Need Bendix Education.... Fast

fiveboy

I FLY THE JUNGLE JET!
Joined
Jan 28, 2007
Messages
2,324
Location
Panama City Central America
Aircraft
AC Tandem Elite F30
Total Flight Time
Almost 200 hours
Ok so I over stressed the lower end of the cable and it exploded into garbage. Got a new cable and installed it today.

Everything works as it should right up to the bendix which turns but does not jump up anymore.

Here are my questions:

Do they break (I think I know the answer).
How do they break?
How exactly do they work?
How do I find another (IOW are they automotive or custom?)

Any and all information & suggestions are welcomed.

Here is a pic of the thing in situ.

What would you do!???

Thanks
 

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How do I find another (IOW are they automotive or custom?)

Of course Tom Milton is the best source for this answer.

I can state for sure although it's the same type of bendix that is used in autos it is disassembled and modified then reassembled and tested. I have watched Tom do this modification to the bendix. But Tom has a fixture he uses and he does it quickly. So I'm sorry I can't say exactly what is done. :(

As far as the sticking. I had a student with a sticky bendix. Turned out the shaft it rides up on was slightly out of round. The bendix would get stuck part way up. He disassembled the unit and put the shaft in a drill press and used sandpaper to even out the high spot. It worked OK till he got a replacement.

Either way. For a replacement give Tom a call or an email.
 
Re Tom

Re Tom

In trying to find a replacement for the cable I of course went to Tom first. In conversing and exchaning data it turns out that Air Command uses some things that are (formerly) Wunderlich and the rest is custom. Based on the size of the bearings in the lower unit we decided it and the cable were just such items. In that the same cable finds its way into the upper unit Im guessing (and it is just that at this point) that its also some wierd AC proprietary blend.

I will dissemble it and try and figure out whats screwed up and then see who can fix what where and how.

Tom if your seeing this please chime in!
 
I have the same upper unit on my 2 place. The center shaft that the Bendix rides up & down on is hollow. Mine snapped off right below the upper support "bearing" or bushing.

I had a solid one machined to replace it & air command sold me another one of their's.

I would suspect the center shaft. I forget the entire situation but I know that I made some improvements that were good.

Let us all know how you make out. Does your Hirth spin the opposite of my Subaru?

Standing behind the machine.....my prop turns clockwise. How about yours ?
 
Did you grease the bendix? Spray some wd-40 on it at least? your in such a humid enviroment that the electrical connectors failed due to moisture, it is safe to say your bendix unit is dry and could be stuck from lack of lubrication.....
 
Hmmm, could be a bent shaft, could be a dry shaft, could be a broken shaft or, could be the pin connecting the top and bottom was snapped?!

Let us know what was the cause of the malfunction.


Cheers
 
Chris & Ron

Chris & Ron

Thanks for the input.

Tomorrow I will pull the unit and look inside. I am wondering how much of whats in there is just automotive and adapted? It may be that one of the (many) automotive repair places here can fix or figure it out before I buy a new one from AC (which I have no problem with except it takes a week at min to get anything in and through customs even when using delivery services!).

As for the direction of my engine. Standing behind it turns clock wise like yours Chris. The little black rubber wheel for the bendix turns counter clockwise.

Doug, at first I thought it might have gummed up because I was using grease grease. I cleaned the thing totally and then did what was recommended and liberally lubed with silicone spray..... nada. The thing turns but it doesnt jump up at any speed.

This is so frustrating because I waited and just replaced that cable and of course was eager to test fly....

Its interesting to me that I cannot really find a good explanation or diagram of how a (or more specifically this) bendix works. I suppose when I take it off tomorrow that will no longer be a mystery.

Chris do you recall if the unit is equivalent in any way to a particular model or make for automotive?
 
I really have no idea where that part comes from ! But let's find out !
 
particular model or make for automotive?

This bendix model is called EBB-75A starter drive or sometimes drive bendix, it's available from different sources. It's used on some older cars and Lycomings engines. I particularly do buy them from manufacturer in India, very good quality.
 

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Bendix interworkings

Bendix interworkings

The bendix (area #2) is essentially a drive gear with a spiral grooved center that slides up and down a shaft with matching external spiral grooves. The rotational force of the shaft causes the gear to move up the shaft to engage the flywheel.
 

