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Replacing the Air Pump Tab PDF Print E-mail
Written by BMWVMCA NEWS   
Friday, 26 June 2009


Many things happen to the bikes we choose to save and restore. It’s a fact of life. So what can we do when parts have been cut off?

One solution is to look for a donor frame, which should be one that is
  a). An orphan,
  b). One so badly mangled that it is not feasible to attempt restoring it.

Let’s face it, as much as we want to save them, sometimes there is little future left for an old part. Several years from now, someone might chastise us for parting out a badly damaged, orphaned frame. We’ll tell them that we are sorry, that we didn’t know any better.

OK, let us proceed with what can be done to replace the 8mm diameter tab that holds the air pump to the frame. For this part, we do not need to cut one off a donor frame. An 8mm partially threaded bolt will do nicely.

First, we need a pattern to work with. This can be from a drawing, or from a spare frame by simply measuring a known good tab. See photo [below]. We will then choose the length of our bolt based on this information. Remember that we are interested in the unthreaded portion of the bolt body.







Next, apply a center punch to the center of where the original tab had been attached to the frame.




Drill out the hole using first a small pilot sized drill bit, then open the hole using a drill bit suitable for an 8mm X 1.25 tap.




After tapping the hole, insert the bolt into the hole until the threads are no longer visible, and transfer your original measurements to the bolt, in order to  know where to cut it off, and where to bend it.

Tapping Operation:



Marking Where to Bend:




The next step requires removal of the bolt head. If you have air tools, fine, otherwise use a hacksaw. It still gets the job done.

Removing Bold Head:



After the bolt head is off, chuck the bolt stud in your drill press, and while running at 300 –450 RPM, dress the end to approximate the chamfer on the end of the air pump tab on the sample frame. This chamfer is needed to fit into the recess of the air pump handle.

Dressing or Chamfering the Stud:



Don’t have a drill press? Think on creative ways: use your bench grinder or belt sander and rotate the stud by hand in order to put a chamfer on the unthreaded end.  If you have an electric hand drill, chuck the stud in it and while the drill is running, dress the end of the stud against a belt or rotary sander, bench grinder or bastard file. Do what is needed to complete this part of the job.

The next step is to re-insert the bolt stud into the previously tapped hole in the frame.

Find the mark where the stud is to be bent, heat it cherry red and make the bend to match the sample.

When cool, rotate the now bent stud to match the position of the sample in the other frame.

If you do not have an acetylene torch, a propane torch will get the stud hot enough to bend. It will not work for the last operation, gas welding. For this,  the frame can be taken to a welder and either gas or TIG welded. Unless the welder is really good, stick and wire welding should not be considered here.

Chamfered Stud in Frame:




Bending Operation:



Welding to Frame:




Special thanks to Bob Zronek for driving 110 miles one way to take these photos and tolerate my bad jokes.

Richard Sheckler

Last Updated ( Friday, 26 June 2009 )
 
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