Assembly forks: allen bolts not finding piston rod??

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Charles
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My Bike: ZXR400, TL1000R
Location: Fourques, France

Assembly forks: allen bolts not finding piston rod??

Post by Charles »

Hi, I just put some new seals into my forks.

Now I'm having the problem the allen bolts don't find the piston rods. I read and followed the fork rebuild
tutorial from Diesel ( http://www.zxrworld.co.uk/zxr400/forks.html ) and tried to compress the forks
by hand as far as possible, but the allen bolts just don't reach the piston rods.

What do I do wrong? Is a hydraulic press really the only solution?

Thanks for any tips,

Charles
1977 DT400
1986 GSX-R750
1993 ZXR400
1999 TL1000R
Ewetea
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Re: Assembly forks: allen bolts not finding piston rod??

Post by Ewetea »

You must devise a way of compressing the fork to bring the rod to the bottom of the fork leg. Unscrew the smaller nut at the top of the fork leg to reduce the amount of compression. I clamped the centre stem of the lower yoke in a vice and then clamped the gold section of the fork in one of the outer clamps (do not squeeze the gold tube in the vice, you'll just squash it). I threaded some electrical wire through one of the caliper holes and looped it over the lower yoke. I then put a flat piece of wood against my chest and pushed against the lower section of the fork to compress the assembly, pushing the other end of the wire through the other caliper hole and twisting it quickly to hold it in place. When I relaxed, the fork extended a little due to the stretching of the wire, but there was sufficient compression to enable the bolt to be installed in the bottom of the rod. It is possible that this procedure will drive the end of the rod further up the fork leg, so you will have to use a longer bolt to engage the thread and pull it down sufficiently for the correct bolt to be installed. If you do not have a longer bolt, try putting a bend on the end of a piece of rod (coat hanger?) and go "fishing" to pull the rod down. The bend would have to be tight enough to go through the tapped hole in the rod. Once the correct bolt is in place you may find that it engages partially, and then the rod just turns with the bolt. Compress the assembly again and slacken the wire to allow the assembly to extend sufficiently to ensure that it is being held by the bolt. This will put tension on the rod and allow you to fully tighten. I hope that you can understand all this. Since you have stripped the forks and replaced the seals you must be confident enough to finish the job.
fork leg clamp.JPG
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Charles
zxr400 oc member
zxr400 oc member
Posts: 20
Joined: Sun Aug 28, 2011 9:16 pm
My Bike: ZXR400, TL1000R
Location: Fourques, France

Re: Assembly forks: allen bolts not finding piston rod??

Post by Charles »

Thanks for your very thorough explanation! :) I will have a go the next few days and will report afterwards.
I only just moved to France and left most of my tools/equipment still at home in Germany. So will have to get some help
from the few people I know here, that is if I can make them understand me, I am still struggling with my french :)
1977 DT400
1986 GSX-R750
1993 ZXR400
1999 TL1000R
Charles
zxr400 oc member
zxr400 oc member
Posts: 20
Joined: Sun Aug 28, 2011 9:16 pm
My Bike: ZXR400, TL1000R
Location: Fourques, France

Re: Assembly forks: allen bolts not finding piston rod??

Post by Charles »

Worked a treat :) Thanks again for your help,

Charles
1977 DT400
1986 GSX-R750
1993 ZXR400
1999 TL1000R
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ricardof1rst3
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Joined: Tue Aug 27, 2013 5:48 pm
My Bike: Kawasaki ZXR400

Re: Assembly forks: allen bolts not finding piston rod??

Post by ricardof1rst3 »

For anyone else landing here...my experiences:

When re-building the shock you arrange the innards with the damper rod inside the spring, its the end of the damper rod that the bolt at the bottom of the fork leg screws into. On the end of this rod is a metal cap, this cap can easily fall off the end of the damper rod and flip onto its side catching on the spring causing issues.

To keep the cap in place the innards should be inserted into the gold outer upside down (so the cap is at the top of the rod within the spring). Then you need to keep the shock upside down whilst you compress it. Full compression is needed ideally (until the spring is coil bound) this will leave approx. 17mm of chrome slider showing. I compressed it by placing a wooden block in a vice, with a couple of holes in it to support the adjusters (remember the shock is upside down). I think the holes were 32mm and 24mm but don't quote me on that... Then I placed another wooden block on top, in which I had drilled three holes. Through the outer holes I used a pair of car spring compressor bolts, with hooks onto a ratchet strap that looped under the block in the vice. The top blocks centre hole (15mm) is used to access the bolt hole at the bottom of the fork. I then compressed the spring by tightening the two tensioner bolts - simples.

Once fully compressed, inverted, in theory you simply screw the bolt into the end of the shock BUT the damper rod drops thanks to gravity so isn't near enough to the hole. If you turn it then the end cap falls off to cause a blockage etc.

So I used a bit of M8 threaded rod I had lying about to "find" the damper rod, screwing it in slightly. I then removed the shock from the vice and rested it horizontally on my bench and pulled the M8 rod, jiggling it about to make sure the damper rod was as close to the end of the fork leg as possible. The M8 rod stops the end cap falling off and pulling on the damper rod seats the end cap inside the end of the fork.

Then I undid the M8 rod and removed it, and very carefully inserted the allen bolt (with copper washer and coated in thread lock). You have to be careful and feel it in because its very easy to simply push the damper rod away from the bolt and out of reach. If you do this, its also possible to knock the end cap off which means stripping it all back again to re-locate it correctly.

Once the allen bolt had caught a few turns I then stuck the forks back in the vice and released the tension to remove the wooden block because my torque wrenches allen fixing wasn't long enough to reach through the wooden block. Once released I tightened the bolt to 20Nm (spec as per the manual).

The wooden blocks I used came from one of those cheap soft wood deck joists from B&Q (38mm x 62mm) and I used a 25mm ratchet strap. I used the spring tensioner bolts to make releasing the tension a slower process. It would be possible to do it with just a ratchet strap (or two) and the wooden blocks but the release would be entertaining (watch your fingers in the ratchet mechanism, I hate those things).

Initially I thought I needed thicker ratchet straps because I was stretching them trying to compress everything so the standard bolt would "reach", but I realised the spring was coil bound, as the effort went exponential when there was 17mm of slider left in view and it wouldn't budge any more. That was when I started thinking about where the end of the damper rod might be inside. Its so much easier with a bit of M8 threaded rod which is also cheap as chips from B&Q.

Hope the above helps.
1983 DT100 | 1985 TS125X | 1986 GPZ600R | 1987 GPX750R
1988 FZR1000 | 1989 FZR1000 EXUP
1991 ZXR400 | 1993 CBR900RR
1996 ZXR400 | 2000 CBR600 | 2004 CBR900RR
2013 ZXR400
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ricardof1rst3
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Joined: Tue Aug 27, 2013 5:48 pm
My Bike: Kawasaki ZXR400

Re: Assembly forks: allen bolts not finding piston rod??

Post by ricardof1rst3 »

If you decide to use a wooden block on the end that the allen bolt goes into, ideally drill a 15mm hole in its centre and whilst compressing the spring leave the drill bit in the wood & fork bottom hole to keep things lined up for when you come to insert the allen bolt.
1983 DT100 | 1985 TS125X | 1986 GPZ600R | 1987 GPX750R
1988 FZR1000 | 1989 FZR1000 EXUP
1991 ZXR400 | 1993 CBR900RR
1996 ZXR400 | 2000 CBR600 | 2004 CBR900RR
2013 ZXR400
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