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Discussion Starter #1
Got my valves from the shop and they aren't leaking. Great! Now I need to get the torsion bars sorted.
Here are the torques I have.
LE: 48 in lbs
LI: 58 in lbs
RE: 80 in lbs
RI: 52 in lbs
I was able to shuffle with another set to get the one good one but I'll have to do something with the rest.
I was thinking of getting someone to weld up the lifters and then grind them back to be slightly thicker. Sound like a good idea? I also need to get my valve stems ground down a bit because when I installed the cam to check tappet clearance I was able to open the valve with the follower adjustment. Lobe set 180 from the follower. Does anyone have any experience measuring this?
 

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Gotta confess, I never realised there were torque values for the torsion bars. Makes sense, but I'd never thought about it.

Not sure the built up/ground back lifter method is going to increase preload. It might have a small impact on the valve closing force, but wouldn't it have a greater influence on the valve timing (as in, when the valves open/close) than the pressure they open/close with? That said, if your valves are too long (which doesn't sound right anyways), that's pretty much the same effect.

It's been a while, but I seem to remember reading somewhere about 450 racers increasing torsion bar preload by grinding off one of the splines(?) on the bars next to the flat spot that's already there and acts as the locator in the assembly. IIRC that means you can apply more twist to the torsion bars before locking them into place, thus increasing the preload.

This isn't the best thread about that subject, but it's one of them . . .
 

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You will over torque the stem trying that old wives tale. And you can't just grind on a hardened surface without penalty. It will end up snapping the bar, and voila trashed motor :) The 450 already is a Super Sport, and you should be able to rev past 10k rpms. If you are trying to race, look into a Kibblewhite valve spring conversion. Then you have the option of choosing spring rate and still have some reliability.
 

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I'm not sure why you would want to increase the tension on the torsion bars. There have been people on this site who have put a lot of effort into matching torsion bars. I'm not sure how much that would help an already very high performance street engine. The CB450 DOHC was the first mass produced DOHC engine and it was also the fist production engine to be rated 100BHP per Litre.
The idea of adding material to the lifter surface will not add preload to the torsion bar. The eccentric lash adjuster has a very small range of adjustment. If the valve stem is too high or the rocker arm too thick, the valve will be preloaded. Don't forget there is a gap in the valve adjustment. After having the valves ground there may not be enough clearance to get the required valve lash. When I had my head done two of the valves needed to be tipped to get the correct lash settiing.
 

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Discussion Starter #5
Gotta confess, I never realised there were torque values for the torsion bars. Makes sense, but I'd never thought about it.

Not sure the built up/ground back lifter method is going to increase preload. It might have a small impact on the valve closing force, but wouldn't it have a greater influence on the valve timing (as in, when the valves open/close) than the pressure they open/close with? That said, if your valves are too long (which doesn't sound right anyways), that's pretty much the same effect.

It's been a while, but I seem to remember reading somewhere about 450 racers increasing torsion bar preload by grinding off one of the splines(?) on the bars next to the flat spot that's already there and acts as the locator in the assembly. IIRC that means you can apply more twist to the torsion bars before locking them into place, thus increasing the preload.

This isn't the best thread about that subject, but it's one of them . . .
The tooth thing is a myth as debunked by @tbpmusic this drastically increased the preload to several FT Lbs.

In this thread there is this picture that shows where a washer/shim could be places to increase preload. This essentially moves the point of contact for the lifter "down" which means the torsion rod has to twist more to reach the anchor.

I don't fancy the idea of a washer being right there... hardened or otherwise. Plus I have no clue were to source such a thing
311405


As far as the closing force that's exactly what I want to increase since the min spec is 60 In Lbs and I'm frighteningly below that on my torsion bars. ALTHOUGH I'm not sure if this is as big of a deal as I think it is...

My valves aren't too long, my issue is that when the valve seats were cut the valve sunk into the head more which left less room for the torsion bar to act.

You will over torque the stem trying that old wives tale. And you can't just grind on a hardened surface without penalty. It will end up snapping the bar, and voila trashed motor :) The 450 already is a Super Sport, and you should be able to rev past 10k rpms. If you are trying to race, look into a Kibblewhite valve spring conversion. Then you have the option of choosing spring rate and still have some reliability.
Again I'm worried about the minimum spec being 60 in lbs. I don't want to float valves after all the work I've put into this motor already. I want to make sure that it's done right the first time.
And I don't want to sink that much more money into this. It's not a racer (yet?) just my first bike :)

I'm not sure why you would want to increase the tension on the torsion bars. There have been people on this site who have put a lot of effort into matching torsion bars. I'm not sure how much that would help an already very high performance street engine. The CB450 DOHC was the first mass produced DOHC engine and it was also the fist production engine to be rated 100BHP per Litre.
The idea of adding material to the lifter surface will not add preload to the torsion bar. The eccentric lash adjuster has a very small range of adjustment. If the valve stem is too high or the rocker arm too thick, the valve will be preloaded. Don't forget there is a gap in the valve adjustment. After having the valves ground there may not be enough clearance to get the required valve lash. When I had my head done two of the valves needed to be tipped to get the correct lash settiing.
The spec for the tension is 80 - 60 in lbs. I'm not really increasing tension as I'm trying to reclaim the distance that was lost when the seats were cut.

