NGK BPR6ES plug cap coming loose warning

[zKars]

So I've been chasing ignition problems lately (see my post re 123IgnitionUSA dizzy and melted cap center button), so I've been going over my total spark system looking for problems. I (re)-discovered one issue with the plugs.

Years ago I had a persistent misfire and finally started swapping out plugs one at a time until I found the culprit.

You may not be aware that the tip of these plugs is threaded on. That tip screws right off. There was one plug with a VERY loose cap. Threaded it back on tight, misfire went away. Magic.

I remembered this last night, so I checked my 6 last night, EVERY ONE was loose from just a little to 1/2 to 3/4 of a turn! Every time you take the plug wires off (something some of use do more than others...), you give that tip a bit of torque I guess, and eventually....

I tightened up the tips, fired it up, and guess what. The smoothest idle I've had in a LONG TIME...

The car ran 'ok' prior to this. Tons of power, just that nagging feeling that it wasn't as smooth as it could be. My AFR gauge used to jump around more than I thought was normal. Under static cruise, you'd swear there was a transient misfire going on. No more. Touch key, car starts, idles nice.

Funny how a healthy ignition system makes you car run better. Big surprise...

Go check your plug caps. Tighten down with a vise grip. Don't bust the insulator, just snug it up. No don't use locktight. Non-conductive.

Edited September 22, 2015 by zKars

[Diseazd]

Great advice zKars.........I know exactly what you mean when it's almost perfect, but not quite. I just changed plugs a couple weeks ago in my green car.....eliminated that almost perfect running and ran perfect. The old plugs looked great. I'll check to see if a loose cap was the problem. Thanks........

[Mark Maras]

 In the dim recesses of my late sixties-early seventies memory, I remember Rajah Clips. There was one model that gripped the threaded portion of the plug, not the cap. We used them in drag racing. A very useful item when your plug wires are exposed to the air rush. 

[rossiz]

i've battled this same issue - total pain because you don't want to over torque the caps and risk damaging the plug by twisting the shaft in the insulator. my solution was to pull the caps off and just slightly crush the top of the cap with some vice grips - just bring it slightly oval at the top, but leave the bottom round so it threads on easy most of the way and acts like a locking nut when the top contacts the threads.

it takes some finesse to not overdo - you don't need a lot, just enough to get it to grip.

[EuroDat]

Rossiz, Thinking about your method, would it be easier to use pliers to grip the threaded section on the plug to form vertical lines on the thread. It is steel instead of aluminium, so it would be harder to do, but that would lightly "damage" the thread and cause the cap to bind.

Squeezing the cap has its risks and my luck I would probably crush one out of six.

[240260280z]

Marred threads (captive mechanism)  in the rear axle nuts of 280zx would be reproduced in this case by deforming the inner threads of the cap.

[John Coffey]

Porsche has been using uses the threaded type of plug connector since 1949.  Never an issue.

http://www.speedwaymotors.com/Rajah-7mm-Spark-Plug-Wire-Ends-Straight,8490.html

[zKars]

John, you mean the porsche threaded plug connectors (and the Rajay ones in your link) actually "thread" onto the threaded end of the plug (with the cap removed)?

If this is the case, that would solve this loose cap issue. Nothing like a threaded connection to prevent loosening. Learn something every day! Thanks.

I find it so hard to believe that something like this that is decades old has this type of design flaw that has never been addressed. Or are we making a mountain out of a mole hill (that's never happened before, has it?)

Edited September 24, 2015 by zKars

[Zed Head]

I've seen the problem in the past but have noticed that the newer NGK's I bought have a different color electrode (darker, not shiny aluminum) and it doesn't seem to come loose anymore.  Almost looks like the flange is part of the "cap" now.  The issue might have been addressed with a modification.  Could also have been a short-term problem caused by a manufacturing change.

 

And there's always thread-locker.  The threads are metal-to-metal contact on one side so conductivity isn't an issue.  Plus contact with the flange.

[siteunseen]

I'll add some height to the mole hill.  When I was younger I always forgot to take that thing off before I put a new plug in my KX 80 dirt bike.  It was a 2 stroke and I went through some plugs lugging around the neighborhoods trying to be quiet. 

[Mark Maras]

Zcars

 No, the Rajah clips don't thread onto the plug, they are a push on pull off. They do grip the threads & sound like a zipper when they are being removed.

[John Coffey]

None of the plug connectors thread on that I know of, except maybe some older setups for magnetos.  The Porsche ones click on like the Rajah.

 

This is generally not a big issue and I take a pair of pliers to the threaded on caps when I changed plugs on my Zs.  Always check the gap too.  And if you're really anal, index the plugs using this washer kit from Moroso.

http://www.jegs.com/p/Moroso/Moroso-Spark-Plug-Indexing-Washers/748785/10002/-1