I thought I had figured this one out but I guess I didn't.. so...
​​​​​​ At some point in its life before I got the car the crank pulley came loose and the crank spun inside the pulley, wearing into the wall slightly. I'll try to upload pics later. Naturally the first time I drove the car at speed the pulley spun off. I chalked this up to my strap wrench not providing enough torque on the pulley bolt. So I built a proper pulley locking tool and using that, a helper, and a two foot breaker bar, tightened the bolt down as hard as we could, easily 250 ft lb if not more, trying to get close to the factory spec. Put some red loctite on the bolt for good measure. Was fine for 800 miles until...
today I figured I'd take the jag to campus for the first time, about a 25mi trip one way. Right near the end of that I got the same issue, pulley spun off. I could wiggle it a bit in my hand, so in my infinite wisdom I grabbed the crank pulley bolt in my hand and got some nasty burns. Got to use soda from vending machines as an ice pack. Towed car home.

with all this said, what are the chances that the crank end surface itself is worn? If I understand right the crank is a lot harder metal than the pulley, but even so... what are the chances putting a new pulley on will still result in the same problem?
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The fix for this is to weld the bolt in place. You will never be able to remove it, so make sure you use a new pulley and bolt. Once you weld it in, it will never come out.

I had this problem in another car and this fixed it for another 60,000 miles.
No matter how much loc-tite you use, it will never hold.

 

is the bolt loose or is it still tight? If it's still tight you might have a problem with the Locking cone.

 

The first time it spun off on me I installed a new locking cone since i suspected the old one. I'll put tools on later when I get home.

the welding is a solution.. I'm assuming welding the bolt to the pulley? I was thinking about making a key into the crank and pulley, as there should have been from the factory... it would be a pain but seems better on the chance I'd need to remove the pulley for work in the future..

 

Did you use a new bolt? It could be stretched from being torque.

 

From my LSx experience (i LSx swapped my bmw), the crank pulley/balancer is pressed onto the end of the crank and held in place with a bolt. From reading this, i am under the assumption that the x308 engine carries the same design thought. I would not suggest you weld it unless you do it in a way that the welds can be ground off. My first thought would be to try a loctite on the interface of the pulley and crank. I would suggest loctite 290. It is a wicking grade medium strength threadlocker. It is good to 300°F. At my work, we use it if we encounter a light press on a bore to bore interface. My other thought would be to look into doing something like this:
A&A LSx Engine Crank Pinning Kit (OE & 8-Rib LS7 Balancer) [AAPK-03] - $79.95 : A & A Corvette Performance, Your C5, C6 and Z06 Corvette Supercharger Specialists

The intent of that pinning jig is to fix the balancer to the crank in a supercharged application. Once drilled, the pin is installed and the bolt is put back in a torqued.

 

I didn't consider that, I had reused the old bolt.

pinning might be a easier alternative to keying, I'll have to look into that kit more. I'm not sure if the press fit loctite will help if the bore is damaged, but I might use it anyway, I think my work has some for pressing bearings.

 

Read page 30 of the assembly section. It states the bolt should not be reused. I have reused once but not more than that.

http://www.jagrepair.com/images/Auto...Code%20168.pdf

 

I had assumed that was because they didn't want you to just reapply loctite to the old bolt, not that the old bolt had deformed. In any case, just ordered up a new bolt from Terry's, since no matter what else I end up doing I should just put a new bolt in.

 

I'd take a real close look at that balancer surface where the cone contacts it. If it had come loose prior to you owning the car, I'd be suspect that the cone can't properly wedge itself into the balancer if the surface has been scored. If I were you in that position, I'd change all 3 components. New bolt, cone and find a good used pulley.

 

Crank pulleys are surprisingly hard to find for the XJR 4.0L, still kicking myself for not pulling the one off the junkyard XJR from months ago. Of course I could get a pulley off a 4.2 and then roll the dice for it contacting the timing cover, and get the 6 rib belt to fit it, and hope that works...

I got the pulley off today and it does not look good. Severe scoring on the locking collet, heat discoloration, and so on... It looks like the collet was only engaged at the inside towards the timing cogs, since that's where most of the scoring on the inside of the collet is.

The end of the crankshaft has a slight taper to it, maybe someone who happens to have an easily accessible engine can tell me if my readings are correct? I measured as best I could and got 1.458 at the widest point near the timing cogs, and 1.407 at the narrowest point towards the end. I have a feeling that taper may be the cause of my problems...

A few pictures to get an idea of the damage:

the camera makes it look less conical, it's a cone as it should be


not what I wanted to see

 

Damn.....that sucks!!

I don't know what your skills are but, you may want to pull the front cover off, grind the crank for a woodruff key, grind a groove in a new cone and in your current balancer and see where that leads you. That or JB weld between the cone and balancer and between the crank and cone.

 

I have 2 4.0 S/C engines, both with dropped valve seats. One has the balancer off so I can get readings for the end of the crank. I'm going to rebuild one of them so I will have an extra balancer. Let me check on the balancers condition in the morning and get your readings for the crank.

 

Sounds good, keep me posted!

I've never cut a keyway before but that was the first idea I had to fix this. With a dremel and a steady hand I think I could make it work. Cutting a square keyway inside the pulley bore may be the trickiest part, probably just means lots of filing. The pulley's probably worst off out of all of the parts, about 1/4 of the o ring groove is ground off, along with lots of other damage.

I looked at the old locking cone and saw some epoxy or something towards the front on the inside of it. I'd thought it was just dried oil or gunk before but it may have been jb weld or similar that the PO's shop used to "fix" the pulley.

 

Measured the end of the crank and I get 1.468" and it is the same front to back. So it looks like you have .06" wear at the front and .01" at the rear. From what I can tell the balancer I have looks good and I have a locking cone for it.
It looks to me by the design the the bolt only rest on the locking cone. So if there is clearance before the bolt rest on the end of the crank the cone should be able to go in deeper into the balancer and hold the balancer. The main concern I have is that is the crank worn evenly? If not it may cause a wobble even if you put a key in it.

I think what I would try is use my balancer and cone and then install it using the old bolt. Remove the bolt and see if it is tight and how the cone looks in the balancer. If all looks good put the new bolt in.

 

Pm sent.

I don't think it's worn unevenly, but I can't know until I put a pulley on. Even if there is a tiny bit of wobble I might just go with it, not really motivated yet to turn the crank to true by using the starter motor. Although I guess I could measure runout since I have that tool...

I was also thinking about filing a bit of the gap out of the collet so it can close to a smaller diameter and grip the surface; when I remove the pulley, the collet is always compressed as much as possible - if that makes sense. The big thing there would be making sure the bolt still compresses it properly, and the collet doesn't "sink" past the pulley outer face when tight.