Spark plugs 383

[Gus chiggins]

I know a 383 calls for champion RJ12YC, but they do not fit. The plugs that came with the motor are autolite, 1904, stamped on the plug body, heat range 25. I tried threading in the Champion plugs, no go, and I reinstalled the autolite plug, no problem. Yes, I inserted a picture of the Champion, and Autolite plug side by side.

 

[RemCharger]

Do you know which head you have?
Some sort of motor home head maybe. Tapered seat is weird..

 

[Jerry Hall]

Are you running stock heads?

 

[Gus chiggins]

Are you running stock heads?

As far as i know they are stock.

 

[WileE]

Factory stock and performance heads, as well as most aftermarket heads, use the standard seat w/gasket type plug. Ex. J11Y, or the RJ12YC now.

 

[BeepBeepRR]

They are probably 452 heads that have the bump out and wont allow the larger spark plugs. Same issue I had with the RV heads. I should have had the guy mill the heads in that area. The bump is aright next to the spark plug hole sand only allows the smaller shanked plugs.

452s with the bump.

906 without.

 

[Gus chiggins]

Factory stock and performance heads, as well as most aftermarket heads, use the standard seat w/gasket type plug. Ex. J11Y, or the RJ12YC now.

The latter plug you mentioned, i tried won't fit

 

[WileE]

You may have rv/motorhome heads.

 

[Gus chiggins]

They are probably 452 heads that have the bump out and wont allow the larger spark plugs. Same issue I had with the RV heads. I should have had the guy mill the heads in that area. The bump is aright next to the spark plug hole sand only allows the smaller shanked plugs.

452s with the bump.

View attachment 1281064

906 without.

Yes, my heads have the bump outs. Don't tell me these are trash heads. WTF.

 

[69Bee]

First, the Autolite plug has a tapered seat, and to my knowledge, NO early (pre 2000's maybe) only use a gasket seat. I have seen GM's that use that extended reach, short thread, tapered seat plug, but not Mopar. The RJ12YC plug should fit your heads, unless someone has screwed up the holes. Does it look like a Timesert Spark Plug insert has been installed? If so, someone might have installed the wrong insert!

I have a set of those "bump out" 452 heads on the shelf, and a Mopar plug like your Champion plug, and they fit just fine.

 

[Gus chiggins]

First, the Autolite plug has a tapered seat, and to my knowledge, NO early (pre 2000's maybe) only use a gasket seat. I have seen GM's that use that extended reach, short thread, tapered seat plug, but not Mopar. The RJ12YC plug should fit your heads, unless someone has screwed up the holes. Does it look like a Timesert Spark Plug insert has been installed? If so, someone might have installed the wrong insert!

What about the 452 heads that have a bumpout?

 

[bolson6333]

motorhome heads, I have two motors out of them and both take tapered plugs.

 

[BeepBeepRR]

They are from the later 70s. In the smog era. However they do have hardened seats. I would not say they are junk. I had them on my 500hp 440 but they were built for the engine. Not just stock 452's.

 

[69Bee]

What about the 452 heads that have a bumpout?

I have a set of those "bump out" 452 heads on the shelf, and a Mopar plug like your Champion plug, and they fit just fine.

 

[Gus chiggins]

First, the Autolite plug has a tapered seat, and to my knowledge, NO early (pre 2000's maybe) only use a gasket seat. I have seen GM's that use that extended reach, short thread, tapered seat plug, but not Mopar. The RJ12YC plug should fit your heads, unless someone has screwed up the holes. Does it look like a Timesert Spark Plug insert has been installed? If so, someone might have installed the wrong insert!

I have a set of those "bump out" 452 heads on the shelf, and a Mopar plug like your Champion plug, and they fit just fine.

RV9YC is the plug i guess i will have to use

 

[Gus chiggins]

They are from the later 70s. In the smog era. However they do have hardened seats. I would not say they are junk. I had them on my 500hp 440 but they were built for the engine. Not just stock 452's.

RV9YC looks like the plug i'm looking for, God, I love walking into ambushes.

 

[Gus chiggins]

I have a set of those "bump out" 452 heads on the shelf, and a Mopar plug like your Champion plug, and they fit just fine.

Good, I'm glad. They fit yours, they don't fit mine. I found plugs for the 452 heads : RV9YC

 

[BeepBeepRR]

Grabbed this from another site. Heads and their comparison.

516, 1966 and earlier, Flat Port Floor, Closed Chamber, 2.08" Intake / 1.60" Exhaust
915, 1967 only, High Huber Hump Intake Port Floor, Closed Chamber, 2.08" Intake Valve / 1.60" Exhaust (low perf), 1.74" Exhaust on HP Engines
906, '68 to 1970, High Huber Hump Intake Port Floor, Open Chamber, 2.08" Intake Valve / 1.74"Exhaust (All)
902/346/452, 1971 & up, Low Port Floor W/swirl hump on siamesed inner Port wall(acts like a short turn), 2.08" Intake, 1.74" Exhaust(All)

 

[Gus chiggins]

They are probably 452 heads that have the bump out and wont allow the larger spark plugs. Same issue I had with the RV heads. I should have had the guy mill the heads in that area. The bump is aright next to the spark plug hole sand only allows the smaller shanked plugs.

452s with the bump.

View attachment 1281064

906 without.

Thanks for your help. It looks like Champ

Grabbed this from another site. Heads and their comparison.

516, 1966 and earlier, Flat Port Floor, Closed Chamber, 2.08" Intake / 1.60" Exhaust
915, 1967 only, High Huber Hump Intake Port Floor, Closed Chamber, 2.08" Intake Valve / 1.60" Exhaust (low perf), 1.74" Exhaust on HP Engines
906, '68 to 1970, High Huber Hump Intake Port Floor, Open Chamber, 2.08" Intake Valve / 1.74"Exhaust (All)
902/346/452, 1971 & up, Low Port Floor W/swirl hump on siamesed inner Port wall(acts like a short turn), 2.08" Intake, 1.74" Exhaust(All)

Thanks for the pix, Champion has a plug RV9YC That should work.

 

[Gus chiggins]

Grabbed this from another site. Heads and their comparison.

516, 1966 and earlier, Flat Port Floor, Closed Chamber, 2.08" Intake / 1.60" Exhaust
915, 1967 only, High Huber Hump Intake Port Floor, Closed Chamber, 2.08" Intake Valve / 1.60" Exhaust (low perf), 1.74" Exhaust on HP Engines
906, '68 to 1970, High Huber Hump Intake Port Floor, Open Chamber, 2.08" Intake Valve / 1.74"Exhaust (All)
902/346/452, 1971 & up, Low Port Floor W/swirl hump on siamesed inner Port wall(acts like a short turn), 2.08" Intake, 1.74" Exhaust(All)

Thanks for the info. I appreciate it a lot.