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 ?

How did this happen? Depending on the level of damage to the crank, it could get ugly. New hub, no problem, new fan, no problem Can you send a pic or two

I can't imagine that this will be JB Weld kinda fix....

I am not sure about the HOW. The O-ring from a rebuild kit was very flat, squished, when I removed it. It is also gouged. Don't know if the gouging came after tho. As I torqued nuts and bolts on this engine, I marked the head with a paint pen. This bolt had the mark on it. Some how came loose.



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moved the light and zoomed in.

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Just trial fit a new woodruff key it the slot to see if it fits tight, if so, no crank mods needed. I bent one also cause the flywheel wasn't torqued enough during cam break-in
Put in new key and all was fine

Dang Doc, That is the best diagnosis I could have imagined.... But are you being facetious?


* Playfully jocular; humorous.
* Given to wit and good humor; merry; sportive; jocular.
* Characterized by wit and pleasantry; exciting laughter.

It looks like the pulley was loose. The key only locates the position of the pulley. It is the taper that does the holding work (mostly). Make sure the crank and opening of the pulley are smooth, clean and free of burrs

Yes, the pulley was loose. ALT belt vibrating like crazy, vibrating other tin around it. I heard it first.

The close up looks like the key slot is really raised up, but, to the touch, it is not. In this case there is a hub that is what is attached here. The key did some damage in the slot of the hub.

I do have a 2nd, undamaged hub. Fan is fine.

What is the groups thoughts on the o-ring source? I found that size is 28 x 3. I can get a large assortment of metric sizes from Amazon for like $7 vs AA has 1 for $5.25 then $7 shipping. Pelican is about the same, but they will take 9 days to find the part and pack it up.... crazy.

I had the same thing happen, except the fan came loose after at least 10,000 miles.
Are the threads in the crank OK? Does the bolt feel tight in the crank? I had to drill out and tap the crank to a larger size. A couple of suggestions:
Clean up the crank and lap the hub to the crank.
Jb weld a new key. Your old key is probably worn
When you get it together check top dead center with relation to the fan marking, this may have changed. A little bit off at the crank get bigger off at the fan. Dave

Luckily, for me, I am just in the garage revving and setting the carbs and timing and heard the awful vibrating and tin rattle. So I think the only damage here is the key slot and the key. I have a couple old 66mm cranks leftover from other projects, so I rounded up 2 keys.

Oh yeah the key is now "S" shaped.

With the key out, i assembled the hub, fat washer and bolt. It threads fully into the crank easily by hand. Not loose and not wobble.

Lapping will be easy. Good idea. Ok to leave the seal in to do that?

What does anyone think about thread locker on this bolt? Medium, High??? or Hell NO!!! I never know for sure when locker is a bad idea.

New key tack welded to the crank. JB Weld could create a bigger problem.

what more trouble could JB Weld cause here?


I would struggle to weld the tiny key to the crank and protect everything from the welding while all still installed, then file down the weld to a point that the hub would slide on.

If it was all out of the engine and on a table, I might give it a try.

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.

I might dress down the material proud of the taper on the crank, inspect the tapered bore, clean everything good and try some prussian blue to ensure you have a decent contact area. I would stay away from any "metal patch" and a new key for sure, it does resist the pumping action of the fan

Negative

The interference taper is the only thing resisting torque.

Thats pretty serious damage ,looks like it may have happened before as someone has dot punched the crank in some insane attempt to fix the problem which in turn only made the issue worse.
The taper fit of the crank/hub is a precision fit and this one may take a lot of "lapping" to get that fit back again and due to the damage in the key area the replacement key will be a poor fit and it will be inclined flog loose unless the taper is restored to 100%.
Another problem maybe getting the key to stay put when the hub is refitted ,sorry to sound negitive but its not a quick or guaranteed repair .
Cheers and good luck.

As I did some lapping for about 45 minutes and cleaned it off, I noticed the "pits" on the taper too. I don't see me getting down thru them.

This is a used 71mm crank a friend gave me. He had checked it out, but IIRC mainly the bearing areas....

Don’t worry about pits below the surface, make sure all high sports are gone and that you have the vast majority of the taper in contact with the hub.

Also get some prussian blue to ensure there is a high percentage of contact. Why would anyone center punch the tapered portion of the crank?

Superhawk has your back here. I'll add to his most excellent response is pits are fine. high spots are a problem

I'll also add my own 914 fan story......

