So I just removed the rocker covers from my 1998 convertible to examine the tensioners and cure a few oil leaks. Former Jaguar specialist car dealer serviced from new, 115000 miles stamped right up to date by a local indy specialist. Uh huh, 5 bolts snapped off. Tightened up by King Kong himself. I discovered a fairly easy way to remove the offending bolts without too much trauma. Leave the rocker covers in place, gently re tighten the bolts which haven't snapped, then remove the bolt heads spacers and O rings from those that have. With the spacers out, there's plenty of room to center punch and drill the snapped threads with a 3mm drill, just 1 or 2 mm deep then hammer a small Torx into the hole, the threads unscrew quite easily as they're no longer under stress, use a small magnet to remove the swarf before removing the rocker covers.. I'm lucky as I have a motorcycle business which yielded plenty of the right kind of bolts for replacement. You have to punch the snapped bolts out of the spacers using a suitable drift, but if you've come this far, that shouldn't be a problem.

Thanks for the tip.
Torque figure for these bolts is 9-11 Nm - so not requiring a breaker bar to fit LOL.

Note that the rear uppermost bolt (the one that isn't captive in the spacer) is 'special' due to its proximity to the cam position sensor and should be replaced with the same type.

Thanks! I'm going swap a leaking gasket this weekend and will keep this in mind.

You've had more bolts snap on this job than all the rest of the membership put together.

https://www.jaguarforums.com/forum/x...ailure-182767/

A regular reported issue is oil leaks from cracked covers where the bolts have been overtightened. Once the tension is off the cracks close up and can be very difficult to spot.

Graham

This was all on the same job! 5 in total it was. I couldn't believe how tight they'd been hurned up to. As someone else pointed out, the bolts can only tighten as far as the spacer/bushes allow, so hurning them up beyond 11Nm is pointless, if the gasket leaks, a new gasket is required, or at least the sparing application of some silicone as an emergency measure.

I should point out the reason I never use stud extractors is because they have a nasty tendency for the tip to snap off, leaving further access blocked by case hardened steel, the only option then is to weld to them. (messy)

'the reason I never use stud extractors is because they have a nasty tendency for the tip to snap off'
You need to bin the cheap ones, (ebay, toolstation, etc.,) and buy a good make. The cheap ones are too hard , you need a bit of give in a stud extractor, I have a Dormer set that have never broken on me, they make dam good drills to.

I had a Dormer set too, and Britool, and a plethora of other good makes. The smaller sizes invariably snapped off the tips. I work on bikes and the common bolt to snap is a 6mm blind stud with minimal depth into the head (Exhaust manifold) In the old days, I would use stud extractors, now I tend to go straight into welding a nut over the broken stud.
Why I recommend the Torx bits for this job is because the studs are generally not seized in, just overtightened (At least, all mine were) and the torx bit cuts into the stud, rather than expanding it. If stud extractors are working for you then that's the way to go (They are the correct tool after all) but I've had too many negative results which have left a hard plug in the stud leaving welding the only option.