I added this question to closing after surgery but maybe having its own thread would be a better choice.
I've twice broken the vvt cam sprocket bolt on reassembly after replacing timing chains and tensioner on my 2000 xj8. The one that is hollow to allow the passage of oil.
It's my understanding that all 4 cam sprocket bolts should be torqued to 112 to 125 nm. After the first time I purchased a new torque wrench and had the same result, at the same location after achieving only about 70% of required torque. Any ideas my jaguar family?

 

112 to 125nm is 80/90 lb-ft

That is a lot of torque, what is the bolt size?
This type of torque would be expected for a 1/2" or 13mm bolt and not hollow

 

I thought it was a lot of torque also. I double checked the manual and you are correct for the 112-125 NM's. Generally when a bolt snaps it is because it is bottomed out and the threads are not receiving the torque but the body is. I snapped a tensioner bolt before realizing the upgraded tensioners needed shorter bolts.
I would check for any debris in the bolt hole or any damage. I would also double check the fit up of the sprockets.

 

I think Vern nailed it: you are using the original bolts, instead of the shorter replacements?

 

Shorter bolts for the vvt cam sprocket? I checked the sng barratt catalog and there is a difference in length at engine# 0108130000.

 

These are not the tensioner bolts that come with the new tensioners, I'm talking about the cam sprocket bolts. They torque the 4 sprockets, that have a tapered lock down, i.e., no key way. The original broke while trying to achieve recommended torque, and subsequently a new one also broke.
The threads are fine and the bolt doesn't bottom out, making the broken half remaining in the end of the cam easily turned out.

 

And yes I realize that the exhaust cams have longer bolts and are solid as well where as the intake cam bolts are hollow and approximately 1" shorter.
But as I read the manual they all require the same torque.

 

my original question remain, what is the size (diameter) of the bolt?
Logic will dictate that if they dont bottom out and even new one snap, something is wrong with the torque load, henceforth my question regarding size

 

The bolt is 1 1/2" long and the diameter is 15/32". This is for the vvt sprocket.

 

OK, that is a 12mm bolt and torque is correct for that size ( see chart below)
so, the only "difference is that the bolt is hollow and torque "should" be less than for a solid bolt.
For example a 12mm hollow bolt on motorcyle for oil line is about 30 lb-ft
It will stand to reason that if the hole is about 30% of the diameter of the bolt, it should be treated like an 8mm bolt
if that was my car, I would torque it to 40/45 lb-ft and use some blue locktite for added safety
No way than an hollow bolt can be torqued as much than a plain one

Metric Bolts
Maximum Torque, in foot-pounds, for clean, dry threads
Check your Shop Manual !

Bolt size Low Grade Grade 8.8 Grade 10.9 Grade 12.9
6mm 3-5 7 10 12
8mm 8-12 17 24 29
10mm 15-22 33 47 57
12mm 39 59 83 100
14mm 60 101 131 158
16mm 60-94 146 202 247
18mm 60-130 201 283 340
20mm 166-188 285 401 482

 

That is a completely logical view and gives me great confidence going forward. But my only concern would be if their parameters were incorrectly stated in the Jaguar work shop manual, what else may be incorrect.
It always comes back to logic.Thanks for taking the time and getting me down out of the tree.

 

Has the torque wrench been calibrated?

More that a few people have done the VVT sprockets
and mentions of the bolt snapping don't come to mind.

Another possiblity is a bad batch of bolts in the supply
chain.

 

It never made complete sense to apply the same torque to a solid bolt as well as the hollow one. Today I closed up the front of the motor having applied approximately 2/3 of the stated torque of 112to125nm. It didn't break and that makes me feel pretty good.

 

So having fully reassembled my xj8 after timing chains and tensioner replacement I was encouraged when it seemed to start and run if only for a few seconds.
The obd reads MAF VAF Faults. Could this result in a no start situation?

 

Dumb question here...Is the air flow sensor connector fully seated onto the sensor? Check where the wires go into the backside of the connector. Are there any wires that look a little flimsy? There could be an internally broken wire but the insulation appears ok.