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 Post subject: Fork rebuild (79 yz 250)
PostPosted: Sat May 11, 2013 3:11 am 
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Joined: Mon May 06, 2013 12:20 am
Posts: 11
so like the title say doing fork rebuild. So have this 79 yz 250 has not moved for 25 years at least but has sat in a shed since.
I am doing paint job, replacing stuff, doing everything top to bottom/ back to front with a fine comb.
Anyways I don't have a repair manual so some specs I do not know or the owners manual. The only thing I could find online and free was PDF of the parts book.

Let get to the point I know the 78 takes 338 ML (100 mm from the top) for shock fluid so I am thinking the same for the 79?
I read something about the springs need to be remove and fully collapsed. This is what gets me I have to take the shaft out to remove to the springs back in or no? If I did then oil would just rush out the seal?

Maybe some one could walk me through it or post a guide so I can grasp this better for the older shock?

The only thing I have read was for a 78 and this is what it says.

338 millilters or drain the oil completely (empty the tubes by removing the caps and turning them upside down) remove the springs, compress the forks until bottomed and fill with fork oil (15W per Yamaha recommendation) until 100mm (4 inches) from the top of the tube. DON'T fill them to the top.

From when I took it apart there was a a shaft, 2 springs, and then that shaft goes in the seal. One spring can be put right in but the other I would have to pull that shaft back out or is that not right?

so any help here would be great.
Thanks


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PostPosted: Sat May 11, 2013 1:03 pm 
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Joined: Tue Aug 31, 2004 1:44 am
Posts: 283
Location: Maysville, AR
makes me sick Yamaha used to provide service data and specs on their Yamaha Motor site and i could not find Service data at the Csnl site either.

if no one has the answer,a shop manual is the only place you may find the specs you need.

here is a result of my ebay search.
http://www.ebay.com/sch/i.html?_sacat=0 ... 250+manual

anyone else can help this guy?

_________________
(2) 1968 DT1 1970 RT1M,1970 DT1C 1971 RT1B Enduro 1974 MT250 1974 DT250A (2) 1975 DT400B 1974 DT100,1978 DT175
1975 CR250M1 1979 CR250R 1979 Kawasaki KZ400H1 Jesus is Lord!!


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PostPosted: Sat May 11, 2013 2:51 pm 
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Joined: Mon Dec 10, 2012 7:27 pm
Posts: 30
Do you have pics of what you are doing? It would help immensely.

Did you dissassemle the entire fork, which I am meaning you took the bolt off the bottom of the fork leg and you now have the lower fork leg and the upper fork leg apart in two pieces? Some of the forks have a spring on the damper rod for topping out.


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PostPosted: Sat May 11, 2013 6:04 pm 
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Joined: Mon May 06, 2013 12:20 am
Posts: 11
I upload a photo.
I do have it completely apart 2 sections and the rod with 2 springs.
I am just trying to how to collapse it,fill it, then take the rod back out to out the springs back on with out losing oil.
Does oil flow in the whole shock top to bottom or just top section or bottom?
Can anyone confirm the amount I stated on each shock?
Also from my understanding it also a air shock about 8-15 psi?
The top cap, bolt, and other parts are in a bag.


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PostPosted: Sat May 11, 2013 8:08 pm 
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Joined: Mon Dec 10, 2012 7:27 pm
Posts: 30
OK,

The damping rod is the shaft or rod or whatever you want to call it that has the shorter spring on it. Slide that down into the chrome shaft/tube and put the bottom bolt back in the damper rod and tighten it up. That's the way it looks on the parts daigram and from your pic. Next add the oil. Then put the main spring back in and any preload spacers and cap and you should be good to go. I think there were some minor differnces between the 78 and 79 but I haven't rebuilt my 79 forks yet. Do not put air in the forks. There is a good possibility that air pressure could blow the seals.


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PostPosted: Sat May 11, 2013 10:44 pm 
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Joined: Mon May 06, 2013 12:20 am
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Yea I got it solved doing a dry run with out seal over the last few hours. They was pretty dirty when I started on them oil all over and dirt. After doing both shock I discover they was leaking on the bottom bolt, took it to the impact, took the cap off remeasured to the top, add as needed with was not much. The bottom spring I found can stay in it does not affect it from fully collapsing the sock but to keep it from extending to far.

I think you are right on them being different a little. I put in I think 375 ml (maybe they meant 438 ml but I stooped measuring and just started pouring) and it was not even close to 100mm from the top.
The top cap also has a air check for air and I have read some place they are air shocks with 8-15 psi (estimated people think).
Otherwise I would not know why it would be there then?
As for the preload spacers hahaha there was none when I took them apart. I saw on the parts book it had them but they was not in there. There might be after market spring they was a pain to put the cap back on. If I need spacers I will make some.

All I know about the bike was it was raced, then sold, then sold again (in swap meet) to my dads friend long time ago, my dad traded is mustang for it to his friend, my dad beat the crap out of it blown shocks, broken wheels, no packing in the silencer (I don't think he ever looked if it had any), scored cylinder from piston chipping so he never fixed it for the last 25 years just put it in a shed. Aside from what he did the prev owners used wrong bolts in places, not correct stuff, shock caps messed up (cant put a socket on it), other crap here and there.


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PostPosted: Sun May 12, 2013 10:40 am 
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Joined: Mon Dec 10, 2012 7:27 pm
Posts: 30
Great that you figured it out. They aren't overly complicated. You could run air in the forks but like I said, you risk the chance of blowing seals. What I do after every ride is let air out of the forks.


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PostPosted: Sat May 18, 2013 8:13 pm 
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Joined: Tue Aug 31, 2004 1:44 am
Posts: 283
Location: Maysville, AR
if you add air to the fork i would go no more than 2 psi.that is a pretty safe pressure to stiffen the forks a bit.

the right way would be looking for the optional springs for the forks and you may need to experiment with different weights of fork oil to get it truly dialed in to your taste,weight and riding style.

_________________
(2) 1968 DT1 1970 RT1M,1970 DT1C 1971 RT1B Enduro 1974 MT250 1974 DT250A (2) 1975 DT400B 1974 DT100,1978 DT175
1975 CR250M1 1979 CR250R 1979 Kawasaki KZ400H1 Jesus is Lord!!


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PostPosted: Sun May 19, 2013 5:01 am 
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Joined: Mon May 06, 2013 12:20 am
Posts: 11
Found a article online from 1979 and it goes over what mods to do on it and they recommend 10 psi.
I don't want to take them caps off again they are already a pain to get on. I don't think its the stock spring in there now. With ho hard it was to get on in the first place I don't see how anyone could get the spacer in there as well. I mean wow it took 2 people to get the caps on.

Anyone know the stock spacer length? Mine did not have them but I can make some.


Maybe its just my snowmobile racing experience talking here but it it has a air valve, air is meant to go in it. If its inside the shock and not outside it not air.

I have them set at 18 right now but that because I want to make sure there is no leaks on the bottom. Had them at 60 psi on accident because the air chuck got stuck for a sec (I have a pump for my race sled we use but it broke) but they did not blow they even held the air all night.

I will get it but the shocks just seam weak with out any air in them.


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