Help needed with B-29 APU spark plug.

[michael schreiber]

Thanks for having me, I'm working on Andover Ranger V32 APU and need shielded spark plug numbers, also any cross reference numbers available. thx for any help.

 

[Bell206]

Thanks for having me, I'm working on Andover Ranger V32 APU and need shielded spark plug numbers, also any cross reference numbers available. thx for any help

Without a picture of the plug or any numbers cant help much. However a better route to take is to contact the staff at the Commemorative Air Force or a museum that has a 29 flying or on display. Plugs can be pretty easy to cross ref in most cases provided you have a good number to start with.

 

[michael schreiber]

Thanks, My plugs are not marked in any way, kinda hoping someone here would have old plug charts that would list ranger aircraft engine as they were used into the 60's. I'll ck with CAF.

 

[Spring Ford]

Spark plug id numbers look daunting but they are fairly easy to interpret.
You can measure the mounting thread diameter and length, the shield thread diameter and pitch, and you can see the Electrode design. Spark plugs have been standardized for DECADES.

That leaves the heat range.
Hot means hotter running, less heat conduction away from the tip. The tip will be slimmer and longer (within the mounting thread region, look inside). I wouldn't suggest this for a flying engine but a visual comparison of the heat range (ceramic nose diameter and length) with other, otherwise identical, plugs should get you close.

A colder plug will foul and a hotter one may ruin your engine. If not sure go colder.

Details of plugs here:-
https://www.sportys.com/media/pdf/champion1.pdf

People on these links mention availability of documentation:-

https://motoredbikes.com/threads/wwii-1943-fairchild-v-twin-what-to-build.22984/
https://ww2aircraft.net/forum/threads/b-29-auxillary-power-unit-apu.13127/

Brief Specification:-
http://rwebs.net/avhistory/images/wix/US_Aux_Engines_1944.pdf

Running engine:-