In the process of the "custovation*" of a well used -- and possibly abused -- motorcycle, you’ll eventually be dealing with threaded hardware replacement.More often than not the decision will be what kind of hardware to select to replace the rusty and buggered fasteners that are holding the parts together. With typically-sized bolts from small to medium sized diameters, the custovator has a choice of threads to repair. These can include SAE, Metric and the always perplexing Whitworth types to match the project’s country of origin. Their availability is widespread and even the more exotic threads can be acquired from hardware specialists. But what about the "plus-sized" hardware? You know -- the ones that were machined at the factory, they take the biggest spanner in your toolbox, or bigger yet, a grande size crescent wrench to grab the flats.
Threads Needing HelpThink about external threads on axles, the steering head shaft, shock bolts and the like. Or on the older BMWs, the 1-1/4 inch diameter metric threaded alloy exhaust header nut. Repairing external buggered threads on these parts means either total replacement or machine shop time. Both solutions are very expensive. I ran into the buggered thread problem a number of times and always had that cold chill of unexpected expense run through my pocketbook. I prefer to spend custovation bucks on parts that pay off in appearance or reliability rather than fixing damage that some careless bloke inflicted on the unsuspecting machine.
To the RescueThe rescue mission is handled by the little known thread file. The guy who invented it should be enshrined in the Custovator’s Hall of Fame, with a forever-burning votive candle standing guard! The thread file is a simple hardened steel four-sided bar with 8 different thread sizes cut into the body. It’s available for all thread patterns -- even Whitworth. The thread sizes are stamped on the sides for confirmation.
Easy to UseIf you are not sure of the thread size, match up the bolt thread to one of the file sides. Some of the thread sizes may appear similar, so I double-check with the file firmly engaged with the section of good threads placed in front of a bright light to highlight that the file is correct for the thread. If the file side is incorrect, light will show through the incorrect thread engagement.
Left: Incorrect fit. Right: Correct fit.Once you’re convinced that you have the correct side, gently stoke the threads just like doing a finish filing job on a piece of metal. Not too hard and not too soft. Don’t worry about cutting too deep or flattening the cylindrical bolt shape, the file limits the cut depth. Sometimes the buggers are isolated deep nicks. Other times it’s a damaged section that’s been chaffed by another piece of metal. Start with the good section of thread just next to the buggered part and start filing around the bolt toward the known bad section. After one file pass, spritz some WD-40 and try the nut for smooth spin-on. If it binds don’t force it -- make another pass instead. Do that until the nut spins on easily. Continue with the file and spin technique; notice that the bad section gets shorter leaving the worst section as the last to be finished.
BMW R65 exhaust collar repair.
ResultsOn the BMW, a $15 metric thread file saved over $600 dollars worth of head replacement or an alternative $300 machine shop bill. On other dirt and street bikes the savings was priceless. Outfitting your tool box with a SAE, Metric and Whitworth thread file set will be less than $75. And guess what? Having that Whitworth file may be just the right excuse for buying that needy vintage British bike you saw on eBay.