Comments on: How cb450 torsion bars work

By: George Stepney

George Stepney — Wed, 06 Feb 2019 21:46:37 +0000

Hi well presented article – I am re commission a 1971 Cl450. I have an inlet valve that will not seat properly. A big clearence under the cam plenty of torque on the b tortion bar – could the lift cam have been incorrectly fitted on the wrong spline by the previous owner. No sign the head has been removed ion the 12k mile bile.

By: Aaron Recine

Aaron Recine — Thu, 28 Jun 2018 20:12:19 +0000

Thanks for writing this article. This is so rad.

By: phil

phil — Thu, 20 Jul 2017 22:25:56 +0000

I would like to add this…as I recall back in the day Honda offered different valve retainer collars….mostly thicker to increase valve spring pressure after a valve job that mostly decreased valve spring pressure due to valves getting pocketed in the seats after cutting….back in those days Honda cared more,,,,there were shims for the cb/cl/ca 72/77 to get better gear engagement in the transmissions….and shims to control end play in the cb/cl450 camshafts…..to see something truly amazing,try looking at Soichiro Iramajiri’s RC166 six cylinder 250cc racing Honda that Mike Hailwood rode to many wins in 1966/1967 there is a youtube video of it running and being torn down afterward….sorry it’s in Japanese but that wont matter to you gearheads….pure ecstasy.

By: phil

phil — Mon, 17 Jul 2017 22:20:40 +0000

I rebuilt many of these engines in the 1970s when I worked at a honda dealer.torsion bars are not new or different.I believe BMW used them in some racing engines….I had a 1963 VW bug that used torsion bars in the front with king and link pins.Later I had a Plymouth baracuda with torsion bar front suspension.One day I was looking at the car and it seemed to be doing a nose dive,I got a shop manual that gave me the spec. for front height and low and behold it was way off….short story you could adjust the front height with a wrench on the stop bolt for the torsion bar. solved the light in the rear problem along with a set of Pirelli cinturato’s….like a different car.anyway a torsion bar is like a fat coil spring stretched out.when a coil spring is compressed the coils actually twist just like a torsion bar.a torsion bar has a very high oscillation frequency unlikely to occur in an engine ..so no valve float or harmonic issues in these engines.

By: Mikey

Mikey — Tue, 14 Mar 2017 15:46:19 +0000

Hi, just wanted to comment on this discussion, Hondas tosion bar valve spring is an over-complicated design but its advantage over coil valve springs is it allows long valve travel without the problem of coil bind, where the spring compresses so much that the coils squash together not allowing the valve to fully open.

By: ed

ed — Wed, 04 Dec 2013 16:05:53 +0000

@Johnathan
Torsion bars are def awesome!
Your 450 looks cool man. I dig it.

What piston kit did you buy?
Henning / Hanson / M3?

Also… what carbs are you running? And what is your jetting / settings / needle etc.
I have stock carbs right now… but I’m going to upgrade to the Mikuni vm32 kit from power barn, so I can dial things in a bit more.

By: Jonathan

Jonathan — Tue, 03 Dec 2013 15:58:44 +0000

Well after working many years on that cb450 engine of mine… I’m still lurning stuff…

I stand as corrected… man I’m more happy to have one of those.

I’ve read many manual on those engines and alway tought that on one end of the torsion assembly they had some kind of spring…

Torsion bar are awsome 🙂

I’ve run the 1tooth less assembly for a year and half and still rockers looks good.

But for sure you’ll wear them more. I run synt oil and try to keep it in tip top shape.

Here’s a pic of my build with 74mm High compression piston kit.

https://lh3.googleusercontent.com/5xMN-rSKTqUnfOTE-9kuNROLC6EWjNcjy_FTDCQMwV8=w958-h680-no

By: ed

ed — Sun, 17 Nov 2013 21:27:59 +0000

@Johathan
At the end of this blog post, I added a new image.
I grabbed one of my extra torsion bar assemblies and took it completely apart.

By: ed

ed — Fri, 15 Nov 2013 21:41:00 +0000

@Johathan
Read this:
http://www.thefang.co.uk/cb500teng.htm

By: ed

ed — Fri, 15 Nov 2013 21:20:32 +0000

@ Johnathan
Trust me, I thought there was a spring somewhere too.
If you want, I can take my extra one apart when I get home and photograph it… both sides taken entirely apart.

