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lb/hp is what it's about!
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Discussion Starter · #1 · (Edited)
I was at a swap meet last Saturday when I spotted this tired old two stroke. It was sewn together, the brakes didn't work, everything was covered in oil, the bars and radiator are bent, and most of the fasteners had been replaced with zipties. It took a while to get it started so I low balled and eventually we had a deal. Now that it was running I took the long way back to the truck and almost looped it twice in the first 20 minutes of owning it. :oops: :D

Best I can tell is it's a 87-89 yz80.




On Sunday some friends were getting together to ride the pocket bikes so I adjusted the chain on the yz, wiped the fork oil off the rotor, and was racing it less than 24 hours after its purchase.





Sundays ride time made me realize how bad the suspension and brakes are. It was never jumped or landed a wheelie hard and we still used up all 9" of front suspension travel. Granted I'm no light weight but I'm thinking the shock is dry too because it pretty much bottoms out when I sit on it. The front brake kind of sorta worked after the fork oil was wiped off.




Check out what the RaceTech website says about the stock spring rate. :LolLolLolLol:








So the plan is keep it cheap and try to use mostly what I already have sitting around.

Front end:
-- cbr600 F2/3 forks, triples, caliper
-- spare KTM 17x3.5 front wheel and rotor
-- take off 120/70/17 tire
I'll have to make spacers for the wheel and caliper and I'll probably just make a new steering stem to adapt the F2 triples to the YZ neck. Unless the F2/3 offset works really well I'll eventually make some billet triples with an adjustable offset.

Rear end:
-- custom extended swingarm
-- spare 17x3.5 rim laced either to the stock YZ rear hub or find a different hub
-- take off 120/70/17 tire
-- maybe go disk brake if I change rear hubs??
-- I've got a bunch of shocks so maybe a F2/3, 900rr, or ATK/Cannondale shock

Bought that front end from Robbo a looooooong time ago.


Playing with ideas for an adjustable triple.
 

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lb/hp is what it's about!
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10,448 Posts
Discussion Starter · #3 · (Edited)
Was looking through my stash for some rotors late last night and found two that will fit the KTM front wheel. There was a 220mm and this 310mm rotor. The 220 will probably be too small and the 310 is likely beyond over kill but it looks sooooo good. If I can't find a cheap 260-280mm rotor I'll probably run this 310mm.

 

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Hack in a barn
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4,409 Posts
So the plan is keep it cheap and try to use mostly what I already have sitting around.

Front end:
-- cbr600 F2/3 forks, triples, caliper
-- spare KTM 17x3.5 front wheel and rotor
-- take off 120/70/17 tire
I'll have to make spacers for the wheel and caliper and I'll probably just make a new steering stem to adapt the F2 triples to the YZ neck. Unless the F2/3 offset works really well I'll eventually make some billet triples with an adjustable offset.

Rear end:
-- custom extended swingarm
-- spare 17x3.5 rim laced either to the stock YZ rear hub or find a different hub
-- take off 120/70/17 tire
-- maybe go disk brake if I change rear hubs??
-- I've got a bunch of shocks so maybe a F2/3, 900rr, or ATK/Cannondale shock



 

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Newbie
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772 Posts
If you are stuck on 17s, I suggest a cbr125 set or an ex250. Cheap and easily adaptable either way. Other than that fuck swaping rims, fuck swapping forks. Put street style tires on the stock rims and rock the fuck outta those, then for the front forks, fill with 20-30wt fork oil and cut the stock spring like 2 inches and then put a 3-4inch pvc spacer in there and rock the fuck outta those.

For the rear shock either find an el cheapo sport bike shock that will and work out maybe an r6 unit or whatever you got will work or if the rear shock has preload adjustment crank the fuck outta it till it moves like a half an inch once you sit on it and rock the fuck outta that.

On old school 2 smokes don't bother making them fancy just wheelie the fuck outta them from corner to corner
 

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lb/hp is what it's about!
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10,448 Posts
Discussion Starter · #7 ·
Cutting the stock spring and putting PVC in there still leaves me with a super soft front end. It just won't dive quite as much before bottoming out.

If I can find a set of the 17" ex250 or wheels for a deal I'd do it but everything I've been finding is around $300+ for a set. Buying spokes and nipples to lace the rear rim to a hub is going to be around $90 and then a new rear hub if I get one will probably be $30-40. Is it worth $150+ to avoid dealing with tubes? I don't think so.

I'm swapping all this stuff on it because it will look cool when it's done and because it gets the parts off my shelves. I know it's never going to be a race winning bike. I just want to look cool while screwing around. When I do actually race it I don't care if I'm at the back as long as there is someone else back there to battle with.
 

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Is my bike ok?
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15,025 Posts
What Garret described on replacing two inches of fork spring with four inches of spacer will increase the spring rate.

Tubes aren't a big deal. But if they really bother you then seal the nipples up. A fat swipe of silicone has worked for many guys through the years. It's not like you're traveling far away from home, so if you have a small leaker it's not the worst thing in the world.
 

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lb/hp is what it's about!
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10,448 Posts
Discussion Starter · #9 · (Edited)
Goal for the weekend was to change the shock and since the airbox never had a filter in it and I had to remove the airbox for easy access to the shock I decided to remove it permanently. One option is to buy a 43mm pod filter and another option that will cost $0 is making a tube to extend from the carb past the shock and to a gs750 air filter I found. It won't look as good but it costs nothing.



I wanted something adjustable for a new shock but the only one I had that could have possibly worked is a 05-06 gsxr1000 shock. Too bad the res is too wide for the frame.



