Author Topic: Fork springs  (Read 636 times)

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Offline Danny sparks

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Fork springs
« on: July 18, 2017, 05:27:32 am »
I have two bikes ones 1986 and the other is 1990.one set of forks has a 3in.space at the top off the spring.but the 1986 has no spacer.is there anyway of telling if the bike has a unrated spring in it...are there any  identification on the springs...just a bit of a puzzle. ..

Offline GeorgeRYoung

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Re: Fork springs
« Reply #1 on: July 18, 2017, 12:04:04 pm »
I believe the stock setup has a spacer.

You can measure the spring rate with a bathroom scale. Push down a convenient amount (e.g. 10mm) and note the reading in Kg, then divide (by 10) to get Kg/mm. If the spring is dual-rate or progressive, this will only give the initial spring rate.

Offline Outback Jon

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Re: Fork springs
« Reply #2 on: July 18, 2017, 04:59:52 pm »
I believe the stock setup has a spacer.
My 06 didn't have a spacer.

At least until I cut the spring down and added one.

I'm thinking that Danny might have a set of straight rate springs in the 1990.  You can usually visually identify straight rate vs. progressive rate springs.  Progressive rate springs the coils on one end will be close together than the coils on the other end.  Often (like on my 06) there is an obvious change in the coiling if you look at the whole spring.  Straight rate springs will have a consistent coil for the whole length of the spring.
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Offline Herb

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Re: Fork springs
« Reply #3 on: July 18, 2017, 05:27:16 pm »
From the factory manual the '86 to '93 had a spacer on top of the spring. The free length of the spring was 514 mm and the service limit 504 mm. The '94 to '06 had no spacer.

Offline Danny sparks

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Re: Fork springs
« Reply #4 on: July 18, 2017, 07:26:20 pm »
That makes sense. .so progressive Springs have a wider coil gap at the bottom is that correct if so the 86 has progressive springs in it and no spacer....

Offline MAN OF BLUES

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Re: Fork springs
« Reply #5 on: July 18, 2017, 07:30:34 pm »
As noted, from 86 thru 93, the forks had a steel tube spacer, and a hat shaped washer over the spring. These were also all air assist forms, with an air crossover tube between the froms that sat just above the lower trippel tree. Those forks have a  hole in the tube, allowing the air equalization between forks, thru that crossover.
All of these springs from the factory, were "progressive" in design, and can be destinguished by examing them, and seeing a variation in coil spacing on the spring.
The dimensions for "free length" were also noted.
If the forks without the spacers are longer than that dimension by about 2", and they have differentiated coil spacing on the spring, they are likely Progressive Industries replacement springs, which are a good product, carried by Murph. Also, those specific springs did not require a spacer due to design, and, longer length. They also do away with the need for additional air assist to function, which increases seal life exponentially. The ones with the spacers still require air, and should not excede 7 psi, added by a small bicycle hand pump.

I hope this assists.

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