Replace the drive shaft key

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My previous transmission was a Hurth V Drive, and one of the reasons I bought a new Hurth of the same model was to be avoid problems with the bushing, shaft length, and details like that. I saved the old bushing and shaft key, as well as the two set screws, so that they could be reused and I'd have one less potential problem.

Unfortunately, the mechanic who did the physical installation and alignment lost a few parts in his shop. During the installation, he couldn't find the key, so just grabbed a 1/4" key and used it.

Unfortunately, it was a little loose, and every time I put the engine in reverse, the key would fall out.

That's not good.

To the left is a picture of a 3" puller, which I used to shove the shaft back through the bushing.

Here's the old bushing. It's just plain steel, and it likes to rust.
On my old installation with the Perkins, this was one big rusted piece of metal. I had cleaned it up and painted it with anti-corrosive primer, and then some engine paint, but of course it was chipped when it was reinstalled.
The tolerance is so tight that there's no room for paint on the inside. That's a good thing. It's interesting to see how fast it started to rust on the face against the prop shaft, though.

I don't think there's any way to prevent rust here. Grease would be *bad* idea, and an anti-corrosive Loctite would also create problems
the next time the bushing needs to be removed.

This key stock came from McMaster-Carr.
One can get 12" lengths of it, and cut it to stock. It's 18-8 stainless, but it's the
"Plus Size" which means it's just a hair larger than 1/4". It's made for situations like this, where the key slots are
older and a bit worn.

Here's a pic of the prop shaft
and key slot.

I also have a through bolt,
in addition to the set screws and key.
The hole for that is visible on the right side of the shaft.

Unlike a normal engine setup, where the prop shaft in forward is pushing against the transmission, the Hurth has the shaft extending through the transmission. So it's very important that the bushing be attached well.

The mechanics also lost one of the set screws that matched the bushing, and fit into little dimples in the the prop shaft.

The little one is the correct one, and it looks like he just found another big one laying around the shop, and used it. It looked really weird, so this is a good time to replace them.

After checking, it's a standard 3/8" thread. So replacements are on order from McMaster-Carr.

November 2006 --

After repowering, there were some "gremlins" to figure out and fix. One of the more annoying ones was the shaft key.

Update November 2009 --

Well, I finally had to replace the entire prop shaft and coupling in Cabo San Lucas.

You can read about it on my
blog page.