Wanted to relate my experience recently.........
Offered solely as information based on hands-on experience, not some anecdotal blathering from someone on a website.
I rebuild a lot of 450 engines, among other problems I see a lot of failing torsion bars on CB/CL 450's now.
Not surprising, they're all pretty old now. Worse yet, many of these bikes have been sitting for years, and invariably one or more valves is open as it sits. Like any spring, torsion bars need to "relax" once in a while, or they don't spring so good any more.
New or even better parts are unobtainium, so I decided to investigate the torsion bar "trick" I've heard people relate for decades.
The suggestion is to grind off one of the splines adjacent to the "key" on the torsion bar so it could be rotated further, increasing the pre-load required.
It's fairly obvious to me now that none of those people have actually tried it, they're all blowin' smoke.
I chose to modify the outer "sleeve" portion of the torsion bar setup, where the crows-foot piece (it contacts the underside of the valve retainer thing) goes on - it's splines are larger and the material isn't too hard to Dremel off.
The photo shows a 2-piece 5-speed torsion bar. The 4-speed 450's have a 3-piece torsion bar that's a major pain in the butt to install, it keeps falling apart. But the two will interchange directly.
The skinny inner part (the actual torsion part) has the same number of splines, but they're much smaller, and that stuff is HARD.
There are 19 splines on the torsion bar's outer "tube" - that means jumping one spline is almost a 19-degree rotation - that's WAY too much, something like 5 degrees would work.
On a really bad torsion bar I have, the preload (torque required to get it up get it up on its knock pin) jumped from ~5 INCH-pounds to well over 15 FOOT-pounds.
Honda's spec in the manual is 4.5 ft./lbs (54 inch/lbs.) so this is NOT an acceptable solution.
That's so freakin' tight the torsion bars are sure to self-destruct in short order, and the valves would be hammered unmercifully till things broke.
The only real long-term solution is to convert to valve springs, and that's pricey.
Wandering a little-
Valves and valve seats are already an issue with 450's - the early 60's materials used can't stand up to unleaded fuel.
The more unleaded miles the bike has, the worse the damage seems to be. Without the "cushion" of the lead additive, the seats just get pounded away, receding further until the valve protrusion becomes an issue. And it doesn't do the OEM valves much good either.
This issue is common among all old engines, not just old Hondas.
On a 450, valve protrusion is critical, affecting the tappet adjustment range as well as torsion bar preset.
Worse yet, if the seat geometry is re-establised by "cutting" the old seats (and assuming protrusion isn't mucked up), you'll get maybe 10,000 unleaded miles until things go south again.
The real solution is brand new seats and valves, made of modern materials (MUCH harder) actually designed for the fuel we have.
Fortunately I have a buddy with a machine shop, actually a Harley/sprint car speed shop. Something about the old twins piqued his interest, and he tooled up to do a lot of stuff for me.
One thing we've done is to work out the details of totally replacing the valve seats with modern stuff. We've also laid in a small stock of Capelini 7mm stainless valves.
With modern seats and stainless valves, it will last a very long time with no leakage. He also does boring, bronze oversize valve guides, porting/flow, dyno work, etc.
I have a spare 5-speed head here that already has the new valve seats, saving my sheckels for a spring "kit" - those all require a switch to 5mm valves. Barring the spring kit, I'll at least put in the stainless 7mm valves.
I hope to switch it all out on my daily rider someday.
