Bolt Failure Report - Front Isolator Bracket

to Head

 Last Edit on 10/18/2008 16:33

I was heading for home on I-70, east bound and running at speeds between 75 and 80 mph.   Without any warning the Buell began to vibrate as though I was riding over a rough road surface.   A quick look at the concrete pavement told me that was not the problem.  The vibration remained strong enough to made use of the mirrors impossible even a freeway speeds.  I pulled off in Rifle, my usual fuel stop on the way back from the Western Slope and Moab, but somehow did not see the missing bolt shown in the photo above.  I filled the tank and then spent the next 207 miles and 2 1/2 hours - over the Continental Divide - riding on what felt like the world's longest rumble strip.

As soon as I got home I put the bike up on the work stand and immediately realized something was missing from the front isolator bracket.  I was late in the day, I was tired (and seriously vibrated) and only had enough energy left to take a photo of the missing bolt and post an inquiry on the BWB.  It wasn't until the next morning, while I was drilling out the portion of the sheared bolt left in the head, that I noticed the broken head shown below.

The raised tab containing the threads in the head had broken off.  The engine had shifted position and the weight of the front of the engine was resting upon broken off portion of the head where it had caught up under the rocker box.  I became apparent that I had survived a long run through the mountains with what was essentially a "gravity mount" holding my engine off the pavement.  Both the reason for the vibration and its severity were now painfully obvious.

Operating under the assumptions that: 

  1. These bolts have failed on more bikes than mine (I already know at about a dozen others)

  2. These bolts should at least last from initial engine assembly through some sort of reasonable life - perhaps the first top end rebuild.

. . . we then need to ask . . ,

Why are these bolts failing?

  1. Rider/Owner Abuse? I am the original owner of my BuellI have never been one to do "wheelies" or "stoppies" on my S3T and the bike has never been down, wrecked or subjected to any manner of trauma that could be a contributory factor to the bolt failure.  

  2. Damage/stress to the bolts (and perhaps the head) during one or more of the other recall procedures?  I recall hearing of cases where the front mount and/or tie rods had been damaged when the engine had not been supported during work on the rear isolators, swingarm and shock recalls.

  3. Damage/stress to the bolts due to improper installation technique - failure to follow the exacting torque procedure detailed in the service bulletin?  The torque specified in the service bulletin is actually 15 t./lbs less than that noted for the stock bolt in the service manuals - old at 73-78 ft./lbs, new at 60 ft./lbs.

  4. Re-use of old bolt rather than using the new bolts provided in the recall kit?  I have learned from Chromate that these high strength bolts are only built to handle one installation and should always be replaced after a single use. 

  5. Outside Sourced Part Manufacturer Quality Control Problems?  There have been in recent Buell history when a batch of "bad parts" were inadvertently used in the assembly of our motorcycles.  A short list would include rear isolators, Showa shocks and many of the Safety Recall parts.

  6. A Sportster Legacy Part insufficient for use with the Buell Design?  See text below.

Questions 2 - 4.  On my Buell, the sheared bolt that sheared off was installed on the bike during the Front Isolator Mounting System Safety Recall (B-018) in the summer of 1999.  It had never been removed, retorqued or wrenched in any way in the 4 years and 20,000 miles since.  The work had been done by a respected and certified Buell technician in the Ft. Collins HD/Buell dealership.  I have too much faith in the person that did the work on my bike (I also watched him do much of the work) to believe that items 2 - 4 of the above played any part in my problem.

Question 5.  See alternative bolt below . . .

Question 6.   From what I have seen the Sportster's engine is attached to the its frame both under the engine and at the front - using the same head (and therefore bolt) configuration that we find on our Buells.  I believe that this is may be where the problem develops.

Since our Buell engines lack any frame support to the front of the engine other that provided by the front isolator and its corresponding bracket, I have to wonder if the same bolt that was adequate for the Sportsters is seriously under strength for the hanging of the Buell engine.  In my way of thinking, the requirement for new bolts whenever the isolator bracket is removed could be interpreted as a way to insure these bolts are replaced periodically - and hopefully before they exceed their life expectancy.  A curiosity - the recall procedure calls for torqueing the bolts to 60 ft./lbs., backing them off one full turn and then re-torqueing them back to 60 ft./lbs again.  Would this constitute a disregard for the "one use" specification?

I suspect that at some point during the decision process surrounding the use of the Evo engine in the Buell frame there was some thought put to the specification of the Sportster's 7/16X14 - 2 3/4" stock bolt in the new higher stress Buell application.  If the stock sized bolt, even in a high strength (greater than Grade 8) configuration, was near its maximum stress specifications the only other option would have been to use a larger diameter 1/2X13 - 2 3/4" bolt.  As I look at the Buell heads, use of this larger bolt would have required using a different head and new head castings.  Was this a cost based decision to stick with a potentially over stressed Sportster component rather than absorbing the cost of a new head and mount system more appropriate for the Buell configuration?

