front fork bottom out ... springs ?

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Jun 1, 2007
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Hi Norton Folk ..

Have just aquired (well permenant loan) a 74 850 Commando

have had triples all my life so this will be some fun and i expect some dumb questions comming from me so i hope you will bare with me :)


First obvious issue with this machine is the front forks bottom out and have very little travel ... I've had a quick look took the caps off and the nuts holding the springs in place ( a tad different to triples up front in the guts ) ... looks to have progressive springs ...

are there any tricks for new players here ..

I measured the travel with no springs and it looks to be about 100mm (4inches) top to bottom of the travel which is a fair bit smaller than i am used to .. with springs in the travel when the bike is off the stand is less than 50mm (2 inches ) ... i would have thought clearly something not right here.

the springs them selves are 480mm long

appreciate any feed back

thanks
Steve
 

L.A.B.

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Hello Steve and welcome.

There are a few other triple owners here already (myself included) who you may recognise from the TOL website!

There should be six inches of fork travel, so if you only have four then you may need to investigate why? Possibly the damper rods or damper bodies or stanchions are too short?
480 mm sounds about the correct length for the springs, but it would appear from the sag and bottoming that they could be too soft or are not preloaded correctly?

My own progressive springs settle about 1 to 1/12 inches off the main stand and certainly don't allow excessive bottoming out.

I would suggest (after checking the fork parts) that you start off by using SAE 20 fork oil and adjust the viscosity to suit your riding style? SAE30 may be more suitable in hotter climates, others use ATF but I personally think that is a bit too thin and can allow the forks to top out.

There have been a few posts about forks recently, so I suggest you have a read through them.

Here is some fork tech info:

http://atlanticgreen.com/forks.htm

http://www.nortonownersclub.org/technic ... etail.html
 
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Aug 26, 2005
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Hi - I had the same problem with my Norton purchase. I replaced the springs with progressive ones, & have not bottomed out since. I do find them a bit stiff however...

In examining the old springs my guess is that they were in fact not Commando springs as they were a bit shorter & smaller than the replacements...

You can't rule anything out on a 30+ year old machine...
 
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Thanks LAB .. i've seen you around on TOL ...

I will take the forks right down as i have no idea what the PO did ... clearly something not right ... I'll have a copy of the workshop manual arriving on Tuesday so i'm hoping all the info dimensions etc i need will be in there ..

with the progressive springs is there any other mod to the fork internals other than the spring its self ?


i suspect i will still have some questions as i am not Norton savy ....

Steve
 

L.A.B.

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snibor said:
with the progressive springs is there any other mod to the fork internals other than the spring its self ?


Just a straight swap, progressive springs sometimes come with extra spacers so they can be tuned for preload, but are not supplied for use with the Commando springs as far as I know?

There are no actual component lengths given in the manual so I would suggest you use the atlanticgreen website dimension info.
 
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Forks .. more info

Lab ...

had a good look at the travel on the forks this evening ....

I jacked the bike up and put the main stand on blocks ... pulled the forks out to max and then pushed them back up (huts off the top of course )

I get about 6 inches travel to to bottom ...

the thing that looks odd is that the thread at the top of the damper rods disappears down the stanchions by 3 1/2 inches ... i made a quick tool up to pull them up as much as i could and without the springs on they still only come up before topping out to 3 1/2 inches below the top of the top yoke .... without a manual and not really knowing what's inside this looks like the damper rods are to short ? what do you think ? or am i barking up the wrong tree here
many thanks
steve
 
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.... without a manual and not really knowing what's inside this looks like the damper rods are to short ? what do you think ? or am i barking up the wrong tree here
many thanks

No, sounds like your barking up exactly the right tree - if you have read the current Forks thread! :D
chris
 

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Re: Forks .. more info

snibor said:
the thing that looks odd is that the thread at the top of the damper rods disappears down the stanchions by 3 1/2 inches ... i made a quick tool up to pull them up as much as i could and without the springs on they still only come up before topping out to 3 1/2 inches below the top of the top yoke

3.1/2 inches does sound odd?

So odd that I checked it myself, and the tops of my damper rods drop to three eighths of an inch below the top of the stanchions with the wheel off the floor and with the forks extended (springs in position holding the rods fully extended)...

However..... I have the Covenant kit sleeves (read about them in the previous fork discussion) fitted so they limit the total amount the forks would drop (with the damper rods disconnected frm the fork top bolts) by approximately 1 to 1.1/4 inches, as the maximum travel I actually measured was 5 inches.
So I would estimate that damper rods should only drop less than 2 inches below the top of the stanchion (with no Covenant sleeves fitted)? The damper tubes and damper rod lengths affect the overall fork travel, as those parts also act as the extension limit stops which reduce the available fork travel by approx. 1.1/2 inches (see atlanticgreen fork info).

