The Stovebolt Site Forums The Shop Area Engine Shop Spark Plugs Needed for 230 6 cyl._2nd Post

I posted this on the 6-66 forum but getting no responses, trying here.
I've seen a lot of references here on the forum pertaining to my question, but I don't see any definitive answer. Lots of respect for all the knowledge here, so I'm sure someone on here can dig a little deeper. Here's my issue, I have a 65 Chevy Truck with a 230 engine 1bbl, my manual says it requires an "AC 46N" spark plug, which they don't make anymore that I can find. The part stores (AutoZone & Orielly's) show lots of plugs that cross reference but they all have a thread length 3/4" whereas the AC 46N has a ~3/8", how can that be??? I must say I have been running the 3/4" spark Plug Autolite 66, for some years. I don't see any signs of damage on them but still, it's not the OEM recommended plug. I do see on Jim Carter truck parts as having a picture of a R45 (SKU# ME550) as fitting my truck which has a 3/8" thread, so that agrees with my manual, but Orielly's indicates that same R45 plug will not fit my truck. I see this a lot when comparing spark plugs between part stores, so you see why I'm confused. I have reviewed the site mentioned here in the forum (www.sparkplug-crossreference.com) but it leaves questions as well. Can someone tell me how a 3/4' thread vs 3/8" thread could possibly work in my 230 6 cyl.? and what plug is available as a correct fit for my engine? To know what plug everyone else is using in their 230 engines would also add some confidence to my selection. Thanks, looking forward to the responses.

As long as the new plugs have the same threads and the reach is correct, don't worry about it. Compare the new plugs side by side with the ones you have in there now.

As long as your 3/4" reach plugs aren't hitting the top of the piston, don't worry. The longer reach plugs improve combustion efficiency.

I tend to want to do that, what your take on the work shop manual indicating 3/8" but the part stores reference 3/4"???

My 1985 AC Delco catalog lists the 63-69 230 truck engine using R46N orR45XL spark plugs. 46 is one step hotter of a plug, good for oil burners or rich running.

Ebay has a ton of the green stripe R46N plugs, I have no problem buying NOS plugs. The pictures don't show 3/8" length, not sure where that came from, they look to be about 3/4' long.

Thanks for the help, much appreciated.
Tried to post picks of the two you mention but couldn't make that work. When looking on ebay, the R46N vs R45XL have different thread lengths, how can both those work???

The 3/8" plug may have been the factory issue. If a longer reach plug doesn't interfere with the piston, go ahead and use it. It places the spark closer to the center of the chamber for a better, more complete fuel air burn. It may even increase power and fuel economy.

Thanks to everyone who chimed in to my question, and I believe your responses are correct. The longer threaded 3/4" plug is better suited today for the reasons you mentioned. I will feel much better now going forward with those plugs with 3/4" thread length.

here are 6 NOS 46 N plugs $18

Thanks, I'll take a look

The head must be threaded only so far and the rest is just open below the sealing gasket. Both plugs will put the tip in the same location, you just don't use all the threads on the R45 plugs. Compare tip to sealing distance, whats between won't matter.

There are many fully threaded 3/4" reach plugs and they're usually found in aluminum heads. You don't want a threaded portion sticking out into the combustion chamber as the threads will fill up with hard carbon and you'll never get them out. A shop I worked in used to retrofit BMW R69S motorcycle heads with 3/4 reach plugs as the 3/8" reach plugs would strip the threads out of the head over time. This involved welding. The S models had higher compression.

This picture is a pair of 3/8" long threaded R46N spark plugs, notice the length from gasket seal to tip of plug, about 3/4", same distance as fully threaded plug. True, you shouldn't extra threads in the open cylinder due to carbon build up, but that won't be the case here.