The standard spark plugs out of the cast heads on my 8BA don't seem long enough for my Offy heads....Should I run a longer plug? Any input would be appreciated! Thanks, Brad
I had the same problem. Stock Champion H-10 plugs are recessed in to Offy heads and don't reach the firing chamber.Very inefficient. Try using NGK GR4 stock#2635 as they are the req'd heat range and are longer. I am using these on a pair of Motor City Flathead heads. Try one on your Offy head and with all the other plugs removed turn the engine over by hand to make sure the piston does not hit the plug tip.Plus NGK plugs have rolled threads and will not tear up alum threads as easily. Use never seize on the plugs threads and do try and remove or install them when engine is HOT.
This seemed the appropriate place for this question. Recently I was giving my old girl a tune up. Had the hood propped up and was putting in new plugs when one of the older gents in the neighborhood showed up to offer his two cents worth. I was complaining of her slow acceleration and poor gas mileage. He recalled that back in the day, they used longer plugs in their Plymouth flathead 6's ( it's a 218). There's plenty of room between the piston and the end of the standard plug so that is not a factor. I ran to my nearby Knect's store (I called Schuck's and Auto Zone too) and asked the kid behind the counter if he could help figure out what plug will fit. He got that deer in the headlights look....stumbled away from his computer and picked up a parts book. Obviously not familiar with that kind of thing, he gingerly opened it and spent 10 minutes finding plymouth....and another 5 looking for 1950. Then guess what? It didn't list any alternatives!! Geez, these kids in the parts stores are not very resourseful. I know that 20 years ago, I could have walked into my localy owned and run parts store and one of the guys (who were all about my dad's age) would have looked up the number of the required plug and ran to the back, pulled open a couple of boxes to compare length and found the right one. Help! How do I figure out what will fit?
If you are running AC plugs the Ply came with, add S to the number on the plug for an extended tip style. If you don't have AC google your Plymouth spark plug apps and then look at the manufactures web page to see what will suit your needs. If the kid in the store won't know about '52 Plymouths it's up to you to learn about your car. The plug in your car is not over the piston but in the area of the exhaust valve. It may or may not be right over the valve. Do not in any case use a plug with longer threads then the thickness of your head where the plug goes. What plugs are in it now? What is the thread length? Look them up and see if you can get an extended tip.
H10 is a 7/16 reach 14mm mid range heat plug. If your heads are thicker than 7/16 measure them. N series plugs are 3/4 reach. L are 1/2 If you wanted the same heat range as an H10 but in 3/4 reach that would be about an N2 or 3. If you wanted projected nose it would be a N6Y or N63Y. Or use a change over chart for other plug makers. Leave the Dremmel tool for the ports.
Ford flathead valves will close the gap on your plugs if they are too long. Stock flathead plugs do not reach into the combustion chamber. A better way is to chamfer from the inside istead of using plugs that may be too long.
Thanks peeps. I checked on the AC plugs and there isn't one for this year. (boo hiss) It would have been a quick boost for this motor. I'm picking up another block to put on the stand and get ready for when this one goes belly up. I will have it chamfered as Straightpipes suggests.
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