Carburetor Base Gasket

[John L.]

Just had my Holley carb rebuilt (List 3247) and the rebuilder included a base gasket with the name Interface Solutions on it. I was told I should use a Holley gasket, does it really matter which brand gasket I use? Also, what are the torque specs when tightening the carb nuts?

[Donald O.]

Re: Carburetor Base Gasket

What year and engine are you asking about?

[Joe L.]

Re: Carburetor Base Gasket

Just had my Holley carb rebuilt (List 3247) and the rebuilder included a base gasket with the name Interface Solutions on it. I was told I should use a Holley gasket, does it really matter which brand gasket I use? Also, what are the torque specs when tightening the carb nuts?

John------


As long as the gasket is properly configured, I don't see a problem. The correct configuration for your application is completely open plenum with no individual holes. No part of the gasket should overhang the opening on the manifold. The original gaskets were about 1/16"-3/32" thick. I have seen some aftermarket gaskets that were "paper thin". If the one you have is one of this type, I would not use it. The original GM gasket was GM #3881847.

Torque for carb retaining nuts is 16 lb/ft.

[William F.]

Re: Carburetor Base Gasket

Not a math major, but wouldn't the 16 ft/lbs. you suggested be way more than the 80-100 INCH -/ lbs. value in Chassis Service manual??

[John H.]

Re: Carburetor Base Gasket

Not a math major, but wouldn't the 16 ft/lbs. you suggested be way more than the 80-100 INCH -/ lbs. value in Chassis Service manual??

William -

The correct torque spec for the application is in the Assembly Manual (UPC 6), and it's 14-18 ft-lbs.

[William F.]

Re: Carburetor Base Gasket

John,
Hate to argue with master, but Holley and Chevy sevice manual say 80-100 IN/lbs. Wouldn't your 14-18 FT/lbs be 14x12=168 in/lbs and 18x12=216 in lbs.? Isn't this way too much if we're talking about torque to mount carb to manifold? Where am I going wrong?

[Terry M.]

Re: Carburetor Base Gasket

Four barrel Holleys had issues with the base cracking due to improper torque. There is wording in one of the C3 AIMs (1972, I think) that describes some specific tightening for them. Of course, like so many other things, just as it was going away they got it right.

Edit Add:I found it in the 1971 AIM for the LT1 section. I will scan it tomorrow at work and post the page. One needs not only the words, but the illustration as well.

[Joe L.]

Re: Carburetor Base Gasket

John,
Hate to argue with master, but Holley and Chevy sevice manual say 80-100 IN/lbs. Wouldn't your 14-18 FT/lbs be 14x12=168 in/lbs and 18x12=216 in lbs.? Isn't this way too much if we're talking about torque to mount carb to manifold? Where am I going wrong?

Bill------


The torque John mentioned is the torque specified in the AIM. So, this is the torque that the assembly line workers at St. Louis would have used. This is also the torque specified for other Holley 4 bbl applications in the AIMs.

I always consider the torque values specified in the AIMs (when torque values are specified) to be "bible". "Anachronisms" can creep into torque values specified elsewhere, including the factory service manuals.

By the way 80-100 inch/pounds would be a VERY light torque for a 5/16" bolt or nut.

[Terry M.]

Re: Carburetor Base Gasket

Here are the instructions in the 1971 AIM. I don't know if the midyear Holleys had the thick gasket that the C3s had. I suspect some of the motivation for these instructions is driven by that gasket.

1971 4-barrel Holley.pdf

[Joe L.]

Re: Carburetor Base Gasket

Here are the instructions in the 1971 AIM. I don't know if the midyear Holleys had the thick gasket that the C3s had. I suspect some of the motivation for these instructions is driven by that gasket.

[ATTACH]51055[/ATTACH]

Terry------


The first use of the thick, insulator type gasket was 1970. I also believe that this gasket is what influenced the need for the change in carb torque procedure.

[David P.]

Re: Carburetor Base Gasket

Four barrel Holleys had issues with the base cracking due to improper torque. There is wording in one of the C3 AIMs (1972, I think) that describes some specific tightening for them. Of course, like so many other things, just as it was going away they got it right.

Edit Add:I found it in the 1971 AIM for the LT1 section. I will scan it tomorrow at work and post the page. One needs not only the words, but the illustration as well.

Thanks for the warning on applying care for torquing the carb! I'd just as soon not crack the gasket

[Terry M.]

Re: Carburetor Base Gasket

Thanks for the warning on applying care for torquing the carb! I'd just as soon not crack the gasket

Dave,
Based on John Hinckley's offering below only the 1970-72 Holleys had the thick gasket that makes this an issue, on the other hand one cannot have too much care in tightening the carburetor to the intake manifold. I don't think one can do any harm using this procedure on earlier Holley equipped vehicles.

[Patrick B.]

Re: Carburetor Base Gasket

My 70 AIM doesn't have this page. Is my manual short a page or was it added to the 71 mamnual after broken carb ears?

[Terry M.]

Re: Carburetor Base Gasket

My 70 AIM doesn't have this page. Is my manual short a page or was it added to the 71 mamnual after broken carb ears?

None of my 1970 AIMs have it either. The date on the revision looks like 10/19/1970, which of course would put it after the end of 1970 MY production. I suspect the cause is/was a number of broken base plates probably causing warranty claims. In the old days (back when I was National Team Leader) I had a way of getting copies of the Engineering Change Request (in this case 35744) that gave answers to those kinds of questions, but that was then and this is now.

Just as a matter of curiosity the equivalent page in the 1972 AIM that I have in the house doesn't have this note. My other set of AIMs are in the garage and that will be inaccessable until the great thaw comes. Snow & ice make excellent security, but they do have their shortcomings.

[William F.]

Re: Carburetor Base Gasket

Not trying to be difficult, but while AIM does state 14-18 FT/ lbs for carb to manifold on '67's, Holley service/rebuild book and carb restores such as Eric Jackson recommend 100 IN/lbs, -big difference, and many specifically warn against over tightening.Any explanation for differeces? What to do?