Crankcase Bolt's Threaded Boss Cracked

[DaveBrit]

Further to my "Splitting Crankcase Halves and Bolt Identification" issues, I am now faced with another problem and I'm hoping the collective forum's wisdom can help.  One of the threaded bosses that accepts the crankcase bolts (number 27 in the diagram below) has burst, I suspect by hydraulic action on a previous tightening.  As you can see from the photos, the bolt's location forms a pinch around one of the main gear shaft bearings.  Here are some of the solutions with which I can get around this problem and I'm hoping that someone with better knowledge than I can comment whether these ideas are any good or really bad:

1. Do nothing and just use the remaining parts of the threaded hole to take the bolt and torque up to the stated 12 Nm (8.7 ft lbs)
2. Insert a helicoil for the M6 bolt and then just tighten up to specified torque
3. Weld up the boss, and then drill and tap so that it accepts the M6 bolt
4. Get new crankcase (definitely don't want to do that one!)

(In the photos the small black mark on the right of the broken boss is a small piece of RTV sealant, not a crack)

Photo 1:




Diagram of crankcase bolts (courtesy Haynes), It's Bolt #27:




Photo 2:




Thanks for any help you can offer - David

[racerrad8]

1. Do nothing and just use the remaining parts of the threaded hole to take the bolt and torque up to the stated 12 Nm (8.7 ft lbs)

Diagram of crankcase bolts (courtesy Haynes), It's Bolt #27:



Thanks for any help you can offer - David

David,

1)  Two thumbs up - Option #1, you have 36 more bolts holding that case together, it really is not going to miss that one.
2)  Two thumbs down - I doubt you will have enough material to install a Heli-Coil.
3)  Two thumbs down - You could weld and tap, but you risk the chance of warping the case surface.
4)  Two more thumbs down, not needed.

If you look at the bolts, that is just a case bolt and does not effect the transmission. The input shaft of the transmission, which that bolt is close to is secured by bolts 18-22 from the lower case.

When you build the bottom end together, I use "Ultra Black" Permantex silicone. A nice thin coat works well, comes apart easily and can fill any voids you might have in the case surface.

Randy - RPM

[DaveBrit]

Thanks Randy, I was hoping option 1 was going to be the suggestion but wasn't confident enough with the decision without some additional corroboration from the wise and learned!