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-   -   CH ignition & spark plug question (http://www.rcuniverse.com/forum/gas-engines-142/1155604-ch-ignition-spark-plug-question.html)

Thunderhead 09-23-2003 06:41 AM

CH ignition & spark plug question
Ive got a CH Synchro sprk ign. It's NOT the one with the Bosch cap, but IS the one with the rubber boot type of end. The plug supplied with my engine (BME 50) is the NGK BPMR6F. Here's the problem, the plug is to short and will not fit all the way into the rubber boot. Its like its too short. My friends fly with Champion RCJ7Y plugs. These plugs do fit nicely in the rubber boot and seat al the way down. Are these the same type of plugs? I mean can I use the Champion and not the NGK with no problems?


Antique 09-23-2003 08:41 AM

RE: CH ignition & spark plug question

rcpilotjae-RCU 09-23-2003 10:43 AM

RE: CH ignition & spark plug question

As RCIGN1 said, yes you can use the Champion RCJ7Y plugs with that engine and the rubber boot ignition. What I don't understand is why the NGK BPMR6F's plugs don't fit the rubber boot. I used them with the rubber boot for about 3 months before I switched. (Switched to the Bosch Cap, but that cap requires a 3/4 hex 14mm plug such as the Champion RCJ7Y, but will not fit the NGK BPMR6F's that you have now.) I did notice that the boot is a bit difficult to put on, but a firm push (and maybe a little twisting, not much) and it should seat just fine. Never came off once.

As for switching to the Bosch cap, I did that to help eliminate RFI and eliminating the ground strap from the spark wire to the bottom of the plug. As I pointed out above the Bosch cap needs a 3/4hex 14mm plug such as the Champion RCJ7Y or the NGK BPMR6A. Bosch caps will NOT fit the NGK BPMR6F or Champion RDJ6J plugs. Gets a little confusing but it's really not. And all these plugs will run the BME50 fine, it's just what plug will fit what boot.

Just a bit of info for you on the BME50. Probably more than you wanted to know other than the 'YES' answer which is correct. These are the reasons behind the answer. It's what plug fits what cap, rubber or metal.

Thunderhead 09-23-2003 11:01 AM

RE: CH ignition & spark plug question
Thanx for the info! As far as pushing the boot down with a little "pressure", not happening. The boot is bottomed out down to the hex and the plug (white part) needs to be another .250 in. long to get up to where the metal is in the boot. Somtimes its easier to see than explain aint it? LOL. I know the Champion fits so OK, thats what I'll go with. So is the Bosch vs Champoin a thing of preference then? (aside from my problem)


rcpilotjae-RCU 09-23-2003 12:10 PM

RE: CH ignition & spark plug question

You've got me wondering now. You know that on the top of that NGK plug there's a screw type fitting. Is it screwed down all the way? Maybe it wasn't (or isn't) and it's making the plug longer than it should. It's just a small metal cap that gets screwed down on a thread that extends at the top of the plug (where the boot fits on). If not, go with the Champion plug (RCJ7Y)

And yes, the Bosch vs the rubber boot is a either a preference thing or to help do away with RF interference into the receiver if you have glitches. Some of the 'booted' units where developing interference with the receiver causing glitches. The Bosch cap usually clears this up (but not in every case). I also like the fact that the Bosch cap does away with the grounding strap being put on the bottom of the plug with a hose connector for a ground. While very effective, it looks odd to me (just my opinion). Remember also to make sure that no part of your cowl rubs on the spark plug wire as a fiberglass cowl will cut through the insulation on it and expose the ground strap to interference. (I've seen them cut right in half and guys wondered why their engine quit!) A trick I found is to use screen spline (used to repair screens in windows & doors). It's very cheap, comes in a big roll and you cut to length, split with a xacto knife (to open it up) then put it around the cowl opening(s). Makes the cowl holes look great and since the 'screen spline' is rubber the fiberglass cowl opening will now not cut your spark plug ignition wire.

Antique 09-23-2003 01:52 PM

RE: CH ignition & spark plug question
The NGK BPMR6A is the same length as the Champion ..Maybe the BPMR6F is shorter..