The first 914 I bought I put like 70k on it and the motor started making some bad noises. My dad was a VW tech in the early 70's so this wasn't a big deal and the car was a beater so 70k was about expected. Well we get the motor on the stand and my dad is pulling the FI off and I go to pull the fan. Well I go in there with a socket and I get nothing. Upon closer inspection I'm surprised to find the bolt is GONE! Motor was spinning almost 6k just days ago with just the press fit holding that hub on.

Again. Pits aren't a big deal. high spots are a problem. clean up that slot. fit a new key. Set your motor at #1 TDC by putting a long thin screwdriver or dowel down the #1 plug hole. Line up your marks on the fan to zero best you can. put on the bolt with the proper washer and torque to spec.

you'll be good to go.

kelly

Amazon has let me down. I did purchase the Prussian Blue yesterday from them with the promise that it would arrive today.....

Now expected on Monday. Gives me a few extra days to lap, I guess.

I have a new 0-ring, and found a woodruff key, so it is all down to lapping and re-checking.

Thank you to everyone that has chimed in. I always learn good stuff from this forum.... Fingers are crossed that I will never deal with this again.

I can certainly imagine the real damage that could be done if the fan were to come off or even just become disengaged.

30+ years ago we lost the fan on Betty's 914 at an AX in Coppers Cove Texas. She had her fastest AX run that day after the fan disconnected itself, and it made an oily mess of the bottom of the engine.

I was able to replace the lost woodruff key and bolt after a local auto parts store owner opened up and sold me the needed parts, and some locktite. I pulled the front tin, and did the work through the fan housing laying under the engine.

She was able to drive it the 2.5 hours home later that evening. The fan stayed on the crank for years after that, untouched from the parking lot fix.

Just make sure the bolt is torqued to factory specs, and put some red locktite on it before assembly. You will be fine.

I stopped using Prussian Blue years ago. I've found a large tip black sharpie works just as well, has a much longer shelf life (than the spray cans) and shows lap patterns equally well. It's easy, quick, and you can find the markers at the grocery store.
I only use the Sharpie brand.

I remember lapping my Ski Nautique prop and using Prussian Blue.....

Lot's of web stuff on lapping valves, this is as close as I could find that was not a valve.

Lap-Fitting-a Propeller

Post keeps telling me that the pictures were bad.... so you don't get great pix, but does help greatly.

I did find one post where they used a pencil to mark vs prussian blue (engineer's blue)

I could see pictures just fine. That can’t be a cheap prop!

he called it MULTI-THOUSAND dollar prop, so yes.

Here is my Prussian Blue...

I wiped it on the hub and hand installed the hub. I slid it on with the key-way semi-aligned, At 1st I just rotated right and left a bit. Less blue transferred, but here in the same place.

Then I rotated the hub 360* and got this....


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That’s starting to look pretty good. Might lap it a little more just to see if you can get a bit more contact but I wouldn’t spend 8 hours doing it either.

Looks like something that should be done on every engine build, but no one tells you about it.

Edit: oh - wait - you applied blue to the hub? So the only transfer is at the high spot on the nose. Need to get that high spot to the left of the key slot down so that it begins to make contact everywhere

When I first saw picture I assumed you put blue on the nose and it was wiped just leaving blue low spots. Makes sense to have a high spot to left of the slot since that is where material was displaced when the key almost sheared.

Like the propeller installation link, I added.

He states in that every new prop should have that done to match the new prop and the old shaft.

So for your comment if you have a new hub or a new crank, then it makes sense that the taper should be lapped using the parts that the engine will run with.

I did not do that. Used gifted crank and an unknown hub. Oops on me.

Getting there but you still have a long way to go as you have a raised area around the keyway,I would get a guality flat file and just carefully work it down then redo your lapping and see what you get,don't be afraid to use course lapping paste as I will give you a good indicator when you blue it again ,then you can go finer if good result.
Your final result will be if the hub can be tapped on with a socket and will be hard to pop back off the taper you need this as it won't be an issue later .
Remove the old seal so you can see better whats going on and keep rotating the crank,cheers.

I would want to see at least 80 or 90% contact area

Hmm. Filing the end of the crank with the inside of the case so close would make me nervous, no matter how the opening is sealed. Steel filings in the oil would be a very sad thing.

Take a 1 inch wide strip of all-mag about 3 inches long and lay it under the crank in the seal opening. Any filings will be caught on the magnet instead of going into the motor.

Just set a neodymium magnet underneath and it will literally “grab” the shavings out of the air assuming it doesn’t “fly” itself up to the crank. The magnet might need a drop of hot melt glue or double sided adhesive to stay put. Crazy strong magnets!

Before you put the allmag strip in there, pack it with wheel bearing grease. It will get any shavings the magnet misses.