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Old 11-14-2019, 02:56 PM   #101
GOSFAST
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Default Re: Spark Plug Protrusion into Head?

OK, one more time, below here is a shot of heads I have here for another "pending" build, customer still up in the air!

These are a set of Offy "400's", still brand new, circa 1996/1997, these came straight from Tay & Vince out at Offenhauser, no "midde-man"!

I placed a better photo below showing a conventional .437" short-reach plug (Autolite 216's) in the head on the right and a conventional .750" long-reach (Autolite 3924) in the head on the left.

The "protusion" on the .750" reach is fairly obvious, same for the "lack-of-protusion" on the 216's, neither fits as-is, period.

Like I stated earlier in my post here we've been down this road many times, it isn't new here! This is why we made our own "spacers" for the correct fit (seen in post #2 above), preferably using the .750" reach pieces!

Thanks, Gary in N.Y.

P.S. You need to look closely but it is an issue that need to be addressed BEFORE installing any brand of heads! So far the Edelbrocks are the best to build on in my opinion?
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File Type: jpg Flathead Offy 400 Head-Spark Plug Lengths B.jpg (83.2 KB, 57 views)
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Old 11-14-2019, 02:59 PM   #102
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Default Re: Spark Plug Protrusion into Head?

Do the 400 cambered shallower 425 deeper. As pics of both heads show as cast chambers where the plug enters & machined over pistons they’re different casting design. tubman’s works w the 3/4” reach mine requires what calculates to 5/8” reach or a bit less.
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Old 11-14-2019, 03:11 PM   #103
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Default Re: Spark Plug Protrusion into Head?

I have a question Anthony, is there a reason you don't want to use the spacers? Seems like the best solution.
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Old 11-14-2019, 03:58 PM   #104
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Default Re: Spark Plug Protrusion into Head?

Gary indicate 2 spacers will do it, thats only .120" @ .060" each. I am 3.5 threads short as it appears Gary's most recent pic of a 3/4" reach is too. 2-14mm threads r .07" 1.5-14mm threads r .06" per thread X 3.5, that's.21- .24 so would take 4 spacers. too many surfaces to seat for good compression. I know Gary showed a head with a 3/4"reach w 2 spacers flush on an Offy head he has. Math don' work on mine. If as post 99 or 100 says there is a difference between my 400 stamped head and tubmans 425 head I think my casting config is different.
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Old 11-14-2019, 05:30 PM   #105
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Default Re: Spark Plug Protrusion into Head?

I just tried the Champion N5C in a new set of Offy heads and they required .200 spacer to get the base of the plug flush with the cylinder head. With .120, they hit the plug electrode. Same with the NGK BR7ES.
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Old 11-14-2019, 05:46 PM   #106
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Default Re: Spark Plug Protrusion into Head?

Is it feasible to make a set of custom spacers the height required? I would want to try and use a common sparkplug depth so that it would be fairly easy to replace down the road.
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Old 11-14-2019, 07:24 PM   #107
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Default Re: Spark Plug Protrusion into Head?

Agreed, & wish I had a lathe, if I did I’d have never started the thread & just made the right size spacers. Drill press is all I have room for. I think I saw 1/2” reach plugs, 1/2” thread depth engagement is more than adequate & chamfer .12”-.15 deep should do it. I’ll check & go minimum on the depth.
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Old 11-14-2019, 08:57 PM   #108
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Default Re: Spark Plug Protrusion into Head?

That's where you need a friend with a shop! I have one of the little hobby lathes I like to play around with for small stuff, works good.
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Old 11-14-2019, 09:33 PM   #109
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Default Re: Spark Plug Protrusion into Head?

I’ve always wanted a multi machine since retiring. Hopefully someday before I’m senile
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Old 11-15-2019, 04:48 AM   #110
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Default Re: Spark Plug Protrusion into Head?

Quote:
Originally Posted by JSeery View Post
That's where you need a friend with a shop! I have one of the little hobby lathes I like to play around with for small stuff, works good.
I have one of these imported "mini-lathes". Mine has a 7" swing and can handle objects up to 14" long.Of course, it has it's shortcomings but it got me "over the hump" of being able to do a lot of things. I had looked at used "regular" lathes, but their size, weight, three phase power requirement made them impractical for my needs. One of these units would be perfect for a project like these spark plug spacers.
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Old 11-15-2019, 11:05 AM   #111
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Default Re: Spark Plug Protrusion into Head?

Tubman, do me a favor if u would, can u do an actual measurement on the reach without the compression washer on ur N5C. I just noticed thereís a sticker on the ones I got indicating for small engines? Wondering if they r the same as the one u got!
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Old 11-15-2019, 11:37 AM   #112
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Default Re: Spark Plug Protrusion into Head?

