OzVMX Forum
Clubroom => Tech Talk => Topic started by: Ji Gantor on March 17, 2009, 05:37:45 pm
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This topic is for information only and is how I have approached the strip down. Please refer to your manual and proceed as per the manufacturers details.
This is a CZ400 1973 fork.
The seals need replacing and the inner tube needs to be chromed due to rust.
Water and dirt has found its way in due to the seal being shot.
These contaminants have to be removed and new seals and oil installed.
Ji
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This fork is 35mm diameter and is secured into the triple clamps by the lower clamp and has a tapered end which is draw up into the top clamp.
Ji
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First remove the fork top cap bolt, spring and drain the oil.
Ware gloves and a face mask as this stuff is toxic.
Ji
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Next unscrew the metal clamp.
Using a piece of wood and a rubber mallet gently tap the mud wiper off.
Ji
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Now that the mud wiper is off we can remove the circlip with a pair of circlip pliers.
Ji
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This next step could have been performed while the forks were still on the bike but I like a challenge so I have removed the dampener rod bolt while on the bench.
The best thing to do is to heat the bolt head area up a bit just in case the last guy that did it up used loctite. When the area is nice and hot place a 12mm diameter rod into the axle hole to secure the fork and with your 6mm Allan key try and get it out the best way you can. I have had no help with this so it is not that hard, just fiddly.
Ji
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Okay the fork is now in two pieces.
The damenper rod is exposed but we now have to remove the circlip to release it.
Ji
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Removing the circlip is usually an easy job but the last brain surgeon that worked on these forks ground the shoulders off the clip ends.
This took a bit of time but it was removed without damaging the forks.
Ji
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The alloy bush in the bottom of the fork leg was solid.
To remove this I employed an old broom handle.
After a few rams the bush came free.
Ji
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With the dampener assembly free the only thing left to strip out is the seals. I find with old and new forks if after stripping them you leave them a day or two the seals come out a lot easier. I think they dry and shrink a bit but I have no evidence of this other than the effort it takes to remove the seal on the day and the next day the seals some times drop out, so to speak.
Ji
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Hey Ji,
Don't worry about the one kid in the school yard that you don't get on with. You can't make everybody happy, no matter how hard you try. Just ignore him and get on with your business.
I have read most of your posts and picked up quite a few good tips. Its all good stuff,
Have another think about it and see you back here tomorrow!!
VMX42
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ji
keep going as in 3 weeks i am doing the same with my 1972 yellow tank 400 cz.you are very helpfull for all cz owners,forget the rest they dont matter
cheers
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Ji ignore the ingnorance of the hecklers ::) ::)
This forum is an open forum and read by a great deal more people than those who choose to post here, why deprive others of your experience just because of the actions of the small minded among us ;)
Some may feel your postings are to elementary but to others im sure they provide some welcome assistance :)
Not everybodys as naturally gifted as Ross obviously feels he is (and he has probably had plenty of practice with the spanners being a Montesa owner ;D) so please continue posting for the benefit of us mortals :)
At some time in the future i will tackle my 75 CZ 125 and your postings here will be a great help im sure
Cheers Bill
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Yeah Ji,
Don't go or TMBill might just have to take your place with his own unique style of technical stories.
You haven't lived until you have seen Uncle Bill at work in the Taupo Works Bunker at 2.00am the morning before a race meeting. What he can do with a gas axe in one hand and a beer in the other has to be seen to be believed. He is the Gordon Ramsey of VMX. I have seen it, and I still don't believe it!
Keep up the good work TMBull [say hello to DJ for me]. See you at CD6
VmX42
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2am, its just glide time Jeff "We do things a little different in little old NZ" and it wouldnt be a vmx meeting in Taupo without a 2-4am night before the race. ;D . How is the big smoke Jeff, are you getting in some riding?
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Thanks to all members current and past that have shown their support for my topics and me.
Okay enough of this Emo stuff lets get back to working on old bikes !
I have not touched an oily bolt all day !
