I am currently swapping the timing chains & tensioners on my X308, 3.2L, 1999.
I will write about that when I have finished.
While I was happily removing parts, two bolts along the way were suddenly not that happy anymore:
They broke off. And this kind of never happens to me - last time about 17 years ago...

First a disclaimer: I am showing here just what I did to save my day. If you decide to be inspired, don't hold me liable for any injury or damage this could potentially result in. Esp.: I am drilling into my engine block (to get the stuck thread out) - obviously, if you do that wrong, this could render your engine useless...

So while I am showing here what I did "to fix the momentary damage" caused by two very different bolts, which broke off, this concept would apply to all broken off bolts...


This special bolt - as you can see - broke off. I was definitely NOT applying excessive force - just normal force via ratchet to get it out. This special bolt can be found behind the timing front cover and it was holding one of the broken guides of the timing chain. This bolt should not have broken! (I read later that this bolt is fixed with loctite, but still...)


This is the remaining, broken off, part of that bolt. I reckon the bolt is mild steel - and the engine block is aluminium. That is quite a challenge!


In preparation of the drilling ahead I protected the engine from the upcoming shower of metal filings (when drilling) with soft cardboard and a huge magnet (to catch the mild steel filings).


Below: I caught quite a few filings. Above: Hole drilled already and screw extractor inserted...: I drilled into the broken off bolt extremely carefully: I used new HSS Co drill bits. Starting with 2mm, then 3.2mm, 4mm, 4.5, 5. That's the way to do it, otherwise you will never be able to drill right in the centre, if you start with a big drill from the beginning. Since I knew the length of the bit stuck in there (by comparing with the bolt from the other side (which I got out), I used a paint-marker on my drill bit so that I knew, when I would get to the end of the bolt (making sure I would not continue on drilling into the engine behind). I also knew (by checking out the hole behind the other bolt, which did come off) that I had a little bit of "spare room" behind it left. So I drilled my holes all the way thru the broken off bit. And I permanently applied "drill oil" (well, I did not have any, but I used transmission fluid (Lifeguard 6, not that that matters) and that worked great as drill oil. Plus, I applied WD40, and even let WD40 soak in from behind over night... Nothing! I used various bolt-extractors, but it would not budge.


But it was unbelievable: The extractors of all sizes starting from very small and getting bigger (with the bigger hole sizes) all had a very good grip, but the bolt-remains no movement. I did not want to break the extractors in that hole. Initially I thought I would not drill bigger than 5mm, but it was not use: I had to go on to 5.5mm, 6mm, 6.5mm and even 7mm. It is obviously very important (and difficult at the same time) to hold the drill ABSOLUTELY straight. Else, I would drill into the the threaded part of the engine block. So the bolt to be removed is 8mm (1.25mm pitch), so 7mm was the absolute max. drill sizes I could dare to use...


So it was time for a different tactic now... and at the end of the day, even though that bolt-remainder would not come out in the shape of the bolt, I prevailed anyway, as I removed it in the shape of 1.000-10.000 particles without damaging the threaded part of the engine block. Those 2 half-rings were the biggest parts left form that bolt bit: It was the outer thread of the bolt.


With my tab (thread cutter) size 8mm pitch 1.25 I cut a beautiful & useable thread into the engine block.
PS: I should add: This was not a straight forward job. First I removed a little bit more material with a 7mm (M7) / pitch 1 tab - very carefully, as that is the wrong pitch, but the M8 tab did not want to go in yet. And then with the M8 tab it was a permanent in and out, cleaning off the particles off the tab and out of the hole permanently with an air-gun (compressed air) and applying oil all the time...


Next problem: Without paying an arm and a leg (and waiting for ages for it to arrive in the mail), such a bolt cannot be procured. But see what I did: I "reused" the broken off old bolt by drilling all the way thru (using a drill in a stand and HSS Co drill bits, starting with small drill bits and using bigger ones thereafter. The result was perfect - I managed to drill right bang thru the centre...


I bought a 8mm x 40mm shouldered hex bolt. I then reduced the thickness of the old hex-head (sleece) to precisely get the same length of thread lurking out as it was before. On the right: I put those 2 parts together and glued them together with high temperature silicone.


On the next day I figured that I could actually make a special bolt instead, which is BETTER THAN ORIGINAL, because the hole it goes into in the engine happens to allow for a bit of extra length: I checked: 5mm longer is good. That way I can use even part of the old unused thread, which is utterly intact even after removing the stuck bit. So I removed the 8mm x 40mm bolt from the "sleeve" and replaced it with a 8mm x 45mm bolt - i.e. now I have a special bolt, which is 5mm longer than original. Actually, take a look the the original bolt: they made it extra thin (that was were it broke off...)


And this is the other broken off bolt I had to deal with: The belt tensioner is marketed as non fixable replacement part. Obviously the bearing of the idler puller on it needs to be replaced. The cost for that complete tensioner are horrendous. I was "hammering" that bolt of the pulley with an air-ratchet... - until it broke off - and only then I saw the trap Jaguar planted there: That was a left-handed bolt!!! What the ...!? The things they do to sell the complete tensioner! Anyway, as you can see above I drilled a hole (starting again with a small hole) and always using ATF as cutting oil and using a drill in a stand and then I inserted a bolt extractor: The tricky thing: The bolt is a left handed bolt! Thus, coming from the front (where is broke off) would not work, as the bolt extractor would go the wrong way round. Thus I used the bolt extractor from the other end of the bolt - doing it that way, the bolt-extractor turns it in the correct direction to get if out - and it did!


I was soooo lucky to find a left handed bolt! They did not have any left handed bolds in our local shop, where they sell bolts, screws and nuts only. But: the lawn-mower shop did have one. About 5mm shorter, though, and I also had to place a properly sized washer there as well to fixate the inner part of the bearing.


But not to worry: 5mm shorter sounds a lot, but it is not that bad, because even the new bolt used nearly all the thread available (further out there was no more thread). Plus, I used the red loctite). Nevertheless, I went over the top, and I drilled a little hole into the new bolt and added another little screw from the other side. And used loctite again.


All good again. I found a new metal idler pulley with bearing, replacing the crappy original plastic pulley (where bearings cannot be swapped). And funny: Hard to see, but the new black pulley is made in Canada (hard to see, printed on the right)...: Which is a perfect match with the rest of the tensioner (see picture above...).

 

Nicely done.

 

Great job! 👏

Check out this drill guide and tap guide set. A little pricy but, when you need to drill and tap straight, it’s worth its weight in gold in my opinion.
https://www.shop.biggatortools.com/C...TMETRICSET.htm

 

There was quite a bit of fortitude required to get through the glitches,
You should be proud of what you accomplished!

 

Thanks all for your comments.
@ ...boost: That gadget to drill straight is a nice idea. But I would not be buying it: Too expensive as you say, plus, it would have been a massive coincidence if I would have been able to use it as it is on the engine block (the only place, where is would have been of use (as I did the rest in a vise on a drill-stand)). Because I would need to use one or better two other threads in the engine block to fix the "tool" with, via bolts, to position the guiding "long-hole" precisely over the broken off bit. And those fixing holes need to be exactly where the threads are... But it would be an idea to start with an aluminum block and design a one-off tool for this exact purpose.

Something else: When I wanted to drill with upmost caution (like with the 6.5mm and 7mm drill bit in the 8mm broken of bit) I even drilled the wrong way round - it takes longer, but works as well. And I think it is takes off a fraction less material off the sides...