Spark Plug Query
 

Hello all,
I'm off to the parts store today to pick up some spark plugs. Since the AC C44 plugs aren't an option, what would y'all recommend? They're for a 61 305D BTW

The AC Delco website has a handy matcher that tells me the 41-832 is an option.

Now, AC Declo isn't available over here. Funnily enough, when I use the NGK cross reference, there doesn't appear to be a match for the 41-832. But, it does say that a NGK B6S is a match for the AC C44.

Frustratingly, some of the cross reference sites I've looked at say that I can use a small engine (IE lawnmower) sparkplug. So yea, the internet is awesome.

Anyway, as always I'm open to suggestions.

Re: Spark Plug Query
 

This is likey a dumb question. Buy, why are the spark plugs on 2, 4 and 6 on a 305 longer than 1, 3 and 5?

I've bought a set of 6 matching, only to realise that they're not fitting on one side (too short). But the other side fits fine?

Re: Spark Plug Query
 

Maybe a head has been swapped from a different engine that used a different style plug.

Re: Spark Plug Query
 

You need some help, from some fellow Ausses, That may have your local market figured out. There is a guy I met this year at the Stove Bolt reunion in Riverside Mo. He came over to go to the truck show, his name is Tim Pryer. Tim Pryor Reinforcing Pty Ltd. Tell Him That You got his name from, Bob That had the V12 at the Stove bolt reunion. He is really a nice guy, might be a good contact

Re: Spark Plug Query
 

So, I'm not crazy for thinking this isn't normal? :ahhhh:

Re: Spark Plug Query
 

It also could be a previous owner mistake. I didn't know there were different heads you could put on that had different length plugs. I guess get head casting numbers and check here before buying/install two sizes. Not computing right now.

Re: Spark Plug Query
 

So, you don't think it's going to cause any harm running one side on short plugs and the other on longer ones? I don't mind the minor oddity, so long as I'm not doing any damage to the engine.

I've been daily driving for a couple of weeks now and it's been running ok.... however, I had suspected the mechanic I went to didn't bother gapping the plugs that he put in (my suspicions were confirmed last night when I pulled them).

Re: Spark Plug Query
 

I just looked at RockAuto site. They list a 3/8" length thread and a 3/4" length thread for the same 61 305 motor. Don't know why. Wait for a guru to reply with the answer. I assume both will be OK or Rock Auto is wrong. See if you have one of each length. Both gapped at .035/.036. Give us the numbers of the two plugs you have. Who bought the plugs? you, the mechanic, already had them in truck?

Re: Spark Plug Query
 

It's already been experimented with (and by me too) - either plug will work fine. Once we thought the long plugs would hit the piston head too, but it doesn't. You can run both and be fine, though it will be funny if you forget this thread when you go to replace them!

:teehee:

Re: Spark Plug Query
 

What I can't make sense of though is why the shorter plug won't fit into the 2 4 6 side of the engine. Is what turbobill suggested the most likely cause? Someone has swapped a head at some point?

Re: Spark Plug Query
 

The plugs (long and short) are interchangable. The threads are the same. I can't see why they wouldn't fit unless something weird did go on like stripped threads and re-threading or a new head.


Edit: I just re-read your mismatch post. Stripped threads are my guess. Someone either busted out some rusted, frozen plugs or they over torqued them and stripped it. Either way, thank goodness they were shorties or you would have had the entire thing stripped out!

Re: Spark Plug Query
 

The mechanic already had the two sizes in the truck.

However, I didn't know that, so I only purchased the 1 size (NGK Bs6) because the conversion chart that I looked at said that would be comparable to the AC C44 that's in the manual.

The longer plug that the mechanic had in the 2 4 6 side was an NGK BP5ES

Side note, for anyone keeping score the plugs the mechanic put in have quite a bit of carbon buildup after only 2-3 weeks of daily driving. Which is part of the reason why I'm replacing them. I had suspected the ones he installed weren't gapped properly (they weren't). So, I'm hoping new plugs with the appropriate gap is going to give me a cleaner burn (and longer lasing plugs).

Re: Spark Plug Query
 

Good info from FMAP. As he said, thread problem. However you DID NOT state what won't fit. We assume you mean won't thread into any hole in that bank? Can't imagine all stripped on one head only. I have to think this out. So on one bank you have long thread plugs and the other has short thread plugs ? and the short only fit one bank? and the long fits.......??

The Jolly AC4 under known good parts is 3/4 long thread. I would go with that. I did.

Re: Spark Plug Query
 

That's what I meant when I said they weren't fitting on one side.

To be honest, I haven't checked to see if it's just one hole or all of them on the same side. Once I realized that I had been driving around with 2 different sizes of plugs I called it a night. I'll check when I get home today/tonight.

