spark plug gap (long post)

[me.guevara]

I just had another fun exchange with the folk at AutoZone (I'm visiting my folks in Wisconsin):

Yesterday I bought 8 spark plugs from them and went with their computer specs - they gave me the RN11YC4. After a look at the workshop manual, I found to my dismay that the OEM specification is RN11YCC, or, for my vehicle, which is the Australian version, it calls for the RN11YC (no 4, which is a "wider gap" required by California). The RN11YC is not available.

Curiously, the "tune-up kit" (distributor cap, rotor arm and plugs) from Atlantic British comes with the RN12YC, which got me thinking about the wisdom of AutoZone.

The 11 and 12 numbers refer to plug operating heat ranges, while the last letters of the designation refer to gaps and insulator tip. Comparing the two together, it is quite apparent that the insulator tip on the 12YC would portrude further into the combustion chamber than the 11YC4 (I don't have access to any 11YC for comparison). Hmmmm.

I'm guessing that AB knows better than AutoZone, so today I went and exchanged the 11YC4s for 12YCs, not before I got into an argument with the guy behind the counter - I ended up just insisting that he give me the 12YCs despite his advice.

During our friendly conversation (really, it never got unpleasant), they mentioned to me that the plugs needed to get properly "gapped" anyway and that their system showed that a 0.032" is the correct gap size. Then they showed me how the 11YC4s had the proper gap, while the 12YCs had a 0.035" gap.

So ran home and looked up the gap requirements in the workshop manual and found that the OEM specs call for a 0.033" to 0.038" gap range. Ha! Score one for MG...

Now I only worry about the specified heat range, the specs call for 11s (not 12s), but I don't know that it's going to make much of a difference. Anyone know something about this?

Any comments from the more experienced and knowledgeable DIYers?

Those of you who run Champions (I know a bunch run NGKs and Bosch P-4s), which product number do you buy?

While I'm at it, Happy New Year everyone!

Cheers,

[Disco Mike]

My $.02 worth so late in the year.
The heat range will show up as a difference in power and a ping that should be corrected by the engine management system. If it drives the same, and is not too long, hiting the piston, then don't loose any sleep over it.
I am running Bosh Platiumn Plus 4's, don't remember what number, and it is raining like hell or I would go out and look, but they are now nealy 55,000 miles old and have really worked well.
By the way, don't know what your mileage is, but have you changed your plug wires, they are probably warn out if you are over 50,000 miles.
Good luck,
Mike J.

[DISCO INCUBUS]

I have been using single electrode Bosch platinums for years with no problems.


The plug i use is Resistor # 4220 that # will be on the box, On the plug itself it will
read WR9DP. Atlantic british have sold these plugs for years.

Autozone sell's them, pepboys as well.

The dickhead's in autozone & pepboys will only recognise the 4220 # on the box

[Rudy R]

the part # for the bosh p-4 are 4478 I just picked some up also.


Happy New Year All!!!

[me.guevara]

Thanks guys!

Once I have some data, I'll post some results.

Cheers,

[Disco Mike]

Originally Posted by Rudy R

the part # for the bosh p-4 are 4478 I just picked some up also.


Happy New Year All!!!

Rudy,
have you up dated your plug wires yet? You really need some 8mm. wires rated at 55,000 volts or higher so you get the full Bosh punch, lots of low end torque will show up with the combination.
Mike J.

[vray]

Originally Posted by me.guevara

I just had another fun exchange with the folk at AutoZone (I'm visiting my folks in Wisconsin):

Yesterday I bought 8 spark plugs from them and went with their computer specs - they gave me the RN11YC4. After a look at the workshop manual, I found to my dismay that the OEM specification is RN11YCC, or, for my vehicle, which is the Australian version, it calls for the RN11YC (no 4, which is a "wider gap" required by California). The RN11YC is not available.

Curiously, the "tune-up kit" (distributor cap, rotor arm and plugs) from Atlantic British comes with the RN12YC, which got me thinking about the wisdom of AutoZone.

The 11 and 12 numbers refer to plug operating heat ranges, while the last letters of the designation refer to gaps and insulator tip. Comparing the two together, it is quite apparent that the insulator tip on the 12YC would portrude further into the combustion chamber than the 11YC4 (I don't have access to any 11YC for comparison). Hmmmm.

I'm guessing that AB knows better than AutoZone, so today I went and exchanged the 11YC4s for 12YCs, not before I got into an argument with the guy behind the counter - I ended up just insisting that he give me the 12YCs despite his advice.

During our friendly conversation (really, it never got unpleasant), they mentioned to me that the plugs needed to get properly "gapped" anyway and that their system showed that a 0.032" is the correct gap size. Then they showed me how the 11YC4s had the proper gap, while the 12YCs had a 0.035" gap.

So ran home and looked up the gap requirements in the workshop manual and found that the OEM specs call for a 0.033" to 0.038" gap range. Ha! Score one for MG...

Now I only worry about the specified heat range, the specs call for 11s (not 12s), but I don't know that it's going to make much of a difference. Anyone know something about this?

Any comments from the more experienced and knowledgeable DIYers?

Those of you who run Champions (I know a bunch run NGKs and Bosch P-4s), which product number do you buy?

While I'm at it, Happy New Year everyone!

Cheers,

If you look at Robison Motors website, they recommend RN12YC over the factory recommended RN11YC, they prefer that heat range , for some reason. I don't know why, but they are an authority on LR. I think their advice can be trusted.

[me.guevara]

Thanks!


I did in fact decide to stick with the 12YCs - AB (and now Robison) have more credibility than AutoZone...