Roadster/Interstate/Thruxton R tank (2020)

I think you know this already Glen, but according to Jim, bigger valves increase power and torque throughout the range. It’s going too big on the ports, and slowing velocity, that hurts the low / mid range. And that’s on a stock sized Commando.

I honestly don’t think we can question that stock valves are too small for a 920.

But it’s a moot point, trying to get it Comnozed now would be nigh on impossible as you say, and would have a huge impact on project timing etc.

And, doing it this way (the same as I did) will give you the opportunity to decide on a course of action for the head later and do a direct before and after dyno hill test! I don’t have a dyno hill, so had to make do with a dyno, but it was a very informative and fruitful exercise.
 
I don't regret having Jim do the full Monty on my FA head, and I am running stock +.040 bore. ;-)

What cam/CR will you be using?

here is the flow tests with the 1.5mm oversize intake and a little work in the valve guide and bowl area.

Nice improvement for a steetbike running a .400 lift cam.


Flow
Roadster/Interstate/Thruxton R tank (2020)


Velocity
Roadster/Interstate/Thruxton R tank (2020)
 
I know I just posted these in another thread, but what the heck....

Before and after of my RH10...

There was no downside to this (apart from time and money), increases throughout the rev range. Peak gain 9rwhp.

Interesting to compare to the Comnoz Fullauto posted above, the Comnoz RH10 has slightly more flow, but the Fullauto has a lot more velocity!

83BA540D-7792-495E-8292-502AF7B9279D.jpeg
C851719C-8AD0-43DD-8CED-96A382CD1A30.jpeg
 
I'll be using a stock cam. I was considering other profiles, but saw that Jim had gone back to stock profile for max midrange in his bike.
Seems a good recommendation as we both ride in the mountains quite often. Midrange is everything there, you hardly bother with the +5000 stuff.
 
I think you know this already Glen, but according to Jim, bigger valves increase power and torque throughout the range. It’s going too big on the ports, and slowing velocity, that hurts the low / mid range. And that’s on a stock sized Commando.

I honestly don’t think we can question that stock valves are too small for a 920.
My fuzzy memory recalls a post discussing this where Jim figured that the oversized valves and porting weren't very effective without more cam and carb.
But I could be remembering that incorrectly.
In any case, that was in reference to 750/850 engines, so yes, these valves likely are small for a 920, even below 5k rpm.
On a side note, but related, hijacking my own thread here.

Triumph has put a hotter cam and higher compression in their new 1200 rs version. They also boosted rpm a bit. All to satisfy those who must have more rpm and more than 100 HP.
It's not much of a bump, 97 to 103. Even though this is a thoroughly modern the hot cam effect occured.
The 103 HP version is less powerful than the 97HP through most of rev range. I would call that a downgrade.

Glen
 
My fuzzy memory recalls a post discussing this where Jim figured that the oversized valves and porting weren't very effective without more cam and carb.
But I could be remembering that incorrectly.
I can’t remember that, but I wouldn’t be surprised. These things do need to be considered as an interdependent ‘system’.

Sad Triumph story !
 
Going thru old posts the Comnoz information is that a bigger inlet valve helps all over, even in a stock cam/ compression Commando. He also suggests that the big inlet it might not have much effect when using Concentric carbs.

Glen
 
Made a bit more progress, although it doesn't look a lot different.
The main difference is that the tank and seat are mounted whereas before the were just propped up on there.
I put about 1 day + into a tank mount system that I later realized wouldn't work, so I abandoned that. It was much like the stock Commando mount system, except the mounts were closer together, too close in fact.
I opted for a mounting method that makes tank removal very easy, much easier than the stock setup.
It took a couple of half days to fabricate. Maybe more, I lost track. Somewhere in there I switched argon suppliers and lost the ability to Tig weld.
After much faffing about I realized there was something really wrong with the Argon.
Fortunately there was a tiny bit of argon remaining in the old tank and that worked fine (Praxair)
The photo shows what was happening with the new argon (w.g.)
A little while later my Tig welder cooked it's AC circuit board. Its probably not worth fixing. The replacement is about $2500. I got 9 years out of this welder, but only hobby use. Not great!
The welder still works on DC so I used it to fit the seat mounts and supports. The Thruxton seat sits on 7 round rubber pads that snap into the plastic seat pan. It was quite a job to build up supports to fit the various locations and compound angles.
That killed another few half days. The end result is a seat that is solidly in place but comes on or off with a click.

Glen
 
I should carry on and fit the fairing, but will take a break for awhile. Can't do much without an AC tig, so will need to get that sorted first.
 
Front mount. The nuts will be replaced with wing nuts. The threaded rod will get cut to length and finished with an acorn nut. The flat bars are slotted so the tank can be lifted off when the wing nuts are slackened. The slots have a 90 degree turn in them so the tank cannot accidentally come up off the mounts. It has to slide forward 1/2 before it can come up. It can't go forward until the rear bolt is removed.
So 1 easy to access wing bolt at rear gets the tank and seat off.
 
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The seat supports , rear tank hold down and seat hold downs. The latch at the rear is a Triumph part made for this seat. The housing for the latch is fabricated and doubles as the rear support for the centre rear rubber bumper. The tank hold down screw will be changed to a wing screw for ease of tank removal.
 
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The seat required a bit of modification. On the Triumph it uses a hold down lug at front. That would not work properly on the Norton frame.
To let the seat sit at the correct height, I chopped that bit out then made up the frame lug seen above. The lip of the frame lug slides in above the plastic seat pan ( in the cutout area) and holds the seat securely down at front. The seat pan is quite sturdy, about 3/8" thick here.
 
This is a big weight savings over the stock seat or a Corbin.
Ive found it to be a very comfortable seat shape, good for long days, 500 miles/day no problem.

 
Thanks!

I forgot to mention
Baz wrote-
"If the seat lock is the same as Japanese bikes use then instead of the remote cable operated key lock for the seat I have found a piece of 1.6 stainless Tig wire formed into a loop works well on these mechanisms
Just reach under the seat and pull the loop"

•••
That suggestion worked great.
It's even better than the Triumph Key in tumbler + cable system.
Less parts, less weight and quicker to use.

Glen
 
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