Stiffening springs

[David Trustrum]

This isn’t a question, more a tip.

In a lower thread I had asked for fork spring specs so I could calculate how much I needed to stiffen the springs. Course I could pop US$50 for new ones & wait for them to arrive, but 20min & free sounded like a better deal.

Basically the less active coils (all the ones that aren’t touching at either end) a spring has the higher (stiffer) the spring rate. (Bend your ruler at far ends then move your hands closer & it gets harder right?).

So how much to cut off?

(Old spring rate x active coils)/desired spring rate.

That gives me the number of coils I want left. In my case I had .3 springs & 33 active coils & I wanted .33 springs. (works with pounds as well). This = 30 coils so I cut off 3 from the original 33. (Usually the numbers aren’t this round, with rear springs be more accurate).

I just used a disc grinder to lop the coils off & then GENTLY using a bit of heat from a handheld propane torch or whatever bend the cut part down to touch the lower coil & dress it up to look like it did before you cut it.

The springs measured 495mm before & 440 after, so we have to make up the difference to keep the preload the same. The std spacer was 85mm so a new one 140mm was cut from a piece of 34mmID (37OD) plumbing pipe. (OK so I spent $2 so sue me!)

Job done.

You can stiffen Front springs, Rear springs, even clutch springs, as long as you make up a spacer to retain the preload. Just beware if you are going to lop off quite a bit -that there is still room so the spring doesn’t coil bind.

 

[Simon Fuller]

Any one tried this?

Free sounds great, I've been moaning about the markup NZ dealers have been putting on springs and delaying fitting stiffer springs to my 98 220. I figure I should look at .40 as I'm 85kgs, plus riding gear.

But, what are the downsides of this mod? Is this a case of "if it sounds too good to be true it usually is"? Has anyone else out there done this and what was the result?

Sorry David I don't mean to doubt you. I've heard that shortening the springs will indeed stiffen them but before I go hacking into my springs I was wondering why anyone would go and purchase new springs when this sounds so easy - there must be a downside surely.

I s'pose at the end of the day if I try it and it doesn't work out OK, I was going to buy new springs anyway!

 

[dirt bike dave]

Have shortened fork springs on my '84 and '90 KDX and seen it done by friends on several other bikes. Just pay attention to the warning about coil bind - measure the space between the coils and multiply by the # of remaining spaces and make sure the distance is still greater than your fork travel.

Have never known of anyone to cut a shock spring themselves, but a buddy with a DR350 did braze little metal wedges between some coils to keep those coils from compressing.

 

[Vic]

I wedged the screw housing part of a hose clamp between the first and second coils on both ends of my shock spring. I 've been running it that way for a year with no problems. At first, I was concerned that the housing would get smashed down into the worm gear (screw) and I would never be able to take them off, but I tried it the other day and they came right off. As has been said, you definitely want to measure to be sure you have enough space between the remaining coils to avoid coil bind.

 

[David Trustrum]

Well I’m glad this finally got some comment. Wanna know the other way to cut a shock spring? (& this is second hand I admit) wedge the spring over a bucket of water & heat the point (using oxy/acetylene) you want cut to red then turn the gas off & leave the oxygen on & the wire will keep burning right through. Then you bend the spring end even more gently. Make up a preload spacer & you’re done.

Yes watch the coil bind.

& Si if you were going to buy new springs what’s the danger? PS Auckland & wgtn shops do put a hideous mark up on everything. Sometimes it’s cheaper to find a good rural shop & get them to freight it. I get all my Kawasaki bits down from Ingram & Worsely, they have a website off silver bullet.

Like the hose clamp idea, very bush! A number 8 fencing wire job we'd call it here. But hey if it works -a good way of testing!!

 

[Vic]

Originally posted by David Trustrum
A number 8 fencing wire job we'd call it here.

We've got a couple of names for it here, too. Probably wouldn't be a good idea to mention them, though. :)

 

[lime away]

Cutting fork springs

Heating a spring to the point where you can square the end up is changing the temper of the wire. It is actually making the wire harder or brittle. This is going the cause it to fatigue and crack eventually. If anyone atempts to do this, I would suggest you stress relieve the spring at a temp of 500/600 degrees F for 30 minutes after heating and squaring. It would also be good to shot peen the end after stress relieving.

 

[Simon Fuller]

I have a 98 220. The std springs are .35 and I wanted to go to .40. Being mindful of coil bind I measured the gap between the coils and multiplied by the no. of gaps which makes 320mm. The fork travel is 290mm. To get to .40 I calculated that I would need to remove 4 coils (31 x .35)/.40=27. Unfortunately this doesn't leave enough free space for the amount of travel.

It would appear that Kawa have done their maths and put in springs just long enough to cope with the amount of travel. I reckon you could only safely remove 2 coils, giving springs of .37kg.

Looks like I'll have to pry open my wallet after all!

 

[David Trustrum]

Lime away, interesting point, probably a bit over the top as I have never seen a problem with this & lots of people have done this with rear springs which are under considerable pressure. Never a bad thing to be over cautious though.

Sorry to hear that things didn’t quite work out for you Si. Good to hear you were smart enough to measure it though.