14mm spark plugs for Franklins

Dan Cullman

Dan Cullman

New member
This is an old topic that I wanted to bring back to life. I have used C-10S, BG 707SR, and REJ 38J plugs and have my own ideas about their benefits and detriments. How about it?
 
I'll wade in on this one. The cost of REJ38s really hurts, though I have probably had the best life out of them. The C10's that I have used don't seem to last as long. I am running AC SA-47's now. I have heard good things about the BG-707 on the Stinson yahoo group, but have never run them or even been able to locate them.
 
Larry,

I have some AC SA-47 plugs also, what is the spark gap setting? I can't find it anywhere.

BTW, I am doing the final assembly of my engine after the cylinder rebuilds (Gene Hamilton helped me). It should be ready to fly next week.

Thanks,

Allen
 
I, too have a can of the AC47 plugs unopened from their 1946 packing date. Allen, most A/C spark plug gaps are .016-.019. Here's my take on the plugs........ As Larry said, the Champion C10s don't seem to be long lived. Maybe 75 hrs if you don't maintain them-----maybe 100-125 hrs. if you do. Check swap meets and E-Bay under 'aircraft spark plugs' for any of the models. I have a couple sets of the BG 707SR plugs, that I bought on E-Bay from an acquaintance in Tacoma. These are four electrode plugs that seem to be very good and a bit hard to find. They might be more prone to fouling, if you use avgas. Make sure you lean after startup. Both the C10S and BG707SR are short plugs and I like them for the pre-war Franklins due to clearance problems with baffling. The REJ-38 is a good plug for the post-war engines. Their longer length is not a factor due to the fact that the plugs are mounted differently than the earlier engines. I haven't operated any of the AC47 plugs,yet. I do have some Autolite PE-30 platinum plugs that I might try. Keep the topic rolling ...............
 
Back 25 plus years ago you could get them cheaply from Fresno Airmotive (Now Fresno Airparts-they have the first ad on the second page of trade-a-plane. I didn't see them in their ad, but you might call them
 
When I had my Stinson 108 (21 years of ownership) I also tried a variety of plugs. The BG707 was absolutely the best, time proven plug. C10's lasted only a few hours. The BG's had a great service life and I never had one go bad. They will collect 100LL lead in the lower position, but I ran mostly mogas so that didn't bother much either. Unfortunately I have not seen them in years. I sold the Stinson with an extra set so Bob's good for many hours. That was NC9631K, aka Katie, a '47 -2 with the F165.
 
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