Aw Shooooooot! Rear Shock Mount Stripped Thread!

[jfheath]

Whatever you do, check carefully how that bolt is supposed to fit. My understanding is that the bolt tightens against the collar at the end of the thread and the head exerts no pressure on the bracket at all. If a collar is used and it is too short, then tightening the bolt will try to pull the two parts of the bracket together - trying to clamp the bottom part of the shock. This must not happen. The final drive housing is cast alloy. It will probably snap. It has been 17 years since I last worked on an 1100, but that is what I remember. Just check.

It is the same sort of arrangement that is used for the clutch lever pivot screw. It tightens against the shoulder at the end of the thread, and does not put any weight onto the top half of the bracket.

 

[dwalby]

Whatever you do, check carefully how that bolt is supposed to fit. My understanding is that the bolt tightens against the collar at the end of the thread and the head exerts no pressure on the bracket at all. If the collar is too short, then tightening the bolt will try to pull the two parts of the bracket together - trying to clamp the bottom part of the shock. This must not happen. The final drive housing is cast alloy. It will probably snap. It has been 17 years since I last worked on an 1100, but that is what I remember. Just check.

I can't think of anything that could go wrong if the shoulder is slightly too long. It will look odd, because the bolt head will be floating away from the mount, but would provide exactly the same function. Except. - on the original, the shoulder is an integral part of the screw. If you use a bolt and separate collar, then that will introduce movement into the bottom shock mounting. I don't know if loctite paste would be up to the job of filling this gap.

It is the same sort of arrangement that is used for the fairing screws that have a shoulder - the screw is tightened against the shoulder so that the fairing cannot go anywhere, but it is not clamped by the bolt head. Also, the clutch lever pivot screw. It tightens against the shoulder at the end of the thread, and does not try draw the top half of the bracket closer to the lever.

all good points, and regarding your concern if the collar is slightly too long, I don't think that will cause any problems. The stock arrangement is like you say, the bolt bottoms out on the pumpkin thread part because the bolt body is larger diameter than the threads. But, the hex part of the bolt is smaller or equal diameter to the shock hole, there is no "bolt head" in the typical sense. The shock eye can't move side-to-side because it's captive in the clevis part of the pumpkin, the bolt "head" has no part in restraining the shock eye side-to-side movement. So, if the collar is wider than the outside clevis width, then the bolt/collar method would be workable because the bolt head would be outside of the clevis part, and the collar would prevent the bolt head from putting any sideways force on the cast aluminum clevis part. I think all the force from the bolt head would be transferred through the collar to one side of the left clevis arm, and the nut would hold the collar tight against the other side of the left clevis arm. So, like the stock arrangement, the bolt threads into the pumpkin itself (which is the left clevis arm) are where all the forces are concentrated.

edit: another thing I was going to mention earlier is if its too difficult to find the right bolt/collar combination, it may be easier to just have a machine shop make a new bolt that has the same basic characteristics as the OEM bolt, but with a longer threaded portion to go through the other side of the pumpkin threads and accept a nut.

Andrew mentioned that its easy to re-thread the larger diameter bolt to the smaller diameter threads at the end, but with the tools I have in my garage I'm not confident that it would really be easy. Maybe he can shed a bit more light on what he means, I've never tried to start a smaller diameter die onto larger diameter existing threads, it doesn't sound easy, but maybe it is.

 

[jfheath]

I agree. Thank you. I wasn't concerned about the collar being too long. Rather that if it is too short, and it is an ordinary bolt, the bolt head would then tighten against the bracket.

I had forgotten that the OEM hex head was smaller than the shoulder !

I trimmed my reply before I noticed you had quoted it ! Thats Ok.

 

[Andrew Shadow]

A shoulder bolt and nut arrangement where the shoulder length is properly sized seems a simpler solution as it eliminates all concerns over compressing the shock mount as well, without needing collars. The length of the shoulder part is not critical as long as it is not short enough to cause any compression of the shock mount. If it is longer than required it doesn't matter. It is only acting as a support rod that captures and restricts horizontal movement of the shock eye. It does not serve to restrict lateral movement.

 

[dwalby]

A shoulder bolt and nut arrangement where the shoulder length is properly sized seems a simpler solution as it eliminates all concerns over compressing the shock mount as well, without needing collars. The length of the shoulder part is not critical as long as it is not short enough to cause any compression of the shock mount. If it is longer than required it doesn't matter. It is only acting as a support rod that captures and restricts horizontal movement of the shock eye. It does not serve to restrict lateral movement.

true, but it seems that the typical shoulder bolt has a rather short threaded portion, due to the nature of their typical usage, that would make it too short to pass through the drilled out hole and easily accept a nut on the other side. The shoulder lengths are variable, but the threaded lengths tend to be fixed for a given thread diameter. Not sure exactly what dimensions the OEM bolt has, but I'm seeing 13mm thread length on 10mm shoulder bolts with 8mm threads, which seems a bit short. That's just a guess as to the thread diameter, I haven't measured the actual OEM bolt. If you know of something with longer threads please share it.

also, after giving this a bit more thought, I'm wondering how drilling the threaded part of the pumpkin out and filing it flat on the other side to accept a nut would affect the structural strength of that support point. If the bolt support were to break while riding that would be a rather unpleasant experience.

 

[Taffy]

Thanks a bunch guys,. Just a quick update. (In between playing polite host to a few Family visitors!)

The bolt is snapped in the shock housing....which may not be too bad after all, I'll just dig further asap. But in any case, thanks for all the replies. They are all really helpful and have given me good things to consider.

Here's where I am at, pics to follow. Cheers all. I will follow through and let know the outcome.