By: ed

ed — Fri, 15 Nov 2013 21:17:44 +0000

@Johnathan

Regarding #1
I’m not trying to sound like a dick, but you are incorrect.
There is no spring inside a locked space.
It’s a solid piece of metal on the one splined side, then the torsion bar arm, then another solid splined arm on the other side.
I’ve had it entirely apart.
Both sides.
No spring anywhere or any piece that springs other than the long skinny torsion bar arm twisting.

Regarding #2
Yes, I’ve heard of people grinding off 1 tooth but I’ve heard that wears down the rocker arm quicker than normal.

By: Jonathan

Jonathan — Fri, 15 Nov 2013 20:56:13 +0000

Sorry but I have to correct some statement.

1st
The torsion bar dosn’t get physicly twisted. If you take a look on one side of the torsion bar you’ll find the spring inside a locked space.

So there’s a spring. Its not just the metal getting twist and taking back its shape.

2nd
If you want to prevent the floating valve on those engine, you can buy nos OR grind one tooth of the torsion bar setup and install it one tooth tighter.

🙂

By: Irman Peck

Irman Peck — Thu, 27 Dec 2012 18:16:13 +0000

What do you mean “no springs”? It’s a spring. Just one of a different shape…

By: Ed

Ed — Sat, 08 Dec 2012 03:17:15 +0000

@jason
Thanks! I’m def gonna try and test side A and I’ll report back once I figure it all out.

By: Jason

Jason — Fri, 07 Dec 2012 15:35:42 +0000

. . . btw, you would perform that test with the rod in place (or secured in a similar manner to how it would be held in the head) applying force with a beam type (not clicker) torque wrench and a degree wheel or some other means to determine that you’d twisted the rod to the desired extent.

Jason

By: Jason

Jason — Fri, 07 Dec 2012 15:33:46 +0000

The spec and testing for torsion rods (and any kind of spring really) is just how much force it takes to move it X distance. In the case of coil springs, the distance would be expressed as linear movement. In the case of torsion springs, it would be expressed as angular movement (degrees of rotation).

So in this case, the spec would be something like “it should take 40Nm to twist the rod 40deg”. Of course, I have no idea of the actual numbers.

Theoretically, there is another characteristic that could be evaulated, but it is outside the realm of the service shop: What is the rate of force applied over that distance. I.e. – force increases XNm per degree. The nature of the material and the shape of the cross section (and the age/fatigue level) determine this characteristic.

Jason

By: ed

ed — Thu, 06 Dec 2012 19:59:20 +0000

and…

this is a great write up of the head assembly:
http://www.hondatwins.net/forum/viewtopic.php?f=5&t=12231

By: ed

ed — Thu, 06 Dec 2012 19:58:11 +0000

@bob
cool…
I was just curious.
I spoke with a guy from team Hanson and he explained how you use a torque wrench attached to the side that sticks out of the head and bend the torsion bar towards the one hole that it bolts into.

Honestly, i’m not 100% certain on how to check the tension spec either. Once I figure it out when I actually try and do it, I plan on doing a little write up on it.

Stay tuned.
I should be doing all this shit in Dec and/or very early Jan.

By: Bob

Bob — Thu, 06 Dec 2012 19:48:05 +0000

@Ed
The engine was losing compression through the piston rings. Turned out the ring gaps were all in line (not in the proper 120 deg. pattern) and the 2nd ring was stuck inside the piston, unable to expand and seal correctly.

The bike has only 4K on the clock. Cam followers and cam itself are in great condition still, no dishing. Right now the engine is staying stock, just replacing the worn top end bits and gaskets.

I didn’t check the bars for tension rate since the mileage is low and the bike has no signs of abuse. Not sure how exactly you can accurately use the torque wrench method. What would you use as a reference point to correlate to the torque spec?

By: Justin

Justin — Thu, 06 Dec 2012 19:33:07 +0000

Nice post. It’s amazing how many different designs there are to accomplish the same thing. Any clue as to the benefits/drawbacks of this system? Obviously a negative is the wearing torsion bar, but I’m wondering what benefit negated the additional point of weakness. Great post!