68 Big Block left side Valve Cover Grommet

[Joe L.]

Re: 68 Big Block left side Valve Cover Grommet

Joe

That is very interesting. Thanks for doing that. I wonder what The Good Doctor’s grommets were based on?


Rich

Rich------


I think I may have found the explanation of the problem. The original GM #3933188 grommet had, according to GM, an ID of 31/32" (0.969"). The 1972 replacement, the GM #3894337 which remains available, has an ID, according to GM of 15/16" (0.938") (which is very close to my measurement of 0.939").

Both grommets have an OD of 1-7/16" but I believe this is measured at the very outer OD of the grommet which is a functionally irrelevent dimension. The important dimension is the OD at the surface which interfaces with the valve cover orifice. For the 3894337 it is 1.211" as I previously mentioned. I do not know what it is for the 3933188.

I expect that what occurred here is that way back in 1972 somebody at GM Service Parts Operations decided that the 3933188 and 3894337 were "close enough" in specifications that the former could be discontinued in favor of the latter. That person was wrong and that mistake has lived on for almost 50 years.

I should also mention that the folks at St. Louis never had to deal with this problem. The 3933188 was used in PRODUCTION for 1968-70 big blocks . The 3894337 was never used in PRODUCTION for any Corvette application.

For 1973-74 the grommet and connector size changed. For these years the 3989347 grommet was used for both the PCV valve as well as the PCV intake in conjunction with the smaller OD connector pipe of GM #330523.

[Rich G.]

[Ronald L.]

Re: 68 Big Block left side Valve Cover Grommet

I went through the Para-problem well over ten years ago.

My solution has been to dig originals out of pre 1970 valve covers!

[Robert K.]

Re: 68 Big Block left side Valve Cover Grommet

Joe,
i will second Rich's statement - thank you for all of your amazing research and replies. I know it takes a lot of your time but you are an extremely valuable resource to all of us.....

Take care,

Bob

[Sal C.]

Re: 68 Big Block left side Valve Cover Grommet

Never had much luck getting them out of old valve covers. Even using heat, most are too brittle and will crack.

[Ronald L.]

Re: 68 Big Block left side Valve Cover Grommet

Sal, Heat is the enemy of rubber, as is the sun. There are thousands of covers that have been taken off and in storage fro decades, just need to find those locations and get access to go picking.

[Joe L.]

Re: 68 Big Block left side Valve Cover Grommet

Well, I've found a solution to this problem:

1) Install a currently available GM #3894337 grommet in a valve cover;

2) Hone the ID of the grommet using a brake cylinder hone until it has an ID of about 1.1"

3) Remove the grommet from the valve cover and cut off the bottom "cap" (which will contain the honed rubber fragments)

4) Re-install the grommet in the valve cover.

5) Install the 90 degree connector

Works perfect.

[Rich G.]

[Joe L.]

Re: 68 Big Block left side Valve Cover Grommet

Great plan, Joe.

I was thinking of how to shave the OD but doing it as you describe makes more sense.

Thanks. I hope you didn’t lose too much sleep over this! 

Rich

Rich------


Shaving the OD will not work as you would have to shave the OD of the groove which actually contacts the valve cover orifice. This would be, at a minimum, extremely difficult if not impossible. The remainder of the OD of the grommet has no bearing on the problem. I believe the only difference between the original grommet and the currently available is a slight difference in the ID. I believe the outer configuration and dimensions were the same.