After some more digging I had two options. Either use a Katana 1100 spring and machine a spacer (shorter spring) on the stock leaky shock or try to make an ex500 shock fit despite being about 3" shorter (~12.5" vs 15.25"). I went with the ex500 shock since it appeared to not be leaking.

In order to make it fit I had to remove the dust cover things for the stock suspension linkage and then widen the shock clevis by 2mm. I just put a bolt through the shock clevis and turned the nuts outward to spread it. Not ideal but it worked and now I was halfway done.

I wanted to make the top extension piece bolt in without modifying the frame. The stock upper shock mount is 30mm wide and the ex500 upper mount is 20mm. I used some 3/16" bar stock to make the extension pieces which gave me a width of 29.5mm. Then I turned a spacer tube and welded that between the plates to complete the frame side of the extension. Problem is it would still pivot...



After a while of playing around with different ideas to keep it from moving I gave up and welded the damn thing in.



It's not how I wanted to do it but it's done and ridable again and doesn't bottom out when I sit on it. It still feels a little soft so if I run across a deal on a 08+ ex250 shock I'll use that instead. It's the exact same dimensions as the old ex500 shock I used but has a slightly stiffer spring. Even so, it wheelies a lot easier now that it doesn't just squat when it gets into the power. :party-smiley:



I still need to do something about the terribly soft front suspension and weak front brake. You guys mentioned cutting the springs and heavier oil. I've never taken forks apart so what exactly do I do? Just pull the fork caps off and I can slide the springs out? I'm 250# so I doubt it will be anywhere near stiff enough (what I was getting at in a previous post) but I suppose the forks aren't worth much as is so I may as well try a cheap fix.
 

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lb/hp is what it's about!
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10,448 Posts
Discussion Starter · #10 ·
Also, the bike seems to be really loud and the muffler can't be repacked unless I weld it back together which I don't want to mess with. Does anyone have an aluminum muffler that can be repacked? If it's for sale let me know!


I'd also like to figure out how to get a headlight and tail light on it to make it more believable that it's street legal. For the headlight I was thinking of mounting a flash light on the bars but light output might suck. For the tail light I was thinking one of those LED strips with a kick stand switch by the rear brake lever and a regular switch on a new front master.

Anyone have a better idea?
 

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lb/hp is what it's about!
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10,448 Posts
Discussion Starter · #12 ·
Haul your ass over to Edgerton and see Ryan S at The Bargain Barn for tons of parts
I sold him a Buell XB front wheel and fairing at Woodstock a few weeks ago. He was interested in my other front wheel but decided against it. I wonder if he'll take it as trade towards parts I need?

This yz needs a radiator shroud too. That's a big part of the reason I've only been taking photos of the left side of the bike. Haha
 

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CAPTAIN AWESOME®
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30,276 Posts
I sold him a Buell XB front wheel and fairing at Woodstock a few weeks ago. He was interested in my other front wheel but decided against it. I wonder if he'll take it as trade towards parts I need?

This yz needs a radiator shroud too. That's a big part of the reason I've only been taking photos of the left side of the bike. Haha

Hit him up
 

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lb/hp is what it's about!
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10,448 Posts
Discussion Starter · #14 · (Edited)
It has been a while with no update so here's the latest.

I bought some 80/90/17 and 80/90/14 IRC nr77 scooter tires for it and it handles much better. The front tire is the same as stock but the rear is significantly smaller. The change in diameter kills top speed but makes wheelies even easier so fun FUN! :wheelie:





I also cut off 2" of fork spring and added 2" of extra preload like suggested. It was significantly better but still pretty soft. I could lean against the forks and easily compress them 3-4". Jump on them and they'd still bottom out. Stock on the right, modified on the left.




A few weeks ago I was at a swap meet and bought a handful of fork springs for $5. Supposedly they are all from early 60's Triumphs. Didn't really care because they were the right diameter and appeared to be significantly stiffer. I rebuilt the forks and put the new springs in with 3/16" preload and 5wt oil and it turns out they are quite a bit stiffer. When I hold the brake and jump down on the forks I can only move them about 4-5". Much better!


Next on the list is a bigger front brake. Plan is to redrill a rotor from one of the bikes under the 21.051 to go from the stock 190mm rotor to a floating 290mm rotor. Not sure if I'll switch to a bigger caliper or leave the stock one alone. I've got a 14mm master in a box somewhere too.


 

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Newbie
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772 Posts
Should be using 10w or higher for a big boy rider bud, get way too much compression with that light oil. 10w-40 motor oil works good in mini motards with old forks because the fluid heats up as it cycles and gets thicker, so giving you more dampening when it is bumpy
 

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lb/hp is what it's about!
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10,448 Posts
Discussion Starter · #16 ·
All I had on hand when I did the fork rebuild is 5wt and 20wt fork oil and I couldn't find any specs online for this old of a bike. Even so, compression seems fine now that I changed springs. I haven't done the math yet to see what exactly all the spring rates are that I've run so far but the new springs are probably twice as stiff as the stock ones when they were cut down.

If anything the rebound seems too fast but these are old school damper rod forks so I'm not sure I can do much about that. The thicker oil might help but it will also make compression stiffer which I don't really want. It's still way better than it was so I'll wait and see how things are when the front brake upgrade is done unless you've got other ideas. I'm not knocking your idea of 10wt fork oil, I'm just thinking out loud.
 

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Oh man you are gonna want that compression stiffer once you put bigger brakes on it. Although the if you are riding it more motard style you can get away with it but if you are going knee down. Stiffen the hell outta that front
 
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