalent parts. I've always recommended reusing rockers/balls and pushrods if they have no evidence of excessive wear, but replace valve springs. You used to be able to buy a set of Sealed Power VS-677 valve springs (equivalent to OE 3911068) for 20 bucks, but now guys are having a tough time finding them. Same with the camshaft.

As long as you are rebuilding the engine raise the CR. Remember, OE is advertised 9:1 and only required 91 RON fuel, which is equivalent to 87 PON. OE forged pistons, either your low compression types or the '69 high compression type may be hard to find and definitely expensive. Look at Keith Black hypereuctectics. Download my compression ratio management paper and shoot for NTE 10.3 if you have 93 PON and reduce 0.1 for each 1 PON below 93.

Duke

[Dennis H.]

Re: Question on replacement Rocker Arms

Joe, thanks for the clairification of the

GM #3974290 and the GM #10089648 rocker arm. I do have guide plates on my L82 heads so looks like I need 3 NOS

3974290 or 3843359 rocker arms.

Mark, while I'm not opposed to replacing all the hardware the L82 heads only have about 40K for miles when they were pulled off the car a few years ago. The rocker arms have about 43K as I just removed them a couple weeks ago.

Duke, where can I find your

compression ratio management paper?

I have a new GM L82 cam and lifters, need 16 pushrods and 3 rocker arms. Can get 16 NOS 3796243 pushrods off eBay for $259.00 and 4 NOS 3974290 "V" stamped rocker arms for $59.00 or

4 NOS 3974290 "O" stamped rocker arms for $175.00. There is also a set of 16 NOS 3911068 valve springs out there for $129.00 but has some minor rust dots on the one spring that was shown.

So that's about $563.00, trying to stay with OEM GM parts is a Pay to Play game for sure.

While I'm ok with good quality replacement parts like Sealed Power I'm drawing a big fat zero in locating any Sealed Power valvetrain parts for this engine.

[Dennis H.]

Re: Question on replacement Rocker Arms

Are the TRW VS935 and Sealed Power VS-677 valve springs both equivalent to OE 3911068?

[Mark E.]

Re: Question on replacement Rocker Arms

Mark, while I'm not opposed to replacing all the hardware the L82 heads only have about 40K for miles when they were pulled off the car a few years ago. The rocker arms have about 43K as I just removed them a couple weeks ago.

New Sealed Power rockers that Joe recommends are less than $7 and include the ball and nut. If it was my car and $ (and it's not), I would replace the 40,000 mile parts to have a new valve train. Cheap insurance.

[Dennis H.]

Re: Question on replacement Rocker Arms

New Sealed Power rockers that Joe recommends are less than $7 and include the ball and nut. If it was my car and $ (and it's not), I would replace the 40,000 mile parts to have a new valve train. Cheap insurance.
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Mark I agree and would order 16 Sealed Power P865R today but they are just not available. I can find 1 or 2 in stock but that's about it, not sure if this is a COVID thing or a discontinue thing. I have hit all my usual go to places like Rock Auto, Summit, Jegs, NAPA etc. Same story for the Sealed Power RP-3093 pushrod.

On the subject of the GM 3911068 valve springs its a crap shoot on what the website says and what's available. Need to call around today and reach out to my head rebuilder on these.

[Dennis H.]

Re: Question on replacement Rocker Arms

Can get the GM Grp. 0.303 / 3911068 valve springs, they are $8.46 EA.

Can get the GM Grp. 0.426 / 3796243 (14095256) pushrod for $14.80 EA ouch....

Still searching for rocker arms.

[Duke W.]

Re: Question on replacement Rocker Arms

Duke, where can I find your

compression ratio management paper?

.


...a couple of ways... copy and paste the following search phrase into a search engine:

"compression ratio explained" Duke Williams

and it should download the pdf from the Corvette Forum.

If the above doesn't work, go to the CF and do an advanced search, threads started by SWCduke.

Duke

[Dennis H.]

Re: Question on replacement Rocker Arms

In my search for NOS GM 3796243 rocker arms I'm seeing some stamped with the letter O, A, V and no stamp at all. What does all this mean?

[Duke W.]

Re: Question on replacement Rocker Arms

Are the TRW VS935 and Sealed Power VS-677 valve springs both equivalent to OE 3911068?

'

Sealed Power VS-677 is identical to 3911068... don't know about the TRW number other than it's very old.

Duke

[Dennis H.]

Re: Question on replacement Rocker Arms

In my search for NOS GM 3974290 rocker arms I'm seeing some stamped with the letter O, A, V and no stamp at all. What does all this mean?

So I did an advanced search on just "3974290" and found enough information on this rocker arm in a single post dated 27 Feb 2011 to answer my question and then some.