Making fork stiffer

Your '77 forks are unique. They were the 1st year for the 35mm forks. Their damper rods, tubes, and springs differ slightly from the later models. If they are still original, you should find a preload spacer already in there (about 40mm long). To stiffen them up, you could just replace that with one maybe 15 to 30mm longer. Another option would be to install the later adjustable caps. They would add an additional 36mm of preload at their lowest setting, each step up adding another 10mm .....

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The oil weight spec for your forks is 20. All the later versions speced 10 weight. This may be due to the beveled holes in the damper rods. I spoke with an engineer buddy of mine and he told me beveled holes flow more .....

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I feel the tubes and damper rods in the '77 forks are of a higher quality than the later ones. Notice how the '77 damper rod shines in the pic above - it's polished. They also mount that fiber wiper ring in a separate metal ring that 'floats" on the rod. The fork tubes retain the bottom bushing via a snap ring where the later tubes simply crimp it in place.

If your springs are stock, they should be about 472mm long. This is 10mm shorter than the later model springs.

I did a lot of experimenting last summer to see what the best fork assembly I could come up with was using all stock parts. I combined '77 tubes and damper rods with '78-on springs, adjustable top caps, and top out springs. I also Minton modded the damper rods. This "hybrid" set works quite well but the springs are still a bit soft. I either need to add some more preload or maybe try some heavier oil (or maybe both).
 
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Do you want to fix it or keep messing with it? What I did with mine was install the correct straight rate springs and set the preload to get the laden sag I wanted. I backed mine up with Race Tech emulators and 15W fork oil. It's like a new bike and it cost less than a decent pair of shocks.

FWIW, I am not a fan of progressive wound springs.
 
are you guys draining everything out and putting in a set amount (over stock)? and how much would you recommend?
 
If you have an XS2 like your moniker implies then I don't have a clue. All the above info pertains to the '77 and newer 35mm forks. You should probably do some measuring. That's how I arrived at the 7 ounce amount for the later forks.

Fill your forks with the stock amount of oil. With the springs removed, compress them fully and measure how far down the oil level is from the top of the tubes. Most aftermarket springs come with install instructions recommending a level of about 6" from the tube top so this can sort of be used as a "rule of thumb". Too much oil in there can blow the seals when you hit a big bump so I wouldn't recommend filling above that 6" mark.

With the stock amount of oil in my '78 forks, the level was about 9" down. I felt that was too low. Adding an extra ounce raised the level to about 7". I decided to try that. It improved the fork action and works well so I never experimented any further.
 
thanks guys. and yes....a '72

I've never had mine open or drained except to pull all of the triple clamp stuff off. no idea whats in there but it nose dives fairly easily (although I have nothing to compare to).

what viscosity would stock oil be. I see where someone above mentions 15w40 ( I think).
 
the yamaha manual says to use 10 wt fork oil. some people use transmission oil or motor oil, but fork oil is readily available at any shop and is not very expensive.
 
Only made 1 year. Parts are so so. Engine parts not a big deal. There is 1 supplier for some aftermarket Hurricane specific stuff.
 
I have a 72 and I used 5w-20 synthetic. I works great!

You wouldn’t believe how low tech I went with the fork oil on my XS2. Walmart 30 weight hydraulic oil. Less than $4 for a qt. I did it kinda as an experiment and am happy to report my forks work perfectly with this stuff.
( on the back label it says it can be used for hydraulics, it’s non foaming)
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Interesting. The shop manual that came with my 72 is for XS1 and 1B. I also have an addendum manual that explains the disc brake and electric starter, but it has no specs on the front forks. You prolly know already that the xs1's had steel lower fork tubes. The 73's have some different geometry and wider setup on the front end to occomadate duals discs, but I don't know if the the forks are the same as a 72. Basically, I have no info on the proper amount of oil for a 72. I will say, that 7oz is too much. At least, the last time I put in 7oz, it was way too stiff. I ended up slowly draining equal amounts from each side, and came to a pleasant medium. Its prolly like 4.5 to 5.5oz.
Anybody?
 
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