Z1OwnersClub GB

I'm hoping I haven't managed to create the mother of all f**kups whilst rebuilding my Z1-B engine. Last engine cover to go on over clutch release pushrod et al, and I found I couldn't engage the thread on the lower left 125mm bolt which was about 12mm proud of the cover (see pic). On shining a light inside the aperture I found what appeared to be a blind about 13mm inside but no thread (couple of poor pics attached)! Have I somehow managed to screw a bolt from the inside of the crankcase, although if this were true then it means there would be an oil path though to the outer cover. It's got me totally flummoxed. Has anyone got any suggestions before I rip the whole bloody thing apart again?

Looks to me like a previous bolt has sheared off inside the thread.

Sorry

Gus

I think I've just twigged! Having just searched my box of old bolts I found this (pictured alongside an original intact 125mm bolt). So would the "blind" I found be the remains of the original 125mm bolt that snapped on the way out? If this is the most likely explanation, any suggestions as to the least damaging way of getting it out, remembering that it has been in there since the bike was built?

Thanks Gus, you're probably correct. I didn't see your reply before I posted my update. But would still appreciate any advice on getting the 12mm of old crap out.

The remains of the bolt will be "soft" and should drill with a normal HHS bit.
The easiest way if you haven't a steady hand is to get a 6 mm OD shank center drill.
These usually have a 2 mm cutting tip.
Use the location dowel ( which is also 6 mm ID ) as a guide and you will be able to get a dead center pilot hole up the broken portion and then work up in size to 5mm.
This should just leave the threads to fish out or run an M6 tap down to clear them.

Many thanks for that Rob. Will try that tomorrow although there's not a huge amount of working area to swing a tap.

Also go with left handed drill bits, you may be lucky and have it back out.

I've also had good results by drilling a hole in the sheared bolt that's a bit smaller than a suitably sized torx bit, applying a short blast of heat to the ally casing to heat it up quick, whacking the torx bit into the hole quick sharp, then turning it anti clockwise. If you're lucky it'll pull the sheared bolt out complete without damaging the thread. Don't use one of those torx bits with a hole down the middle as they aren't very strong.

Don't even think of using an easy out. They are the devils work.

Olly

A Bahco stud extractor should work well here, they come in a set.
Regards
Steve

Thanks for all the help guys. Had a bit of a result with this as you can see from the pic. Followed Rob's advice and used a 6mm bit to create a pilot then a DeWalt 2.75mm HSS bit (although they call it a "No. 8" for reasons known only to them). As the bit was almost breaking through the orphaned bolt I had to run it slowly counter-clockwise to pull out and the pic shows the result! Brilliant. Just had to retap the thread and the new bolt went in by hand. This was the last major rebuild issue before re-fitting the carbs and pipes and so I'm pretty happy.

Again, thanks for all the input guys. Definitely would have been a lot harder without your kind words.

Well done that man, always a great relief to get broken bolts like that out without causing any more damage or having to take it to an engineering place !!
Glad you got it sorted

There is something very satisfying looking at your pic, knowing how relieved you must have felt when it came free.

Great job, well done.

Very satisfying to see that come out in one piece.

When HD built my Sportster, they managed to save several cents by putting in every steel screw into alloy casings absolutely bone dry. When I had to strip the engine after a crank pin surface turned to glitter, I found that ten years of British weather and road salt had seized many screws, particularly in the chain case. They either snapped or had to be drilled out. I was introduced to a mobile guy known as ‘the stud man’ (yes, he could have been a gigolo) who removed broken fasteners and put in helicoils, if needed. He got rather sick of the sight of my bike.