Hi,

Can anyone tell me how much difference in height there is between a 5/8" taper seat plug and a CM-6 plug with an adapter?

I have a tight cowl situation with a twin and need to know how much distance I can save by using a CM-6 plug with adapter as opposed to the current 5/8" hex taper seat plugs in the engine.

Thanks,
AV8TOR

Av8tor, the CM6 is one inch high + .075 for the gasket. The Denso is about the same, and can be bought at Advanced Auto supply.....far cheaper. The adapter you use could be custom made to shorten the total length somewhat. You are handy....you may come up with something better than a over the market adapter. Best Regards Capt,n

About 3/4" after everthing else is factored in.

So 3/4" distance saved when using the CM-6 including the adapter if I understand correctly. Right?

Thanks,
AV8TOR

+/- 1/8" per side, yes. I didn't bother with exact numbers due to various plug and cap heights, personal habits when setting a plug cap, thread adaptors, etc.

Using the right type of plug cap and even more height reduction can be obtained but the Chinese don't make those types of caps. Only place you can get them now is through Valley View RC by special order.

Thanks TOM. Hmmm, only 3/4" per side saved. Don't think that will do it for me. It'll be tight...

We are talking about PER side right?

Those RCEXL metal caps take up some space too. Any reason why one couldn't change the cap to the rubber style as was used by CH Ignitions, and just ground the shielding to the engine? Of course you would have to use a resistor plug if doing this....

AV8TOR

That is per side. Sometimes you just have to cut a hole in the cowl if you want to use that engine. Call Valley View about the possibility of obtaining a billet cap ignition. I've been using them for a fair number of years now.

Ok, thanks again TOM.

AV8TOR

The Rcexl ignition I have has a resistor inside the cap & the CM6 plug is a non resistor sparkgplug. It sure seems like a small rubber boot may work as long as the braid had a short wire with a lug bolted to engine ground. I guess a guy could set one up and do some extensive range checking. Capt,n

Below are photos. The caliper is set too 1 inch. With cap & gasket = 1.25 inch. All plugs in photo are 1 inch...with-out gasket.

Thanks Captain!

AV8TOR

Rubber boots work just fine when assembled correctly. Essentially the same process used in a stamped cap. Nothing new in using a boot on a CM-6.

Take the metal shell off, use a small zip tie as a clamp where the plug wire goes into the silicone boot, solder some wire braid to the shielding but preserve as much of it as possible as close to the cap as possible. Crimp/solder a lug on the new length of braid and attach it to a motor mount bolt. Clean the inside of the silicone boot and the porcelain of the spark plug with rubbing alcohol and let dry completely. install the boot over the spark plug all the way and use a small zip tie as a clamp. Done

That's a good idea. Thanks to you as well Jody!

Note to anyone else trying this: Be sure you get a good soldered connection to the shielding, and a good ground connection to the engine. If not, you'll blow your sensor..... (I've had it happen when my ground failed on the CH systems.)

AV8TOR

NGK males a resistor cap for CM6s...Not too much longer than the steel cap, but the ignition has to be grounded to the engine....
The old Falkon ignitions had the NGK bakelite cap inside the metal shell...I have a few here somwhere, the part numbler is LC05 something...

Do not use anything with a bakelite cap! Why do you think Falkons failed so often?

Don't know...If the ignition has a good groound there's no reason the cap would have anything to do with it...Seems like there would be less carbon tracing in bakelite VS silicone...The bakelite cap has a metal piece that clips on to the top of the plug....

I'm not going to provide specifics but simply accept I know more about this subject than most. DON'T use a bakelite cap.

OK, what do all the other non airplane engines that use CM6 saprk plugs do for a cap ?
Like Honda generators ...

Seems like Bosch used to make some very good bakelite caps....I agree with Antique. He has forgot more than other people ever will know.

I just went out and looked at the Bakelite caps on my Motorcycle. They also have a rubber boot that fits tight on spark plug. The inside of cap has metal grips that makes it hard to even pull the entire cap off sparkplug. The brand is Denso....they also make spark plugs. Capt,n

Do what you will but be assured you've been warned.