3.0L twin plug - second plug doesn't fit
 

I'm building a 3.0L engine with twin plug heads. Got it assembled to the point where I wanted to check the plug clearance to the piston. Ok, my first twin plug mod and I should have done this earlier but that's where I'm at. I could not get the stock 14mm plug to screw into the newly machined second plug socket as it hits the head nut (see pic). I've been reading all day about options but, so far what I've found as potential solutions are as follows:
1. disassemble the engine and add spacer shims under the cylinder jugs
2. use 964/993 head bolts (apparently slimmer than the stock 3.0L ones)
3. use a slim spark plug with a 14mm threaded end but a smaller ceramic insulator
I obviously would like to avoid disassembling the cam towers, heads and cylinder jugs if possible but I want to make sure this is done right.
I'm fine if I have to disassemble and start it again, just wanted to know if there are options or other things I should consider before doing this work.
Thx
Jon


http://forums.pelicanparts.com/uploa...1611097483.jpg

Supertec head studs will prevent this issue but now that we're at this point, a flanged 10x1.5, 15mm nut works great.

https://www.mcmaster.com/10mm-nuts/flange-nuts/nut-type~flange/

These nuts are also an exceptional option for bell housing nuts.

http://forums.pelicanparts.com/uploa...1611107844.jpg
http://forums.pelicanparts.com/uploa...1611107844.jpg

Henry has the easy button. The 964 head nuts look like they would help but they are tall and can have the same problem. They work fine on a 964 because the head studs are further out than on earlier engines.
964 head nut:



johnhttp://forums.pelicanparts.com/uploa...1611115158.jpg

And if, for some reason, you don't want to order (maybe you need to get the motor going tomorrow?) and use the reduced head flange nuts Henry shows, plan B is to remove the six barrel nuts which are causing this issue, and grind their tops so they are beveled (sort of cone shaped) enough for the plug- and a thin socket - to clear. That's what I did on my first twin plug build, not knowing about flange nuts. It worked, but flange nuts are way better. I'd replace all of the barrel nuts with them.

The starter nut from an early 911 is also a reduced diameter barrel nut. Harder to find but they will also work.
The flanged hex nut will work but we found a much more elegant solution to compliment our head studs. Class 12, serrated flange, 12 point nut actually sourced through Porsche.


http://forums.pelicanparts.com/uploa...1611145379.jpg
http://forums.pelicanparts.com/uploa...1611145379.jpg

Henry, Walt and all. Thanks and I did think about grinding the barrel nut but didn't want to go that route if there was an alternative. Sounds like McMaster has what I need (Thanks Henry!). I'll be ordering them today.
I"ve been off the forum for a long time, apparently long enough than my "post count" is reset. Good to know it is still helping us back-yard guys get out of our self created pickles.

why not just try with a small head plug. I had to and it is an easy fix

Get 6 VW Head Nuts. Problem solved. It was the solution long before fancy head studs, nuts, and washer sets existed.http://forums.pelicanparts.com/uploa...1611198646.jpg

"The solution"...
A rock was the solution long before the hammer. I guess it just depends on your level of craftsmanship. SmileWavy

Henry, I went to McMaster-Carr and found the nuts. Problem is they don't appear to come in the yellow chromate color, like the ones in your picture. Ok, they do but only Nylocks. Any chance you can point me to an alternative source for them in yellow chromate? The owner of the engine wants them to match all of the other hardware, which is that color.
Thx
Jon

Ok, found them at Fasteners Inc Tool Outlet.

Belmetric!!!!

https://www.belmetric.com/flat-bottom-flange-nut-c-3_48_1592_59_1294/nffh10ylw-flange-nut-smooth-yellow-zinc-cl10-p-7760.html?zenid=29g359ea74gd7q8kekgf56fo75

Belmetric is a great source.

The nut pictured was from my inventory. We may have plated it in-house.

We have some in stock for anyone looking for a high quality nut. As stated, they work great for bell housing nuts.

McMaster-Carr

https://www.mcmaster.com/metric-flange-nuts/thread-type~metric/thread-size~m10/nut-type~flange/material~steel/fastener-strength-grade-class~class-10/thread-pitch~1-5-mm/width~15mm/height~10-mm/?SrchEntryWebPart_InpBox=metric+flanged+nut

And my battle continues. So, while waiting for the cylinder head nuts to arrive I checked the piston to head clearance using the "acid core solder" method. Good to report that it is just over 2 mm (2.04 and 2.08 on my two tests). Not wanting to leave anything to chance and seeing that the second plug has significantly less clearance I decided I had to measure the plug electrode clearance. Pretty simple, take a correctly gapped plug and measure it's overall length, then bend the electrode out until you have at least 1 mm more length in the plug. Install and torque the head, turn over the engine and disassemble and measure the plug length. Sad to report that I have less than 1 mm clearance to the plug electrode (.71 mm first test, .77 mm second).
I guess the alternatives are to machine the pistons or, maybe, find a plug with a shorter electrode? Open to ideas here as, from what I read I really want 1.25-1.5 mm clearance. I understand I can go as close as 1 mm but that is more of a full race engine.
Any opinions or ideas welcome. Thx

What plugs are you using when you measured?

Bosch R6's. On the barrel is WR7DC+RUSSIA 856 if that matters. That text is followed by +1.

We use a 5/8 drive, duel electrode NGK R6EKUB. Bosch makes an equivalent but I don't remember the number. They are easy to source because they cross reference to an Audi or something. Clearance is no longer an issue. It may also help with your head nut clearance issue.
An benefit is that they seem to resist fouling in MFI engines better than most.


http://forums.pelicanparts.com/uploa...1611443092.jpg

Henry, you are the guy! I'll be sourcing some of these plugs ASAP and then, because I'm anal, I have to repeat the clearance tests. Hope you understand. ;-)

A bit crude, but you could add a washer.

Spark plug washers have some mystery to them. Some authorities say you should use new washers each time you have the plugs out. The regular plug washer is a crush washer. But I have never been able to find a source of these washers, and you have to cut the old ones off.

But for this (in a pinch), any copper or even aluminum washer of the right ID to slip over the threads should work.

This is the first time I have seen a reputable source show a reason to use one of the multiple electrode plugs. Looks like the right solution.

Henry and Walt, Thanks. Good info and it gives me a plan.