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Sheared rocker cover bolt

Chadlebowski

Cruisin' Guzzisti
Joined
Jul 28, 2015
Messages
149
Location
West Sussex; UK
Hi,

Just had a rocker cover bolt shear off, about 2mm down from the bolt head. It snapped as if it was made of butter and I was hardly applying any pressure!

What can I do? Obviously the engine can't be run, and the "SPECIAL SCREW" (as listed in the parts manual) buried in the rocker arm support is so small that using a screw extractor would need a lot of finesse (assuming I could even get the right size).

And surely I don't want to risk re-tapping the rocker support?

Anyone had this problem before? Anyone recommend a DIY solution? TA! 20170826 1424117271
 
Ok - I like the custom machined replacements, but my bank balance doesn't allow it sadly. I will get some LH drill bits.
If the bolt is an M6 what size reverse drill bit should I use?
Also, because of how the bolt snapped, there's a raised profile that will make centre-punching quite difficult. Does that matter?
Plus I'm fairly confident I can do this right if I get the correct tools and take my time, but should the reverse drilling fail, won't I be further up the creek without a paddle?
 
If you don't have a flat surface, make one with a hand file. And again, be sure to cover everything to prevent metal filing going where they shouldn't.
 
Unfortunately, the broken bolt is half turned in, and sitting below the top of the rocker cover.
I'm going to try a well-placed centrepunch, and then work up through drill sizes.
Will definitely plug every possible space, and drill as little as needed.
 
I had one do the exact same thing and because of the uneven break, I was able to back it out with a small flat blade screwdriver and a bit of patience.
 
Unfortunately, the broken bolt is half turned in, and sitting below the top of the rocker cover.
I'm going to try a well-placed centrepunch, and then work up through drill sizes.
Will definitely plug every possible space, and drill as little as needed.

Perhaps try a small stone on a dremel tool?
 
Success! Thanks for the advice.
1mm drill bit: too small for my drill.
2mm drill bit: snapped instantly.
2mm LH drill bit: started well, then snapped. I kept using it to get the pilot hole.
3mm LH drill bit: pulse pulse pulse BITE bolt turned till flush with top of rocker, then stopped.
Repeat, deeper pilot hole, back to the 3mm LH bit. Nothing.
Panic.
Switched to a flathead screwdriver, and directional taps with a hammer. 1/4 turns a pop. Slowly but surely.
Wider flathead screwdriver into the drilled hole - turning freely now.
Managed to grip the bugger with my thumb and forefinger, and unscrew the last few turns by hands.
Longest valve-clearance adjustment ever.
 
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