Honda-SOHC

SOHC.co.uk Forums => CB750 => Topic started by: StevieWonder on October 11, 2019, 01:35:55 PM

Title: TORQUEING REAR AXLE
Post by: StevieWonder on October 11, 2019, 01:35:55 PM
Does anyone know, if the rear axle bolt can be torqued up without removing silencers/mufflers #3 and #4?

The 24 mm axle nut has a torque setting of 58 – 72 Ft/Lbs, which in itself calls for significant leverage and more than an open ended spanner.

However, I have found that with the silencers supported and the pillion foot peg/ silencer support withdrawn the additional space around the rear axle nut is still insufficient to fit a socket or a crowfoot spanner/wrench and attach the torque wrench.

As the axle nut must be regularly accessed to make drive chain adjustments, surely there is a technique to set the torque with silencers in place?
Title: Re: TORQUEING REAR AXLE
Post by: Nurse Julie on October 11, 2019, 01:48:46 PM
No...silencers need to be removed or do what we do, just use a very long spanner and stand on it till the nut doesn't move any further, that's about 65 ft lb torque 😁
Title: Re: TORQUEING REAR AXLE
Post by: Bryanj on October 11, 2019, 02:06:04 PM
I always used the tool kit flat hex ring with an appropriate, bent, fork tube!
Title: Re: TORQUEING REAR AXLE
Post by: StevieWonder on October 12, 2019, 03:55:49 PM
Trying to tighten the rear axle nut to the correct torque as based upon the kind advice provided by Nurse Julie and Bryanj – ‘Stand on it’ and ‘use the tool kit flat hex ring’ – I got all technical and calculated the bar length required to produce 65 ft Lbs torque.

Torque (ft Lbs) = Lever length (ft) x force (Lbs)     all calcs assume force at 90 degrees to lever.

65 ft Lbs = Lever length x 1 fat b*****d (182 lbs) stood on it.

Lever Length =      65         .
                    182   

Lever Length = 0.357 of a foot ~ 4.25 inches about the length of the tool kit hex ring, without the extension would produce the 65 ft Lbs of torque required, if I stood on the end of it.

So I stood on the unextended hex ring and ……………………. It loosened the nut!

So to tighten the nut to 65 ft Lbs, if I use a bar lever of 10” (0.834 ft)

Force =        Torque   .
                Lever Length

Force =         65       .
                 0.834

Force = ~ 80 Lbs   or 5 Stone 6 Lb   but I don’t know what that feels like?

So if I use 34” of 22mm copper pipe to extend the tool kit hex ring – I know the bend in the bar reduces the force slightly.

Force =                65     .               =  ~ 23 ft Lbs     I know what that feels like.
                   2.834 ft (34”)

So tightened axle nut, but now the hole for the split pin doesn’t line up!

Note to self: Next time take off silencers #3 and #4; torque up properly with a socket; use washer shims to align split pin hole; paint in use split pin slot in axle nut. On next chain adjustment tighten to align split pin.

Did I get that wrong? Any better suggestions? :-\
Title: Re: TORQUEING REAR AXLE
Post by: Nurse Julie on October 12, 2019, 04:17:00 PM
Blimey....that is tech. I couldn't tell you if its right or wrong as my brain is not wired for maths (other than Medical maths etc) or foreign languages. But.....stand on the spanner again until the split pin holes line up and you're done 👍👍👍 You really don't want to keep removing those 2 silencers everytime you adjust the chain, so this is a maneuver you would be good to master.
Title: Re: TORQUEING REAR AXLE
Post by: Spitfire on October 12, 2019, 04:36:53 PM
I'm with the tool kit spanner and foot brigade.

Cheers

Dennis
Title: Re: TORQUEING REAR AXLE
Post by: Bryanj on October 12, 2019, 04:38:34 PM
And just keep going till the pin hole lines up NOBODY EVER used shims
Title: Re: TORQUEING REAR AXLE
Post by: K2-K6 on October 12, 2019, 04:42:27 PM
Looks correct from calculations point of view.

I'd have gone 65 divided by 3 (36 inches equals 3 foot) gives 21.6 lb/ft with a 3ft lever or 1 yard in old money  :)

I do like your inclusion of one fat b'stard as part of the calculations though,  as I've got "one fat Pete the policeman" as a standard mate to help out with strenuous lifting etc.

