Topic: Forks bottoming out? Progressive spring question

[Buttmask]

So after installing brand new cycle x forks on my '75 750F (same length as oem) and progressive springs, every once in a while when I hit a decent bump or pothole I feel the front end do, what I can only assume, is bottoming out. There is a loud CLACK too when this happens.

 It's not the frame or headers hitting anything, the sound and sensation comes entirely from the forks.

Now when I installed the springs, I didn't use a spacer, because the springs were sticking out around an 1"-1.5" out of the top, and I was under the assumption my fork cap nuts would create enough preload.

Could this be a bad install issue? Need preload? How much is recommended? More fork oil?

Just looking for the right direction before I take apart my front end again.

[Jerry Rxman Griffin aka MuthaF'er]

Is it banging on rebound or compression? I followed progressive instructions and mine seems to bang on rebound. Using 150ml 20W fork oil. Other than that it feels great but I've only put <150 inconsistent miles on it since.

[Buttmask]

I think it's compression? Not 100%, it all happens so fast. Every time I freaked out and got off my bike because I thought I crushed my headers or something. It's really loud too.

[Retro Rocket]

You'll know if your forks bottom out, its like being hit in the palm of your hand with a metal pipe, it jars like hell and hurts... Ask me how i know...

[Brantley]

You might want to install those spacers; Progressive provides them (I'm guessing) so they can have one length spring that will work for a LOT of 35mm forks- look at how many makes/ models 11-1104 fits... I've installed probably five sets in 750's (and am about to on my current ride) and have had to throw a good bit of muscle at getting the filler caps to thread into the tubes every time with the washers and spacers. If you bought Cyclex's forks springs with those seemingly 3" spacers you NEED to install them. You won't have to disassemble the front end to do it. 

[faux fiddy]

You might want to install those spacers; Progressive provides them (I'm guessing) so they can have one length spring that will work for a LOT of 35mm forks- look at how many makes/ models 11-1104 fits... I've installed probably five sets in 750's (and am about to on my current ride) and have had to throw a good bit of muscle at getting the filler caps to thread into the tubes every time with the washers and spacers. If you bought Cyclex's forks springs with those seemingly 3" spacers you NEED to install them. You won't have to disassemble the front end to do it. 

I thought it was when in doubt leave it out....

+1 on trying that.

Does the washer seal anything?

[bwaller]

Start from the beginning & get the sag right. Read up, suspension tuning is all over the internet. This isn't a difficult process and will be rewarding compared to what's going on now. What's the spring rating?

[oldhatt45]

Buttmask,

Funny you should bring this up.  I just took some pictures of the Original Honda Fork springs on my 750 K6 (1976), S&W Progressive rate springs and the brand new Progressive Industries, progressive springs that I installed on the bike.

I also posted a note in my build thread which I repeat below.

Just measured the springs.  I was wrong Steve.  THe original springs are currently shorter than the S&W's.
The ORIGINAL Honda Spring (R) single rate - 8,000 miles and 1 year of riding. = 18.625 inches
The S&W Spring (R) Progressive rate - 16,000 miles and 11 years of riding and then
             25 years just sitting in the garage still assembled. = 20.0X inches
The Brand new Progressive spring - 0 miles and 22mm shorter than the S&W spring. = 20.0X - 0.86 = 19.14 inches.

Here are the pictures.
First picture is the Original Honda Spring side by side with the S&W spring.
Second picture is the NEW Progressive spring side by side with the S&W spring.

Also, I rode with a Vetter Windjammer fairing the whole time, if that has any affect or bearing on the length of the old springs.

And just as an FYI, I used 150ml of Bel-Ray 30wt fork oil in the forks with the S&W springs and never bottomed out.

Hope this helps.

Charlie

[Brantley]

Does the washer seal anything?

It provides a surface for the pvc spacer to ride on the spring.

[Muckinfuss]

Don't overlook the obvious....how much do you weigh?

[Buttmask]

I weigh 190, and I'm using ATF. I'm switching to a heavier weight oil, and if that still doesnt work, then onto the world of the spacers.

[ekpent]

Sure its probably just your fork set up but make sure all the other front end components are tight and good if you had it all torn down. A front caliper for instance can be a 'clacker' over bumps if it has a problem.

[bwaller]

If it's bottoming either your springs have too light a rating or you need more oil. (which limits air volume) Thicker oil will increase damping, (obviously both compression & rebound) but too thick makes the suspension harsh and can mask the real problem. Spacers are to preload only for sag adjustment.

I know you have progressives and so do I in a couple bikes, but I discovered shorter, straight rate springs, and much prefer them. It leaves plenty of room to adjust preload spacers for proper set up. Fork valves work good too if the forks aren't worn out.

[Muckinfuss]

ATF is around a 7 weight.  Jump to a 15W and see what gives.  If that's too light...you may have an internal problem.  If the springs are the right length and the valving hasn't been messed with, 190lbs is within range.  When springs get 'soft' from old age, they sag....get shorter than spec whether linear rate, progressive rate or dual rate.  They don't stay the correct length AND not work right.  For troubleshooting, we always start with dampening mainly for the rebound and spring rates for the compression.

There's always the one percent problem areas....someone heated a section of the spring to 'soften' the ride, or they messed with the valving.  OP's do crazy stuff that Sherlock would have a tough time finding.

[Stev-o]

Is it banging on rebound or compression? I followed progressive instructions and mine seems to bang on rebound. Using 150ml 20W fork oil. Other than that it feels great but I've only put <150 inconsistent miles on it since.

Did you install the PVC spacer?

I did not, bike handles fine and has never bottomed out.

[chewbacca5000]

Did you do a side by side comparison of the length of the old and new springs.