[Flanagan]

what are the differences between these two triumph motors?? which is more preferred for power? reliability? etc.

thanks

 

[magnetoczar]

The TR6 was a single carb, much easier to keep in tune and as fast or maybe a little faster out of the hole (don't forget the 360 crank was originally used with one carb in mind), but the twin carb T120 has an advantage in the top end dept, but really not a lot. In 63' ,when the unit big twins came out, TR6 and 120 cams and a few other things were different, but by 66' <I think> it was the same engine with different heads that accomodated single or twin carbs.

Both these models are commanding the highest Triumph prices today, the Bonnie T120R, being the highest. If you'd like a rather nice 66' Bonnie, that seems to run fine and aside from needing a good detailing and has a small dent in the back of the tank, Steve Ritzko has a nice one for sale, M&S Cycle 518 377 7980. Once he cleans it, fixes the dent, lubes the cables and puts new rubber on it, it will be worth between 6K and 7K, depending on where he tries to sell it. I think right now he wants somewhere around $4500. You'd be an idiot to cafe this bike, though, as it's original and nice; just been sitting in somebodies garage for awhile. He's also go a real nice BSA Lightening for 3K, but that needs some engine work.

I'd get a 73' and up that runs well but needs cosmetics. Then you've got a 750 with that great Triumph 5 speed. Take someone with you that knows Triumphs, if you can.

Good Luck,
Dgy

 

[jbranson]

Dgy,
Do you have any further insight into the "360 degree crank for single carb" concept?
When I first started working out the details of hopping up my 175 I had thought some about trying a single carb. Seems to me that the even intake pulses of a 360 crank would be well suited to a properly designed intake. Ideally the intake charge from one cylinder helping along the charge for the next. Any thoughts?
JohnnyB

 

[magnetoczar]

That's pretty much the whole idea, a constant shaft of mixture through the carb alternating from one side to another on the even 360 cranks power pulses. This works well at more or less normal RPM ranges, but at high RPM's the dual carb set-up is superior as the column is suddenly stopped by the closing of the intake valve and becomes pressurized as it compresses on itself, thus supercharging the cylinder when the valve opens again, this given that valve timing and all that goes with it is correct<"comes up on the cam">. With an outlet supplied to the opposite cylinder, as with the single carb, such pressure buildup does not occur but rather smooth torquey performance.

At least, that's the way I see it.

Dgy

 

[jbranson]

Yeah that makes sense. I was trying to invision a manifold that would be suitable to flow switching from one side to the other at 10,000 rpm....and I couldn't. The charge running into the closed valve on one side of the intake at high gas velocities has got to play hell with the flow of the side with the open valve.
Sure wish it wasn't that way....tuning and maintaining a single carb would be...well....half as hard
JohnnyB