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Jul 21st, 2025 | | | | Joined: Apr 2011 Posts: 523 Shop Shark | | Shop Shark Joined: Apr 2011 Posts: 523 | I finally received the correct size insulator block for the Rochester carb for my '55 235 engine., I have the carb to insulator gasket. Do I need a gasket for insulator to manifold? If so, can I just use some gasket compound instead?
BobS46
| | | | | Joined: Jan 2013 Posts: 2,194 Moderator: Interiors, Texas Bolters, Name that Part | | Moderator: Interiors, Texas Bolters, Name that Part Joined: Jan 2013 Posts: 2,194 | If it is the same as my 216, there is a gasket that goes between the carburetor and insulator, nothing more. I assume it would be the same since they are so similar. Others will chime in if I am wrong.
Chris | | | | | Joined: Sep 2001 Posts: 29,262 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,262 | Chevrolet stove bolt engine truck shop manuals show/describe no gasket on either side of the insulator.
If I am incorrect, please post the year of the manual and the page(s).
However, most people use a gasket between insulator and carburetor (with appropriately placed "cut out" in the gasket). A gasket between insulator and manifold is usually not needed, but would cause no harm (unless it leaks). | | | | | Joined: Mar 2010 Posts: 10,059 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,059 | I would use a gasket between the new insulator and the manifold, as well as a gasket between the carburetor and the new insulator.
The aftermarket insulator is made of a different material than the original one. It appears to be hard plastic.
But I also would recommend the two gaskets for a used original insulator due to slight deterioration common on this 60 year old part made of who knows what.
Carl
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Mar 2014 Posts: 4,208 Moderator, Electrical Bay | | Moderator, Electrical Bay Joined: Mar 2014 Posts: 4,208 | I'm using a bit of inner tube I saved from an old tire I removed. Butyl rubber can be cut to match the flange to insulator gasket, should be fine in this situation and will not lose vacuum. Ask any tire shop to save you an old inner tube. They're not as common as they were 30 years ago, but people still use them. I need to remove another old tire and will see if there's a tube in it. You're welcome to some of this if you want it.
Jon
~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
| | | | | Joined: Apr 2011 Posts: 523 Shop Shark | | Shop Shark Joined: Apr 2011 Posts: 523 | Thanks all. I had a bit of gasket material and decided to cut my own gasket and plan to install both gaskets without any gasket sealer on either gasket.
BobS46
| | | | | Joined: Aug 2012 Posts: 1,214 Shop Shark | | Shop Shark Joined: Aug 2012 Posts: 1,214 | Since the new aftermarket insulator I installed was hard plastic (or similar material), I went with a gasket on both the top and bottom surfaces.
When making your gasket, make sure to add a small vacuum hole in the gasket to match the vacuum hole in the bottom of the carb. Roch B's utilize a vacuum actuated power piston to add more fuel to the engine under load. It gets this vacuum from the small hole on the bottom of the carb flange where it bolts to the manifold. You'll notice the OEM gaskets and insulator has this hole and a small channel cut in them for this purpose, just match it.
Good luck
Dave | | |
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