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'03 Sprint.
Does anyone have any observations on which way round progressive springs should be fitted, and why? The Haynes manual, which lumps together Sprint and Tiger fork overhaul, which suggests the forks are of a very similar type (as opposed to Daytona and Speed Triple which are of a different type) says the closed coils go to the top on the Tiger and to the bottom on the Sprint(?). The instructions with the replacement springs (Hagon) says the closed coils go to the top. When travelling on a smooth road surface the front of mine seems to bounce up and down (nothing to do with tyres or wheels). Pushing down on the forks when stationary they seem sluggish to compress and return slowly to their original position without any overbounce. I have read in other threads that the Sprint is under sprung and over damped. If the oil is too thick, (Hagon supply 7.5wt) this would slow down their movement as observed, and because of too much compression damping, make the bike bounce up and down on an undulating surface instead of the forks compressing and the bike staying level. It also seems to me that the open coils would be the softest part of the spring therefore with the closed part of the spring at the top, the wheel would be more inclined to move up and down with the bike staying level only stiffening up with heavy braking. If my thoughts are correct why is the Tiger different to the Sprint and why is Haynes different to Hagon?
 

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Pehaps i need a slap across the head, but i have no idea why it would make it difference which end the 'closed' spring end would be placed, top or bottom. Seems to me compression force would be exerted equally top and bottom?
 

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I'm with danall,

but when in doubt I'd go with the parts instructions.
 

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You could put one up & one down & it wouldn't make a difference as far as the science goes. (It would drive me nuts knowing they were like that, but not for any logical reason.)

Cheers, HTH,
-Kit
 

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I believe the stock oil weight is actually 7 not 10.

I run 15wt in mine and so does dolson from memory.

DaveM:cool:
Dave, and all - somewhere on the site is a detailed description of the oils used in forks (and shocks). The OEM fill is something called '8'. One cannot find '8' fork oil in the 'States', so one must use 0, 5, 10, 15, etc.

To cloud the issue further, the number of the fork oil is not the 'weight'. I don't remember, but 15 weight oil was roughly equivalent to 20 fork oil. Which, also IIRC, is the consistency of ATF. Which supposedly makes a fine fork oil. At a fraction of the cost.

I'm certain OnD or one of the other gents will chime in on this.

If we get a lube guy, I've always wondered; if you mix equal parts of 5 and 15 weight oils, do you get 10?
 

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Dave, and all - somewhere on the site is a detailed description of the oils used in forks (and shocks). The OEM fill is something called '8'. One cannot find '8' fork oil in the 'States', so one must use 0, 5, 10, 15, etc.

To cloud the issue further, the number of the fork oil is not the 'weight'. I don't remember, but 15 weight oil was roughly equivalent to 20 fork oil. Which, also IIRC, is the consistency of ATF. Which supposedly makes a fine fork oil. At a fraction of the cost.

I'm certain OnD or one of the other gents will chime in on this.

If we get a lube guy, I've always wondered; if you mix equal parts of 5 and 15 weight oils, do you get 10?
Oh I didn't know that it was like that in the US of A, no doubt OND or the like will know.:)

DaveM:cool:
 

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Observant members might have noticed that every now and then I try to remind the peeps that fork oil weight is not always the same from each manufacturer. That is why I recommend to select a brand and stick with that brand if you are going to try different weights. Once you switch brands, you have lost all references, and are starting from scratch again.

As long as you are using the same brand, and portions are relatively controlled, mixing 5 and 15 to formulate 10 is considered acceptable.

Here is some easy ready on the subject:

http://www.motocrossactionmag.com/m...0&tier=3&nid=06892BA6B9A740CF833A439ACD16632F

There are other online sources of info including several attempts to correlate the different brands to each other. Those charts are quite surprising.

This is the heavy reading, and the surprising charts:

http://www.peterverdonedesigns.com/lowspeed.htm
 

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If we get a lube guy, I've always wondered; if you mix equal parts of 5 and 15 weight oils, do you get 10?
OK...you've got a lube guy here...I'll try not to get too carried away.

There are a couple of issues here:

1. SAE viscosity grades, designed for engine oils (0W, 5W, 10W, 15W etc) are fairly wide bands, measured at 100 deg C., aren't really accurate enough to measure differences in light fork oils at 20-30 C. Finding the Cst @ 40 C would be much more accurate.

2. As OnD has mentioned, fork oil viscosities listed by manufacturers don't neccessarily even follow the SAE grades. (check out the Peter Verdone site link).

3. Viscosities aren't linear, they are logrithmic.

But...to answer the question, assuming a blend of an SAE 5W with a viscosity of 4.0 Cst @ 100 C mixed 50/50 with an SAE 15W of 6.0 Cst @ 100 C would result in a viscosity of 4.8 Cst, which would fit in the band of a 10W, so yes...it might technically be a 10W. What's more important is that it WILL be heavier than the 5W you started with.

I can post an ASTM viscosity blending chart if anyone really wants it.

The good news is that Peter Verdone's site, as posted by OnD, is pretty good. It's not perfect, but it certainly has the concepts pretty well covered, and it has some pretty good data on actual fork oil viscosities, assuming it's reasonably up to date.
 
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