So the published (and generally accepted fork travel figure) of 6 inches would appear to be wrong in practice, as it would actually be nearer to 4.1/2 inches!
 
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Damper rods

Is there any good reason why the damper rod should not be threaded another 2 inches or so ? that way you could pre load springs to suit ..

steve
 
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Steve,
Before you start preloading etc, are you sure the bike is fitted with the correct springs? The Progressive springs I fitted, as LAB says, came without spacers and did lift the ride height a tad. I notice things like that being vertically challenged.

Cash
 
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Cash

i have the opposite problem where the front is low and only has 2 inches travel before bottoming out .... I can bottom it out from a standstill just using the front brake and shoving forward hard ...

steve
 
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Steve,
The PO may have fitted springs from another lighter make of motor cycle.

My question is, are you sure the springs are for a Norton Commando?

Even with the correct springs the bike will roughly have 1" to 2" inches sagg, so there's little movement left normally. Perhaps the compression damping is a little weak.

What oil are you using in the forks?

Cash
 
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Sorry for the all caps I wasn't shouting just can't stop the word program from a old preset.
THERE WERE THREE GUYS WORKING ON THIS KIT. WE TALKED AND LOOKED,
AND LOOKED SOME MORE.
FIRST STAGE, STRIP DOWN FORKS TO ONE
FORK STANCHION, ONE SLIDER, ONE STEEL BUSHING WITH CLIP TO RETAIN,
ONE HIGH HAT BUSH, ONE SEAL AND ONE SEAL RETAINER ASSEMBLE DRY
AT THIS POINT. CHECK TRAVEL, GOT SIX INCHES PLUS WITH NO DAMPENER TUBE,
VALVE, ROD OR SPRINGS.
OK SECOND STAGE, ADD STOCK DAMPENER TUBE
WITH VALVE SUPPORTING ROD, TUBE CAP, SPRING, STOCK SPACER, JAM NUT.
NO FORK CAP NUTS OR FLUID SO WHEN YOU SLIDE THIS BACK AND
FORTH THE SPRING ASSEMBLIES ARE COMING IN AND OUT OF THE TOP OF
THE FORK STANCHIONS TOPS. THE TRAVEL WAS FOUR AND ONE HALF INCHES.

NOTE THAT IN THIS STATE THE SPRINGS ARE LOADED AGAINST THE TOP OF
THE DAMPENER TUBE CAP AND ARE TRAPPED BY THE JAM NUTS AND THE
SPACER ON THE OTHER END SO THE DAMPENER VALVE IS TIGHT UP TO THE CAP.
UNTIL THE BIKE IS FULL ASSEMBLED WITH THE DAMPENER ROD JAM NUT
TIGHT TO THE FORK CAPS AND THE WEIGHT OF THE RIDER IS FELT THE
VALVE IS ALWAYS GOING TO STAY THERE UP AGAINST THE CAP.

THE STOCK LENGTH OF THE ROD IS LIMITING THE DISTANCE THE
SLIDERS CAN MOVE. DO THE SAME TEST WITH TWO INCH LONGER RODS AND
AN EXTRA SET OF SPRINGS FOR PRELOAD AND YOU GET BACK THE
SIX INCHES OF MOVEMENT. THE TRUE LIMIT, THE MAX TO BE HAD,
IS WHEN THE TOP OF THE STEEL BUSHING HITS THE BOTTOM OF THE
HIGH HAT.
NOW YOU DON'T WANT TO RIDE THE BIKE IN THIS STATE WITH
THE TWO BUSHES TIGHT TO ONE ANOTHER THERE'S JUST NOT ENOUGH
SUPPORT AND THE FRONT TIRE WILL BOUNCE BACK AND FORTH AT
STOP LIGHTS. SO WE CAME UP WITH THE TWO INCH LONGER MODIFICATION
FOR THE ONE AND ONE HALF INCHES OF TRAVEL GAIN SO THAT UNDER
NO CIRCUMSTANCES COULD THE DAMPENER VALVE BE USED
TO LIMIT THE TRAVEL FOR THIS WE WANTED A FLUID STOP AND NOT A ONE AND
ONE HALF LONG LOOSE FITTING BUSHING BETWEEN THE TWO
BUSHINGS ALREADY IN THE FRONT END LIKE THE COVENANT KIT HAS.

