Cylinder Head Guard Bolts

I did think you made a good point. However I've done this twice and in both my cases came out with a great fix that was stronger.

FYI... my chart says 4.77 (which I thought seemed tight)

and yes I did see the original pics.... and the thread was mostly gone for half its depth, which to me it looks like the guards come with a spacer and thus ought to get new longer bolts (including the length of the spacer, plus the thickness of the guard). But, and I think I've seen this before (see bold in a minute) thus only half the thread depth it should have had was holding it together. Likely the reason it got stuffed. So either BM are animals and don't supply the longer bolts, the guy fitting didn't use them, or worse still forced longer ones in somewhere else...

Mistacat said:

Look at the photo on #1 and you can see that it has pulled the threads. = 6mm.
The original hole before being tapped would be 5.1mm not 4.7mm. At 4.7mm you would stand every chance of breaking the tap in the hole, another of my pet hates removing broken taps.

Click to expand...

I love people bringing me broken taps and easy outs in components... lots of easy money .... well it would be if I actually charged for it....

Solid carbide drills and taps are a bit more difficult to get out.. but I have a way..

And as for drilling out for Helicoils, easy if you can get the part on a mill, bit more tricky by hand..very easy for the drill to ‘snatch ‘ and screw itself in to the hole .... and then snap..
I have found grinding the cutting edge flat helps to avoid that scenario..I also have collars that fit on drills to avoid drilling too deep..

Over the years I have fitted thousands of helicoils ( only use genuine helicoil) in all sorts of material... never had an issue with them..