Ji
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Okay, I wiped all the oil off the fork seals yesterday and left them to dry over night. I don't know if the oil makes the seal swell or if it is a temp change but as I said I have stripped down modern and old forks before and struggled to slide hammer the seals out of the first fork on the day of strip down, only to have the seal on the second fork that was left overnight virtually fall out. Forksmiths may not have experienced this because they can not afford to wait, they have to get the job done, but I would be interested to see if any one else has had the same experience.
Just to let you know , yesterday I placed a lever under the first seal slide and it would not budge. This morning I placed one finger under the same seal and out it came. The manual states that there should be two seals and a few washers but I have discovered a fibre slide seal or packer and only one seal ( no washers ).
This may have been some kind of trick way of doing it in the past, one would have to read every test article to know.
I will be replacing this system with a Leak Proof Fork seal when the tubes come back from RAD.
Ji
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Tomorrow I have some time so I will drop the inner hard chrome fork tubes off at RAD.
Rad is a mile from where I live and work and the only way there is through the city traffic so this is not a fun trip.
While I am there I will ask the owner if I can take some pictures of the process so I can post the images here. As a lot of their work comes from out side QLD this should give other state members an idea where they are sending their rare bike parts to.
RAD not only hard chrome fork tubes but they also HC shock shafts. The boys will rebuild shocks if required and they will straighten bent fork tubes for $20.00.
Ji
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I try my very best to restore my bikes mechanically back to the way they were when they came off the show room floor. With this in mind one has to refer to the manual constantly to see if the parts on the bike were from that year or even that marque. The fork top cap bolt should as per the manual have an "o" ring but this one does not so I will have to order a set.
Ji
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The manual also tells me that the dampener rod is held in place by a flat bladed screw driver type M8 bolt and a fibre sealing washer.
This has been replaced with an Allan key screw and a S/S washer.
I have to admit the Allan key screw is a big improvement, as I doubt after 30 years of poor maintenance I would have got the flat bladed screw driver bolt out from its recess.
The S/S washer will be replaced with a copper washer similar to the Maico forks. These copper washers on the Maico's also keep the gearbox oil where it belongs.
Ji
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This posting is for info only I don't recommend any one trying this.
Because the bushings are not being replaced, I have marked the tubes that are off to RAD. I feel that all the components that came out of the left fork should go back into the left fork. Because all the parts have worn together over the years they should not exhibit any dramatic ware in the future if they are returned to their original position. Well that is only my opinion.
I totally supported the tube with some wood and then drove two dots into the inner of the non-drum side fork. I will have to buff the surface when I get them back but that is okay, you are encouraged to clean your tubes before assembly anyway.
Ji
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I thought things were going to well.
I was right when I said 30 years of poor maintenance would prevent a flat blade screw driver bolt from being removed. The S/S Allan key bolt was stripped due to, may I assume, some one using the wrong size Allan key.
Anyway you are going to get this some where on an old bike I just wish it was not in this location.
I could mill the head of the bolt off but I will try drilling it out first. When drilling out a bolt or when cutting new threads always use a cutting compound or coolant. This will make the job easier and stop the bit from over heating.
When working with anything S/S always use High Speed Steel bits, taps and dies.
Ji
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After many hours the drill finally cut a 7.6mm diameter hole 8mm deep into the top of the bolt. I then tapped the bolt head with a punch back and forth until it broke off. Half way through the drilling process I tried to turn the bolt and it did, unfortunately it was also turning the dampener rod. Anyway the fork is now in two pieces.
Ji
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If I wanted to see if my fork tubes are bent, place them together and roll them. If one or both are bent you will see a gap. Yep there is a gap, so they will have to straighten them for me.
Ji
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Well the inner tubes will be back in 2 weeks so that gives us enough time to clean all the other parts.
First I will start with the lower leg or outer tube.
These outer tubes had a polished finish so lets break out the polish.
Ji
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I have polished the drum side fork lower tube to show the contrast.
It is not a mirror finish but it is okay for a fork leg.
This polishing process was all done without any polishing tools except my hands.
Ji
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Here is a closer look.
I hope you can see the surface.
Ji
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Hopefully this image will show the quality of hand polishing.
