Cheap and easy front fork upgrade

[scott s]

The front forks on my '75 were horrible. Leaking seals, saggy springs. Major dive under braking and downright scary handling in the twisties. I could tell by the oil leaking past the seals that they were compressing as much as 6-8"!

I disassmbled them as you would any forks (these are 34mm, but I think this procedure would work on any XS650 fork). It always helps to have a good shop dog, though.

 

[scott s]

The insides were in good shape. I think the springs have some sag to them, but I have a fix for that....

 

[scott s]

The stock spacer is ~92mm long. We cut a piece of heavy duty PVC pipe and added a washer that is the same diameter as the stock washer that sits on top of the spring. I still used the stock washer in it's original locatio. The new washer sits on top of the PVC pipe.
The total length was about 100mm. Maybe a tad longer, as it was hard to cut the PVC exactly on my mark.
This essentially compresses the spring by ~8-9mm and adds some preload.

 

[scott s]

I used 15w fork oil. Stock is 10w30 motor oil or about 10w for oil. I went with something just slightly heavier.
The stock amount is 155ml. I used 170ml. The extra, heavier oil, along with the spacers and new fork seals made and AMAZING difference!
The front end is firm but still very compliant. I have maybe 2-3 inches of dive now, instead of 6-8 inches. The ride and handling are both a MAJOR improvement.

I also added new EBC brakes shoes to the rear (to get rid of the crappy MikesXS shoes...downright dangerous and ineffective. But, that's another topic...) and bumped up the settings on the stock rear shocks to the firmest setting. Totally different bike.
This bike is stock with Avon tires and handles and rides great. If you added some better shocks and different handlebars, it could actually be called "sporty" then!

It would be very easy to tune stocks forks for much better or aggressive handling using just a different length spacer, different (heavier) oil and different oil levels. I didn't want to go too far on this bike as it is still stock and more of a cruiser.

 

[leggers]

The stock spacer is ~92mm long. We cut a piece of heavy duty PVC pipe and added a washer that is the same diameter as the stock washer that sits on top of the spring. I still used the stock washer in it's original locatio. The new washer sits on top of the PVC pipe.
The total length was about 100mm. Maybe a tad longer, as it was hard to cut the PVC exactly on my mark.
This essentially compresses the spring by ~8-9mm and adds some preload.

I'm curious to know what the longevity of the pvc would be in the forks. If you have more info on this I would appreciate it. I'm looking to rebuild mine as well.

Thanks for sharing nice bike btw

 

[paulie]

Ideally, when you put a pre-load spacer in your forks, the length would be determined by the "sag". Take all of the weight off of the forks (lean it over on the side stand) Put a zip tie around the fork at the seal. Then sit on the bike with all of your riding gear on and your feet on the pegs without your stand down. Have your buddy balance the bike so that it's only your weight on it. Then get off of the bike and take the weight off of the front again and measure the distance between the fork seal and the zip tie. For the street, it should be app. 40-50mm. For the track, it should be less (25-35m depending on the track). Cut your spacer to suit and your good to go! I always leave the zip tie on so that I can see how far my forks travel during a ride. Fork oil weight would also be determined by the riders weight. A lighter rider might use 7- 10 weight oil, but a big guy might use up to 20 weight. These old XS's aren't the best handleing bike, so they're easy to improve with a little bit of work.
Have fun!!

 

[Growl]

no problem - the pvc lasts just fine (based on my experience)

 

[scott s]

Paulie, that's a great tip. Had I known that, I would have done a little "calculating" beforehand. So far, it feels really nice.

I'm 180+ lbs., so I hope I'm in the range. A good long ride will tell....soon.

The PVC is the heavy duty stuff. Schedule 80, I think is what they call it? I'm too lazy to walk out in the garage and see what's printed on the leftover piece.

 

[1974jh5]

I did PVC spacers in dirt bike forks, as long as there's a washer between the PVC and the spring it will last indefinitely. I've also made them from aluminum tube, same thing, you need washers so the spring doesn't grind it away.

 

[stuarth]

One more suggestion. Bite the bullet and get decent fork seals and OEM dust seals. I first used the mikesxs stuff, and it was terrible with a lit of "stiction". Changed to All Balls fork seals and OEM dust seals and the forks are much more responsive to smaller bumps now. Well worth the added cost. But I'm still not satisfied with my stock '76 forks and will be installing Race Tech Cartridge Emulators next.

 

[jd750ace]

PVC in SH40 or higher has enough column strength to endure your suspension loads just fine. As long a no phosphate-ester based oils are introduced, they should not soften over time. If you are going to install cartridge emulators, I highly reccomend Race Tech straight rate springs as well for the optimum setup. I installed straight rate springs and emulators on my 02 SV650, and it was completely transformed. The guys at race tech are awesome as well. If you call the help line and tell them what you are setting up, they will give you all the notes they have on tuning for your situation. If you are racing, they have a seperate deal, but for street, just call. Can't say enough about this company and the products they sell.

 

[mwp309]

In my '07 sv650 I used schedule 40 pvc for spacers (with 90kg springs, race emulators and synthetic oil). Rock solid front end now! Gsxr shock on the rear, handles like a race bike!

 

[jd750ace]

+1 on the Gixxer rear shock. Have a 99 GSX-R750 shock on the back. Flushed it clean, installed .90 Race Tech spring, re-filled with 7.5 wt oil for slower damping rate, since I'm pretty good sized. Topped with 105 PSIG of nitrogen. Really transformed the bike. Also increased the oil height in the front forks by 5MM. I have nearly 70 thousand miles on this thing since I bought it, and would not sell it for anything! The 03 Roadstar gets the Race Tech treatment next, then the 79 Special project, which will be a Resto-Mod.

 

[Explorer352]

Sorry to resurrect an old thread...
I'm getting ready to work on my forks. I'm wanting to get everything ready before I tear the bike apart. Does anyone know what diameter pvc is needed? Thx in advance
David

 

[jd750ace]

One inch Outside Diameter PVC in 34 or 35MM fork tubes

 

[stuarth]

When you go to the hardware store, ask them for 1/2" PVC. It's cheap- most stores sell short sections- 2'-3' sections in addition to standard 10' lengths. Alternately you can get a short length of gray PVC meant for a hose riser.

 

[XDirtyC]

We have the same type of shop dog. love ACD's

 

[hotrdd]

So if you measured 80mm of movement and wanted 50mm would you add an extra 30mm to the PVC spacer?

 

[stuarth]

By the way, I replaced my stock shocks with Progressive Suspension Series 14 shocks in standard length and they transformed the rear of the bike. I went with their #1353 spring first which was too stiff for my stock '76 (I'm 195 geared up). I bought the next lighter spring and (#1352) for commuting and playing in the hills, they're perfect. I can walk away from my friend on his 2012 Moto Guzzi V7 Classic through the turns in the mountains near my house, and the bike is very comfortable around town and with my wife on board (2 additional steps of pre-load for her 130 weight). These shocks are black with a stepped collar for adjusting pre-load. I bought the chrome springs for a more stock look.

 

[grizld1]

I don't know how the hell the OP was getting 6 to 8 inches of travel out of a front fork in which the sliders can move only 5.12", but we'll let that, uh, slide.

Spacers and sag aren't the only things you need to worry about when you tune up the front end. If you add too much preload on sacked out springs you'll wind up coil binding. Multiply wire diameter by number of coils and subtract that number from the free length of the spring. From that, subtract the rated travel of the fork. The result is the maximum preload you can apply to keep the coils from binding before maximum slider rise.