Welding timing gear to spacer on 08+

[motoguy]

I've got an '09 XT with a sheared key for the timing gear. It killed the gear but luckily didn't booger up the shaft too badly. I'm getting it all put back together and I'm wondering if there's any reason I wouldn't want to weld the timing gear to the spacer after rebuild (assuming proper key alignment, etc). This would allow the timing gear / spacer combo to use the full length of the woodruff key for strength instead of the little nub the timing gear currently uses. The welded assembly should still be able to be pulled as one part if needed.

Side note: I've been told this failure is indicative of a loose nut holding the assembly in place, which allows a bit of play leading to failure. It's been suggested that I increase the torque used to secure the nut to 80 lb/ft or so and apply red loctite to prevent future failures. I'm curious if there is any input on the validity of this suggestion.

 

[Cooter]

Got a pic of what you are talking about?

 

[motoguy]

Photos

 

[motoguy]

more pics

 

[motoguy]

You can see the sheared woodruff key and the fractured gear. I have new replacements for both. The machine shop cleaned up the keyway. We're wanting to install the woodruff key, install the spacer (undamaged in photos), install the gear, install the nut and torque it all down. Then weld (not full weld, but more than a tack) the gear and the spacer together. This will link the two together, allowing for more of the key to drive the gear (via the spacer which is welded to the nut).

 

[Kurlon]

I'm all for improving things when I can but... this one has me potentially overthinking...

This is the first discussion i've seen of this failure mode on these engines, I'm sure it's not the only one to ever happen, but it doesn't seem common enough for there to be much community chatter about it. That timing gear shouldn't be a super high load part given what it has to drive. It does see variations in the load as the cams do their thing, so I can see where a loose jam nut would allow it to fret the woodruff key over time. I would think, if that key wasn't intended as a fuseable bit HD would have gone with a spline drive for the timing gear instead?

TLDR I think you found the root cause, loose jam nut, and the fix is easy, proper torque and correct thread lock. I don't know that welding the spacer to the gear will do anything other than delay the failure for a bit if the nut becomes loose again, I wonder if you could run into a situation where the damage would be WORSE if you have a failure that woodruff key is meant to absorb?

 

[motoguy]

I've had discussions with several (handful or so) of people who have had similar failures on their Buells. That's actually where I got the idea of the loose nut / increasing torque / welding them together (served as a fix for a couple of folks). Prior to that input, I was being told the sheared key would necessitate a complete crank rebuild.

The Google searches I did for sheared Buell / Harley timing gear yields results of basically the same thing I have. Granted, in the age of the internet I'm probably going to learn about a failure suffered by a shaman in the jungle of the Amazon, but I found enough to learn about possible repairs.

You are the second person I've come across who mentions the idea of the keyway being a mechanical fuse in the system. I'm curious what benefit this would serve? If there is piston/valve contact of sufficient force to bend the valves (and thereby shear the key) then you've already got issues requiring the teardown of the engine. Valves causing shearing of the pin doesn't seem like a big benefit at that point.

If the key shears (as it's done here) from whatever...then you get valve/piston contact requiring the teardown of the engine. Again not see a big benefit. If it's a fusible feature I'm not sure I see what it's protecting.

FWIW, according to the prior owner, the bike was running 45mph or so down municipal road when it sheared. He said it was like someone hit a kill switch, which makes sense given the complete loss of the timing system. It didn't happen during a spirited ride or anything, however a loose nut cares not when it strikes.

 

[Kurlon]

So, as you noted in your friend's case, the bike just acted like someone hit the kill switch instead of the crank also binding and acting like the motor locked going into a full skid?

 

[motoguy]

So, as you noted in your friend's case, the bike just acted like someone hit the kill switch instead of the crank also binding and acting like the motor locked going into a full skid?

Yes, however I feel the key is the weak link in causing the engine failure vs the other way around. Just my opinion based on conversation with others who have experienced these failures under "not particularly harsh" circumstances (Buells and Sportsters).