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Mystery Solved

Mystery Solved

I took that bendix apart and discovered it

A. Needed a major cleaning. It was gunk o rama.
B. Works fine​

Put everything back together.... still didnt kick up and engage.... just spins and makes a wussy clickety sound.

Thats when I discovered that the new cable was made 1/2 inch shorter than it should have been (thats always been my excuse) . That squared off end was tickling that receiver like a fellatious tease.

The manufacturer was very apologetic and a replacement is being made as I write this.

I am hoping Mr Murphy will now move on to someone who has a better sense of humor.
 
Congrats Jungle Jet. Glad you found the problem.

The Bendix drives are held together with small "circlips" They are very hard to R&R and nearly impossible to find new. Taking a Bendix apart is not for the faint of heart. They are spring loaded and take 3 or 4 hands to reassemble. Having said that, they are easy to clean and pretty straight forward inside. The outer spiral unit can be incorrectly installed upside down. It will not work correctly like this.

Also, anyone using an automotive starter drive will probably have to remove and discard the detent plunger and spring assembly. The detent is used, on autos, to keep the drive engaged until overridden.


The Bendix drive I use is probably a lot like Air Command and Alex's.

The Wunderlich Bendix starter drive is an old, obsolete unit from the late 50's. I had to search the country for them. I then found a starter drive distributor that would find them for me. Two from Cali, one from Tex, four from NY.... I was fed up with the hit and miss treasure hunt.

I contacted a starter drive manufacturer who agreed to make me brand new obsolete units. I have to order them in a big, expensive quantity and put up with a long lead time BUT. I get them entirely cad plated, with a bronze bushing in the pinions and the internals modified for prerotation use. HOTCHA ! Another problem solved. The ring gears are much the same deal (only another company) old, obsolete outboard motor units. I have them custom made from blanks, cut using Dick's hob.
 
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Tom,

If you still need these drives then probably my Indian source still manufactures them and has them in stock. Try to contact them at http://paulautomobiles.com/
They are good guys and from a dozens of drives I bought from them quality is good and stable.
 
Educational Thread

Educational Thread

I hate that I have had this issue. My son is visiting and so far we have taxied out twice only to find we couldnt spin up.... but this has been one of the most informative threads for me to date.
 
fiveboy,

I don't know if this is the very exact bendix but my supplier is less than a mile from me.

I looked at the bendix on a lot of these prerotators and man I gotta say, they look exactly like the Bendix on my 49 for 9N tractor.

I think my suppliers name is NAPA auto parts and they keep em in stock.

You can also get one off ebay.

Search ebay for (9N Bendix).

I get the impresssion that some people like keeping this stuff "top secret".
 
I hate that I have had this issue. My son is visiting and so far we have taxied out twice only to find we couldnt spin up.... but this has been one of the most informative threads for me to date.



That's a bummer about having your son there and can't fly because your pre-spinner didn't work.

Not to get on you but, have you ever worked at trying to spin your blades up for the takeoff roll...without using the pre-spinner? It can be done but takes a bit o patience and knowhow.

Most, or rather all of the old gyro guys had to learn/use this procedure to fly because there were no pre-spinners then.

One of the video tapes the late Doc Finnegan had made and had given me, has a section showing a fellow in a SparrowHawk...who had lost his pre-spinner...working up and back on the runway, to get his blades up to speed for takeoff. The pilot didn't want to RON in this town and wanted to get home.

Doc made the comment several times on the tape that he didn't think the pilot was going to get the blades up for takeoff, but I could tell by the method he was using that he WOULD make it...and he did. The biggie on this tape is that there was NO appreciable wind to help out.

I have commented several times over the years that this spin up method should be practiced and mastered, cause you won't be stuck on the ground somewhere because your pre-spinner broke down. ;)


Cheers :)
 
Harry, yes I considered it and there is usually a pretty good breeze at the field...but.... my mast is 9 foot 2 inches off the ground. To spin it up would be asking my son to stand on the seat and do something he has zero training in. I would then have to risk blade flap with him on board.

In an emergency I have little to no doubt I could manage it, but this wasnt an emergency.

The issue ultimately came down to the supplier having sent me out a cable that was half inch short of what was requested. They were very apologetic and allegedly Ill have another tomorrow (this being Panama and it being Christmas eve Ill believe that when I see it and if I do it will be another religious miracle).

In a nutshell, yes but no.
 
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