FZ400 fork spring woes and advice needed (longish)

I've been working on Elly's FZ400 these past few days,
preparing the bike for its MOT and subsequent daily useage. One of the
jobs that needed doing for the MOT was to ensure the forks didn't bottom
out, as they had been previously. I've fitted new seals and the correct
grade and quantity of oil, and had come to the conclusion that the
springs were bordering on tired. When sitting still the bike exhibited an
amazing amount of sag, with the fork stanchions sitting way down the
sliders

Now back in the old days, when I was a tightfisted urchin living on
boiled string and fried dandelions, I used to pop a couple or three
2pence pieces on top of each fork spring to give them a bit of assistance
and upping the preload. So I went down this route with the FZ, only to
find that three 2ps on each spring caused the front to be almost solid.
So I decided to drop the amount down to two 2ps.

I started with the left fork and whipped the top cap off and the bike sat
pefectly upright and with the right fork leg fully extended still. All
good for when I come to stick the top-cap back on I thought. I removed
one coin and put the top-cap back on. Lovely.

Turned my attention to the right fork leg and did the same, off came the
top-cap, and the bottom yoke nearly clouts the mudguard as it drops. WTF?

What I can't understand is how just 1.5mm of spacer can make that much
difference to the way the front springs act. To put the top-caps on both
forks took roughly the same amount of downward pressure and there was
appx the same amount of spring sitting above the fork top when the cap
was off each side. So I know that the damper units in each fork leg are
seated at the bottom OK.

I've since fitted 2 coins into each side and the front end seems to sit
alot better with a minimum of sag and the forks don't bottom out any
more. However, I'm still not at all sure I've done a proper job of it and
can't ride it yet to be able to tell. That left fork not supporting the
bike on it's own has thrown me. The right one coped very well doing the
same job. Could I have just got the damper unit unseated on the right leg
causing the preload to be way too hard the first time round, and if so,
why did the top cap go on so easily that time? Anyone got any clues?

--
Lozzo
ZZR1100D, GPZ500S, CB250RS
BOTAFOT#57/70a, BOTAFOF#57, two#49, MIB#22, TCP#7, BONY#9,
ANORAK#9, DIAABTCOD#14, UKRMT5BB, IBW#013, MIRTTH#15a/16,
BotToS#8, GP#2, SBS#10, SH#3, DFV#14.
Url for ukrm newbies : http://www.ukrm.net/faq/ukrmscbt.html
www.mjkleathers.com

 

Lozzo wrote:

Some of us still do use 2p pieces to up preload on bikes with non-adjustable
suspension. Well, I do anyways even if it means drilling a hole in the
middle of them to allow the damper adjusting rod through.

As it should really.

Assuming the resting state of the springs means they are both at the same
'height' in the fork when they are fully extended, about the only thing I
can think of is one spring has a much much lower compression rate.

I changed the springs in the GTR yesterday with the bike on its mainstand,
so the front wheel was on the ground all the time ( couldn't find my jack
until I'd completed the job, as is usually the case ). Each leg was capable
of supporting the weight of the front on its own. Mind, it probably only
puts about 50-75lb onto the front wheel when on the mainstand.

Personally, I would be cautious of riding it until I'd solved the mystery,
just in case.

 

Champ fascinated us all by saying...

No shit Sherlock

I'll take them out and strip them again tomorrow, paying extra attention
to the variable damper units and the way they sit in the damper rod tops.
I think the right hand one wasn't seated right after I fitted the 3 coins
to the top of the spring, hence it was able to support the whole bike cos
the preload was set at about 400% of maximum available. Quite how I
managed to get the top cap on is beyond me though.


--
Lozzo
ZZR1100D, GPZ500S, CB250RS
BOTAFOT#57/70a, BOTAFOF#57, two#49, MIB#22, TCP#7, BONY#9,
ANORAK#9, DIAABTCOD#14, UKRMT5BB, IBW#013, MIRTTH#15a/16,
BotToS#8, GP#2, SBS#10, SH#3, DFV#14.
Url for ukrm newbies : http://www.ukrm.net/faq/ukrmscbt.html
www.mjkleathers.com