Forks topping out.

Tim L

Tim L

XS650 Addict
Messages
238
Reaction score
18
Points
18
Location
UK
Hi all,
I fitted a pair of 'progressive' springs when I rebuilt the forks on my 77D.
Fork oil level is as recommended in the manual.
Just started to do a few miles and I have noticed that the forks top out on the recoil with a bit of a bang.
Has anyone else had similar problems? If you did, what did you do to cure it?
Many thanks.
 
'77 was the first year for the 35mm forks and they didn't use a little top out spring yet, hence the "banging" you're experiencing. You can add one from the later forks if you like .....

2hZZYXd.jpg


You will lose a little fork travel and it will lower the forks slightly (maybe 1/4" to 3/8"), but that's not a bad thing. It would be the same as the popular mod of lowering the forks slightly (raising the tubes in the trees). This more firmly "plants" the front tire and improves steering and handling slightly.
 
I had the exact same issue on my XS, which also happens to be a 77 D model, when it was completely stock.
When I changed the sagged out springs, I also fitted emulators (Progressive springs and knockoff emulators from Heiden Tuning, same as MikesXS. In hindsights, I should have gone for proper RaceTech items....)
Then I also reduced unsprung weight og the front by around 5 kg (11 lbs), by converting from the stock dual disc setup, to a single 320 mm disc, a Brembo 4 piston caliper, and an alloy front fender.
After these changes, I haven't had much issues with hard topping out, but still plan to install top out springs as well, and possibly upgrade to proper RaceTech springs and emulators.
Without doing any of the listed mods, a heavier oil and possibly more sag (less preload) may help.
 
Thank guys. I will look out for parts from later forks with springs fitted. Would a higher oil level help to slow down the recoil?
 
Tim L said:
Would a higher oil level help to slow down the recoil?
Click to expand...
No or maybe. To slow compression/recoil in stock forks you should increase the viscosity of the oil. Raising the level will slow the high speed damping on the large movements. I believe you need to leave at least 5.5 in (fork compressed) air space in the top of the fork. Not enough space can result in seal failure. You will have to play around with it because you can't mess with one thing without affecting another. I'm not a suspension guy, just a hack. Also best not to use emulators with progressive springs. The mixed technology makes them difficult or impossible to tune.
 
Tim L said:
Thank guys. I will look out for parts from later forks with springs fitted. Would a higher oil level help to slow down the recoil?
Click to expand...
I would say rather the opposite. More oil gives less air volume, which in turn makes the "air spring rate" higher, causing the fork to rebound faster. A bit like a stiffer spring or more spring preload would do.
I guess a softer spring or less preload, combined with more oil may help, as that would make the total spring rate more progressive, and reduce spring force when the fork is fully extended.
In any case, slightly thicker oil for more rebound damping, and top out springs would be the better solution for avoiding this issue. If the thicker oil then causes excessive compression damping, "Minton Mods" may help. If that does not give the desired result. Emulators and new springs are the next steps.
 
Those rebound springs are hard to find I think. Does anyone have one they could measure for me. If I have the important dimensions, length, i/d and o/d, wire thickness, etc, I can get something from a spring supplier on line. Thank you.
 
arcticXS said:
I would say rather the opposite. More oil gives less air volume, which in turn makes the "air spring rate" higher, causing the fork to rebound faster. A bit like a stiffer spring or more spring preload would do.
Click to expand...
I do believe the air in the fork is progressive. So, it will slow movement as the compression increases. I see what you're saying and I agree. A higher oil level won't slow recoil. That is controlled by how fast the oil can pass through the holes in the damper rod. So, in my thinking, higher viscosity makes for slower recoil. It also means you won't soak up the big bumps as well.
 
OK, got some info for you. First, let me say that there is another option when searching for a suitable spring. Some other Yamaha models used a very similar spring, those being the XS500, XS750-850, XJ750, and XS1100. It may be easier to find since it was used on so many. The 650 spring only came in one other model, the SR500. Both springs have the same O.D. (About 1" or 25mm), I.D. (about 3/4" or 19mm), and wire thickness (about 3mm). The lengths vary slightly (22mm for the 650, 24mm for the 500) and the 500 spring appears to have one more coil .....

V5JCrVb.jpg


ELEdqHn.jpg


By the way, the damper rod has a 17mm O.D. I don't think using the slightly longer 500 spring would hurt anything, and I don't feel exactly matching the spring rates is that important either. But, from just pinching them by hand, they do feel about the same. This is just a little bumper spring after all, padding the top of the damper rod when it strikes the bottom of the fork tube at full fork extension. Basically, it just has to be soft enough to give a little but not so soft that it squashes flat.
 
Actually, it's the other way around. While the Standard had a top-out spring too, it's shown on the parts diagram as part of the damper rod and not listed as a separate part.
 

Similar threads

Kevin Werner
Fork rebuild questions.
Replies
16
Views
332
jetmechmarty
jetmechmarty
zrx1100
Race Tech kit and adjustable fork caps
Replies
2
Views
341
jetmechmarty
jetmechmarty
Kevin Werner
Forks and the "Joe Minton" mod
Replies
9
Views
831
JRP01
JRP01
B
80 xs650 forks wont fully lower.
Replies
2
Views
97
Jim
Jim
S
Fork piston question
Replies
9
Views
265
spresser
S
Back
Top