What do we think is causing this? Is the bore not the correct size? is grinding the threads pretty much mandatory for these to work?

 

It depends on the wheels, nearly all have voids in the back between the lug holes and some are deep enough and wide enough for the studs to fit without touching/fouling but some are not.
F-Type 20" wheels are a good example, only one OEM 20" wheel works without fouling on 15 mm or thinner spacers and that is the Blade wheel which luckily for me is what I have, with all the others the studs have to be shaved/trimmed/cut by some 4 mm.
Heaps of F-Type owners have done exactly that with no problems as the 4 mm or so which needs to come off is simply most of the blank/unthreaded bit on the end of the stud (which you have circled in red).
Edit - whoops, missed the second part of your question, the gap between the face of the hub and the back of the spacer.
There definitely should not be any gap, the spacer must sit flush and tight to the hub.
Are you sure the spacer is sitting the right way up?
If it is then it seems the stud holes in the spacer are not wide enough and a little reaming is needed, or else the spacers are simply the wrong ones for an XK150.
Either that or as you suggest the spacer hub is caught up on the bore because the bore hole is too small.

 

Bore on the backside of the spacer is too small. Ditto the comment on the poke through of the original studs, to shave or not to shave, will depend on the wheels. Sentas will require the shave with a 15mm spacer. Fit ok with a 20mm spacer.

 

I am going 20mm front 25mm rear ^.^

Thank you! I got an angle grinder with some sort of grinding pad today in the instance I needed to use it. Sounds like if I am above 15mm then I may be good with the sentas.
Can't the spacers only sit 1 way? With the studs pointed out away from the hub?
Either way, sounds like a bore job - will need to figure out what kind of tool could ream something like that.

 

That’s correct, and your earlier photo has the centering ring correctly oriented.
I’m surprised that the backside of the spacer isn’t fitting the centering ring of your hub.
Do the spacers fit each other, i.e. nest together smoothly?
Do the spacers fit the wheels correctly?
Are the spacers returnable? (Find some that don’t require modification to fit.)

 

Yep, 20 mm and wider spacers should be plenty so that the studs clear the backs of the wheels and no cutting or grinding is needed.
And yes the spacers can only fit one way with the hub ring facing out, and I can see the hub ring in your pic is facing the right way.
The centre bore for all modern Jags is 63.4 mm so it looks like you got spacers with a slightly smaller centre bore, maybe send them back in exchange for the correct ones?
I would be very wary about reaming out the existing spacers as the centre bore needs to be not just the exact right size but also perfectly round so that it fits nice and tight around the existing hub ring with little or no slop.

 

Update - was able to spend a massive portion of today outside getting a new passenger fender installed. Finnnnnaallllyyyy found one with my paint code, PEF, on eBay.
So the picture of the spacer on the hub+bearing - the whole reason this post exists - was missing something I didn't think about. Rotor! The rotor is not on the hub lol - there was always going to be a gap. Spacers line up with the hub flush + the Sentas. Have some other kinks to work out as there are some new moans and groans that were not there before the spacers. I believe this is just an exaggeratio of suspension issues that already exist. https://www.jaguarforums.com/forum/x...eering-288576/ to be exact.
Thank you all!

 

rotors. Ok, if that was a quiz, we failed.

 

Yep, total fail!
We should also have noticed that the pictured spacer looks way wider than 15 mm, it's gotta be at least 20 mm if not 25 mm, and therefore the studs should not be sticking out at all!

 

Just to add, F-Type propellers on my 2007 XK did not require grinding with 15MM spacers

 

FWIW, you are significantly adding to the scrub radius... fine for looks. Not so fine for a real driver.
https://www.wheel-size.com/calc/

Cheers!

 

Looks might be more important than how a car drives for some of us.
Most people don't seem to notice that the car doesn't handle as well and as easily as it did as designed.
I have made the mistake of buying wheels with the wrong offsets and they never improved the way the car drove but did make the car look more aggressive. I guess it depends on the compromises you want to make.

 

There will also be added force to the wheel bearing, so that bearing will wear faster. Not a lot, but it still will.

 

If spacers are a good idea, why don't manufacturers or dealers offer them as accessories?

Simply put, dealers don't want the potential liability. Spacers change the geometry of the suspension design specified by the engineering department for proper functioning for the intended market. For most of the X150 models, it's a quiet, comfortable grand touring ride, and not a bone-jarring sports car that can be driven to the track. For customers who want a "wider stance," manufacturers offer factory wheel upgrades with the correct offset, as these have been tested to work with the vehicle's geometry. If you add spacers, you probably will void your factory warranty. But that's a moot point because all X150 models are too old to still be under warranty.