I also need to grind down the valve tips. Any tips on getting the right measurement of material to take off?
 

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Just curious as to where you found a spec for the torsion bar tension? I looked through the FSM and couldn't find any reference to it.
 

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Discussion Starter #7
Just curious as to where you found a spec for the torsion bar tension? I looked through the FSM and couldn't find any reference to it.

It doesn't seem like the original service manual accounted for 40+years of sitting and cutting valve seats. (I don't think cutting seats was common practice) if you search 'cb450 torsion bar spec' you can find a lot of sources with the same information
 

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You are aware that, using a crow's foot wrench as indicated in the linked article, yields a lower torque reading than if you fitted a socket directly over the end of the torsion bar?

Also, the only reference to preload in the FSM is this figure:
311406

Assuming the figure shows the actual preload applied, I estimate point a to be about 0.4 kg-m, which converts to 35 lb-in. I've yet to find any, even remotely, official numbers.

Update: I found the paragraph about applying torque to the torsion bar holder to the 'proper value', but nowhere does it say the proper value is any but shown in the above figure.
 

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I think you are over thinking this. A lot of R&D went into this engine. Without further engineering analysis you will run the risk of over stressing a valve or torsion bar. That would be disastrous. what are you trying to do? Make up for worn parts or get more performance. When I put my engine together I picked the best valve parts from three heads. The 450 DOHC is a reliable high perfromance engine. It is easy to mess that up.
 

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The FSM refers to valve face dressing down to an edge thickness of 0.5mm minimum - quite a lot compared to a new valve. It also gives part numbers for seat cutters and refers to seat cutting. To my way of thinking there's an allowance in there for torsion bar tension to still be within limits with valve and seat refacing, unless this work is carried out excessively. Does anyone have any actual experience of valve-float with these engines under normal road use? Most people would probably buy a bike on appearance and whether it smokes or rattles (or not) and never give a second thought to torsion bar tension so long as the bike runs OK. There must be many bikes that are running with slack tension.
 

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Discussion Starter #11
You are aware that, using a crow's foot wrench as indicated in the linked article, yields a lower torque reading than if you fitted a socket directly over the end of the torsion bar?

Also, the only reference to preload in the FSM is this figure:
View attachment 311406
Assuming the figure shows the actual preload applied, I estimate point a to be about 0.4 kg-m, which converts to 35 lb-in. I've yet to find any, even remotely, official numbers.

Update: I found the paragraph about applying torque to the torsion bar holder to the 'proper value', but nowhere does it say the proper value is any but shown in the above figure.
I think you are over thinking this. A lot of R&D went into this engine. Without further engineering analysis you will run the risk of over stressing a valve or torsion bar. That would be disastrous. what are you trying to do? Make up for worn parts or get more performance. When I put my engine together I picked the best valve parts from three heads. The 450 DOHC is a reliable high perfromance engine. It is easy to mess that up.
The FSM refers to valve face dressing down to an edge thickness of 0.5mm minimum - quite a lot compared to a new valve. It also gives part numbers for seat cutters and refers to seat cutting. To my way of thinking there's an allowance in there for torsion bar tension to still be within limits with valve and seat refacing, unless this work is carried out excessively. Does anyone have any actual experience of valve-float with these engines under normal road use? Most people would probably buy a bike on appearance and whether it smokes or rattles (or not) and never give a second thought to torsion bar tension so long as the bike runs OK. There must be many bikes that are running with slack tension.
I do tend to overthink things... I just want to make sure I cover everything before this goes back together. I've had it apart too many times lol.

You guys think it'll be fine then? Just shorten the valves and go? I assume I need a machine shop to do that
 

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Unless you have a home machine shop you will need someone to tip the valves. This needs to be done to the thousandths of in inch. Otherwise you will destroy the valve.
 

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What's the maximum tappet clearance you can achieve for each valve within the specified adjustment range?

If the valves need tipping it would be prudent to calculate how much for each valve - there's a limit to how much can be ground off. Many valve refacing machines have a micrometer tip grinder built in and this is the easiest way. The ground surface needs to be precisely 90 degrees to the stem and it's possible to rig up a fixture in the home workshop to do this accurately. I have used a custom split collet in the lathe to hold the stem, and a toolpost grinder with a cup wheel. That way you can use the handwheel division to take off a predetermined amount.
 

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When I had my head work done I asked about grinding the valve tips, I was told they ground 0.005" off each, how accurate this statement was I will never know but when I put it all back together it all went well with setting the valves to the cams. I'm quite pleased with how my engine runs, as long as I get decent acceleration, it holds a good cruising speed with the occasional high speed blast then I'm happy, at the end of the day it's a 48 year old bike.
 
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