AC R43's spark plugs won't go into my 62 head

[Paul P.]

Hi,
I receive my AC R43's from Zip parts and proceeds to try to replace my old plugs, which were NGK Br6fs (australian model number).

However, only 4 of the 8 plugs would ever go into the head.

Thinking that Zip has these made by a Chines Partner, I when and purchased the standard NGK equivalent here (BP5S, which is equive to an XR4 in US) but i still have the same issue on the cylinders that the R43's had.

The original plugs will go back in the cylinders, but not the new ones.

The BR6FS's are only a 5/16 nut instead of a 13/16, and they are 2mm longer in the thread reach, but the thread diameter is exactly the same, so they should at least start to screw into the head, but they will not.

Any ideas?

[Duke W.]

Re: AC R43's spark plugs won't go into my 62 head

The BR6FS is a 14 mm thread, taper seat plug with .460" reach. If you have original '62 heads the correct plug geometry is 14 mm thread, gasket seat, 3/8" reach. So you had the wrong plugs installed - both in terms of seat design and reach. The taper seat could have bunged up the beginning of the thread. The correct plug geometry is 14 mm thread, 3/8" reach, gasket seat.

I suggest you get a 14mm spark plug thread chaser, and carefully run it into all the spark plug bores. Then install a proper geometry, proper heat range spark plug, which is NGK B4 or Denso W14-U, They are equivalent to the out-of-production AC 45. AC heat range 3 is way too cold for road operation, but it's fine if you have a serious road racing car that doesn't see normal road use.

However, before you proceed, you should get an appropriate mirror and inspect the plug bores to see that they are really gasket seat type, or pull a valve cover and check the head casting number and report back here.

If you proceed blindly, you may do some serious damage.

Duke

[Paul P.]

Re: AC R43's spark plugs won't go into my 62 head

Hey Duke, you are spot on re the chaser - I just went and purchase one.

The PO has just had a local mechanic do the work for him and the guy looks like he's just gotten any plug that will do the job. I'm very certain I now have the right plugs, I just have to get them to all screw in.

re the mirror, do you have any tips?

I was thinking about the new optical inspectors with a led light, but they are fairly expensive.

Paul

[Paul P.]

Re: AC R43's spark plugs won't go into my 62 head

Now I'm getting confused!

I cleaned up the plug thread in the head and still could not get the "right" plugs to fit. It was if the plug thread didn't even make contact with head.

So I bit the bullet and removed the passer side rocker cover and have these numbers:

Head Casting Number 3973487
Head Casting date k 60 0

Block casting number: 3782870
engine code : S06443P

These do not look like 62 327 numbers to me.

Can anyone tell me what I have?

Paul

[Michael W.]

Re: AC R43's spark plugs won't go into my 62 head

Those heads were used on '71 small block Corvettes and many other GM cars. Casting date of November 1970.

[Joe L.]

Re: AC R43's spark plugs won't go into my 62 head

Those heads were used on '71 small block Corvettes and many other GM cars. Casting date of November 1970.

Mike and Paul------


...and this head is machined for tapered seat spark plugs. While it is possible to install a tapered seat plug in a head designed for gasketed plugs, I don't think it's possible to properly install a gasketed-type plug in this head because I don't think the counterbore in the head is large enough. So, if this head is going to continue to be used, tapered seat plugs will have to be used. If the engine still has the original head on the other side, that means that gasketed plugs will need to be used on that side.

My recommendation: replace the non-original head with an original head or, at least, with a head of gasketed plug type and with original valve size and combustion chamber configuration and volume.

[Duke W.]

Re: AC R43's spark plugs won't go into my 62 head

A dental mirror or small lady's compact mirror along with a small LED flashlight should allow you to determine visually if the plug bores are taper seat or gasket type on the other side.

The original plugs for that head are AC R44TS, but I recommend one heat range higher for normal road driving, and non-resistor would be preferable, so that would be the AC 45TS. The cross reference to NGK and Denso is UR4 and T14PR-U. both of which are resistor type. However Denso offers the T16P-U, non-resistor type, which is a little colder, but no colder than AC heat range 4.

