Tech Tip: Restoring Faith & Frame Interference (Triumph T100 Swingarm Spindles)

Tech Tip: Restoring Faith & Frame Interference (Triumph T100 Swingarm Spindles)

1962 Triumph 3TA

Earlier this year (2020) I purchased a beautiful and fully restored 1962 Triumph 3TA motorcycle

It was perfect in everyway; beautiful bronze color, UK plates, grey top seat with the full "bathtub"... man it was sharp 

The Triumph 3TA (T21) has always been my dream "Triumph" since I first laid my eyes on it..

Something about the front fender and "bathtub" really gets to me..

As pretty as she looked, she came with a lot of baggage that I was slowly unpacking

Piece by piece.. 

To get to the point, I had tear down the entire the bike including the motor (that’s another story), frame, wheels, and everything in between because my swingarm spindle was stuck 

Today I wanted to give you my thoughts and tips on Triumph unit 350 & 500 unit twin swing arms as I think this conversation is very necessary based off my troubles and learning curve

If you own a Triumph 350 or 500 unit from 1957-1974, you should read this post as it will save you time, money and headaches 

We will cover a large range of of topics including how to prevent damage to your frame, how to install and remove spindles properly and how to restore interference (and faith)

Lets dig in 

Stuck spindles

Triumph T100 Stuck Swingarm Spindle

Stuck spindles on Triumph 350 & 500 unit twins is becoming a common problem

In fact, this pretty much goes for any Triumph frame that features an interference fit spindle (Triumph pre-unit, BSA models, etc)

Your spindle will need to be removed should your swingarm bushings become worn and need to be replaced, or if your frame is in order to be painted

A stuck spindle usually happens when your spindle literally rusts or becomes "1" with your frame

I used a 12-ton press to try to remove the spindle from my frame, I also used heat, pullers, grade-8 threaded rod; you name it, I tried everything I could think of but the spindle wouldn't budge

Finally the spindle was removed by a local shop that had a larger press (20-ton)

 

The real problem

Oversized Bore

Once you get the spindle out of the frame you might have solved one problem but now you're on your way to problem #2

Upon removing my spindle from the frame, I measured the bore and it was enlarged by about .005" (.0025” on both sides) causing my new spindle to drop in place with NO interference 

Further below I will cover how to repair this problem, but first, let's start with how to remove (and install) swingarm spindles the correct way vs the incorrect way 

How to remove (and install) the spindle (wrong & right)

As a rule of thumb there are multiple ways that you can remove and install the spindle properly from the frame, however there is only one way that can damage your frame 

I recommend the following when removing and installing your swing arm spindle 

For installing tips, just reverse the removal tips..

The wrong way

Here is the most common problem that most folks naturally turn too that I do not recommend

  • Using a hammer

Using a hammer often works and may get the spindle moving in the right direction, however when used improperly you will mushroom the spindle end as you continue to drive the spindle out of the frame

If the spindle is not budging, put the hammer down before you damage your frame and pride..

 

The right way

Swingarm Spindle Puller Tool

To do the job the "right" way it takes more time, pastenice and set-up

Below are a few points that I recommend when removing the swingarm spindle out of frame  

  • Use a puller stye tool to draw the swingarm spindle out of the frame 
  • A 12-20 ton press with the frame located to prevent distortion to push the spindle out 

If your puller is not doing the job, your spindle will need to be pressed out 

Make sure you locate the frame in the proper location to prevent distortion, twist and flex during removal   

 

Repairing the lost interference fit 

 

There are 4 ways (that I’m aware of) that you can repair a frame that has been damaged or lost its interference fit  

 

  • Oversized spindle 
  • Sleeving
  • Pins
  • Plating

 

Please keep in mind that fixing a frame will require a machine shop or a skilled individual

Rule of thumb: your frame bore must be round and true 

 

Oversized spindle 

 

A reputable machine shop should be able to fix a damaged frame or make a new spindle..

