The 270 degree TRX firing order

[alextrx850]

A lot of owners of the TRX might have heard of the 270 degree firing order that the machine has and maybe wondered why different to others....i think it is an important piece of info to share.
Picking up a copy of Classic bike magazine [ JANUARY ]..where the process has been explained best.
The topic was mainly on a Laverda sf 750 which had been changed to our 270 degree and why, i think it is a good foundation to knowing the TRX motor.
Basiclly, the thought is,..twins come in two styles, 180 degrees, one up and one down at TDC, 360 degrees, both up and down together at TDC.
Brithish twins usually have the 360 style,.while Japanese twins such as the honda superdream went to the 180 degree.
Either stroke will have a momentary [DEAD SPOT] either at top dead centre or [BOTTOM DEAD CENTRE],..where everything comes to a momentary stop in direction. Inertia from the flywheel keeps things moving meantime.
The 360 motor has a problem overcoming vibration as the two pistons rise and fall together, while the 180 is concidered the smoothest as the two pistons are always moving to counter each other.
Phil Irving , of the Vincent engine development reasoned that phasing the crank pins at 76 degrees ment that one piston is at BDC on power stroke, while the other is at its highest speed [ upwards or downwards depending ]..to keep motor momentum...this means that mechanical flatspots are overcome without the need for a heavy flywheel.
In practice,.90degrees proved a more practical solution than the 76 , but still remains fundementally true to the theory.
Irving must have been right with the 90/270 degree firing order as Honda is using it in their NC700X ..as with the Triumph twins...our TDM/TRXs and others...
Note, none of this should be confused with the so-called big bang configurations of the Yamaha YZFr1 and some other GP bikes as these engines fire more like coupled pairs of 180 degree TWINS.
So thats a 270 degree firing order.

[Con Rod]

[trixynut]

...and the trx 270 firing order was developed as a solution to balance power and grip in sand in the TRXTZ paris dakar racer.
Think of it as fire, fire, miss, miss .....repeat.....

[Bikemike]

The cynic in me thinks the fact that the 270 degree order makes it sound like a V twin might have had a lot to do with it as well.......

[andyaber]

Don't I remember reading about xs650's with 270 cranks for racing in the 70's or 80's?

And racers playing with crank timing on triumph parallel twins even earlier than that?