Thunderhead 09-23-2003 03:50 PM

RE: CH ignition & spark plug question
How about the Bosch vs Champion as far as the plugs themselves go. Any difference? Or is it again preference? Also is the BPMR6A a plug I could use. I mean I aint that big of dummy , so I know that the BPMR6A is gotta be different than the BPMR6F, but how and where is the diff?

rcpilotjae-RCU 09-23-2003 04:26 PM

RE: CH ignition & spark plug question

Ok, now I see what you mean (I'm slow sometimes, old age is setting in). OK, the difference is in the style of the plug. The Bosch cap will only fit the short 3/4hex 14mm spark plug. Such as the Champion RCJ 7 Y or NGK BPMR6A. The Bosch cap will NOT fit a Champion RDJ6J or NGK BPMR6F.

2nd question, yes you could use the NGK BPMR6A but it might not fit your rubber cap right. The 6A is a bit taller (longer) and fatter then the 6F. The big difference is the size of the base (or the hex nut on it that you use to tighten or loosen with). The 6A has a 3/4 hex to fit the Bosch caps. The 6F is smaller and has a 5/8 hex base (better to fit the rubber boot). This is the only difference. All will work in the BME50, they are just different in size to fit the ignitions cap.

3rd Question, There's no higher performance, etc, between the plugs (either Champion or NGK) as far as they go, it's just the size of plug that's different and what size will fit either a rubber boot or Bosch cap. If your looking for a higher performance plug I'm not sure of what's out there and if it would come in the size we need for the BME50 engine. There probably is, maybe someone here may know. I wouldn't jump to get one, what we use now in the plugs mentioned in these posts are fine, in fact they are the result of years and years of spark plug making and are of the finest.

And on a different note.....The R in all of the plugs numbers/letters means it's a resistor plug. Also good for eliminating RFI. (Radio Frequency Interference) (FYI)

Hope I cleared it up for you. Cheers!

rcpilotjae-RCU 09-23-2003 04:36 PM

RE: CH ignition & spark plug question

I don't have a Champion here to look at, but between the NGK's (6A vs 6F) the ceramic part of the plug is fatter. Also between the Champion & NGK, it's also a matter of base size 5/8 vs 3/4 hex. Why the difference in the ceramic I don't know. All the ceramic does is insulate the pos and neg of the plug.

Antique 09-23-2003 05:44 PM

RE: CH ignition & spark plug question
Exactly right....Years ago I found An Autolite spark plug that had no metal top on it at all..The porcelain was hollow on top and the connector was made to fit down inside..It was shorter, but not resistor, and I haven't seen one like that for many years...I used them on my custom Indian 45 Scout so the spark plugs wouldn't hit the bottom of the gas tank.....

tkg 09-23-2003 07:18 PM

RE: CH ignition & spark plug question
Some of the NGK shipped with the BMEs by Keith have the little hour glass top cut down for cowl clearence in twins. Maybe one of these shorties got in your engine. A stock NGK will fit OK in all the plug caps used by CH

Thunderhead 09-24-2003 08:42 AM

RE: CH ignition & spark plug question
Yes, after talking with others locally yesterday, thats exactly what we suspect was that a twin plug was slipped in and not the single plug. I had read before about using shorter plugs in the twins to help with clearance in tight cowls. Im 99.9% sure thats what happened, due to the fact BME only offers 1 single and several twin motors.
Problem solved. Thanx for the input everyone!


rcpilotjae-RCU 09-24-2003 09:15 AM

RE: CH ignition & spark plug question
Thunderhead, no problem. That's what these forums are for, to learn. I suspect that you may have got one of the 'rimfire' plugs installed in yours (made for twins) as you stated.

But now you know what plugs you can use for replacement and they can all be found at your local car parts store.

BTW, you're gonna' love that engine.

