Buell Motorcycle Swing Arm Modifications

Buell Motorcycle Swing Arm Modifications.

Wicked change over and modification this job.

My customer has asked me to modify and extend a cast aluminium swing arm to give him a wider rear wheel section.

Here is the Non standard swing arm to modify.


Now the Buell motorcycle that this aluminium swing arm is to mate up to has a simple steel swing arm affair (the difference shown below). And there are also pictures showing the aluminium swing arm offered up to the original steel frame and back end gearbox pivot mounting. Note that we are extending the swing arm by 100mm to ensure the next size belt drive fits and extend the wheelbase marginally which helps reduce front end lifting so easily under accelleration.


If you have ever considered a similar modification for your motorcycle you will know that there are many things to consider.

Points to consider

  1. Mountings
  2. Bearings
  3. Swing angle
  4. Coil over / linkages if used?
  5. Offsets of wheel
  6. Offset of Mounting in Frame
  7. Offset of drive sprocket to wheel centre and frame centre
  8. Relocation of pipework, cables
  9. Chain or belt clearance
  10. Revised mountings for chain guard, rear sets, exhaust, rear brake
  11. Any areas of interference e.g. is the assembly going to hit any part upon compression of suspension.
  12. Maintaining rear / front wheel alignment / centres
  13. Accurate and equal measurements between wheel centre and new pivot point centres,otherwise rear wheel will be out of alignment.
  14. Strength, rigidity, flexibility
  15. Welding and machining skills, design and manufacture skills
  16. and so on !

So all in all not a job for the feint hearted. As you can see there are many things that need consideration before any work takes place.


How did I complete this job?

A complete breakdown of this modification can be seen below.

Measure, measure and check again! 

I use any number of methods to work out all the above. First and foremost an image in my head of how I think I can tackle the job, what the end result may look like, will I be able to make it “work”. Its no surprise what people throw at me as far doing custom made jobs. Often upon initial conversation / email I may not know if I can make / modify / fit / manufacture what the customer requires. Often its a case of getting more information / pictures / sketches / notes / dimensions etc to fathom out if indeed it is even possible and will work.

Once I have pictured the overall job and agreed that I can do it, there may be several steps involved in being sure I can make what the customer wants as I may have a different picture in my head to what the customer thinks.

Anyway this modification was quite logical in planning and implementing.

A marked out layout was completed on my work bench using the wheel centre as a datum point. I then overlayed the original and also the new swing arms. Instantly this gives me a layout that I can pattern from. By doing this I can compare what dimensions I have to work from to make the new swing arm fit to the back end mounting in the frame for the original pivot point. At this stage a flat template was made from aluminium as a check and compare guide.

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Once the template had been made and offered up to the frame and original pivot mounting points I could clearly see that the pivot mounting point and frame centre line was some 10mm out of alignment. This meant that the template and layout had to be adjusted to ensure that the centre line of the rear wheel was moved over to correct the offset and ensure the frame and rear wheel centre line is on the same plane.

Designing the new Swing Arm Extension

Once the correct layout, centre lines and overall plan is checked and double checked again, I know what we have to work with. At this point I have designed a 3d model of the infill piece which will extend  the swing arm by 100mm. The item will be machined from one block of material and be pinned and welded to the aluminium swing arm.

This positive positioning will be via 2 aluminium “top hat” pins that will be a press fit into the adapter / extension piece and also the bearing bore on  the actual aluminium swing arm. Once happy with the fit these will be welded in position and the slab side of the extension will also be fully welded all round to the swing arm. Creating a fully fitted extremely strong extension piece which is now one part with the swing arm.

Initially several sketches were made to clear my mind dimension were correct and also to put my ideas on paper to be able to produce a model. Careful thought needed putting in to design of the item to meet all the parameters and miss vital components such as the back edge of the main framework.

2014-08-26 21.50.25 2014-08-26 21.50.47 2014-08-26 21.51.08 2014-08-26 21.51.25 2014-08-26 21.51.51

Sketches always help me with considering a design for a one off job and clarifies points in my head and what I want it to look like. From the sketches I can easily make a 3d model as below
swing arm mods (2)

The above image shows a 1 piece extension unit complete with front pivot bearings and rear top hat pins in place. From this an engineering drawing was produced to enable manufacture. This included all dimension required to ensure dimensions and fits for bearings and pins are all to tolerance and “work” accordingly as designed.

swing arm dwgpin bosses dwg

Points to consider when designing this part !

