Triumph chopper FAQ’s


This is a work in progress and by no means covers all possible items or ways of building your chopper. Contributions to this FAQ can be sent to to be included in the next revision.


The first thing to do is make sure you have parts and service manuals for your particular bike. They say there is no such thing as a stupid question, but without a manual, you’re likely to prove this wrong.


This is meant as a general guide only. We are not responsible in any way for your failure to build a safe chopper.





Pre-Unit vs. Unit


Pre-unit engines had a separate transmission. This design was used on the 650’s until 1962. Alignment of the primary is critical to prevent excess wear.


The unit construction came out on the ’63 650’s. These engines have the transmission housing cast as part of the engine cases. Alignment problems are avoided.



Engine size


The most popular engine for a Triumph chopper is the 650 twin. Engine parts are readily available and fairly inexpensive. Other popular engine options are the 500 and 750 twins and 750 Trident 3 cylinders.





Pre-unit transmissions were 4 speeds. A rare option was the “slick shifter”. This was designed for racing and allowed shifting without having to pull in the clutch.


Unit transmissions were 4 speeds until about 1972, when Triumph switched to a 5 speed. A popular upgrade on older Units is to swap in the 5 speed gears. This requires a minimal amount of machine work.



There are several options to consider.


1. Stock frame, with swing arm.

2. Stock front frame with bolt-on hard-tail or plunger section.

3. Stock front frame with weld on hard-tail or plunger section.

4. Aftermarket hard-tail or plunger frame.


Any welding on the frame should be done by a qualified welder. Poor craftsmanship can result in frames breaking.





This is another area where there are several options to consider.


1. Stock front end.

2. Stock front end, with extended tubes.

3. Jap or HD front forks. This may require spacers to be machined to fit properly.

4. Springer or girder front end. This may also require spacers.


Verify that your fork geometry has proper trail to ensure safe handling. Choppers do not have to be poor handling bikes.
Trail calculator





Triumph had both single and dual carbs on the twins. A single carb is easier to keep tuned up, as it does not require synchronization. A single 930 or 932 Concentric will handle street riding very well.


1. Amal Monobloc, usually seen on older bikes.

2. Amal Concentric, they work great when tuned properly.

3. Mikuni, more difficult to tune, but well proven once properly set up.



Ignition systems


What is the best ignition system for your bike? That depends on several factors… Money, the type of charging system, and your wrenching ability are the main factors.


1. Stock points, condensers, and coils. Check your manual for details.


2. Stock points and condensers, with aftermarket or Harley coil. If using a dual lead coil, you will need to wire both sets of points together. You will just need one condenser, and the plug wires can go on either plug, since it will fire both at the same time.


3. Stock points, Chevrolet condenser mounted at the coil, and a Harley coil. Simple, and dependable, based on my experience. Gap the plugs at .020”, wire the points together, and attach the condenser to the opposite end of the coil that the power source hooks to. Run the plug wires to either plug.


4. Electronic ignition. Follow the directions that come with the ignition.


One of the problems that people seem to have is timing both cylinders. If you are running points, the Haynes manual tells how to use a timing light to set both sides. It’s almost a 2 person job, but with determination, you may be able to do this while setting on the bike.


Charging systems


The general consensus is that stock just doesn’t cut it. The most common options eliminate the Zener diode and stock voltage regulator.


1. Stock stator & rotor with Mity Max, can be used with or without a battery.


2. Stock stator & rotor with Typanium, can be used with or without a battery. Some older units may require a capacitor to be wired in if running without a battery.


3. Podtronics. I’m not familiar with this unit. If you are, I’d appreciate any info on it.


4. Boyer power units. This is another that I’m not familiar with this unit. If you are, I’d appreciate any info on it.