Keep in mind that the spindle must be heat treated and ground to size after manufacturing 

The proper O.D. of Triumph 350 & 500 unit spindles is .874-.8745" (almost 7/8")

When making a larger spindle you have to ensure that your frame bores are both round and sized properly along with your swingarm bushings 

 

Sleeving 

Boring Triumph 500 Spindle

IMO I believe that sleeving is the most logical repair

For my 350, I took the liberty of boring out the frame on my milling machine then sleeving each bore back to spec

Boring the frame was a simple task and did not have to be "perfect" in terms of the set-up - make sure the frame is flat and the bore is in line with the spindle using an indicator 

I bored each hole (one at a time) over 1" (approx 1.020-1.030")

I used an adjustable reamer with a pilot shank and reamed one side of the each bore to ensure it was inline with the opposite side.

Once done, I put the frame back on the table and bored the other side then repeated the reaming steps over again to make sure each bore is in line 

 

Triumph T100 Swingarm Frame Sleeve

I made a sleeve from 1018 steel with a wall thickness of approx .065" allow a .001-.0015" press fit in the frame 

Once installed both sides where reamed to the same size as the spindle allowing an interference fit 

 

Pins 

I have been told by a few local "hometown heroes" that the desert racers use to pin the swingarm spindles in place 

I have not personally seen this but I understand the philosophy behind the concept 

I could only assume your frame has to be in somewhat in good condition to allow this mod to work 

If it works for you, please comment in the section below  

Plating 

Should your frame be oversized by a few thousands I see no issues with having a stock spindle plated to build up the OD

Be sure that your bushings are sized to allow the larger OD spindle..

 

Final thought

Final Thought

 As frames are starting to get picked, and motorcycles are coming together for resto's you may find yourself dealing with this problem 

In all honesty, if your swingarm does not need to be removed, I highly encourage you to leave your frame alone 

If your swingarm bushings are not worn, please leave them and move onto the next task

However, if you have a frame that suffers from the same problems above just understand that your frame can be fixed and your faith will be restored 

 Always check and double check your work!

Thanks for reading

Thanks for reading todays Tech Tip post

Have something to say or want to join in on the conversation? - leave us a comment in the section below 

Click here to view our entire collection of Tech Tip posts 

Thanks and ride safe!  


7 comments

  • Classic British Spares

    @Nick – thanks for clearing that up Nick. I am not a machinist however the term “press” gets thrown around loosely. The frame is not a bearing surface as the shaft will no be pivoting in the frame. Measure the frame bore and shaft bore are the same using my .0001" indicator so I assume that is a interference fit. Is it not? Thanks for the comment!

  • Classic British Spares

    @Dave – Side to side would be a shimming issue, rocking would be a worn bushing issue. Let me know if that helps! Sounds like a shimming issue to me..

  • Nick

    Please note that, in engineering terms, an “interference” fit is just that; the two parts literally interfere with each other and are, at the very least, pressed together! The minimum tolerance (diameter) of the bore is ALWAYS smaller than the maximum tolerance (diameter) of the shaft going through it! This is a tight fit that is not required to move or rotate.
    The fit we are talking about here is a CLEARANCE FIT! This means that the minimum diameter of the bore is ALWAYS greater than the maximum tolerance (diameter) of the shaft going through it! This is because the shaft is required to rotate in the bore (i.e. freely slide in the bore) as a bearing surface.

  • Dave Kitching

    A very timely tech tip, thank you! I noticed on my 1971 T100C that the rear swingarm moves back and forth. And this is with the bike sitting with both wheels on the floor, shock absorbers installed, and everything tightened up, and engine installed. Is this a bushing issue or is the spindle loose? Or do I need shims? Any help would be greatly appreciated.

  • Trevor Jones

    I restored a 3TA and had to have the spindle pressed out. A major problem is the lack of a proper means of greasing the bushes in service. There is a grease nipple in the middle of the frame tube housing the spindle which is supposed to line up with a hole in the spindle, (I’m not sure how the alinement of this hole with the grease nipple is accomplished when installing the spindle). Grease pumped through this nipple is supposed to find its way to the two ends of the spindle, through holes drilled in the ends of the spindle( you can see them in the ‘Frozen spindle’ photograph above) and then into the channels in the bushes. I recommend removing the spoke holding the two discs covering the spindle ends, and forcing grease into the holes with your finger. Sounds crude but I think it works as well as anything given the design, and it might avoid another trip to the 20 Ton press!

Leave a comment

Please note, comments must be approved before they are published