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75 YZ 125 (ish) project

  • Storbeck
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75 YZ 125 (ish) project was created by Storbeck

Just picked up a 75 YZ 125, unfortunately (maybe fortunately?) it has a DT175 motor in it, and it is a bit of a basket case, but it is mostly original YZ125B parts. I am not a hard core motocross guy, not even on a "modern" bike, once upon a time I was a semi-decent hare scrambler and still more at home in a flowy woods single track than moto, but I plan to ride this thing in anger on both moto track and single track, but probably not much actual racing. I would like to get it functionally good and aesthetically decent. 

   
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10 Oct 2021 11:20 #1

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Replied by Storbeck on topic 75 YZ 125 (ish) project

Bringing it home: 

 

Digging in a little to see what I got: 

 
10 Oct 2021 11:26 #2

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Replied by Storbeck on topic 75 YZ 125 (ish) project

It came with a bunch of random stuff, much of which is not even related to this bike, so that's fun. 

There are definitely some missing parts here, and it has the standard collection of random mismatched fasteners, square head, slotted head, inch sized bolts rammed into metric holes, a bit of baling wire here and there, but it does have some cool (to me) old school YZ parts on it, so I'm stoked. 
 
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10 Oct 2021 11:32 #3

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Replied by Schu on topic 75 YZ 125 (ish) project

That's quite a conglomeration of 175 engine parts you got there. I think the engine in the frame is an earlier version of a CT175 judging by the ignition side cover. The experts will chime in and confirm that eventually. It's going to be a fun project. Good Luck 
Schu

CT175B, CT175C, JT1' JT2' DT360A, GT80B, DT100B, DT125B,
DT175B, DT175C, DT250B, DT400B, Z50, SCR950

Someday, you'll own some Yamahas
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10 Oct 2021 11:43 #4

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Replied by MarkT on topic 75 YZ 125 (ish) project

Nice find and project!

I think that's a CT engine (pre 74 175). 

Does the rear lower engine mount line up?  It won't unless frame was modded.

If you had a DT175 (74-on) the mounts would line up with stock frame.

A DT175 engine in a YZ125 is popular and makes a fun, reliable bike.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
10 Oct 2021 11:47 #5

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Replied by Storbeck on topic 75 YZ 125 (ish) project

So, two things I'd like to start on. 

1. Pegs. These stock pegs look like they were not great on thier best day and now they're worn out and saggy. 

Any suggestions on what to do for decent pegs on this thing? 

I see this thread: 

www.yamaha-enduros.com/index.php/forum/y...z-mx-footpeg-options

My 125 frame/pegs are a little different but it looks like I could do something similiar with parts from a DT/MX 125. I kinda like the newer style KTM pegs (My "modern" bike is an XC350) and the relatively common readily available DT mounts, but I'm not so sure about moving the location of the pegs. 

Open to any and all suggestions. I'm not opposed to doing a little bit of fabrication or machining, I'd prefer not to modify the original frame, but not SUPER against it. 

2. Forks 

The original forks this thing came with are basically empty of all oil, and I would imagine pretty worn out. The tubes are not super terrible but they have some nicks, so if I'm going to be rebuilding and replacing some parts, I might as well do it to something that is an upgrade if it makes sense to upgrade. 

I'm seeing a lot of threads suggesting MX/DT 250 forks of similar year range as a more or less bolt on upgrade. Is that the way to go? Is there some other option with more travel or better construction (actual bushings seem like a good idea) or more possibility for modifying/improving the valving? I am open to gold valves or some such and again basic machining or fabricating is no problem. 

 
10 Oct 2021 11:49 #6

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Replied by Storbeck on topic 75 YZ 125 (ish) project

Looks like you guys are right, not a DT motor. 

Which is kind of a bummer I guess. 

I'm going to focus on the more mundane stuff first, ergonomics, suspension, brakes, that sort of thing, and then decide what I want to do with the motor. I am somewhat imagining some home job porting on a 174 and possibly might even try my hand at a pipe, but we'll see. 

First things first and I need to have a place to stand and something to hold the bike up off the ground, so feedback on the pegs and forks would be much appreciated. 

Pics of motor stuff: 


Pics of motor stuff: 
  
Last edit: 10 Oct 2021 12:34 by Storbeck.
10 Oct 2021 12:33 #7

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Replied by Storbeck on topic 75 YZ 125 (ish) project

It came with some extra motors, they appear to be CT or AT motors, not DT. 

It came with some extra motors, they appear to be CT or AT motors, not DT. 

  
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10 Oct 2021 12:35 #8

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Replied by Storbeck on topic 75 YZ 125 (ish) project

Are DT, MX, and YZ 250/360 forks from around 74/75 all the same except for valving? Or is there some reason to seek out some specific fork? 

 
10 Oct 2021 13:15 #9

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Replied by Schu on topic 75 YZ 125 (ish) project

No they are not all the same. The forks in your photos don't look too bad. You might want to just use them until you sort out your engine. Take them apart, clean them up, and reassemble with new seals and oil.

Trying to mix and match parts can add a whole nuther level to the tasks you have ahead of you with this project.
 
Schu

CT175B, CT175C, JT1' JT2' DT360A, GT80B, DT100B, DT125B,
DT175B, DT175C, DT250B, DT400B, Z50, SCR950

Someday, you'll own some Yamahas
10 Oct 2021 14:41 #10

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