Help with rear springs please

davamb said:

I find that 1 lb/in = 0.017kg/mm and thus the stock rate of 126 lbs/in is 2.14kg/mm

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Well I got 40mm of travel for 80kg of force using Graeme's method. This is 2kg per mm which is pretty well spot on for 126 lbs/in. Better see what the damping is set to now and then have a look at the swingarm pivot...

I'm a bit late to this discussion, but here's a little more input. Dunstall recommended the 110 lb/in rear springs for the average Commando road rider. I used to use 80/100 lb/in progressive springs on my Commando road racers. The standard 126 lb/in spirngs are a bit stiff unless you ride two up and/or carry lots of luggage. Konis sold for the Commando usually had springs closer to the 100 lb/in rate. My memory says they used 70/100 lb/in dual rate springs, but it's not real reliable anymore.

Ken

lcrken said:

...The standard 126 lb/in spirngs are a bit stiff unless you ride two up and/or carry lots of luggage. Konis sold for the Commando usually had springs closer to the 100 lb/in rate. My memory says they used 70/100 lb/in dual rate springs, but it's not real reliable anymore...

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Thanks Ken, that would seem to tie in with what DPO used to say - it handled better with GF on the back. I've decided to dismantle the rear end and check the swingarm pivot anyway (not a lot of effort) and might try some softer springs while I'm at it. 100lb/in sounds like a good place to start.

Shocks are now off. Groan. Whole swingarm and motor moves over a cm each way from centre-line with little effort, pivoting on the front iso. Looks like the rear one has either not been assembled properly or is knackered. Looks like some serious investigation work ahead.

Ugh-roan, sounds like routine barn find sound state I hear myself make too. In for a penny down for pounds and pounding.

Thing that really irks me Hobot, is that I paid good money to have the bike rebuilt and that apart from pulling the motor down, there's not much of that work I haven't redone. A case of "a fool and his money" perhaps? Don't answer that, I'll just console myself with the thought that maybe I have higher standards.

Lot of work to get the rear iso apart? Does the motor / gearbox have to come out first? Time to research first before getting stuck in.

edit: Found the info:
post37469.html?hilit=isolastic%20replacement#p37469

Dave, don't feel alone with the paid someone who knew the way with these Norton things and had to do it again yourself.
I didn't know the English way or secrets so I sent the motor and gear box out to the experts also. Italian bikes and their strange ideas I knew, but not English.
But now after lots of miles and breakdowns and shimming , bearings, clutch issues, selector problems, valve guides, valve springs and seats, oil leaks, electrical gremlins, exhaust threads, etc, my head hurts,,,,
They aren't hard or expensive to fine tune.
It seems that they only behave once you've caressed each bit yourself.
Good luck.

graeme

Ouch. If the cradle needs machining, the gearbox comes out, and that almost means the motor, although it's possible without, but a big pain. It'll be worth it when you're done though. No swing arm play is the place to go. I shipped mine to Nithburg in CA (2003) and he did a nice job with a new SS oversize spindle and bored the bushings too. Kind of like ludwig's job, not the Kiegler mod. You might get away with the Kiegler job if you just pull out the spindle, but it won't be right if everything's worn.

Dave
69S

Aw man I was still grinning on the Motoguzzi video in other section then lost the grin on reading Dav's deeper history. I've only been at Commando's since summer of 99 and best I can glean, is you either pay like 6000 for some forced private lovers loss of at least 50% on the dollar in parts/processing and zero for the blood sweet and tears to build a fully fettered C'do, or pay nearly 20k for professional custom or piece meal and ride piece meal and ride, or bite the big bullet and start from scratch. The sad truth is C'do's are one of the most simple complex machines conceived and essentially everything including tire condition profile and air pressure must be pretty darn spot on or annoyance of one sort or another plagues the joy.

