The Stovebolt Site Forums The Shop Area Engine Shop Carburetor Insulator Spacer and Gasket

All the literature says not to use a carburetor gasket if a heat insulating spacer is used. However, the few stovebolt engines I've seen have a gasket between the carb and spacer. Is it common to use both in spite of what the books say?

Well most of the trucks I have seen caught out in the wild had a only one gasket and it was between the spacer and the carb.
Mike

Ran across your question while looking for info on installing bushings in my Rochester throttle body. I just rebuilt my Rochester and the instructions said to NOT use a gasket if an insulating spacer was used, so I looked at the bottom of my carb and, sure enough, there was a hole there that the gasket would block. The hole lined up with a cutout in the insulator. Near as I can figure, the hole is connected to the power piston. If the gasket blocks the hole, the power piston does not receive manifold vacuum and the carb thinks you are running full throttle all of the time and runs rich. The manual said that the power piston activates when manifold vacuum is less than 5" of mercury, I think.

You are all correct.

If you use a gasket, be sure the cut-out in the insulator is lined up with the cut-out in the gasket, which must be lined up with the hole in the bottom of the carb.

Just curious but why the need for the insulator?

Jeff,

Great question...I think the spacer is a thermal insulator to prevent engine/manifold heat from percolating the fuel in the carburetor.

Guess what..I think that spacer, which is referred to as phenolic, is know by another name too..Garolite! Small world.

Stuart

The insulator stops the transfer of external engine heat directly from the engine to the carburetor thus causing vapor lock. This is especially critical if the intake manifold is bolted to the exhaust manifold for the transfer of heat to the intake for proper operation by preheating the fuel prior to its entrance into the intake ports. If the exhaust manifold is not bolted to the intake manifold and heat is supplied to the intake for preheating through another source, such as water, the insulator is not as critical because there is not a direct link to the external engine heat.

Joe

Now Stu, I think I know you better, ya just knew some body was gonna come along and further define that statement, didn’t you?? I taint pickin’ on ya, just want to make sure the younger members are fully informed in the correct terminology.
A page from the Professional Plastics catalog does a good job of explaining it: Garolit, http://www.professionalplastics.com...fnbr/101497/sesent/00/Garolite-Phenolics , Phenolic, http://en.wikipedia.org/wiki/Phenolic_resin , Bakelite, http://en.wikipedia.org/wiki/Bakelite

Basically the spacers that were made by GM were made from a fiber filled Phenolic resin. A more familiar term, which is now also used as a generic term for this thermoset plastic, is Bakelite.
Bakelite usually had a non-woven fiber reinforcement such as paper, linen, canvas, nylon, asbestoses. There were other fillers such as walnut shell and clay sometimes seen in the Bakelite radios of the 30’s and 40’s. This is also the material that we see in electrical insulators and as handles and knobs on cooking utensils. It has no grain and will brake if dropped, struck with a hammer or crushed with an over tightened fastener.

Garolite on the other hand is a trade name for the McMaster Carr line of Phenolic woven laminates. Originally coined Micarta, which was a Westinghouse trade name for their Phenolic resin laminate. This is the material that we see typically see in circuit boards and are often referred to as G-9, G-10, G-11, etc. Garolite can be made with a variety of binders, i.e., Phenolic resin, Melamine resin, Epoxy resin, Polyamide resin, etc. It, on the other hand is very tough can take bending loads and impact without breaking and is flexible to a degree.


Oh yes, the original question, I agree with what the others say, it's simply an insulator and originally was used without a gasket. I was a parts man for Chevy back in the 50’s & 60’s and can confirm that. But the question still remains, why did they ever make the gaskets in the first place. Probably because the insulators and carb bases got scratched up during service and would leak without the gasket. Since we are looking for a thermal break at this point I see no reason why you couldn't use a gasket on top of and under the spacer if you choose to do so. As long as it does not interfere with the operation of the linkage or fuel and vacuum connections and ports. All of the aftermarket gaskets that I have seen have four vacuum slots so no matter how you put the gasket on it won’t block the port.

Picky, picky, picky! Ok, I’m done! Gotta go make breakfast for my “big old wife.”
Denny Graham
Sandwich, IL

Wow! I did this post almost two months ago.
When I removed the carburetor it had a gasket on top of the insulator.
The gasket had the four notches in it but they did not line up with the notch in the spacer.
This blocked off the vacuum port for the power piston.
The gasket in the rebuild kit was the same way. I installed the carburetor on top of the spacer with no gasket like the book said.
After several attempts at trying to tune the carburetor I suspected that I had a vacuum leak around the spacer.
I finally took the spacer down to NAPA and found a gasket that had notches that matched the spacer.
It was actually two gaskets stapled together, just like the book said.
I removed the staples and put one gasket on the bottom of the spacer and one on top and reinstalled the carburetor.
A check with a vacuum gauge confirmed that I was leaking around the insulator.
Then I checked to see if the power piston was working.
This is easily done by removing the vacuum line from the vacuum port on the manifold.
The engine will momentarily speed up and then start to stumble from the vacuum loss.
Place your finger over the vacuum port to block off the leak until the engine idles smooth.
Then remove your finger and see if the engine speed increases again. It should be a substantial increase in speed.

Denny Graham,

Thanks for the in-depth education. I won't be so casual with my phenolic/Bakelite/Micarta/Garolite definitions hence forward!


Stuart

Jim,

"I finally took the spacer down to NAPA and found a gasket that had notches that matched the spacer.

It was actually two gaskets stapled together, just like the book said."

What book (and section/page)? I thought I had read about the use of the gasket(s) but I could not find a reference in a Shop Manual. I've always used a gasket between the carb and the insulator/spacer but had not looked for a reference until reading this thread.

Thanks,
Tim

Hi Tim,

My reference is the Chevrolet Truck Shop Manual. 1948 to 1951 models with the 1952 supplement.
I found the information on page 13 in the supplement. This is at the back of the book.

Just had ta one up ya Stu, you know I don't use those thar smilly things, that is most of the time!!!
Denny G

Thanks, Jim

And I think now is a good time to mention the importance of stopping all vacuum leaks! Many of us have small vacuum leaks on our trucks and performance could be so much better if we would check throughly for vacuum leaks on a periodic basis. The elimation of a gasket at this spot is just asking for a vacuum leak. Why take the chance?

A "healthy truck" makes for "healthy driving"!

Joe

Between Denny and Stuarts discussions I dont know which turns me on more!

I just better go spend some alone time with my truck.

After I added the dual exhaust and Fentons, I put it bake together with a new spacer and no gaskets. Ran O.K., but definately had that popping and spitting sound when decelerating. My neighbor is a great mechanic and fixed it for me by adding the gaskets. He also fixed my sticky linkage that I didn't get right.
But here's where the story gets interesting. He was having a heart attack while finishing it. When he was finished, he figured something wasn't right and called the ambulance which saved his life. That was a year ago last September. Now he eats a better food and is 60 pounds lighter. What do you do for a guy who just about kills himself working on your truck?