Cooling fan woodruff key, Crank is damaged Options

[malcolm2]

Have only run maybe 4 gallons of gas thru a new rebuiltengine. Ran on the bench and recently installed. My cooling fan came loose.

Woodruff key is damaged along with the slot in the crank where it sits. Hub too.

Is there a way to suitably repair the crank without total engine removal and teardown ?

[Superhawk996]

First up - let’s talk about how this is designed.

The key is only there to align the fan to the crank so that timing marks are in proper location. The key isn’t there to resist any significant shear / torque force.

The fan hub is held to the crank by the taper and having sufficient clamp load on it to keep the hub in TIGHT interference around the whole taper. A taper like that can carry a lot of torque provided there is uniform contact around the whole diameter of the taper. This is the way many machine tools operate via taper fit (R8, CAT 40, Morse Taper, etc.)

There are two reasons yours came loose

1) you didn’t torque it properly and didn’t have enough clamp load when it was first installed to create a good interference fit in the taper.

2) your taper was damaged to some degree already with a high spot somewhere. Without proper interference around the whole taper, it can only carry a fraction of the torque it is designed to carry. Also it may begin to wobble on the high spot further accelerating its demise.

What to do?

If there is any chance of this being reliable, you need to ensure the taper doesn’t have a significant high spot. Either at the damaged key slot or elsewhere.

I would lap it and use some Prussian Blue to ensure that the taper is making contact everywhere and to correct it if needed.

Then reinstall using the proper torque with a torque wrench.

If they key slot is damaged so much that it won’t hold a key, JB weld or tacking welding the key aren’t going to help - you will have some variability in where your fan ends up in relation to the crank but it won’t be huge as long as there is a key there. This will cause some variability later on setting timing. Example: 30 degrees at the fan may only be 27 degrees or perhaps it could be 33 degrees at the crank. You get the idea. You can eventually find the sweet spot but there will be a little more trail and error setting timing.

Thread locker is useless. Once the taper has been properly installed onto the crank, the bolt technically doesn’t do much. It’s like a tie rod end. Once it is torqued intro the steering arm, you should (in theory) be able to remove the nut and throw it away. Of course no one does this - keeping the nut in place serves as a factor of safety to keep it from dropping out completely should it somehow loosen. It is for this reason that tie rods rarely come with castle nuts and cotter pins nowadays. Same principle in play here.