Rear spring rate has a big influence on how it wags the tail to shake the head. I've dealt with 3 swing arms with worn bushes that wore a lips in unsecured [collared] spindles that they could not be extracted w/o damaging the swing arm geometry, 3rd one is my buddy Wes's '71 and he just gave up put on collars and tolerates some wiggle and extra care in hanging turns. So far I like plain bushes with grease zerks put in, but read one rider found that worn out even faster than oil residue system of factory 750's. Needles sure sound good and all praise them so may fall back on that on my special too someday.

I've wondered in depression how in the world anyone could/would do what it takes to go through and restore a C'do. It can be similar to raising a child got to look years down the road to see what all the trouble was for.

Hello Dave, I fitted some Ikons to my Commando this year, and ordered them from Norman Hyde in the UK. Previously I had Hagons on which worked quite well, but they were cosmetically tired. The new shocks were fitted, and on the back roads that I tend to use with the Norton they were terribly harsh, and so I contacted Norman about them.

Apparently, on the Ikon shocks that he supplies (and which presumably are supplied to him by Ikon for the Commando) he removes the standard mono rate spring that it comes with and fits a progressive spring. We checked the spring code on my shocks (and also visually I could see it was mono rate) and reallised that the spring hadn't been changed by his staff proir to dispatch, and based on what I had told him i.e. I wanted a compliant ride, and the typical weight that I run on the Commando (I usually run 2 up with a combined weight of 19/20 stone), we agreed to opt for the spring rate below the one he fits for the Commando, and he supplied me with the type he fits to a Bonneville. Unfortunately I can't remember the rating, but the code on the spring is "Ikon 230#." Edit (I just looked it up and the spring rating is15/21/26 KG load rate (83lbs to 145lbs)
Equivelent to a 90lb single rate spring).


If I am totally honest with myself, although the ride is now reasonably good and much improved over the original mono springs fitted to the Ikons, I wouldn't say they are very much of an improvement over the original Hagons but they do look a lot nicer

So in conclusion........I don't have a conclusion, except if you get something you like, stick with it.

http://www.racingsuspensionproducts.com ... 20rate.htm Pretty easy to calculate spring rates if you have an accurate vernier to measure the wire size.

Thanks for the info everyone. Will continue to dismantle and investigate over the following week (nights) but today decided to go for a decent run on the TRX. Sometimes you get hooked on the maintenance and forget what riding's all about! All work and no fang makes Dave a dull boy.

Do I really have to take the motor out to check out the rear isolastics?
Looks like soooo much work damnit.
Maybe I should strip it completely and do a frame paint job at the same time.

No you don´t have to take the motor out or your primary ! on a good day it would take you about 2 to 3 hours ! theres a few old posts concerning this . good luck and it´s not that hard ! cheers

Thanks Blaise, went through the in-frame method only to discover the swingarm's locked solid. Removed the rear iso bolt and carbs, zorst, top iso etc, etc and with the motor cradle supported the swingarm should move freely with the shocks removed. It doesn't, it moves the engine/tranny as well. Think I may as well pull the motor at this point and do it all properly. Groan. Make that double groan. Might mean the shocks are not that bad afterall (he says, hoping for a glimmer of sun to break through the clouds).

Time to get out the penetrating oil and warm up the propane torch. Did the bike sit for a long time?

Yep it's been about 12 years since it was last on the road full time BatRider. I've been taking it further and further each ride, hopefully this is the last major chore to getting it fully road sorted.

This is really not so good. The swingarm pivot is severely rusted:



and



Have poured in heaps of WD40 and have worked it up and down a couple of times using brute (well, the best I can manage anyway) strength. Getting some movement. Will keep pouring in the lube and working it. In the meantime have to locate some pipe to make an extractor device. I've cleaned out the thread and that's serviceable at least.

Can also see on the inside of the transfer case where the end of the swingarm pivots cover has been banging against it. Now I haven't done many miles on this thing at all, so looks like the isos were stuffed when DPO was riding it.

Bought pipe, made extractor and it just snapped the bolt I screwed into the thread. Bolt removed, thread's still ok, but now I'm in the poo. If I dismantle the clutch and take off the whole transmission housing, can I drive the swingarm axle out from the left side? Bereft of ideas now.

What size was the snapped bolt, and did you use heat?