Antique 09-24-2003 10:39 AM

RE: CH ignition & spark plug question
The Rimfire spark plug has a 1/4x32 thread and is only 1 inch long, made to fit into engines that were set up for a glow plug..They are made in Tempe, Arizona and outlast the 1/4 32 plugs made by NGK about 4 to 1...They require a special plug wire from C&H, all metal, shielded, and work like a glow plug adapter, push down and turn to lock on..
They work well but at about $15 each are somewhat pricey....No current manufacturer supplies engines with these plugs except by special order....
Rimfire plugs were originally made for the scale Bentley radial built by Paul Knapp..He found the NGK plugs to be unreliable, so he made his own....Old time ignition engines used these small plugs, made by Champion, Autolite, and others..Glow engines caused their demise....

rcpilotjae-RCU 09-24-2003 12:44 PM

RE: CH ignition & spark plug question

Good info....I sorta' knew the Rimfire had something to do with the glow/gas conversions but wasn't sure. We all have our little 'expertise' in these areas. Now I know. Thanx.

GBFLYER 11-08-2003 09:47 PM

Here is a problem I am having regarding RFI. I have built a 1/4 scale GB Y. The engine is a J-A Engineering Sachs 3.2. Ignition is CH with the Bosch metal cap. The ignition system, battery, remote kill switch, manual switch, battery and charge are all in front of the firewall. The radio system with optical isolator and batteries are below the rear cockpit. I have removed the stab (metal) struts. The antenna is out of the fuse. There are not servo extensions in the fuse. The radio I am using is a new and realigned RD8000 with a Hitec Supreme receiver. The only time I have a glitch is when the tail of the plane is going away from the receiver. Has anyone had this problem and solved it?

rcpilotjae-RCU 11-09-2003 09:02 AM


Does this happen once in awhile, or all the time on a consistent basis?

bentgear 11-09-2003 09:40 AM

Thank You, needed a good chuckle this morning. When I got to the bottom of your post the first thing I pictured in my mind was the plane flying along with the receiver dangling behind, hooked only by the antenna. The answer is so simple, just fly loops and circles with no straight lines.

Now that thats over with, could it be that it is glitching because the transmitter antenna is pointed directly at the plane at that point. Some people do this without thinking and when you have the two ends of the antenna's pointed directly at each other it makes for bad signal reception.

BTW, welcome to RCU.

Ed M.

rcpilotjae-RCU 11-09-2003 10:38 AM


I was thinking the same thing, that's why I asked if it happens all of the time or just some times. It's the fading effect and happens with all radio transmissions, especially since most of the time our receiver antenna's are on a horizontal plane and our transmitters are on a vertical plane, right there is a loss of 20db of signal. This would explain the glitching.

P.S. Good chuckle....

GBFLYER 11-09-2003 10:54 PM

Tlhe situation occurs when flying a race course left to right on the up wind run at about 200' altitude about 300' south banking to the left. I keep my transmitter antenna pointed down at about 10 degrees from parellel to the runway. I flew flat 8's and the occurance happened at the same place consistanty.

rcpilotjae-RCU 11-10-2003 07:35 AM


If this interference or glitch happened at the same place consistently, then it's either one of few things. The first could be in that area your Rx is picking up a strong outside signal from some other source that's giving you the glitch. Second it could be just a spot in that area where there's a drop off in your signal (there's a technical term for that which I can't remember off hand). And third, (and I just found this out about a month ago) is if your flying over farm land and it was freshly plowed you can get a thermal from the ground, which really isn't a glitch, but rather the plane is hitting a thermal caused by the plowed land and the way the sun & wind blows over it. I know that sounds weird, but it's true. At this point (and I'm just guessing) I think your plane just goes by a area where there's a drop or loss of your signal for a fraction of a second causing the glitch. I highly doubt that there's any problem with your plane as it runs fine other wise. I have run into the same thing where I fly and haven't found a real solid answer to it yet. But I can tell you if there's any metal fences in the area, or steel cables that run through concrete posts (for the purpose of marking a area), telephone or electrical lines that are near the area, all these could also be the cause.

Here's a link to (almost) the same question on interference that I posted. There's some interesting answers there. Maybe one of them might lead you to your problem.


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