Either way, from what y'all are saying it sounds like there's no real issues with the (admittedly weird) setup that I've got going on at the moment?

Re: Spark Plug Query
 

You are confusing us.
1. It is B6S NOT BS6. The B6S is short 3/8, the BP5ES is long 3/4.
2. BOTH are 14 mm threads!!!! AC4 is 14mm.
3. No reason one fits only one bank.
4. B6S crosses to AC C44 (short) and 14mm thread.
5. You have not mentioned any other plug numbers that I know of.
6. So I don't get what plug fits in what, so called, bad holes? What plug won't fit where? They all have the same bloody thread.

Re: Spark Plug Query
 

Sorry, fat fingers on the BS6 vs. B6S.

#3 is pretty much the source of my confusion with this. I don't know why the B6S fits in one side but not the other.

Re: Spark Plug Query
 

You missed 5 and 6 on my list. Bottom line, change whiskey brands.:champagne:

Re: Spark Plug Query
 

Whiskey at work would make the day so much better LOL It might actually make me more sensible as well.

Ooook, here goes. Start to finish.

There are 3 B6S short plugs on the 1, 3, 5 side of the engine.

On the 2 4 6 side there's 3 of the longer BP5ES plugs.

I'm wanting to replace all of them. I've purchased 6 B6S plugs.

For the moment, all I know is that the B6S plug won't thread into the #2 cylinder. It looks like it's just not long enough to catch anything. I haven't tried it in 4 or 6.

Putting the reason aside for the moment (since I'm not sure yet if we're talking 1 stripped plug or a head mismatch at some point in time in the old boy's life) will it cause issues to have the 2,4,6 side of the engine on long plugs and the 1,3,5 side on short ones?

Re: Spark Plug Query
 

Popped home during lunch.... The short plug won't fit into any of the even numbered cylinders. So, are we thinking mismatched heads?

Re: Spark Plug Query
 

Could you take some pics of the heads? Might help diagnose the issue.
Thanks!

Re: Spark Plug Query
 

http://uploads.tapatalk-cdn.com/2016...5e3484e960.jpg

#2

Is there an issue? Or do I just live with 2 different styles of plugs?

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Re: Spark Plug Query
 

Let's not worry about what I want to hear LOL I'm happy to keep digging

I completely agree.... it was weird enough that at first I was just assuming that I was having a moment.

Most of this is by feel, because I can't see anything. But, the best way that I can think of to describe it is that the plug just free spins. Considering that longer plugs I had in were also 14mm, and they went in fine, logic is telling me it's got to be that the shorter ones are just to short.

The photo that I took is the best look I've actually been able to have.... But, nothing looks glaringly wrong. When I look at the threads on the plugs that I've pulled (the long ones that fit) they don't look damaged or anything like that.

Completely understand. I spent a couple of hours last night going over it again and again, because it just doesn't make sense.





Some digging on the NGK site has provided some clarity.....

https://www.ngk.com/product.aspx?zpid=9371

It looks like the tapered seat (which apparently is all about how it makes a seal) can come in the same pitch and thread size as the gasket style plugs. They're not interchangeable.

Re: Spark Plug Query
 

I thought you were asleep and was re writing my post when you posted, that's why it's gone. But you have it quoted. I see it's 5:30PM there, sorry.

It is possible that you have a tapered head with non tapered plugs that "seems" to fit. That is what we are both thinking. That's what Turbobill said way back. If that is possible, you don't want that. Others will chime in tomorrow. BigBlockV6 has a post talking about tapered for larger motors. D10 plug.

ALSO: Your spark plug hole picture does not look right at all for 305. Is that a weld fillet holding in an insert or greasy spot painted orange? What the **** is that? It's either what Big V6's look like or it's a fix. That's what FMAP said way back. Show a hole in the other head.

Thanks to K:champagne: for asking for a picture.

Re: Spark Plug Query
 

http://uploads.tapatalk-cdn.com/2016...2624fe1bdf.jpg enlarged picture of the #2 (one of the ones that won't take the short plug [all 3 look the same]

http://uploads.tapatalk-cdn.com/2016...8320f99745.jpg
Enlarged picture of #1 (one of the 3 that will take the short plug [all 3 look the same]

I can see now that the difference is that the even cylinders are inset. So the short er plug won't ever work because the threads won't reach.


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Re: Spark Plug Query
 

It look like sometime in the truck past a head was change out.You might want to make sure the threads in the heads is the same length as the spark plug reach. If the long reach plug is place in a hole design for a head with a short reach the expose threads could cause a couple of problems. It could have a build up of carbon making it difficult to remove the next time and/or could create a hot spot in the combustion chamber and pre-ignite the fuel charge (cause spark knock and loss of power).

