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Conventional valve springs in a Bomber?

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AshimotoK0:
I went to see a bloke recently who sells me parts from time to time  and has Honda classic race machines and most of the remaining original /UK-stocked spares for them.

He told me that a lot of CB450 racers and some owners of standard machines have converted to conventional valve springs, as the torsion bars degrade after 50 odd years in torsion and are hard and expensive to come by NOS. I had never heard of this before  but it seems he is correct.

https://www.caferacer.net/threads/cb450-valve-spring-conversion.11894/

K2-K6:
I've been reading through that thread Ash,  but it's like being blasted with a scatter gun of variable quality reasoning  ;D much of it born of misunderstood engineering principles.

The subject is so dispurse because of the above it's hard to make conclusive decisions around it, other sites the posters seem to hold the view that there are no springs in there at all !!

https://www.hondatwins.net/threads/new-or-used-torsion-bars-test-of-6-used-cb450-doch-heads.37856/ looking at this one, I can't visualise just how he's checkng the load (physical arrangement) but the numbers appear repeatable and interesting.
Initial thoughts are that the interpretation of the data,  specifically for B torsion bars, in showing that variance,  are a concern.  But he has no reference of their original (obviously) performance to say that they've changed.  There exists the possibility that the original samples had significant differences straight off the shelf.

The A bars look more like you'd expect from initial metallurgical theory.  Can't be sure of exactly the material used,  but general principle suggests "creep" ( bar loaded continuously without respite) of 0.1% per year,  making  5% from new to now if left under load for entirety.

Have you got facilities to test them?

Would have thought it's possible to reproduce something like this currently,  F 1 routinely use torsion bar in suspension.  Possibly the scale may be within someone's capability to batch produce.

the-chauffeur:

Seems to be fairly common in the 'states in vintage race classes.  Team Hansen is one place to go for spring conversions.  Sounds like they used to do a drop in conversion kit at one time.

There's a bunch of other places that do camshaft regrinds for race 450's, and there's a number of profiles that are accompanied by the warning only to be used with valve spring conversion heads.

AshimotoK0:

--- Quote from: K2-K6 on June 26, 2020, 02:12:53 PM ---
Have you got facilities to test them?


--- End quote ---

I don't have anything set up yet but I have about 5 sets of torsion bars and I need to select the best set for my engine very soon, so I will have to make something up. From my understanding, the Honda Twins guy merely assembles the torsion bar in the head as normal (the bars are not splined all of the way around the diameter so are effectively 'keyed' in position). He then applies torsion with an accurate  torque wrench until the locating hollow dowel (knock pin) in the head  is in line with the hole in the torsion bar 'arm'. He then notes the torque figure. It must be quite tricky to determine when the dowel in excactly in-line with the hole though because there is only a small amount of angular deflection even on a new torsion bar. So even a small amount of misalignment of the pin relative to the hole will make a big difference to the torque value measured.

K2-K6:
I've not seen their method,  but assumed it was something like you've described.

With the engine/ head held in a jig of sorts,  you could apply effort to the torque wrench with something like a rope loop that you put a "stick" into and twist to keep raising torque level until an able assistant  ;D can slot the pin home.

Or, in the same fashion,  use one of those double ended yacht rigging tensioner to gently wind on more load and hold while you read off torque when pin locates.

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