Ji
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Hi Ji, my forks are due back tomorrow from RAD and they where very helpfull they called me last night and said it all went well so back on the practic track on Sunday . I have a question for you or any other cz guru's out there, do you no the amount of air I should pump into the forks ? HL
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Hi HL400,
Mark showed me a pair of CZ fork tubes today.
Do yours have 3 different out side diameters?
What year is your CZ?
Ji
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Yep thats what he said, are yours the same ? HL
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Hi HL400,
No.
My 1973 forks only have two different diameters.
Ji
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I think CZ used what ever parts that where left over form the Russian space race.
mine is a 1973 984-1 so they should be the same HL
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Hi HL,
Really, Wow. yours looked nothing like mine.
Okay, cough, cough.
Arrrrr right.
How much air.
I wounder if your forks are from a later model, do you know how much travel yours have or what diameter they are.
Can you post an image of the parts that you have now?
I will look at all the manuals I have to see if I can track down what year your forks are.
I don't think that any 1973 CZ forks could handle any compressed air internally, may be the schrader valve (if there is one) was so you could easily remove built up air.
Ji
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I will have a bash over the weekend with the photo and see how I go.
as far as I no the bike is totaly stock and is still on the standard rings.
I will mesure the travel when I put the fork tubes in.
HL
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Hi
CZ fork tubes are 35 mm from top to bottom if they are original or new , when you are having them re chromed remember that they have a taper at the top, where they tighten into the top clamp,
when re assembling slip an 8mm spring washer into the lower fork slider ,where the damper rod goes ,this make it easier to undo the damper rod bolt when you disassemble next time,if you are replacing the circlips that hold the oil seals in make sure the ends dont scrape your new tubes , two 35 47 10, or three 35 47 7 seals, try NAK seals,you can get them from that little bearing shop next to the Kawasaki shop in Albion,
cheers
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Hi Jikov,
The hard chrome fork tube for CZ 1968 to 1974 are all the same as per my two workshop and parts manuals. The fork tubes on my 73 are 34.97mm diameter from the bottom to just above the lower triple clamp where it necks down slightly. Mark at Rad today told me that that was typical for CZ fork tubes. I am not trying to start an argument I only ask so I can learn. Do you have some information that states that the fork tubes should be one diameter from top to bottom? If so I will instruct Rad to make mine one diameter right through.
Ji
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I have just got off the phone from Jikov and the fork tubes are only one diameter from top to bottom. My manual shows a step at the top but this must have been an alteration to stock. There is the taper at the top so the fork wedges into the triple clamp and this is the only change in line.
I have phoned Mark at Rad and asked him to chrome mine one diameter all the way through. Mark told me again that the step was very common for CZs but it is easier for him to make them one diameter rather than work on two.
Thanks Jikov your many years of working on CZs is much appreciated.
Ji
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With a little more time spent the harder of the two lower legs is polished.
All done by hand, no machines.
Ji
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The next step is to go over the tube with a wax remover and solvent. I use gloves when doing this so I don't put oily finger prints on the surfaces. Then 2 acrylic clear coats are applied to seal the surface from moisture and filth.
Ji
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This took a while to do Photo Shop wise.
This image should give the best contrast of all.
Ji
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The other tube is now starting to reflect some light.
Almost there.
Ji
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Here is the contrast shot or the before and after image.
Ji
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Handy tip # 371
If you have trouble finding the right tool for the bottom bolt in your forks then simply weld a socket onto it.
This will save precious time when you next rebuild your forks as all you need to look for is the ratchet handle :o
(http://i15.photobucket.com/albums/a393/gmcloa/Stuffedparts-2.jpg)
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Yeah, but the ratchet handle is probably welded to the tractor…
Or is the tractor welded to the ratchel handle?
Hmmmmmmmm????
VMX42
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The fork lower tubes have had the wax removed and cleaned with a solvent and I have applied their first coat of clear.
This clear is available at Bunnings.
Do not spray this clear anywhere near enamel paint as it will bubble it like paint stripper.
Ji
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If you do have enamel paint that the clear will cover I use this Dulux product. It is also available from Bunnings.
Ji