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Are some spark plugs shorter than others?

digidocs

digidocs

Well Known Member
I'm looking for a spark plug that's shorter (more clearance to the cowl) than a Tempest UREM38E. Are Champion plugs or other plug P/Ns any shorter?

Thanks,
David
 
digidocs said:
I'm looking for a spark plug that's shorter (more clearance to the cowl) than a Tempest UREM38E. Are Champion plugs or other plug P/Ns any shorter?

Thanks,
David
Click to expand...

I found the Tempest ones a bit shorter than the Champions.

Not sure if you have a basic clearance problem, or a tool access problem. If it's the second I found a deep socket could be cut down for more clearance and one of these used.

pro-67575.jpg
 
Tempest are the shortest of the std aviation plugs but no reason why you can't swap out to car plugs and as Mickey shows, the NGK's are excellent.
 
NGK BR9-EIX are the ones.

Resistor plugs with Brad's factory harness, never a buzz and good plugs.

I get them either from Amazon or get Reilly's to price match locally - a very good shop in my opinion.

Should batter them down to about $8 a plug.
 
Thanks for all of the good ideas so far. The auto plugs are definitely shorter, but would require hacking up the harness. Still a good tool to have in the box if it comes to that.
 
Update:

Just spoke with the Tempest tech rep. He said the the 37BY plugs have a shorter barrel than the 38/40.

David
 
lr172 said:
I use the Autolite 386's (18 mm) on my EI with good results. THey are resistor plugs and do not produce any noise for me.

Larry
Click to expand...

Many moons ago I used to run Autolite 386's with my electronic ignition. Then one day I was flying along minding my own business when a fellow RV was sighted. I pushed the throttle open and was in for the chase. I was leaned for cruise and did not push the mixture forward and I had a severe detonation issue, my bad. The engine lost power large time and nothing I did with any of the knobs would make the engine run smooth. A fellow RVer guided me towards a grass strip; I was high so I pulled the mixture and slipped in for a successful landing.

Now I'm on the ground. I fired the engine back up and all seemed well except for a rough engine on a mag check. It ran fine on the mag and rough on the electronic. We pondered the problem and I decided to fly it back the 10 miles to the home aerodrome on 7 plugs.

Upon inspection #3 cylinder's Autolite 386 had turned into a glow plug. The electrode was melted around the ceramic core. I ended up replacing #3 due to broken rings and toasted piston.

I switched to REM37BY's for the electronic side and have never looked back nor had any problems.

I am now a real fan of the proper spark plug for the application. I've been burned by automotive plugs. YMMV
 
I have researched this issue and spoken to the Tempest tech rep. The UREM37BY Plug is about 1/2 inch shorter above the cylinder and it does provide more cowl clearance. HOWEVER it also extends further into the cylinder. You need to check with Tempest to see if it is approved for your engine. Check their website for approved engine plug combinations. Using this plug in a high compression engine risks interference between the plug and the piston at top center.
 
All good advice;
Non Resistor plugs can be topped with NGK Resistor caps. https://www.ngkntk.in/ngk-plug-caps/ The resistor does not have to be 'in the plug'.
Autolite 386 are a hot plug, I use them in a 7:1 Lycoming O-290 just fine. I wouldn't use them in my Lycoming O-360 8.5:1. They are an 18mm resistor plug, which is somewhat rare.
Extended tip plugs are awesome, the UREM37BY is supposed to be more likely to fire a poor mixture, and tolerate oil better because of it. I use them too.
If you can tolerate 14mm plug adapters, NGK BR9ES are good, including the exotic iridium BR9EIX tips if you want to pay more.
Next condition inspection I might try the NGK BPR9ES 2.5mm extended tip plugs....
I like to use automotive plugs on the top of my RV-8 because of the baffle clearance as you observed. I make up the plug leads from bulk 8.5mm MSD superconductor wire, and MSD plug boots.
NGK Resistor caps fit over 7mm wire, Taylor and Pertronix make excellent 7mm spiral core suppression wire.
I don't know if you need resistor plugs or resistor caps if you have spiral core wires.
My spark plug experience is limited to 7:1 Lycoming O-290 in my T-18, and an 8.5:1 Lycoming O-360 in my RV-8. My wife's RV-4 has Slick mags, aircraft plugs and a Marvel carb with VAN's air filter. I don't mess around with her plane.
 
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zilik said:
Many moons ago I used to run Autolite 386's with my electronic ignition. Then one day I was flying along minding my own business when a fellow RV was sighted. I pushed the throttle open and was in for the chase. I was leaned for cruise and did not push the mixture forward and I had a severe detonation issue, my bad. The engine lost power large time and nothing I did with any of the knobs would make the engine run smooth. A fellow RVer guided me towards a grass strip; I was high so I pulled the mixture and slipped in for a successful landing.

Now I'm on the ground. I fired the engine back up and all seemed well except for a rough engine on a mag check. It ran fine on the mag and rough on the electronic. We pondered the problem and I decided to fly it back the 10 miles to the home aerodrome on 7 plugs.

Upon inspection #3 cylinder's Autolite 386 had turned into a glow plug. The electrode was melted around the ceramic core. I ended up replacing #3 due to broken rings and toasted piston.

I switched to REM37BY's for the electronic side and have never looked back nor had any problems.

I am now a real fan of the proper spark plug for the application. I've been burned by automotive plugs. YMMV
Click to expand...

Are you suggesting that the auto plug caused the problem? It sounds like classic detonation (melted electrodes are a common byproduct of significant detonation), likely due to high load with too lean of an AFR. It would seem from your description that severe detonation occured, trashing the plug and the piston. Not sure why you would attribute the cause to the plug. When a plug is too hot, it usually causes pre-ignition and not detonation. Pre-ignition will typically blow a hole in the piston top before it gets hot enough to melt a plug.

The massive electrode plugs have much more meat on the electrodes and I would not expect them to melt for some time after the much thinner electrode on the auto plug. However, that doesn't make them better at preventing detonation, only better at surviving it. However, as you learned, having the plug survive the event doesn't really help that much in the grand scheme of things. Though I suppose the aviation plug probably would have given you limited use (busted rings would have prevented full power production) of that toasted cylinder during landing.

Larry
 
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