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

[Paul P.]

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

Paul------


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

yeah, that's what I'm thinking, also.

Paul

[Carnell M.]

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

Just curious Duke. Why do you not recommend resistor plugs?

[Duke W.]

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

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

The reason you have fouling is because the prior plugs are too cold, so a hotter plug is called for.

Denso 14 and NGK 4 heat ranges are equivalent to AC 5. With Denso and NGK a lower number is hotter. This is opposite to the AC convention, where a lower number is colder.

For normal road driving, I recommend AC heat range 5 or equivalent for both small and big block engines, which may be one or even two heat ranges hotter than OE, but decades of experience by many vintage Corvette owners indicates that the typical OE heat range is too cold for normal driving and can result in premature deposit buildup and fouling.

My circa 2000 NGK catalog does not list a BP4FS. The only non-V-power plug in this geometry listed is the BP6FS. If you can buy a BP4FS, that's what I recommend, but if not, go with the V-power UR4, which is a resistor plug.

Duke

[Duke W.]

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

Just curious Duke. Why do you not recommend resistor plugs?

Resistor type plugs were installed beginning circa 1968 to comply with stricter RFI requirements, but they "steal" some energy that would otherwise reach the plug gap; and being as how the single point ignition system has minimal reserve ignition energy to begin with, I prefer a non-resistor plug if one is available in the proper geometry and heat range.

In some cases, only a resistor plug may be available, so that's what you have to use, but if you use the proper heat range, unleaded fuel, and the engine is not passing a lot of oil into the combustion chambers, fouling should not be a problem.

Here's an interesting case. My '88 MBZ 190E 2.6 originally had Bosch "Super" non-resistor, copper core plugs - what I call a "two dollar spark plug". (Well maybe nowadays they cost about $2.50) The wires are very low resistance, but there is a resistor built into the wire terminal at both the cap and spark plug ends. The first time I replaced the plugs, circa 1991, I used the new Bosch Platiums (resistor type), which were inexpensive and readily available, but after installing them I noticed the inline six picked up some idle roughness, and there was a dramatic increase in HC emissions on the next emission test, which was a two-speed, no load test back then - 2500 and idle. It barely passed.

It turns out that the additional resistance lowered energy to the plug and altered the secondary voltage wave form to the point that the number of idle misfires increased dramatically, which is why the idle roughened and HC emissions went up.

So I threw away the Bosch platinums and found a place where I could order the OE non-resistor Bosch "Super" H9DCO plug, which has a "heavy duty" (larger) electrodes, or the H9DC which is the same other than having normal size electrodes.

Now, Bosch no longer manufactures these non-resistor plugs, even though millions of Mercs uses them as OE. All they offer now is the resistor version of this plug, HR9DC, but I caught wind of this an stocked up on enough non-resistor H9DCs to last the rest of my life, and then some.

Duke

[Paul P.]

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

Thanks for the excellent info, Duke, I was lucky to have you respond to my question ;-)

I have managed to order the BP4FS's and they'll be here tomorrow so, hopefully my spark plug and fouling problems will be behind me.

BTW, what does "OE" mean?

Paul

[Don H.]

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

Duke is a senior citizen and turns in early, so I will take the liberty of answering for him.....
OE = original equipment, ie. OEM is original equipment manufacturer.

[Paul P.]

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

Ahh! Of Course!

Thanks Don, and Thanks, again, Duke.

[William P.]

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

If your 487 heads were origonally on an LT1 they would be valuable . They would have screw in studs, push rod guide plates and O rocker arms . If they do you should be able to get enough $ from them to get a good set of early heads .

Bill

[Duke W.]

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

Duke is a senior citizen and turns in early, so I will take the liberty of answering for him.....
OE = original equipment, ie. OEM is original equipment manufacturer.

Yeah, very funny, Don.

The fact of the matter is about that time last night I opened a bottle of wine and put "Basic Instinct" (which I have never seen before) into the DVD player.

After watching the movie and all the special features, I didn't get to bed until about midnight, and then I had trouble getting to sleep, and I was sure glad that I was sleeping alone!

Duke

[Paul P.]

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

They would have screw in studs, push rod guide plates and O rocker arms.

Bill

Hey Bill,
you'll have to forgive my ignorance, but you'll need these spelt out for me, or would a pic of the head with the rocker cover removed be a better idea?

Paul

[Joe L.]

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

Hey Bill,
you'll have to forgive my ignorance, but you'll need these spelt out for me, or would a pic of the head with the rocker cover removed be a better idea?

Paul

Paul------


A picture would be the best way for us to advise you. However, it's still possible that the heads could have been converted to screw-in studs with guide plates. But, there will likely be "hints" of that we could discern with photos.

[Clem Z.]

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

i have run into the problem when the welded on ground electrode weld was sticking out too far to allow me to start the plugs into the heads. i just filed the excess weld off with a file

[Carnell M.]

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

Good explanation. When i was younger the resistors were recommened because it cut down on radio interference. Is that still relevant today? Thanks

[Paul P.]

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

I'd upload the pics, but I keep on getting errors (with no explanation) when I try to upload them!

[Paul P.]

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

IMG_0118_small.jpgIMG_0119_small.jpgIMG_0120_small.jpgIMG_0121_small.jpgHere are some, with more to come

Paul