My failure scenario . . .,

I have tried to come up with a plausible scenario for this failure in the three months since coming back from what had been, up until the failure, a great trip to Southwestern Colorado (Ouray, Durango, Telluride, Hwy 141) with my friends John and Sherry Blackfeather,  I can almost convince myself that I remember having something hit me in the leg the month before while riding around Boulder, ostensibly the missing portion of the bolt.  At other times I can recall the bike had been delivering increased peg vibration and a clunk from the front end prior to the Ouray trip.  In order to believe that the bolt had sheared off sometime before leaving for Ouray, I would have to admit to having not noticed the gaping hole in the bracket during at least two washings, an oil/filter change, primary gasket change and a starter gasket replacement.  Stranger things have happened, but I suspect that the bolt sheared while on the trip.

I now am more drawn to the possibility that the bolt failed while riding on Highway 141, thus saving me from having to face the possibility that I was oblivious to such an obvious problem before the day of the failure.  I suspect that the bike continued to run for some time until the head broke, and it was at that point that the metal to metal contact sent the vibration through the Buell and ruined my day.

Preventative replacement, the only viable remedy at this point . . . 

The repair or periodic preventative replacement is a fairly straight forward procedure that can be done without major mechanical gymnastics.  The only tricky part is to make sure the engine is tied off and supported to the point where the alignment of the bolts, bracket and head does not change as the bolts are switched out.  If the alignment is maintained, each bolt can be removed and replaced in turn and then torqued as per the recall bulletin's instructions (oiled washer, oiled bolt head, red Locktite, 60 ft./lbs, back off one turn, 60 ft./lbs).  I believe there is plenty of room to do this without removing any other parts.

Alternative bolt or the Buell offering . . .

Putting aside all the assumptions and speculation, the practical question that remains is - "How much of a liability are these bolts?"  Right after the initial question comes, "How can I avoid going through a bolt failure?" Considering the relative cost of new bolts as opposed to replacing a broken head, this falls easily into the category of "preventative, pre-emptive periodic replacement."  Having first person knowledge that the Buell bolts (made by f911) can fail, I began looking for an alternative bolt source - hopefully a less failure prone strength profile.  I was able to locate high strength and corrosion resistant bolts from Chromate Industrial Corporation (, and their Mountain States representative Wendy Kaiser  Although it was difficult to acquire comparison points in relative Grade (8, 10, 12+?) from either F911 or Chromate, I was able to determine that the Chromate products were at least as strong as the f911 bolts and since I already knew the f911 bolts could fail . . . . I went with Chromate CIC200.  I do not believe that corrosion was a factor in my failure based on the condition of the one remaining bolt.  However, eliminating it as a possible seemed to have some merit and Chromate's high quality anti-corrosive coating  (Pro Shield) supported my decision to use the their bolts. 

 I have a limited additional supply of these bolt and washers graciously provided by Wendy from Chromate and will be happy to send them out to anyone interested in trying them on their Buells.

My repair adventure . . .

Since my repair was substantially more involved than a simple bolt replacement, I had to resort to more drastic measures on my Buell.  If it had only to deal with a sheared off bolt, I believe that I would have removed both the bolts and the tie rods (top and front) in order to let the engine and bracket separate enough to drill out and "easy out" the threaded portion of the broken bolt left in the head.  Once there was room to use the drill motor, the job was very easy.  But, with a broken head to deal with I faced some more serious challenges and decisions.

After determining that welding based repairs were too complex and risky I decided that restoring the threads in the head.  After some false leads my friends at McGuckin's hardware then showed me "EZ-Lok" thread inserts.  These steel sleeves are threaded both on the inside and outside surfaces.  Purchasing an replacement 7/16X14 insert requires drilling and tapping a 5/18X13 hole in the head - the thread of the outside surface.  I decided to stack two inserts on top of each other - providing me with a full 1 1/4" inch of threads into the head.   The EZ Lok inserts have an encapsulated epoxy coating on the outsides that bonds quickly to the threaded stock once the inserts are installed.  I had to trim up the second insert with a Dremel tool a little to clear the broken head tab - on which I had drilled out the threads to a diameter closely fit to the smooth shank of the replacement bolt.

EZ-Lok Thread Inserts

The Finished Repair

The assembly went well, with the holes, bracket and threads all lining up without any stress.  I applied JB Weld to the surfaces the head and tab where the break had occurred, bolted up the bracket and then left the assembly overnight.  The next day the new threads took the required torque without incident and the bike was back on the road.

Had I a couple of thousand dollars to splash around, I would have liked to have replaced both heads with XB parts, bored the cylinders and put in new pistons.  Since this was not in the budget the thread replacement was the next best option.  I have spoken with several independent HD/Buell technicians that assure me that the steel replacement threads are at least as strong as the stock set-up and I am glad I did not attempt the more risky welding based repairs.

Buell owner help needed . . . 

In the next 6 months I will attempt to gather incident data from my contacts on BWB in an effort to determine what kind of incident frequency and failure mode information I can compile.  I would like to be able to determine if there is a common factor in the failures - mileage, use, model, year, recall and/or maintenance/repair.

For now I believe the prudent step for tube frame, and perhaps even XB/Blast owner, is to assume that there is some failure mode on these bolts that periodic replacement will resolve.  Assuming that the replacement procedure relatively painless,  and the price of the bolts remains negligible it stands to reason that when weighed against the possibility of replacing a head the bolt replacement is an effective investment.

If you have had one of these bolts fail, or know of anyone that has gone through this, please contact me at: