TheSamba.com :: View topic - Crank pulley woodruff key: how tight does it need to be?

Wed Nov 25, 2020 3:48 pm

My woodruff key in the crank snout comes out fairly easily. As in, if I invert the crank, the key falls out. But it has no detectable lateral movement (side to side) and the crank keyway seems to be in good shape. No wallowing out or rounded edges. But the fact that the key slides in and out easily tells me it likely has some very small capacity to wobble a few thousandths. Do I need to address this before engine reassembly, or just make sure the key is in and flat after pulley installation?

Basically I don't know if the key is required to handle rotational force of the pulley/crank or is just there to position the pulley, and the bolt torque/pulley to crank fit handles the rotational force during use. The pulley itself is quite tight on the crank (will need to be tapped on and needed a gear puller to remove), and I have a new bolt to install (with loctite) when the time comes.

I realize that keys are cheap. It's just that I don't have one and was hoping to get the engine assembled during the long holiday weekend. I considered putting a few beads of steel on one side of the key with my welder and then grinding it down until it is snug.

Thanks for your expertise and advice.

Wed Nov 25, 2020 4:21 pm

It really should be tight, the pulley and generator are the damper and any play will get tested back and forth every time the engine fires, a little slop can become big wear in very little time.

In a pinch you can hammer the key slightly flatter vertically so it expands horizontally, but swap it out once the new one arrives.

Wed Nov 25, 2020 4:23 pm

busdaddy wrote: It really should be tight, the pulley and generator are the damper and any play will get tested back and forth every time the engine fires, a little slop can become big wear in very little time.

In a pinch you can hammer the key slightly flatter vertically so it expands horizontally, but swap it out once the new one arrives.

Thanks busdaddy. Seems like it would be a challenge to get the new key installed once the engine is in. Is there a good way to do this without being a contortionist?

Wed Nov 25, 2020 5:13 pm

It's challenging, but far from impossible: https://www.thesamba.com/vw/forum/search.php?searc..._chars=200

Thu Nov 26, 2020 7:07 am

So I might have to change my optimism on the state of my crank after closer inspection. When I place the key in and snug it to one side of the crank, there is a noticeable gap the full length of the other edge as shown. I recently had an aluminum CB pulley fail, and now I'm thinking that the force of that loose pulley widened the mouth of the top of the key way. Any way to repair this, or should I just get a new crankshaft? I want this to be the last time I build my lower end. It's possible this was there the first time I rebuilt and was the cause of the CB pulley failure--too much wobble causing stress failure of the the aluminum. I'm paying much closer attention to every part this time around.

Thu Nov 26, 2020 9:43 am

For what it’s worth here I am removing one and it’s supposed to be interference fit. You could flatten out the rounded end to make it fit tighter and it would probably work but since we’re not there it’s hard to say.

And going back on

Finished product

If it wasn’t too bad and you tightened it up making adjustments with BFH
Malletizing then using the Loctite product designed to hold bushings followed by a good old stock steel pulley it would work. I’ve seen stock pulleys that fit loose and when installed with bolt tightened to spec it doesn’t seem to matter.