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706 w/ a 282 Timing gear train failure


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10 hours ago, Cooter said:

This pump has he anodized aluminum bushing in it and felt tight with the shaft inserted, no excessive play at all.

I wonder if it is too tight. I like the ASH pilot tubes, but I have had a few bite me, but never this way. I generally don't use the ASH tube when the tube is acting as a guide bushing though. 

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So I got my pump back from the shop yesterday.  It cost me $75 for them to put it on the calibration stand to re-check it and not find anything wrong.  They guy who works on them has been doing it for 42 years and seemingly knows these pumps backwards and forwards, so I trust what he says.  He said it wasn’t out of spec at all and ran out fine without any noises.  He kept saying how lucky I was because it doesn’t take much deflection to bind the rotor into the cam ring and seize the pump. He said the stresses of the gear teeth climbing each other is shocking to him that it didn’t bind enough to cause the drive shaft to snap; he just kept saying how lucky I was that it didn't damage the pump internally. He also said the drive shaft was straight and serviceable.  They rechecked the drive bushing protrusion and that was in spec, so it's got a clean bill of health.  Whether there was actually anything wrong internally or not, I will never know, but I am inclined to believe him.  

SO, that leads me back to square one:  What caused it?


This is the bushing in the idler gear and you can still see the machining in the bearing and it is tight.  I was going to put a dial indicator on it when I put it back together to check backlash, but I don't see this as the failure.

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This is the pump drive gear.  There aren't any abnormal wear patterns, chipped, or broken teeth.  There is some witness marks where it saw some abuse chewing the teeth off pump gear.  Probably the reason why is because this is machined steel where the pump gear was cast.  Do you think it is reusable?

 

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I have a spare idler gear, although it isn't in the greatest shape.  There is some pitting on the face of the teeth, which may not really matter.

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I found this interesting upon closer examination.  There is an odd wear pattern on the pump drive gear where the defacing of the teeth moves to the middle of the tooth where as others are the full width.

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Here are my choices of pump drive gears, one with and one without additional timing adjustment. Is that additional timing adjustment advantageous?  Or better yet, why was it necessary?  Specific application? 

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I guess the reason that I keep circling the wagons with this is because I have not found a cause of the failure, which is really bothersome.  And because no one has chimed in saying that this a relatively common problem, then I assume that it isn't.  Which means that either that this was a weird fluke and may not ever happen again OR I haven't come across the problem yet; so either one of these two can cause it to happen again.

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Looking at your drive for the pump, it looks to me like it's pitted, my best bet is that it has had some type of foreign object in there at some point of time, or the heard layer of metal is worn off the face and literally ate the teeth off from the other gear being harder. 

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I'm starting assembly, but I wanted to double check a few things with you all before I finished.

 

Bushing is flush with the back cover.

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How much of a gap is there suppose to be?

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Even more important is, does this movement seem excessive?  The pump shop said that the bushing and shaft were tight, but this seems like A LOT being that I replaced the idler shaft bushing and it wasn't really even that wore.  I can see this causing excessive gear wear.

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The old gear has been rubbing on the front cover.  I don't know if it did that whilst it was chewing itself apart or during normal operation....

5CEC2B31-F90C-4196-AD00-A191ED979F86.jpeg

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The drive gear that has wear or pitting on the gear I would throw away.   It will only chew up the other gears.    Have you mic’ed both driveshafts where they ride in bushing?    Are they comparable?

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your pilot tube looks to me like a heavy duty steel one, like the 361/407 use on the DB or the DC pumps. Those are usually used along with a drive assembly with it's own front support bearing. Even on an AC with a DC like a D21/210/220, they use a separate drive adapter which has it's own bushing to support the shaft. 

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i personally dont like the looks of all that wobble/slop on that gear but maybe its ok, sorry i dont know more but that would concern me also and I would be asking here too if that is normal. I realize these things are old with wear but that seems excessive 

 

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Is the spring/ plunger that goes into the front of the pump shaft ok, does the spring have any tension to it anymore? 

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That is a lot of slop in that idler. Try a new bushing to take that out?

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On 5/22/2020 at 7:05 PM, nate said:

The drive gear that has wear or pitting on the gear I would throw away.   It will only chew up the other gears.    Have you mic’ed both driveshafts where they ride in bushing?    Are they comparable?

It's not as bad as it looks, sandblasting it made it look a lot worse than it actually is.

On 5/24/2020 at 10:11 AM, RBootsMI said:

Is the spring/ plunger that goes into the front of the pump shaft ok, does the spring have any tension to it anymore? 

Spring and plunger is Ok, but I am pretty sure that isn't where my problem is.

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On 5/23/2020 at 11:52 AM, Injpumped said:

your pilot tube looks to me like a heavy duty steel one, like the 361/407 use on the DB or the DC pumps. Those are usually used along with a drive assembly with it's own front support bearing. Even on an AC with a DC like a D21/210/220, they use a separate drive adapter which has it's own bushing to support the shaft. 

When I took it in the first time they told me that it was anodized aluminum, but it seemed pretty hard.   I have learned SO much about these pumps in the past few weeks and all the major differences that they have; basically that only the aluminum casing is the same, everything else is different.  

This pump originally came off an 806.  I put it on here 5 years ago when the torsional vibration dampener came apart on the original 706 pump.  As a matter of fact when they were rebuilding this and setting it up, I learned that the internal timing advance was different between a 7 & 806.  So I have to account for the total timing with the engine running so I don't get a bunch of diesel knock.

I played around some older core pumps that I have and discovered that I need to have a brass bushing in this one on the 706, not the hardened steel.  The bronze bushing appears to be longer and doesn't have the long taper in the front. 

What carries the load on the rear of the shaft?

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actually, the main housing is different too. The std duty DB uses advance plugs with about 4 threads, about 1/4" long, the heavy duty DB and all DC with advance use the long advance plug threads, about an inch long. The pilot tubes all should protrude the same distance, .300" by the tool. The shaft is supported in the back simply by the rotor.

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1 hour ago, Injpumped said:

actually, the main housing is different too. The std duty DB uses advance plugs with about 4 threads, about 1/4" long, the heavy duty DB and all DC with advance use the long advance plug threads, about an inch long. The pilot tubes all should protrude the same distance, .300" by the tool. The shaft is supported in the back simply by the rotor.

Would you recommend the bronze or anodized aluminum for the 282?

The pump shop said it was going to be $200 to put a new bushing in. 

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well, it ran before. I'd be cautious though, and put a bronze pilot tube in it. The steel one they remove will still be usable though. See how loose your shaft is in the pilot tube. The bearing surface of the shaft is the largest diameter just forward of the seals. 

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