Snapped fork pinch bolt

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beckh · #1 Post by **beckh** » Thu May 24, 2007 8:04 pm

I dont believe it ! Got back from Le Mans, Take out front wheel for new tyre fitting, sheared a bleedin' pinch bolt in half

Get an extractor on it (threaded rear section) and lose the diamond drill bit (snapped). Go in from the front and end up coming out off centre and fekkin the fork bottom up. Upshot is, I think I need either a new fork bottom (whats the official name for it ?), a new fork or set of forks. I got a suitably hard bolt,nut and nylock locknut on it with thread lock. 22nm torque as manual, but I reckon the plum who torqued it before I got it must have maxed it out. There is fatigue in the middle of the bolt, like it had been twisted

Can anyone help with advice or parts ? Bike was quality again in France, 760 miles 2-up, didnt miss a beat.Only saw 1 other Falco all weekend and that was a UK one, black/bronze, leaving the track about 5.30 Sunday. Was that anyone here ?

Falken · #2 Post by **Falken** » Thu May 24, 2007 8:20 pm

Had a similar problem but managed to drill it out ok and re-tap the thread.
It is a re-action between the alloy and the steel, that causes it to sieze together.

If you can get the leg of, get it to a machine shop who should be able to drill it out.
If not look at spark erosion. This should be cheaper than a new fork leg
Plenty of grease stops it siezing.
Alos the front mudguard bolts do the same.

Pierre · #3 Post by **Pierre** » Thu May 24, 2007 10:20 pm

http://cgi.ebay.co.uk/APRILIA-RSV-MILLE ... dZViewItem

£95 buy-it-now inc delivery. Dam BARGAIN. 1 mudguard hole drilled but thats safer than losing a pinchbolt.

Mind you I wouldnt lose any sleep over it as long as the big bugger of a nut is on the end of the spindle it'll never move. Infact I might take mine out to save weight

the duke · #4 Post by **the duke** » Fri May 25, 2007 8:59 am

Falken is right. If there is a hard drill bit snapped off in it you will have no chance of re-drilling it so spark erosion is your best choice.
And when you went from the other side and went off centre that could also have been down to the hard material pushing the drill out.
If you do get it eroded out and find the off centre drilling has taken out some threads, fret not as a helicoil should sort it out and the thread will be stronger than original.

And i know you were joking Pierre but those bolts are quite important as their main job is to clamp the fork down to the axle and prevent movement as the forces trying to twist the wheel and axle out of the botton of the forks are pretty high. The big nut on the end of the axle only does part of the job of making a rigid structure, the pinch bolts do the rest.

There is a bike out there (I don't know which, someone please correct me) which actually has the spring in one fork leg and the damping cartridge in the other,
all in the name of weight saving and cost reduction but all the same sounds like a stupid idea. Everytime you compress or extend the suspension the forks will try to twist at the axle.

Sorry a bit of topic there i just got waffling.

Hope you get it sorted beckh

Ben

Falcoholic · #5 Post by **Falcoholic** » Fri May 25, 2007 9:13 am

Your local machine shop is the way to go.

They'll do a nice job on it for you.

HowardQ · #6 Post by **HowardQ** » Fri May 25, 2007 12:13 pm

I had the same trouble with the mudguard bolt, which is much smaller.
Somebody had replaced the pucker bolt with some monkey metal tat. Sheared off instantly when I took the mudguard off after the off last December. Spent bloody ages getting a tiny drill into the old sheared bolt, then opened it up so I could get the smallest possible extractor in and instantly sheared the extractor. Couldn't get a grip on the broken extractor, couldn't drill it, spent ages with no joy. Being an old fart I don't have as much patience these days, (although I did spend about 4 hours). I ended up drilling with a tiny drill around the edge of the tap and finally got it out, but the hole is now a right mess and funny shaped. Have fastened the mudguard with a stainless self tapper and clip plate on the rear, but embarrassed every time I take it off. Problem now is that if I drilled it out round to retap it would be too big a bolt for the mudgaurd stay. Ain't worth new forks so just hide it! Suppose it might just hellicoil at a push, but is it worth the hassle.

beckh · #7 Post by **beckh** » Fri May 25, 2007 1:01 pm

Duke, you are quite correct, the snapped drill bit caused the off centre problem. Damn hard those bits.Spark erosion is a new term to me though. Wassit all about then? Pierre, I would love Mille forks to go with the swingarm,shock and wheels I already have but cash is tight.Thanks for the pointer though.

the duke · #8 Post by **the duke** » Fri May 25, 2007 6:19 pm

Spark erosion is just that, passing a current between the job (whatever it is) and an electrode that literally sparks and burns away part of the material, no matter how hard it is. Also at the same time coolant is constantly washed over the job to both stop it overheating the surrounding area and to wash away the debris.

Tis a perfect way of clearing a hole that has a tap snapped off in it or a drill for that matter.

The only other way. To get the snapped drill bit out is, if it's not to deep. Just use a centre punch and bash it till the drill shatters and blow/hover the debris out then the way is clear to have another go a drilling.

Have fun

Ben

beckh · #9 Post by **beckh** » Mon May 28, 2007 4:51 pm

Thanks Duke. I did in fact look up spark erosion on the net after asking the question (lazy git,eh ?). I think any engineer should be able to handle it so as soon as the rain stops I will strip it and sort it out. Thanks all