Because Owning And Flying Your Beechcraft Can Be Done Safely AND For Less Money!
  Low Cost Spark Plugs for IO-470/520

CSOB Spark Plugs:


BG-341 Spark Plugs - Limited Quantities Available

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Are you still spending over $20 each for spark plugs for your Continental 470/520 Engine? Does your engine call for an RHB32E plug? Did you know that a Military Surplus spark plug is STC'd (SE69WE) for many Continental Engines at something less than half the cost of Champion or Unison options? It is the BG-341 Spark Plug!


Note that the 520B and 550B/BB Engines are not listed in the STC documentation, but they do call for the RHB32E plug......You and your mechanic decide!


Check the Champion Application Listing Catalog HERE


See the BG-341 STC Numbers below and HERE


Download the STC provided by request of a the FAA by a CSOBeech visitor HERE


See the full set of STC Documents for this plug HERE



Apparently, there are thousands of these Brand New Sealed in plastic spark plugs still in circulation. Buy a dozen now with the Buy It Now button below, limited quantities available.



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Lower Bonanza Plug Removal Tips Article by Fernando E., BE33 owner: HERE


Spark plug testing info from Tempest HERE


PS: It does not look like it is STC'd for the 520B and 550B/BB. But, remember, these engines call for a Champion RHB-32E plug and for all those other engines that ALSO call for an RHB-32E plug, the BG341 is an STC'd replacement. You and your mechanic decide what is airworthy for your aircraft. Things that make you go Hmmmmmm!



Here is a pirep watch out from Stan S. regarding the use of BG341's in the IO470C, -J and -K Engines. Note that these engines are not listed on the STC paperwork either!


Note those BG 341 spark plugs that are the equivalent of the Champion RHB32E are not appropriate for the 225 horsepower versions of the IO-470 (the IO-470-J and IO-470-K) because they are a colder plug designed for a higher compression engine. Those 225 horsepower engines require a plug with the number 40 in heat range, a warmer plug. The 32 heat range is too cold for a low compression engine and will foul regularly if used in a low compression engine.



Worst Case is that you pay about $9 for this plug at Aircraft Spruce their PN: 08-03699. I've been using these plugs in my IO470Ls for over 1000 hours with no issues and keep a stash in my hangar. Clean 'em or throw them out at annual if you don't like the looks of them.



Here is a spark plug rotation method from "Old Bob", he calls it "Spark Plug Swapping for Dummies"!


"Old Bob"


"Easier yet is the "Swapping for Dummies" method that I use.


I have a twelve hole Champion Spark Plug Caddy. It is marked one through six for the cylinders. With the numbers right side up, I place the plugs in the caddy as they are removed. Top plugs above the numbers and bottom plugs below the numbers. After they are all cleaned and being careful to make sure each goes back in it's proper spot, I rotate the caddy one hundred and eighty degrees.


I then rename the holes as one through six with what was number one now becoming number six. What were the top plugs will now all be on the bottom.


If they are placed back in the engine with the top left being top number one and so on you will find that all of them will have been switched in just the manner Champion recommends."


Click HERE for a bulletin from TCM on spark plug rotation and spark plug application guide for their engines.



I have been flying behind NOS BG-341 spark plugs for nearly 10 years in both of my IO-470L engines and have no complaints about their performance and plenty of accolades for their price (when you can find them).


If you'd like to buy some BG-341 Plugs. I'll make you a great CSOB deal on some of my stock and you'll be happy to know that your purchase helps support the efforts here at



$135.00/dozen including USPS Priority Mail Shipping w/Delivery Confirmation to US addresses. Still better than the price of Champion or Tempest plugs!


Support with your purchase. Use the "Buy it Now" Button Below to Order.


Limited Quantities Available


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Here are representative pics of the BG-341 NOS plugs. Some of the plugs you may receive had the plastic sleeves burst open after 50 years in storage, however, you can see that the cosmoline preservative has done it's job and the electrodes are in fine shape.




Still thinking about fine wire plugs? I'm told they last a much longer time than the massives, but in my CSOB opinion may not be worth the acquisition costs unless you fly +FL200.


More Fine Wire info Here



Fine Wire Woes?


Recently, a visitor contacted me with the info relating to problems he was having with some RHB32S fine wire plugs after only a couple hundred hours TIS (time in service). His fine wires were measuring OPEN resistance. Image of his resistance vales are below. The user reports poor starting hot and cold and poor combustion performance measured by his digital engine monitor.


His reference to "change out" refers to the use of resistors salvaged from NOS (new old stock)BG341 plugs.



Here is a close up shot showing the tracking lines and arcing of the original RHB32S resistors



High resistance values in spark plugs (OPEN is as high as it gets) causes the ignition system to work very hard. Parts within magnetos will see excessive stress and can wear out prematurely.


After replacing the resistors in his plugs and measuring the values noted in the above image, the submitter noted the poor performance was gone.


If you have plugs with high resistance - this could be a possible reason for some of the poor performance you are experiencing in your engine. 




Plug Wire Tool Find



Here is a tool find by Beech Lister and Bonanza Owner, Greg G. that helps to deal with that pesky ignition wire to spark plug nut. Even better it is sourced at CSOB Tool Heaven, Harbor Freight, for a whopping $7!


It's an offset oxygen sensor wrench with the perfect 7/8" socket opening and a 3/8 drive. The cutout for the sensor wire leaves ample space to slip the TCM ignition wire through it.


Big thanks to Greg for his contribution to the CSOB Club!


We've just extended Greg's CSOB Membership Card for another 6 months FREE .



Here's another cool Harbor Freight 7/8" socket that could do a nice job on our aviation spark plugs.



A whopping CSOB $7!





CHT Probe Socket Tool Mod


While we're on the subject of cool tool mods for aircraft stuff, here's a mod by Beech Lister and Bonanza owner, Ben W. that he used for installing the CHT probes for his GEM engine monitor install



Ben's mod consists of a 3/8" drive 1/2" deep well socket with a 1/2" hole drilled in the side for the probe lead to come through. You'll note this was in a Harbor Freight socket from Taiwan so drilling into it proved easy for Ben.


Big thanks to Ben for his contribution to the CSOB Club.


We've just extended Ben's CSOB Membership Card for another 6 months FREE .




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