Strength, weight, size, machine-ability, weld-ability, fit, finish, conflict with other parts (as its a moving part).

So all above considered this was the final machined extension piece manufactured from T6 Aluminium.

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Once checked dimensionaly and any sharp edges removed the next step was to offer up to the cleaned up swing arm, removing all the original paint to ensure no weld contamination in the welded areas we could tack up and check against the frame before final welding.

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2 images above show the main extension welded to the original swing arm. Location was critical and so top hat pins were machined up to a light push fit into the new extension and aligning with the original bearing bores in the swing arm. This ensures a “true” aligned extension piece. Once all tacked and aligned the whole unit was fully welded using the TIG welding process. As the swing arm incorporated an oil tank within the pivot end of the swing arm, some difficulties occurred in welding as due to the nature of alloy being porous oil soaks into the material somewhat. This is fine but during the welding process this contamination “burns out” and floats on top of the weld pool.

Once welded the surface of the weld was cleaned with a skotch pad to remove any surface contamination. Weld integrity is critical on a job like this where so many forces are travelling through and acting on the pivot point. In this instance there is in excess of 600mm of weld all around the added extension piece to original swing arm so its not going anywhere.

Infill panels were then cut, positioned and welded in position to finish the “boxing in” of the extension piece.

2014-10-11 15.58.272014-10-11 16.15.412014-10-11 16.16.32


To add more strength and infill the area above the new extension I added a fabricated triangulated section which ties in the extension fully to the original swing arm – see image below.

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Final shots of the new swing arm fitted up to the frame – below

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Thanks for looking, hope this blog was useful to you and remember if I can help you with your project please don’t hesitate to give me a call, or use the contact form above.









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Custom made Aluminium, Stainless and Mild Steel Parts for all makes and models.

BMW kit of parts for Throttle Body swap over

Pictured below is a set of parts made up for a BMW Specialist. These guys do some great mods on BMW including power increase modifications and re tuning, spares and accessories.


We now complete regular batch work for the company for some of the specialist upgrade kits they offer BMW owners.

We can offer 1 off parts or batch parts, or complete assemblies to your drawings or designs.

From a simple weld on tab / bracket to a complete throttle body manifold.


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Suzuki Srad Fuel Tank Pump Flange Modifications

Suzuki Srad Fuel Tank Pump Flange Modifications

A typical fault with the Suzuki SRAD tank was the pump seal arrangement on the bottom of the tank.

If the pump and flange plate were removed for any reason and then refitted, there was a big chance that with a fraction excessive tightening of the clamp bolts that the spot welded flange would distort and then the sandwiched seal ring would not pull tight against the flared opening flange of the tank.

Major problem if you had done the above, filled the tank and had fuel pouring out the bottom of the tank on a nice hot engine / gearbox casing. Very poor design by Suzuki really.

Anyway, my customer having spent a good wedge of cash on getting his tank repainted was left in the same position the first time he put new fuel in his nice newly painted tank. Upon inspection it could be seen that the flange the clamp bolts thread into had distorted and hence the seal ring was not sealing against the tank flange lip.


As can be seen from the image above the original set up takes the form of a 4mm thick flange that is spot welded to the main tank in between the threaded bolt positions, you may also be able to see the dimples in the tank under the positions where the clamping bolts sit through the flange so the bolts dont actually damage the tank shell. You can also see the pressed up flange around the opening that the seal ring actually seals against when the whole thing is tightened up. Clearly also shown are the positions where the spot welds have been positioned in between the drilled and tapped holes.

1451558_10201812688110578_1319495453_nAbove image shows where I have had to drill out the spot welds in the original flange in order to get the damn thing off – best spot welds I have ever removed! This took a bit of tugging and hammering to get off and the next image shows that I then had to do a little panel beating with a small aluminium block to level the panel work back up a bit.

1488167_10201812686750544_1878547800_nA little bit of flushing off and a bit of sanding down and cleaning up and we are ready to fit the new flange.


Laser cut, mild steel, thicker 6mm pump mounting flange offered up in place on the original tank. This will be tacked and welded in  place using a 10mm thick top plate to help soak some heat away and to help stop the new flange from distorting whilst welding.

