Tech: Thread File and Motorcycle Thread Repair
Custovation Tip: Thread File – A Money Saving Tool
by Joe in Dallas for webBikeWorld.com
Motorcycle Tool Reviews | Owner Comments (Below)
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 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.
Think about external threads on axles, the steering
head shaft, shock bolts and the like. Or on the
older BMW’s, the 1-¼ 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
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
To the Rescue
The 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 Use
If 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
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.
On 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.
SAE and Metric Files: Available from chain auto parts
stores like NAPA and AutoZone as well as internet
*Custovation is a combination
of customizing, and renovation. Not a restoration, which
means to bring back to an original condition.
Custovation has a more specific meaning: CUSTOMIZE - to
make or alter to individual or personal specifications
combined with RENOVATION which is to restore to an
earlier condition, by repairing or remodeling.
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From "M.M." (1/09): "I’m writing to second your
endorsement of these tools – they’re AWESOME! I worked on bikes
for 15 years before I found them. Everyone who works on machines
of any type NEEDS these in their toolbox. They are truly
From "S. McD.": "Hey guys, great article. Just
wanted to note as an additional and frequently much less expensive
(Craftsman 48 pc. SAE & Metric Thread Restorer Kit; Sears item # 00942275000) kit from Craftsman.
At 60 bucks (often less) it's a great deal
and has saved my bacon a number of times. I have found it
invaluable for cleaning up the threads on Showa and KYB shock shafts
when doing rebuilds. Depending on the model, you have to carefully
grind off the nut that retains the valving, and most of the time this
will ding the threads up a bit. One of these files is the perfect
solution for this type or similar work, as you've noted."
Editor's Note: I have
one of these kits also and you're so right, it has saved me several