Views on open ended spanner,  a Bahco adjustable will easily do that job and torque rating if you want to buy something generally very useful.  Very good quality.

The axle is more of a minimum torque rating to clamp the wheel sufficiently,  with the upper limit highly unlikely to be breached mechanically by then aligning the split pin. If you use the method of reaching the minimum torque setting, then turn further to match the split pin,  it's not going to give a problem.

Title: Re: TORQUEING REAR AXLE
Post by: Trigger on October 12, 2019, 07:42:46 PM
You old boys worry too much.
As Bryan said, the holes never line up at the torque settings and that is the important bit  ;)
Title: Re: TORQUEING REAR AXLE
Post by: Moorey on October 12, 2019, 11:05:44 PM
65 ft Lbs = a bit of a grunt as you pull the spanner. :D
Title: Re: TORQUEING REAR AXLE
Post by: Bryanj on October 13, 2019, 10:27:10 AM
3/8 nut in elbow joint and when it flies out or hurts a lot youre there!
Title: Re: TORQUEING REAR AXLE
Post by: StevieWonder on October 19, 2019, 06:36:47 PM
Thought I'd try a slightly more elegant solution. Pete the policeman/ fork leg not required. Found a 24/17 mm hex ring spanner from a YAMAHA tool kit (nice quality to be fair). Drilled and filed a square 3/8" hole near the 24 mm end to take the torque wrench. Set a 90 degree configuration as per pic. Loosened, but did not removed foot peg nut, to increase clearance. Tested existing torque and found previous guesstimate to be 48 ft/Lbs - good job it's still running in! Gradually increased torque, as wasn't sure spanner was robust enough, but it was. Set at 67 ft/Lbs, unfortunately smack between split pin holes! Estimate next split pin hole alignment will far exceed max torque 72 ft/Lbs.

At a latter time. I realised that there are 2-holes for the split pin through the end of the axle at 90 degrees to one-another and the second one was lined up.
Title: Re: TORQUEING REAR AXLE
Post by: Bryanj on October 19, 2019, 06:39:30 PM
You are way overthinking this
Title: Re: TORQUEING REAR AXLE
Post by: Green1 on October 19, 2019, 06:46:48 PM

Never  torqued up the axle and never will.
Not lost a wheel yet.  ;)
Title: Re: TORQUEING REAR AXLE
Post by: Nurse Julie on October 19, 2019, 06:49:18 PM
It's a bike, not the Starship Enterprise....keep it simple.
Title: Re: TORQUEING REAR AXLE
Post by: StevieWonder on October 19, 2019, 09:29:21 PM
Thanks for your opinions. My initial appeal was for help in torquing the rear axle without removing the exhausts, but none of the suggestions provided certainty that it would be correctly tightened. Having devised a solution I thought I'd share it. There are only a few torque settings on the CB750, so in my opinion these are important and in fact my rear axle was too loose. I now have confidence that it isn't and future chain adjustments can be done correctly and conveniently. Correct me if I'm wrong.
Title: Re: TORQUEING REAR AXLE
Post by: Green1 on October 19, 2019, 09:45:20 PM
Not wrong things should be done propperly. I'v just never done things like that as tight as the manufacturer suggests as there almost always imposible to undo at the side of the road with tools supplied.
Have you ever tried to undo a wheel on your car with the brace supplied when torqued up to the manufacturers spec
Title: Re: TORQUEING REAR AXLE
Post by: StevieWonder on October 20, 2019, 10:46:31 AM
Thanks Green1, I hear what you say, car wheel nuts can be difficult to remove. However, the rear axle suggestions provided (stand on it/ use a long leaver) would likely result in an over-tightened axle nut hindering removal and even if you could loosen the nut, changing a bike wheel at the roadside is hardly an option. Though I will try and undo the correctly torqued nut with the standard tool kit shortly and advise.

Evidently over 50-years and some 400,000 CB750K examples, there have been few if any problems associated with tightening the rear axle. It seems to withstand over-tightening and under-tightening, supported by the chain adjusters. I just want to tighten it correctly and now I can.
Title: Re: TORQUEING REAR AXLE
Post by: StevieWonder on October 21, 2019, 04:10:19 PM
Just to complete the story. A rear axle wheel nut tightened to 67 ft/Lbs can readily be removed with a size 10 shoe and the standard tool kit hex spanner with extension. Just undo the footpeg nut a few turns.
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