Transmission output flange fell off Yanmar 2QM15 - Theories re: why?

[JeffBurright]

• This is the same nut that originally failed. I reused it by filing off the older calked spot. The threads look good on the nut still, nearly perfect with minor scoring. I plan to replace this nut now that we're back to civilization and a better repair is clearly needed. However, couldn't a person just chisel in a new calking in the old nut in a new location around the rim?
• I agree that the inside of the flange looks and feels suspiciously smooth. The thing is, the schematic drawing, while tiny, does show longer teeth. Also, I found a machinist here who had an old rusted out flange that was unusable but did have fuller teeth. It would make my month if I didn't need a new flange, but the evidence so far seems to point the other way.
• From what I can tell, the flange does go all the way onto the spline. When the nut is torqued as far as I can get it, turning the flange turns the gears in the transmission. However, those tiny teeth seem such a tenuous hold on an awfully long spline, and if the calking on the nut is the only thing keeping this whole show together, it seems like an awfully weak link.

Here's a picture of the spline. Apologies, I'm not near the photographer that my wife is.

[Faster]

The spline on the shaft looks serviceable still.. that's the good news, I think. But it's very hard to believe that the mating spline on the original coupling wouldn't have been similarly matched for full engagement so now one has to wonder if the damned thing didn't machine itself... But it wouldn't happen overnight and I'd have thought you'd have noticed some slippage or unusual behaviour/noises prior to failure.. it's still hard to credit.

Odd problem. Would there be an original part number to use on an image search?

[knuterikt]

Originally Posted by JeffBurright

• This is the same nut that originally failed. I reused it by filing off the older calked spot. The threads look good on the nut still, nearly perfect with minor scoring. I plan to replace this nut now that we're back to civilization and a better repair is clearly needed. However, couldn't a person just chisel in a new calking in the old nut in a new location around the rim?
• I agree that the inside of the flange looks and feels suspiciously smooth. The thing is, the schematic drawing, while tiny, does show longer teeth. Also, I found a machinist here who had an old rusted out flange that was unusable but did have fuller teeth. It would make my month if I didn't need a new flange, but the evidence so far seems to point the other way.
• From what I can tell, the flange does go all the way onto the spline. When the nut is torqued as far as I can get it, turning the flange turns the gears in the transmission. However, those tiny teeth seem such a tenuous hold on an awfully long spline, and if the calking on the nut is the only thing keeping this whole show together, it seems like an awfully weak link.

Here's a picture of the spline. Apologies, I'm not near the photographer that my wife is.

Agree that the flange and shaft seems an odd pair.

Looks like a "bodge job"..

I had a prop shaft flange split along the keyway once.
First we found that the key was just a bit of scrap iron, did not fit at all

Had to get the original drawings from the manufacturer to get a new flange made.

We then discovered that the nut should be conical fitting into a conical recess on the flange locked with a set screws.
But some genius had modified the flange to take a custom made hex nut where only the corners had contact with the flange and no set screw at all

So the old flange had been sitting on the cone only (probably a long time).
When it started to slip the scrap iron piece split the flange hub.

[Faster]

Hopefully this is clear enough:



Not well drawn but it looks like the spline on the shaft and in the coupling half are meant to be matched.. certainly there's no detail showing a small ridge of teeth to engage the shaft.. mysteriouser and mysteriouser...

[JeffBurright]

Originally Posted by Faster

Odd problem. Would there be an original part number to use on an image search?

Here's the best I could come up with using the part number from my Yanmar guy in Portland.



This syncs up with the picture in my maintenance manual .

I'm liking where this is going though -- the problem was with the "bodge job" somebody did in the past when machining the flange. This was just fated to fail, nothing I did wrong through poor maintenance, right? Right?

I guess for now I just stay the course and try to find a way to get a new flange and nut to La Paz. Nobody here seems to be inclined to recondition the teeth on the existing flange (way difficult machining IMHO so I don't blame them). Then I guess we wait and see if it breaks again.

Thanks all for the help so far.

-----

PS - Faster, I think I finally understand what you meant when you suggested a drill and pin option. You're suggesting drilling through the flange and the spline crossways, then fitting and securing some kind of bolt or key into that hole right? Would that hold up to the strain on the engine? I feel like it'd just warp and/or crack the spline over time.

[Faster]

Originally Posted by JeffBurright

PS - Faster, I think I finally understand what you meant when you suggested a drill and pin option. You're suggesting drilling through the flange and the spline crossways, then fitting and securing some kind of bolt or key into that hole right? Would that hold up to the strain on the engine? I feel like it'd just warp and/or crack the spline over time.

That is what I meant, but very difficult to do in situ.... and at best a stopgap measure to get you 'home'...

Your latest image surely shows full length spline teeth in the coupling half..

[Capt. Gary Randall]

the flanges always a softer metal than the output shaft./check output shaft seal!
looking at picture three there appears to be damage or wear on the boss output shaft coupling. Take great care to fit both couplings together to see if the boss aligns both couplings ( output shaft coupling/shaft coupling any play here could cause your problems.
get new output shaft coupling and nut remove shaft coupling machine both couplings at a machine shop to fit.
Install output shaft coupling and nut.
Install shaft coupling.
Slide shaft forward to transmission coupling.
Using a feeler gauge to check all around circumference of shaft couplings.
A- line even as necessary to make these distances equal.
tighten all bolts and nuts.
And turn the shaft in neutral by hand to see if there is any binding. CaptG

[knuterikt]

When you push the flange onto the drive shaft - do you have a tight fit?
Or does it feel wobbly?

[aa3jy]

Any of these Yanmar dealers can help you out?

Dealer Locator | Yanmar

[Faster]

Looks like Cabo is closest..