Fork spring help

[Pat D]

So back in the fall I ordered parts for a front end refresh this spring. Fork seals, dust covers, and springs. I ordered based on my application, '74 TX650A. While I know that parts get swapped over time by previous owners, my forks seem to 100% reflect what the '74 parts fiche breakdown shows. But the springs I ordered are looong. They come right to the top of the fork tube, whereas the old springs allow for the spacer to fit nicely with no preload at all. Old springs are roughly 15 1/2"(390mm), while the new ones are roughly 19 5/8"(495mm). The spacer is roughly 4".

So- do I just toss the spacer? That will allow just a touch of preload. Installing the spacer means compressing the new springs 4" to get the cap on- seems like a LOT of preload, with a significant degree of difficulty getting the cap on w/o cross threading it or otherwise boogering the soft aluminum threads. I've searched about every thread I can find on this topic, and it "seems" like in most if not all cases there is minimal preload/minimum spring compression needed, the spring/spacer combo seems to sit right at or below the top of the fork tube. I don't remember who I bought the springs from, so return is not really an option. But I for sure did order for my application.

So my options appear to be, 1. Eliminate the spacer. 2. Cut down the springs to allow for the "proper" amount of preload (which is???) with the existing spacer. 3. Cut the spacer down (don't want to do this, part is NLA) to allow the as yet unknown amount of preload. Other than cosmetics, the bike is bone stock, I'm not trying to lower it or customize/tune the suspension in any way. And it's hard for me to imagine the factory springs have "settled" 4" over time, the coils appear to have the same spacing as the new springs.

Any thoughts? All input much appreciated!

 

[bosco659]

I just replaced fork seals this winter. My springs are the same length as your new ones. They were installed by the po. I figure with the caps fully tightened they might have 1” of preload at most. If they are progressive rate springs I wouldn’t cut them.

 

[Pat D]

I just replaced fork seals this winter. My springs are the same length as your new ones. They were installed by the po. I figure with the caps fully tightened they might have 1” of preload at most. If they are progressive rate springs I wouldn’t cut them.

I have no reason to believe they are progressive rate springs, I did not specifically order progressive rate springs, just the springs the vendor listed for '74. More than likely from Mikes. EDIT- upon further investigation, Mikes does call them "progressive" in the tech description. https://www.mikesxs.net/yamaha-xs65...?fits-motorcycle=Yamaha/TX650/all-models/1974

When you say that you have 1" of preload with the caps tightened down, is that with or without the factory spacer? Because with the factory spacer I've got about 4" of preload, I'm not sure I can even get things compressed enough to get the caps on with the factory spacer.

 

[bosco659]

I have no reason to believe they are progressive rate springs, I did not specifically order progressive rate springs, just the springs the vendor listed for '74. More than likely from Mikes. EDIT- upon further investigation, Mikes does call them "progressive" in the tech description. https://www.mikesxs.net/yamaha-xs65...?fits-motorcycle=Yamaha/TX650/all-models/1974

They looked progressive in your pic. Wound tighter on the left side than the right.

 

[Pat D]

Well, after more searching, it looks like I found my answer in this thread- https://www.xs650.com/threads/fork-spring-length.17506/

Bottom line, the aftermarket "progressive" springs (you get "progressive" springs even if the description doesn't call them that, ya gotta dig deeper into the tech specs) are 495mm, whereas the factory springs are only 390mm. So you have to leave the factory spacer out. Seems like that would be a relevant bit of data to include in the sales literature, but where's the fun in that? Or maybe add that thread to the "Tech" thread collection?

 

[5twins]

I would say no preload spacer required with the new springs. If they're too soft like that then you could start experimenting with custom shorter preload spacers (1", 1.5", etc.). Oh, and install the new springs with the tight wound coils up. If you put them down, sitting in the oil, they will displace more of it and raise the level.

 

[GLJ]

Leave the spacers out.

 

[mrtwowheel]

Pre-internet, right or wrong, any bike, I always did it this way. I always made my own PVC spacers to a length that allowed me to put the caps on with some pressure but still only enough preload to still put the caps on comfortably. Worked for me for 50+ years.

 

[steve zodiac]

Just a thought. Would preload spacer's not make the forks more prone to topping out?

 

[arcticXS]

Well, after more searching, it looks like I found my answer in this thread- https://www.xs650.com/threads/fork-spring-length.17506/

Bottom line, the aftermarket "progressive" springs (you get "progressive" springs even if the description doesn't call them that, ya gotta dig deeper into the tech specs) are 495mm, whereas the factory springs are only 390mm. So you have to leave the factory spacer out. Seems like that would be a relevant bit of data to include in the sales literature, but where's the fun in that? Or maybe add that thread to the "Tech" thread collection?

Just a thought. Would preload spacer's not make the forks more prone to topping out?

Well, the ideal amount of preload (and in fact ideal spring rate as well) totally depends on rider weight, type of riding, bike modifications, riding position (i.e handlebars and footpeg position, and individual "posture") So there is no "correct" suspension settings. Just making a wild guess, I would say the stock suspension on a 74 would be suitable for a 60-70 kg rider (132-155 lbs) and just too soft for anyone heavier than that. For optimal spring rate and preload, try the spring rate calculator on Racetech's website.

Topping out may be worse with excessive preload, or insufficient rebound damping. And made worse by dual brake discs (increased unsprung weight). This was really bad on my Euro 650D, you could feel a heavy clunk when taking off briskly. Later models have a top out spring outside the damper rod to improve things. CB750 top out springs also fit the damper rods in the 77 onwards 35 mm fork.

And just another thing: Cutting any spring will INCREASE its spring rate (lbs/in or N/mm), i.e making it "stiffer". A shorter spring will obviously have less preload, all else being equal, but the force will increase more as it is compressed.

 

[Max Midnight]

The springs are progressively wound (as opposed to the manufacturer Progressive) therefore they will have a variable spring rate.

When replacing any spring for those with a different rate to those fitted the 'proper' amount of preload will be determined by the degree of rider sag.
That is how much the suspension drops from fully extended when the bike and rider compress the forks.
The 'ideal' amount of sag varies depending which web site you visit but as a starting point somewhere around 30 millimetres is a good starting point.
Assuming you are using a spacer it is better to start on the firm side (less sag) as it is easier to shorten the spacers than to add length.
(Helpful hint: Use a pipe cutter to ensure that ends of the tube are square)
Method to set the sag is here.