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Slammed my Plasma’s stem last night; Detailed tutorial with photos.

Tuesday, November 17, 2015 by  
Filed under Daily Blog

November
17
2015

A stack of headset spacers on a race bike is one of those things that, aesthetically, I find almost offensive. A sharp vertical rise on an otherwise beautiful aero machine looks extremely awkward and out of place to me. Headset spacers abrade something off in the dark OCD corners of my brain. This is not something I have control over, it just… is.

Before I write another word, I want to be absolutely clear about something: if you have headset spacers on your bike, I don’t care. More power to you. I get that spacers serve a very useful purpose. Bike fit is far more important than aesthetics. Ride comfortable. Be happy.

That said, I’m a fairly limber dude, and I like being as aero as possible on the bike. If I could, I’d take my stems right down to the frame, but most modern race bikes sport carbon steerer tubes and require a 5mm spacer between the headset dust cover and the stem. Some people ignore the manufactures’ warnings to run at least a 5mm spacer under the stem (and some manufactures–Trek, for example–also require a 5mm spacer above the stem), but I’m not willing to risk my life over 5mm. Bike engineers are a lot smarter than I am, so I listen to them.

My new Scott Plasma time trial bike has a carbon steerer tube and, predictably, Scott requires a 5mm spacer under the stem. Scott, however, does not require a spacer above the stem, which makes me very happy. A small 5mm spacer under the stem is somewhat tolerable, but spacers stacked above the stem are about the ugliest thing on a bike this side of a dork disc.

When I built up my Plasma, I realized that I somehow no longer had possession of my Park Tool carbon hacksaw blade. I ordered a new blade, but it took like 10 days for it to show up.

Relief finally arrived in an unremarkable padded envelope. I wasted no time prepping my Plasma for surgery, and last night she went under the blade.

A few years ago I wrote a tutorial on slamming the stem, but this bike is a little different (in a good way, see below) so I thought I’d do another one with lots of pictures. Note that I don’t cover the basic stuff, such as how to remove your fork, remove the front brake, etc. If you’re not comfortable doing any of those things, take your bike to a qualified mechanic for a professional slamming.

Slamming the stem is not hard, but you want to be very careful and precise. Once you cut the steerer tube down, there’s no going back. Cut the tube too short, and you’re buying an expensive new fork.

Are you merely slam-curious? I recommend that you slam the stem, and move the spacers to the top of the stem without cutting the steerer tube. Ride around for a few weeks and see what you think. If you don’t like it, simply move the spacers back to their original configuration. No harm done.

Here are the tools you’ll need:

 

Here are a bunch of photos, see the captions for further details (click any photo to enlarge).

Step 1: Dry fit.

The first step to do a dry fit. About 35mm of god-awful steerer tube will be removed. Note the small 5mm spacer below the stem; Scott requires this (it's a safety thing). Use a Sharpie to trace a line around the tube at the top of the stem (note that this is NOT where you'll be making the cut, see next photo).

The first step to do a dry fit. About 35mm of god-awful steerer tube will be removed. Note the small 5mm spacer below the stem; Scott requires this (it’s a safety thing). Use a Sharpie to trace a tight line around the tube at the top of the stem (note that this is NOT where you’ll be making the cut, see next photo).

 

Step 2: Marking the cut location. Triple check this, there’s no putting the genie back in the bottle once you make the cut.

The top line was drawn in the previous step (this is where the top of the stem was). You'll want to make the cut about 5-7mm below this mark, as the steerer tube should be below the top of the stem. A digital caliper is helpful here.

The top line was drawn in the previous step (this is where the top of the stem was). You’ll want to make the cut about 5-7mm below this mark, as the steerer tube should be below the top of the stem. A digital caliper is helpful here.

 

Step 3: Using a hex wrench, remove the reusable compression nut (carbon tubes only). Most aluminum tubes use a star nut, and when you cut the steerer tube you’ll need to use a brand new star nut and a tool like Park’s Threadless Tubed Nut Setter.

 

This is Scott's patented compression plug. Unlike a star nut, this guy can be reused over and over again.

This is Scott’s patented compression plug. Unlike a star nut, this guy can be reused over and over again.

Compression nuts slide into the steerer tube, and then a hex wrench is used from the top to expand the collar.

Compression nuts slide into the steerer tube, and then a hex wrench is used from the top to expand the collar.

 

Step 4: Cut the tube with your hacksaw. When cutting carbon some people like to wrap the cut location with masking tape. I don’t find this to be necessary, but it won’t hurt. A vise and a saw guide are highly recommended.

Ready to cut. A vise and a saw guide are must-haves for a straight, clean cut. If you've got a carbon steerer tube, be sure to use a carbon-specific blade.

Ready to cut. A vise and a threadless saw guide are must-haves for a straight, clean cut. If you’ve got a carbon steerer tube, be sure to use a carbon hacksaw blade.

 

Step 5: Use a bit of sandpaper to smooth the cut. Be sure to get inside and all around the cut surface.

A perfect cut. After cutting use a little sandpaper to smooth all the edges.

A perfect cut. After cutting use a little sandpaper to smooth all the edges.

 

Step 6: Re-install the fork (note that if your tube uses a traditional star nut, you’ll want to install the new nut before performing this step). If you’ve got a carbon steerer tube, use a little carbon gel during assembly. Also, particularly with carbon, it’s critical that you torque the bolts to spec. I have a Park beam torque wrench, but for parts that require 20 Nm or less torque, I much prefer the accuracy and peace of mind that a click-style torque wrench provides. I highly recommend the TEKTON 24320 torque wrench. Note that if you’re using Park’s 3/8″ socket and bit set, you’ll also need an adapter/reducer set if you’re using the TEKTON wrench, which is 1/4″ drive.

Note the steerer tube is about 6.5mm below the top of the stem.

Note the steerer tube is about 6.5mm below the top of the stem.

 

Step 7: Using a torque wrench, install the compression plug (carbon tubes only) to manufacture’s specifications.

Here's the steerer tube with Scott's compression plug installed.

Here’s the steerer tube with Scott’s compression plug installed.

 

Step 8: Using your torque wrench, install the top cap and then tighten the two stem bolts. I use Blue Loctite on the the two stem bolts.

Complete!

Complete!

 

Step 9: Step back, crack open a beer and admire your work. Job well done!

Ah, much better.

Ah, much better.

 

Finally here’s the beach cruiser “before”, and the race-ready “after” (click to enlarge):

Before and After.

Before and After.

 

John Stone Fitness Comments

17 Responses to “Slammed my Plasma’s stem last night; Detailed tutorial with photos.”
  1. What is the blue thing in the before?

    I’ve never seen aerobars before, it looks like when your elbows are on the pads and you are holding the straight out handles that there is no way to brake is that correct?

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    • The blue thing is the Park Tool Handlebar Holder. The handlebar holder is really useful when working on the bike, particularly when it’s in the stand. Keeps the bars from flopping around.

      Correct, there are no brakes on the aerobars. This is one of the reasons using aerobars in a paceline is a no-no.

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