Tech Tip: Restoring Faith & Frame Interference (Triumph T100 Swingarm Spindles)
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 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
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
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
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
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
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
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
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
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..
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
Thanks and ride safe!