If originality is important you might want to consider finding some OE heads and installing them. Assuming you have OE type flattop pistons, the '71 heads have dropped the compression due to larger chambers and you can probably get away with a lower octane rating than the highest available to you.

In any event, you should at least have the same size chamber head on both sides, so the best thing to do is pull the other rocker cover off and find out exactly what you have.

Duke

[Paul P.]

Re: AC R43's spark plugs won't go into my 62 head

Guys,
excellent point about the opposite side, given it took 3 of the 4 new, gasketted, spark plugs!

And thanks for the heads up on the right plugs for the 71 head.

cheers,
PP

[Paul P.]

Re: AC R43's spark plugs won't go into my 62 head

OK, the Driver's side Head has:
Head Casting Number 973487
Head Casting date L 1 0

notice the casting numb has no 3 prefix? Is that significant?

Paul

[Paul P.]

Re: AC R43's spark plugs won't go into my 62 head

The original plugs for that head are AC R44TS, but I recommend one heat range higher for normal road driving, and non-resistor would be preferable, so that would be the AC 45TS. The cross reference to NGK and Denso is UR4 and T14PR-U. both of which are resistor type. However Denso offers the T16P-U, non-resistor type, which is a little colder, but no colder than AC heat range 4.
Duke

Duke, in Australia the T16P-U are equivalent to a BP5FS, which is one heat range higher than the original BR6FS's (however the original were resistor type).

Should I go for the BP5FS, or the BP4FS, which is a higher heat range again - I do have a lot of problems with fowling and engine soot with the BR6FS's, so I'm tempted to go the BP4FS's.

Any thoughts?

Paul

[Michael W.]

Re: AC R43's spark plugs won't go into my 62 head

OK, the Driver's side Head has:
Head Casting Number 973487
Head Casting date L 1 0

notice the casting numb has no 3 prefix? Is that significant?

Paul

Sometimes the casting numbers are not quite perfect in appearance, in this case the initial 3 might be hard or impossible to see. This cyl. head is the same casting number as it's companion but with a casting date of Dec 1, 1970.

[Paul P.]

Re: AC R43's spark plugs won't go into my 62 head

Thanks Michael,
This must be the case....I had a very good look and the 3 must be that badly cast that I thought I saw a shadow but convinced myself I was seeing things.

Anyway, I just have to decide on which heat range to get the new plugs.

Cheers,
Paul

[Joe L.]

Re: AC R43's spark plugs won't go into my 62 head

OK, the Driver's side Head has:
Head Casting Number 973487
Head Casting date L 1 0

notice the casting numb has no 3 prefix? Is that significant?


Paul

Paul------

No, I'd say the missing digit is just a foundry error. No matter, as Mike says, it's the same as the other head.

So, why do 3 of the gasketed plugs seem to fit this head? That I can't figure unless they are only grabbing a few threads and the plug is seating on the surface external of the counterbore. I don't think any of these tapered seat heads had a counterbore large enough to accept a gasketed-type plug.

At least you seem to have matching heads. That means you can continue to use them if you wish although you will suffer a reduction in compression ratio compared to the original heads and you'll have to continue to use the tapered seat plugs.

[Paul P.]

Re: AC R43's spark plugs won't go into my 62 head

I think you are right re just grabbing a few threads....on the only I played with and cleaned up yesterday the plug just could not grab a thread to start. So I'm guessing that the head casting on the other 3 are just off enough to allow this to happen.

I'll stick with these heads until I get some more pocket money, then start looking for the originals. ;-)

Any thought on whether I should go 1 or 2 heat ranges up on the old plugs for the new ones?

Cheers,
Paul

[Joe L.]

Re: AC R43's spark plugs won't go into my 62 head

I think you are right re just grabbing a few threads....on the only I played with and cleaned up yesterday the plug just could not grab a thread to start. So I'm guessing that the head casting on the other 3 are just off enough to allow this to happen.

I'll stick with these heads until I get some more pocket money, then start looking for the originals. ;-)

Any thought on whether I should go 1 or 2 heat ranges up on the old plugs for the new ones?

Cheers,
Paul

Paul------


If it were me, I'd go TWO heat ranges up to the equivalent of AC 45.