Bendix carb finger-filter thread repair

[Robert Lees]

While doing an annual I see the threads on the finger filter in the carb has stripped to the point of no return (see picture below).

According to the manual, these are 3/4-20 tpi, but helicoils (thread inserts) are only available for 3/4-16 tpi.

Does anyone know of a repair scheme? (approved or not it doesn't matter...we're experimental).

Any help will be appreciated.

[cvavon]

Re: Bendix carb finger-filter thread repair

Robert I don't know how to fix it but it is something to add to list of things to check and use never seize on to keep from pulling the threads out of the casting good luck on fixing

[waltermrich]

Re: Bendix carb finger-filter thread repair

If you have a machine shop available you could possibly bore out the old threads and press a bronze sleeve into place but probably would be better and easier if the threads were done in the sleeve before pressing inplace. it also looks like you have 4 good threads in the bottom of it, that might be enough to hold a non critical part in place

[Hank Jarrett]

Re: Bendix carb finger-filter thread repair

There are several ways to fix the torn out threads.

Starting with the easiest, there is an Epoxy compound that can restore the threads. I would use it on a lawn mower or a static display, but you would have to be nuts to try it on an airplane carb.

Second is to "make" a custom thread repair at a machine shop. It looks like you have enough wall thickness to cut the old threads out with a flush bottom end mill and then cut in new threads to put a threaded sleeve in to restore it. Again, I might go that route for a car, but NOT AN AIRPLANE.

Third, you could go with a pressed in internal threaded sleeve. I would never do it on a certified plane, and probably not even an experimental.

Forth, you could repair the bore with weld. Again, I wouldn't for flight. Maybe an air boat.

Next to last, how about a custom fitting with longer threads to engage the good threads at the bottom of the bore. You couldn't certify it, but I would feel comfortable with the safety.

Last, why not a new casting? Probably the easiest and cheapest fix.

Hank

OF course you could just plug the hole and not use the screen, replacing it with an in line filter. Again, no good for certified, but would work on an experimental and probably provide a LOT better filtering.

Do a flow test to be sure you can pass enough fuel. You might need a pretty big filter.

[Guest]

Re: Bendix carb finger-filter thread repair

look for a spark plug thread insert and use that?

bore the hole oversize, re-thread and fabricate plug for it??

[Guest]

Re: Bendix carb finger-filter thread repair

oh yeah here's one - buy a used bowl from me that has that thread in good shape but needs an insert in the place where the screw goes that locks the float pivot in place

you will need a 6-32 or 8-32 insert and mill or heavy drill press to fix it

[Fred Johnson]

Re: Bendix carb finger-filter thread repair

Use the 3/4 x 16 and manufacture a new cap.

[Robert Lees]

Re: Bendix carb finger-filter thread repair

Hi Fred, long time no see,

We're thinking along those lines, but with the existing 3/4 thread shagged, we might go up a smidgon of a size (be it metric, BA, BSW, Whitworth, UNF, UNEF or whatever) and make a new brass nut; I'll keep you posted.

But because the brass washer is so thin, it needs to be a fine thread to get the seal against the carb body, so we are unlikely to go for 16tpi.
And because the brass plug length is short (so as to avoid fuel flow restriction to the finger screen chamber), I would be unlikely to use even a normal "fine" thread...there are only 4 threads available. I might make a dedicated copper washer; more "crushable".


Thanks for all the suggestions to date...and Hank, I agree with your sentiments 100%, and would love a new casting were that they were made.

Dave Rude, can you send me more details? I might have that carb body off you just for stock. That small thread, I can do a metric conversion and use a metric grub screw to hold the shaft.

Thanks again all. This brass nut is the only one on the Stromberg carb that needs removing every year (because of the cr@p that can gather in the finger filter), so make sure yours gets checked. The same applies to the long filter screen for the Marvel-Schebler.

Rob

[Fred Johnson]

Re: Bendix carb finger-filter thread repair

Rob and or Tribe
What is the proper gasket for under the finger screen. Is it Brass or Copper and should it not be replaced at annual/100hr?. I tried to find a new one for 44467 this year. McFarlane Aviation makes a copper PMA'd for the MArvel Schebler carbs. Inquiring minds want to know, good to see your post Rob. Cheers.

[Robert Lees]

Re: Bendix carb finger-filter thread repair

I have seen both brass and copper. The manual says it is Bendix part no 174S22 (not 174522), alt p/no 12221-3. Aircraft Spruce include then in the carb gasket kit, and their part number used to be 07-02203, but looks like they don't stock it any more (I suppose they could be asked).

It's not a crush gasket, so could be reused IMHO.

Aircraft Spruce Germany do seem to stock it: http://www.aircraftspruce.eu/BENDIX-...1-3-GASKET.htm

[Pearson]

Re: Bendix carb finger-filter thread repair

Mill the sealing surface down or use JB Weld epoxy and retap the threads, it is good stuff.

[Robert Lees]

Re: Bendix carb finger-filter thread repair

Richard, you can't mill the sealing surface down...the brass plug seals the finger filter in to the bowl.

I'll let everyone know what I do later in the week.

[astjp2]

Re: Bendix carb finger-filter thread repair

I may have a good lower body. Dont dick around with this, if you screw it up, you can get a fire or loss of fuel/power through a leak. Its JUNK and you need to gently walk over to a nice solid bench and smash it with a quarter stone hammer so you will never consider using it again. There are still lots of these carbs around, you might even try to contact fresno and see if they have an NOS one. Tim

Richard, you can't mill the sealing surface down...the brass plug seals the finger filter in to the bowl.

I'll let everyone know what I do later in the week.