Wrong spark plugs
Thread Starter
Heel & Toe
Joined: Nov 2024
Posts: 24
Likes: 1
From: Louisiana
Wrong spark plugs
Hi new member here
Have inherited a 75 C3 - havent't worked on a car for some time so looking for advice. Engine is L48 matching with VIN.
Car is in pretty good condition - idle is a bit rough around 900 rpm
Thought I would start with checking spark plugs - according to the manual the correct plug should be a R44TX set at .060 - however the plugs installed are R45TS at .045 which are the plugs for the 76 engines.
Did someone previously install the wrong plugs or is it a 76 engine in the car.
The title shows it as a 75 and looking at other posts one of the differences are the vents behind the rear window - my car has the vents but believe they were deleted in 76.
Want to make sure that I put the correct plugs in - any advice. FYI the plugs I removed do have some heavy soot type deposits but no oil.
Thanks for any help.
Have inherited a 75 C3 - havent't worked on a car for some time so looking for advice. Engine is L48 matching with VIN.
Car is in pretty good condition - idle is a bit rough around 900 rpm
Thought I would start with checking spark plugs - according to the manual the correct plug should be a R44TX set at .060 - however the plugs installed are R45TS at .045 which are the plugs for the 76 engines.
Did someone previously install the wrong plugs or is it a 76 engine in the car.
The title shows it as a 75 and looking at other posts one of the differences are the vents behind the rear window - my car has the vents but believe they were deleted in 76.
Want to make sure that I put the correct plugs in - any advice. FYI the plugs I removed do have some heavy soot type deposits but no oil.
Thanks for any help.
Tech Contributor
Joined: Aug 1999
Posts: 14,370
Likes: 6,364
From: At my Bar drinking and wrenching in Lafayette Colorado
The spark plugs are no indication of the year of the car or engine. The two plugs are basically identical - it's just a difference in heat range. The 45 is a slightly "hotter" plug, so it will run a little "cleaner." The Chevy gap spec is .045", which is a good spec for the Corvette engine. The Buick and Olds engines with very low compression run the wider .060 gaps. The tighter .045" gap will reduce the chances of plug wire cross-arcing and misfires. In other words, your plugs and gaps are just fine. No problem.
Lars
Lars
Melting Slicks
Joined: Apr 2021
Posts: 2,642
Likes: 2,093
From: Minnesota
Welcome to the forum!
If your idle is a bit rough I would consider checking your ignition timing. If you don’t have one already a dial back timing light is a valuable tool when working on these cars and engines.
If your idle is a bit rough I would consider checking your ignition timing. If you don’t have one already a dial back timing light is a valuable tool when working on these cars and engines.
Last edited by Piersonpie; Dec 1, 2024 at 01:58 PM.
Tech Contributor
Joined: Aug 1999
Posts: 14,370
Likes: 6,364
From: At my Bar drinking and wrenching in Lafayette Colorado
Nothing worng with an .035 gap - that's a good spec for a high compression engine to assure no cross-firing and misfiring at the wires or inside the cap/rotor. For the low-compresion engines, you can run the wider gaps with the HEI without fear of misfiring. The .035 gap won't cause any engine issues or problems.
