My home inspection of Speedmaster heads

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TurboGLH said:
Bosch has's some pretty detailed info about their plug numbering system. The one I found has a standard length electrode, and a .875 reach (vs .750). It fits a 2.4l Nissan from the 80/90's, but it's discontinued (PN 7925). I used that to cross search and found a compatible plug. Standard reach, but with an extended electrode.

It's a standard 14mm, flat seat, .750 reach plug. But it has an electrode that is 7mm vs 4mm. That's an extra .118 of protrusion.

I haven't picked one up yet, but I have to go out today anyways, so I'm going to try and grab a test plug and I'll post pictures/results later.

Bosch Number - 6721 / FR8HPP30X
Champion - RC12MC-4
Neverlight - 5224


NISSAN 240SX 1989 - 1990 2.4L
NISSAN AXXESS 1990 24L
NISSAN D21 PICKUP 1990 - 1994 2.4L
NISSAN PICKUP 1995 - 1997 2.4L
NISSAN STANZA 1990 - 1992 2.4L
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With that extended electrode isn't that going to make it far too hot of a heat range?...
 
j par said:
With that extended electrode isn't that going to make it far too hot of a heat range?...
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It's one heat range up, so It will be like a RC12YC instead of a RC9YC.
 
Second chamber, same thing 64.5cc

IMG_20200404_131111.jpg
 
j par said:
With that extended electrode isn't that going to make it far too hot of a heat range?...
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If the plug is further in the chamber it gets more cool fuel and air blowing across it when the intake valve drops off the seat.

They can also make the porcelain contact more of the shell to dump more heat to keep the heat range the same.

On my big power stuff I always made more power with short tipped plugs and more timing. When I go to the dyno I’m hopefully May or June I’m going to bring at least a half dozen different plugs and heat ranges to test.

Unless the piece of crap unloads it’s guts on the dyno, then it will be one or two hero pulls and a clean up.
 
Tell here it for the kitchen and a special meal your going to cook for her:poke::D
 
Picked up two plugs, the ones I listed in my other post are longer than a standard plug. It's unmasked entirely. Plugs are installed finger tight, so it would get better after torque.

Autolight 5224 on the left , RC9YC on the right.

IMG_20200404_162013.jpg


Autolight

IMG_20200404_163335.jpg


RC9YC

IMG_20200404_163330.jpg
 
What plug does a comparable chambered iron head take? the 273's were 9YC's and the 318's were 14YC's. The 9's were really too cold for those 273's unless you beat on them like a red headed stepchild.
 
TurboGLH said:
Picked up two plugs, the ones I listed in my other post are longer than a standard plug. It's unmasked entirely. Plugs are installed finger tight, so it would get better after torque.

Autolight 5224 on the left , RC9YC on the right.

View attachment 1715500586

Autolight

View attachment 1715500587

RC9YC

View attachment 1715500588
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I'm just thinking those aren't the appropriate heat range for the head? I think there's a recommendation for a colder plug when using aluminum heads isn't there?...
 
My wife would find it humoras as i don't cook and when i put the top roman in the pan and us it to add a 100ml to make it ahhhhh just right!:realcrazy::rofl:
 
Recommended spark plugs are Champion RC12YC or equivalent 14mm x 3/4" reach with flat gasket seat. Deck thickness: 5/8", pushrod diameter: 5/16".
That's from the Edelbrock recommendation. And as I take it these are Edelbrock copies..
 
toolmanmike said:
What plug does a comparable chambered iron head take? the 273's were 9YC's and the 318's were 14YC's. The 9's were really too cold for those 273's unless you beat on them like a red headed stepchild.
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RN9YC/12YC/14YC. Has a 13/16 hex instead of a 5/8.
 
spark plug don't work any different with 13/16 spark plug socket then it does with a spark plug that has a 5/8 spark plug socket.

I like the 5/8 for header/wire clearance
 
You knew I would ask, does an aluminum head use a hotter plug or a colder plug?
 
Time for my own question. I measured the guides at .530 OD, so I ordered a set of Comp 518 valve seals. Old ones the seal runs down the whole bore, making it rubber lined vs the new ones that have just the seal at the stem ID.

Old ones go on nicely, new ones are slightly undersize and will not go on. I've done the usual, tapping them using a socket as a driver. Nothing.

Anyone who's replaced a seals on a set of SMs. What did seals did you use?
 
TurboGLH said:
Time for my own question. I measured the guides at .530 OD, so I ordered a set of Comp 518 valve seals. Old ones the seal runs down the whole bore, making it rubber lined vs the new ones that have just the seal at the stem ID.

Old ones go on nicely, new ones are slightly undersize and will not go on. I've done the usual, tapping them using a socket as a driver. Nothing.

Anyone who's replaced a seals on a set of SMs. What did seals did you use?
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When I brought my heads to the machine shop they said these are nice seals..
(6 weeks ago:BangHead:..)
 
j par said:
When I brought my heads to the machine shop they said these are nice seals..
(6 weeks ago:BangHead:..)
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I'll admit they look nice. I've upgraded the springs, keepers, retainers and spring shims to go with a roller cam. Didn't seem to be any point in taking the chance for a $18 set of valve seals
 
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