1st we need to drill and tap out the holes. Drill out 5mm (4.8mm actually) diameter in order to tap M6. I did this using a battery drill set at low torque setting to prevent breaking the tap off in the hole. Notice that I didnt get the holes laser cut as this leaves a “hard” surface on the material which is a nightmare to thread out then, so all I did was get the laser to put a cross mark exactly where the holes come, ensuring dead accurate marking.

1461168_10201812687470562_548027505_nOnce all the holes were drilled and tapped out, a double check on the orientation and bolt the blanking flange up, sett up on the tank for accurate tack up.

1465371_10201812685430511_1213561555_nOnce tacked up, I removed the blanking plate and double checked the tack up and positioning. I had to make sure that I clamped the tank panel work tight up to the flange. Unfortunately even with the new flange tacked tight up I still had a gap to fill where the original dimples in the tank are, so I had to weld as cool as possible but a large fillet size to cover the dimples.

601593_10201812684590490_1838420620_nOnce the weld had had time to cool down I removed the blanking plate, although the flange had stayed flat and level there was a bit of shrinkage in the panel work.

The blanking plate was the used as a template to make a silicon rubber seal for testing, I also had to drill the blank plate and weld 2 pipe stubs on so that I could connect an airline and pressure blow off valve.

The seal and clamping plate were bolted back in place and tightened up I connected an airline one side and a pressure relief blow off valve the other. Spraying soapy water around the welded area and then pressuring up the tank if there is a leak you can see air bubbles bubbling out of pinholes etc.

1422412_10201812680470387_1229572719_n (1)1477370_10201812683110453_1967566878_n (1)

On to dry off, clean up, bit of paint and jobs a good un!

Just waiting for the laser cut nitrile seal to clamp up and finish the job.


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Ducati Oil Catch Tank

Ducati Oil Catch Tank

A nice little fabricated aluminium oil catch tank to fit up behind the head stock and between frame spars on a customers special build Ducati motorcycle.

Initially a simple card mock up was made and changed several times just to get the tank to sit tight up and at the right angle to the frame miss all parts required.


Once the mock up was complete and we was happy with it, I cut out and pressed up the tank in 2 sections of 1.5mm ns4 aluminium.

Just to make sure I tacked the tank up and we tried it in position to ensure it wasnt going to catch anything as it is maneuvered into place. Once held in position we could see what actual room we had available to us and where we could put breather, site glass, filler cap (to empty in this case), and of course the mounting points. Very little room was left and we decided to mount the tank on welded brackets to each side frame spar, this also then needed thought to be able to bolt the tank in position. The best idea we came up with was to machine top hat, blind threaded bosses to weld into the bottom of the tank. Shown below.

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Now the mounting top hats are welded in we can see that there is very little room for the breather and inlet pipe, made from 6mm aluminium tube with a 1mm wall thickness.

67062_10201573501611065_1449171905_nSo above you can see that the bottom of the tank is quite “busy”, the pipes had to be welded into the bottom of the tank as there was no room above or down the sides of the tank to run flexible hoses.

1380439_10201573500891047_1419960809_nSo if we look at the other fittings on the tank you can see the black filler bung is on the top, the sight gauge is mounted half way down the tank (black with clear lens) and if the oil mist ever fills enough you will see oil in the tank.

Both of these fittings had a simple little machined threaded boss with a “flange” round the top. My customer actually provided the machined fittings, only the filler threaded fitting had very little top flange to weld to. This with aluminium can be a problem as unless we have a flange with a little “meat” on it will rapidly be saturated in heat and “blow” away before we fuse to the main tank.

Aluminium dissipates heat very quickly unlike stainless steel or mild steel, but as this tank was so small and thin it quickly became “heat saturated” and you really have to watch the heat input otherwise the weld will “flood out” and look poor as well as being uneven and have massive excess penetration into the tank.

249077_614518415260670_1364078305_nAbove you can see how small the flange was on the filler boss, only approx 2mm in section.

67062_10201573501611065_1449171905_nSo once complete and welded up the tank needed to be tested for leaks, a simple process whereby we block all the holes up, add air pressure into the tank and simply brush soapy water around all the joints and welds. If there are any pin holes then the air will bubble through. Luckily this had no such issue.


Above you can see the finished article and the basic drawing we worked to.

Now the tank is complete my customer is taking the whole bike to Italy to a specialist frame builder to have a frame built.


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Don`t forget to email or call us for all your custom made 1 off bespoke items.

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