 

[ST1100Gold]

Probably not as bad as you first thought. Now you have a piece of the original bolt in the housing.
Easiest way is drill a hole through the broken piece, insert an easy-out, apply copious amounts of release agent to the thread, and possibly some gentle heat on the outside of the casing, and the stud piece should come right out.
Might be an idea to hunt around the garage for something that can be used to centralize the drill bit (a guide sleeve the same OD as the original bolt, with a centre hole the same size as the drill bit - guarantees you're going into the centre of the broken piece)
After that, you still need to source a replacement OEM bolt ... ...
BTW, the lower section of the shock doesn't look to be the standard ST1100 unit ...

 

[ST1100Y]

My guess is that a left hand drill bit would already deal with the matter...

As for the cause: either too high torque or loose and breaking due the vehicle load...

 

[Larry Fine]

As for the cause: either too high torque or loose and breaking due the vehicle load...

It's easy to forget that shouldered bolts tighten differently. When the shoulder hits bottom, that's it.

 

[SMSW]

I had a problem with the final drive on my 1300 and discovered used low mileage units available on ebay for $100. Having discovered that ez-outs are really not so easy, and time is worth money, I'd do a quick search to see what used 1100 final drives cost. I think this has already been suggested - I second the motion.

 

[dwalby]

I don't have much experience with sheared bolts and stripped threads thankfully, but how weird is it that the steel bolt sheared off before the aluminum threads stripped? Wasn't expecting to see that.

But that would seem like a pretty easy job for a machine shop to drill that out and clean up the threads, so your solution is easier than first expected.

 

[Andrew Shadow]

Not sure exactly what dimensions the OEM bolt has, but I'm seeing 13mm thread length on 10mm shoulder bolts with 8mm threads, which seems a bit short. That's just a guess as to the thread diameter, I haven't measured the actual OEM bolt. If you know of something with longer threads please share it.

I have no idea of the OEM size bolt either. Shoulder bolts are available in all different lengths, in that size probably as long as 76 or 100mm. My suggestion was, if a correct match could not be found, get one of the correct diameter with a shoulder longer than is required and then cut and re-thread the shoulder end to whatever length and thread size is desired for the repair. It isn't very hard to do. If a person doesn't have the tools to do it a machine shop or any competent garage can do this rather easily.

also, after giving this a bit more thought, I'm wondering how drilling the threaded part of the pumpkin out and filing it flat on the other side to accept a nut would affect the structural strength of that support point. If the bolt support were to break while riding that would be a rather unpleasant experience.

I personally wouldn't have any concern over that. I am not suggesting removing 50% of the material. It only has to be filed enough to provide a flat with enough surface area for the lock washer to sit against so that it will compress and lock. That won't require very much filing.

All moot now as it turns out that it is a broken thread portion. As it no longer has any force on it hopefully soaking in some penetrating fluid for a while will allow it to screw right out.

 

[Upt' North]

I'll second the left hand drill bit.
Shouldn't be tight.
Upt.

 

[St-Gerard]

Having had to remove more than my share of broken off bolts, left hand drill bit and centering collar would be my first choice , on "rare "occasion have managed to unscrew the threaded section with a dental pick.

 

[draser]

Looking at your pics and the bolt size.. there's enough meet there to drill a smaller hole in the broken bolt and try an Easy-off gently on it. Spray some penetrant before in there and gently with the easy-off as they snap easily. Does the broken piece protrude from the other side? (so you can grab with a needle nose and see if it rotates..)

 

[rwthomas1]

Chances are the threaded portion is NOT bottomed in the blind hole. The shoulder would contact first and continued over-torqueing broke off the threaded portion. Left handed drill bit, EZ out's, etc. are probably the solution here. Along with as much care as possible. Good luck.

 

[Al st1100]

Mine broke the same way. If I remember correctly I took the pumkin off and drilled from the back side. Mine came right out. The shoulder has to be the exact size or it will rock and snap off again,.

 

[Al st1100]

not a blind hole

 

[Taffy]

Cheers all. I will follow through and let know the outcome.

Success!

As promised to everyone, the update, AND it is good news. I fancied my chances (as kindly suggested above) of having a go at using the left hand easy out tool, which I only used for the first time a few weeks ago, on a similar situation with a top strut, mount bolt, on my car shocks.

Pleased to report, no, sorry, very pleased to report...... it went well. Bolt out, thread seems still good enough. Have included photos for the use of anyone who they may help!!! Video link to share the joy, for anyone who has never used an easy out tool. Be patient on the links, may take a minute or two, valid for 7 days. Enjoy! https://we.tl/t-qZ8cME36dZ

Took my time, checking the centering of the punch tool and the pilot hole often. I have found a light touch essential to get that first bite for the drill tip.
Similarly, after a pilot hole or, deep enough hole is made, (mine went all the way through) the easy out tool bite long before that but care is required to start it off. Hope this makes sense, I just didn't rush it.

Thanks a bunch everyone, will order a new bolt asap. Whoopee

 

[STRider]

The ST1100's shock absorber bolt is unlike most bolts you'll ever encounter. It doesn't match the definition of shoulder bolts that I generally encounter. It's a special beast and I wouldn't use anything other than the OEM in this application personally.

NEWS FLASH!

As I was writing this, Taffy just posted success in extracting the broken stub of the shock absorber bolt. Huzzah!!

For posterity I'm including some work I was doing to assist Taffy... but how can I compete with success?

Appreciate that fundamentally this is an M8 bolt and its torque requirements are consistent with that spec.

23 N-m / 2.3 kg-m or 17 ft-lb​

To the uninitiated, it might be easy to assume some greater torque than this.

Congratulations @Taffy !