Will do.
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Old 11-15-2019, 12:20 PM   #113
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Default Re: Spark Plug Protrusion into Head?

I measure .710 to the end of the threads and .750 to the end of the plug cylinder. According to NGK literature, reach is defined as the length of the threads. Is this an industry standard? I also understand that a 1 piece spacer is ideal, but is there a problem with stacking them to the desired height?

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Old 11-15-2019, 02:42 PM   #114
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Default Re: Spark Plug Protrusion into Head?

Thx flatjack9, I’d still like a measurement from the ones tubman got as it seems there’s a couple of PN#’s listed, one for small engine & one for cars.
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Old 11-15-2019, 03:01 PM   #115
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Default Re: Spark Plug Protrusion into Head?

The number equivalent to N5C on the box is 120.
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Old 11-16-2019, 08:36 AM   #116
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Default Re: Spark Plug Protrusion into Head?

Rational for having tubman physically measure the Reach on his N5C is, I went back on Amazon & found there r two N5Cís listed. One is a PN#120 for small engines, the other is a PN#A-N5C. Amazon took the N5C PN# 120 small engine plugs back no charge.
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Old 11-16-2019, 12:02 PM   #117
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Default Re: Spark Plug Protrusion into Head?

Anthony, if you can't or won't solve your plug issue with the washers then you'll need "spacers/bushings", these are machined as a 1-piece item. We've done this with a number of customers including a few members up here!

They can be machined (as mentioned above, I think a few times) to any required lengths to make up the needed "thickness", been doing this for years now! It is a bit more expensive than the washer deal but it is what it is so to speak!

Thanks, Gary in N.Y.

P.S. Here's a shot of the "bushing" sitting on a plug, the one pictured is ready to be finish-machined for the needed heights.
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File Type: jpg Spark Plug Spacers - Alum Custom.jpg (83.3 KB, 44 views)
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Old 11-17-2019, 10:07 AM   #118
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Default Re: Spark Plug Protrusion into Head?

After all the back and forth on this, I decided that there must be something else going on. At Anthony's request, I went to my shop yesterday and spent some time looking more carefully at all aspects of this. It has become apparent that I am responsible for some misinformation here, and I want to correct the situation.

I made a bunch of measurements that Anthony requested and I think I found the problem. My N5C measures just under .750" from the bottom of the main plug body to the bottom of the minor plug body (the part with the threads). I then measured from the bottom of the washer to the bottom of the minor plug body and got .663". I then measured the depths of the holes in the head. I measured a couple of times just to be sure, and got between .540" and .580" for the 4 plug holes (yes, there was that much variation). Given these figures, my plug should have protruded about .100" from the bottom of the head. But it doesn't. With 20 lbs torque on the plug, the bottom is just about even with the bottom surface of the head. I tried up to 40 lbs, but it was still the same. This was quite puzzling to me, so just for the heck of it, I tried to thread the plug up from the inside of the head. I tried all four holes and try as I might, I couldn't get a plug started from the bottom. This leads me to the inescapable conclusion that the heads are not tapped all the way through and the N-series plugs are bottoming out on the threads in the head. I do not have a 14 mm tap, but I do have a quality "K-D Tools" spark plug thread chaser. I could not force the thread chaser all the way through the heads, even though I applied what I considered to be reasonable force. t appears that the N5 plugs are bottoming out on the threads in my never used heads and are sealing that way, and not with the normal gasket surface.

I'll bet that was what was happening back when I was racing as well. Since we never ran the engine for any extended periods of time, I don't think I ever even knew this problem existed. Who knows? Maybe a set of N5's would work well in an engine with my new heads, but it wouldn't be right.

So bottom line, the N5's are not the answer and we are back where we started from. I am very sorry that I have mislead everyone, but I guess this is the kind of the thing that can happen when you get casually involved in a thread and don't fully research the problem.

The bottom line is that I still believe that it would be better to have plugs that fit the heads properly, but it looks like that just isn't the case here. I guess spacers may be necessary.
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Old 11-17-2019, 10:44 AM   #119
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Default Re: Spark Plug Protrusion into Head?

Quote:
Originally Posted by tubman View Post
After all the back and forth on this, I decided that there must be something else going on. At Anthony's request, I went to my shop yesterday and spent some time looking more carefully at all aspects of this. It has become apparent that I am responsible for some misinformation here, and I want to correct the situation.
Nice writeup Tubman! Lot of information there.
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Old 11-17-2019, 11:34 AM   #120
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Default Re: Spark Plug Protrusion into Head?

I ran into the same thing Tubman did. That's why I posted #15 & #67 on this thread.
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