THE SPRINGS THAT COME WITH THE KIT ARE FROM FORD TRACTORS AND ARE
THE SAME O.D. AND I.D. AS NORTON AND PROGRESSIVE SPRINGS.
THEY START WITH A TWO AND NINE SIXTEENTHS FREE LENGTH AND HAVE
HAVE A BOUND LENGTH OF ONE AND NINE SIXTEENTHS FOR ONE INCH OF TRAVEL
. FROM WHAT WE KNOW THE STOCKS SPRINGS HAVE ONE HALF OF AN INCH TO GO WITH
THE SLIDER BOTTOMED OUT, THAT IS THE BOTTOM OF THE STANCHION HITS
THE BOTTOM OF THE SLIDER. WE ADD ONE AND ONE HALF OF TRAVEL
WITH LONGER RODS AND THE EXTRA SPRING ADDS ONE INCH AND
THE OLD SPRINGS HAD ONE HALF INCH TO GO SO THE SPRINGS SHOULD
BOTTOM OUT JUST AS THE FORK STANCHIONS DO.
NOW FOR THE FLUID CONTROL
IF THINGS WERE IDEAL ONE WOULD HAVE FULL MOVEMENT WITH HYDRAULIC
STOPS AT EACH END THAT IS NICE AND SLOW ACTING RIGHT AT THE
ENDS OF TRAVEL. THE BEST WE HAVE COME UP WITH SO FAR
IS USING ATF FOR FLUID AND LEAK PROOF BRAND SEALS IT WORKS
ON FIFTY BIKES SO FAR WITH NO ADJUSTMENTS NEEDED NOT
THAT THERE ARE NO ADJUSTMENTS. I HAVE ONE BIKE WITH STOCK SPRINGS
AND ONE WITH PROGRESSIVE SPRINGS AND I HAVE TO SAY
THAT I FIND THE PROGRESSIVE BETTER BUT THE STOCK SPRINGS WORK
WELL TOO.
ON THE CENTER STANDS THESE MODIFIED BIKES DON'T
LIFT THE WHEELS OF THE GROUND ANY MORE BUT STILL WORK FOR ME.
THE IDEA IS TO GET THE BIKE TO GO DOWN FROM YOUR WEIGHT
AT LEAST ONE AND ONE HALF INCHES. THAN RIDE AROUND WITH FOUR
AND ONE HALF POTENTIAL INCHES FOR BUMPS AND THE
ONE AND ONE HALF FOR POT HOLES. NORBSA
I also have another way to get the same effect without raising the Bike. It uses one inch shorter legs and a one inch longer dampener rod and a different set of springs still get the full 6 inches travel and fluid stops but goes better for the vertically challenged and center stand unsteadiness. If your running a disk brake you may need to make a new bracket and hard line but I also offer this kit.
_________________
 
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cash said:
Steve,
The PO may have fitted springs from another lighter make of motor cycle.

My question is, are you sure the springs are for a Norton Commando?

How can i tell ... they are 480mm long, progresive springs ... but i did notice they have blue paint on the ends ...

Even with the correct springs the bike will roughly have 1" to 2" inches sagg, so there's little movement left normally. Perhaps the compression damping is a little weak.

could well be ... i will put new seals through it at the weekend (can't wait for the suprises there )


What oil are you using in the forks?

Unkown ... whatever was in it ... i

steve

Cash
 
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Jun 1, 2007
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Modified forks

NorBSA

what you say makes perfect sense to me but then again i'm used to ridding a Hurricane which feels like it has a foot of travel in the front end ...

4.5inches does seem a tad small but i belive that the Roadholders have a better reputation that the Triumph forks so maybe 4 1/2 is enough ...

what i need to do is get more than 2 inches ... sorta smells of wrong springs ... they are the correct length according to the specs but could well be underated commpression properties ... i mentioned in a previous post the the springs have blue paint on them ... i have a recolection that blue is soft and red is hard ?

steve
 
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Jun 1, 2007
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Thanks

Oh and by the way ..

many thanks to all of you for your input to this and being patient with a newbie to Commandos ..

steve
 
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An old set of stock springs I have here are 18 and 3/4 long or about 4755MM.Checking the travel with the front springs under tension is a waste of time and energy. see the all Caps post for the right way.
Reg a guy in your town has one of my kits. I would be looking into the end of the travel were the hole in the end of the fork leg begins to get to be a ever tightening fit over the taper on the dampener tube. Some of the new fork tubes don't have the right size hole inside the bottom end but it has to be right. As you can well imagine I have done a large amount of these refits and it is also not unusual to find the two mm dowels folded over from hard top outs. When you add travel to the stock set up by using longer rods it makes the oil work better on both ends of the travel. I use F type ATF I like it because I can feel it wear stiffening the action and forcing me to change it at least twice a year. If I was going to oil I would be using one of the new Synthetic 7-10 WT oils for forks on new bikes.
 
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Have you tried assembling the forks without the spring to see the total travel you get? If it's the full 6.15 inches then clearly it's the springs are wrong and nothing else.
 
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pommie john said:
Have you tried assembling the forks without the spring to see the total travel you get? If it's the full 6.15 inches then clearly it's the springs are wrong and nothing else.

yep have done that and get the 6 odd inches ... so looks like the springs ...

cheers
steve
 
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john you in Brisbane too :)

John

If you don't mind would like to pick you brains for a few other things on the Norton ... send me an email if you can ...

steve
 
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