My truck heads required the long reach but only the tip half of the plug is threaded into the head. They use to make plugs this way but decided to do away with them to cut their inventory (see picture). I also have two spare set of heads. One is made like the one in my truck the other is machine for a short reach plug.

Re: Spark Plug Query
 

I can't tell for certain from the picture. But, it looks like the older style plug doesn't have a metal gasket on it, is that correct?

The reason why I'm asking is I'm trying to work out whether or not the plug I need has a tapered or a gasket seat. Is there some way that I can tell by looking at the plug hole?

Re: Spark Plug Query
 

Your pictures show the head seat area very dirty, however it look like both of them is taper. Can you clean it up a little better and see if they match one of the pictures?

Looking at my pictures (of my spare heads) the long reach has a squared off seat. The short reach has a taper seat.

Re: Spark Plug Query
 

Yes that plug picture is a taper seat plug. The pencil is pointing at the taper.

Re: Spark Plug Query
 

It is a bit atrocious how dirty they are. I hit them with some air while the old spark plugs were in. But, it clearly didn't do the trick.

What have you used to get yours so clean? I'm super paranoid about letting anything fall through into the chamber.

Re: Spark Plug Query
 

I use an awl, the one you normally would see with a 90° bend on one tip and the other end is straight with the plug install about half way in, and scrap around the plug. Then I use a air nozzle with a long small snout to blow out all loose debris. Then I removed the spark plug and insert a rag large enough to plug the hole and finish cleaning and blowing it off.

Re: Spark Plug Query
 

Thanks for the tip. Clearly the can of compressed air that I'm using isn't up to the job...... sounds like as good an excuse as any to by a compressor LOL.

The more I dig into stuff like this, the more I'm thinking that the previous owner had a pretty slack attitude about things..... Which doesn't speak well for being able to have a reliable daily driver that can do long trips anytime soon. I mean it runs and does all the things that it's supposed to do. But, it's little things like this that keep cropping up.

Re: Spark Plug Query
 

Buying a small pancake compressor should be all you need, it will be light weight and easy to carry around. Then you can air up your tires (if you are not using Nitrogen in your tires) and blow things off when cleaning them.

Re: Spark Plug Query
 

I used a shop vacuum with a small piece of hose taped the vac hose. necking it down to 1/4-5/16 ID hose about 6" long. Reaches into areas like around the spark plug. Sucks out stuff as you dig and scrape.

Re: Spark Plug Query
 

That works too. Good thinking.

Re: Spark Plug Query
 

I like that idea a bit better actually. One of the things I found the other night is I was just chasing crap around from one cylinder to the next. It was funny until it wasn't.

With the shop vac that wouldn't be an issue.

Re: Spark Plug Query
 

You will end up making sort of a cone shape when necking down from vac hose size to small tube. If your vac motor sounds like it is being "starved"/held back, poke a few small holes in the tape at cone to allow some relief for vac motor. Don't want to burn it up.

Re: Spark Plug Query
 

AZKen has already brought up the fact that 73-74 379, 432 and 478M V6 engines use a short tapered plug which was originally the AC R43T plug superseded by the AC 10 plug which I have a set of and will probably never use. Other factors to consider is the newer big cubic inch head has larger valves than the stock 305D head. 379's share the same intake valves with later 305E engines(305D have smaller valves) and have the larger Magnum Sodium filled exhaust valves, while the 432 and 478 heads have the larger Magnum intake valves over the 379. To find out which later model head you have a look at the intake and exhaust port sizes will determine that. 379 heads have the smaller ports like the 305. 432 & 478 are the big port Magnum heads, I think your best bet is to find a matching set of heads. I would also like to mention that not all 73-74 478M engines used the short tapered plugs. A replacement crate engine built in 73-74 could have the 3/4 long reach plugs for older applications. I have a late 73 478 that came out of tilt cab TM7500 series with the short tapered plug while the 74 478M in my 68 was a new replacement crate engine that came out of a 63 6500 series tilt cab and came with the 3/4 long reach plugs.:ok:

Re: Spark Plug Query
 

Having two different heads/plugs, and who knows what else, does not feel right. If you were here in U.S. you could find some matching heads, as said. Over there, it is probably going to be difficult, but send out feelers on the wanted here and maybe contact the guy mentioned by Bobdylan. Shipping from here would be really high but if you want to pay for it, let us know. Someone will have heads. If you can get into a container being shipped over, it could be free if you know a guy who knows a guy.

Re: Spark Plug Query
 

I've a set of 68 305E heads that were freshened up shortly before I started the 478 conversion:upyes:

Re: Spark Plug Query
 

Thanks for the tip. I've sent out a feeler. He's going to get back to me. [emoji106]

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