Good grief ... that's a factor of 12 times too high. I would have thought that it would be very obvious that a bolt which should be tightened to 10 lbs ft could not possibly be tightened to 120 lbs ft. However, I'm probably being unfair as stuff is much easier when you have experience.

Richard

 

I have a broken bolt in my valve cover thanks to leaving my torque wrench on the wrong setting from doing a different bolt - a whole 2nm over spec was enough to break a bolt. Thankfully its at the top, not the bottom, and hasn't leaked a drop so I've left it alone as a problem for another day. No nice/easy answers to that one.

 

Well the bolt is going to sheer long before it gets to the 12x torque value dialed in on the wrench, so it really isn't going to be obvious the setting is wrong, until it is too late. I think you would have to be quite experienced with tightening whatever hollow bolts the OP was tightening to know from feel alone that there is something wrong. Anyway, by the fourth bolt the OP had in fact gained enough experience to know not to overtighten it, which is the nature of learning. Even with the trouble they will now have to go to to extract the broken bolts, it's will still represent a good $$$ saving on going to a professional mechanic in the first place, who would probably just have broken something else and charged the customer $150 an hour for the privilege.

 

Guess we’ll say the bolt has a hole through it instead of hollow. Holds your intake, and exhaust sprockets.

Hole through it.

I sheared the bolt in the main sprocket

 

OP, thanks for letting us know what happened, snapping bolts is a constant fear. I've done a few in my time and it is such an awful feeling when the torque wrench suddenly becomes easy to turn and it sinks in what just happened and how much extra work it will be to fix.

You're deeper into your engine than probably 97% of any Jaguar owner ever goes, using a torque wrench was the right step, and you aren't the only one to have experienced a conversion error, see: https://science.nasa.gov/mission/mars-climate-orbiter/. At least the tuition you just paid on this is relatively cheap; it'll only cost you a few days and ~$40 to fix, rather than $327M, 9 months, and the opportunity cost of a failed NASA Mars mission.

Finally, on the upside, a hollow bolt should be trivial to extract. Hopefully your unrestrained cam didn't rotate or do any valve damage from valve spring pressure pushing the valves into piston tops. I believe this is an interference engine.

Let me give you a lesson I learned... I _never_ work on an open engine case like shown in your pic without the space just below where I'm working tightly stuffed filled [edited for our Oz members] with a single large towel to keep stray sockets, broken bolts, or other hard things falling deep into the bottom of the lower timing mechanism. I learned the hard way on an XK engine that dropping even a tiny metal part down there can mean a lot of extra/unnecessary work dropping the front subframe and the oil pan to retrieve the dropped part. And if you use multiple rags, you have to keep count and be sure you get them all out.

The hollow bolt will mean any "mechanic's feel" you might have is mostly negated by the lower fail point.

I found ZAMM to be highly formative for me and really like its description of "mechanic's feel" (there's lots of free pdf copies out there: https://www.google.com/search?q=zen+and+the+art+of+motorcycle+maintenance +type:pdf )

From pg 332: "There's what's called ``mechanic's feel,'' which is very obvious to those who know what it is, but hard to describe to those who don't; and when you see someone working on a machine who doesn't have it, you tend to suffer with the machine.

The mechanic's feel comes from a deep inner kinesthetic feeling for the elasticity of materials. Some materials, like ceramics, have very little, so that when you thread a porcelain fitting you're very careful not to apply great pressures. Other materials, like steel, have tremendous elasticity, more than rubber, but in a range in which, unless you're working with large mechanical forces, the elasticity isn't apparent.

With nuts and bolts you're in the range of large mechanical forces and you should understand that within these ranges metals are elastic. When you take up a nut there's a point called ``finger-tight'' where there's contact but no takeup of elasticity. Then there's ``snug,'' in which the easy surface elasticity is taken up. Then there's a range called ``tight,'' in which all the elasticity is taken up. The force required to reach these three points is different for each size of nut and bolt, and different for lubricated bolts and for locknuts. The forces are different for steel and cast iron and brass and aluminum and plastics and ceramics. But a person with mechanic's feel knows when something's tight and stops. A person without it goes right on past and strips the threads or breaks the assembly...."

Best of luck recovering from this and keep us apprised of your progress.

 

+1 to cramming old towels in the engine bay just below the area you happen to be working in. That can easily save you hours of searching for those tiny bits you just dropped down into the bottomless pit of engine bay hell....

 

Please find and read all the TSBs for your car.
Gus has them on his site.
Jaguar spent time to publish all these documents.

 

Actually, there is . . . because you have the mating bodies of head and cam cover. If the sheer point is at or below the bolt head, it may protrude far enough to slot it and use good ole screwdriver to remove, or perhaps even far enough ti use vice-grip pliers. Alternatively, the sight of a bolt that has sheered at or below its threaded hole is still fixable, although the nature of the cam cover materials demand extra care . . . and a mate handy with a lathe!

For that fix, you need a few special bits of kit, all fairly easily obtained . . .and follow this process . . .

1. turn down brass rod to diameter of firm fit inside the cam cover hole; then counter drill (on centre) a smaller diameter drill hole (say 3mm);
2. purchase left handed drill bits of diameter matched to bush inner hole; and another matched to just less than shaft of sheered bolt;
3. then mount smaller bit in a drill set to reverse (ccw rotation);
4. with bushed cam cover back in place and using drill lubricant, carefully drill an on-centre hole (ccw) down into sheered bolt;
5. remove cover, change to larger ccw bit and drill to larger diameter just shy of the bolt's shaft;
6. using EziOut to match this larger diameter hole down centre of sheered bolt, turn (again ccw) to ease out the bolt from undamaged threads.

Perhaps even more importantly, but imperative in any event that requires removing a cam cover, the first priority must be to cover the open area to prevent swarf entering the guts of all that goes "whizz" inside. There can't be anything worse than a fix that creates more problems than it solves.

Cheers,

 

There are 100’s of once promising forums no longer viable by result of failing to establish just such rules/guidelines.