1977 Yamaha YZ125 (or so I thought):

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SMMWest

Mod Ban
Dec 7, 2008
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I got dupped by I am really not that upset about it. I purchased what I was told was a 1977 Yamaha YZ125. I believed it by looking at it as it carried the Black Steal Sub-Frame.

Well come to find out it is a 1980 Yamaha YZ100 Frame and that is why it carries the Black Steal Sub-Frame. The side pannels should of been a dead give away but I guess I let my joy of believing it was a 1977 Yamaha YZ125 get in the way.

:bang:

The motor is in fact a 1977 Yamaha YZ125 so I am happy about that.

My question to all of you 1977 thru 1979 Yamaha YZ guys are will 1977 thru 1979 Forks and/or Shock fit on this frame?

I had plans of building a 1977 Bob Hannah Replica just the way I built a 1985 Honda CR125 Ron Lechien Replica, but this Frame thing kinda throws a Money Wrench in the Program.

Thanks in advance.
 
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dirt bike dave

Sponsoring Member
May 3, 2000
5,348
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The '77 YZ125D had 36mm diameter fork tubes.

How big are the tubes on your YZ100?

I found on the web that the '80 - '81 YZ100 had 35 mm tubes and the '76 YZ100 had 34mm tubes.

Can't find any specific reference to the '79 YZ100, but my guess is it had 35 mm tubes and not the 36mm on the '77 125.

If the whole purpose is recreate a '77 YZ125D, I think you are going to want a different frame.

OTOH, those little YZ100's were pretty fun bikes, so you should have a blast with it until a '77 125 comes along.

FWIW, I had a '76 YZ125X with the dual chamber air forks (just like the '76 250 and 400 had). I'll advise you NOT to put those forks on! They sucked!
 
S

SMMWest

Mod Ban
Dec 7, 2008
160
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The forks are 35mm. I know the the old RM125's and RM100's of the same era used the same frame and parts just different motors and wheels, I was hoping that the Yamaha YZ125's and YZ100's used the same theory but it isn't looking that way, it looks like they were 2 completely different beasts.

Yeah I am going to get going on the project while I am looking for a 1977 YZ125 frame comes along, as I want to get the cylinder bored and ported,Jemco pipe, Boyesen reeds and the such and I can get started on those things. Really sucks that someone fitted that great Vintage Motor into the incorrect frame.

Anyone with further details on the 2 bikes please chime in. THANKS.
 
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SMMWest

Mod Ban
Dec 7, 2008
160
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Finding out so much about this pieced together bike, but I am still happy as can be. After checking all the numbers on the Bike (Frame and Motor) and Bill of Sale. The motor is not a 1977 but a 1976 YZ125 (great cause the is the year Bob "Hurricane" Hannah won the 125cc AMA National Motocross Title). The frame is indeed a 1980 Yamaha YZ100.

I am currently looking for Front Forks that will give me more Travel and a Heavier Spring set-up. I am looking at both 1980 Yamaha YZ250 Triple Clamps and Forks and also 1982 Yamaha YZ490 Triple Clamps and Forks.

I am looking at Rear Shocks from a 1980 YZ250 and also a 1981 Yamaha YZ465. Don't know if the Shocks will fit but even if I can use the Shock Spring it will give me both a Higher ride out back (more travel) and a Stiffer more Firm ride.

Hope it all comes together.

Everything else is in order and parts are really easy to track down.
 
S

SMMWest

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Dec 7, 2008
160
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Brian Kirby said:
But...if you are building a '76 Hannah replica, why change all this? If you look at pictures of his '76 bike it did not have super long travel or big forks, it had 9-10" travel and spindly little forks just like what is on your bike.
Click to expand...

This guy was so right and got me back to remembering what my whole goal was with purchasing the bike in the first place. I am so thankful to him.
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
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Merrillville,Indiana
A lot of them old shocks can get rebuilt. And Cannon spring can make anything for any weight. Slapping bigger on does not always work properly, and some times causes changes elsewhere$$$ Vintage Bob
 
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dirt bike dave

Sponsoring Member
May 3, 2000
5,348
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FWIW, the water cooled OW works bike that Hannah rode to the title in '76 had little to nothing in common with the two air cooled '76 YZ125 production models, which were the 125C and the 125X.

The production '76 frame was also horrible, with a spindly little steel swing arm. The '77 and later had a much improved frame and an aluminum swingarm, and looked much more like Hannah's '76 works bike than the '76 YZ did.

I think the radiator on Hannah's '76 works bike was mounted behind the number plate. The first production water pumpers were several years later.

The 125X had a more radical motor (bigger carb, different porting) than the 125C. The C model was down a couple of horsepower power compared to the CR125 and RM125. The X could hang with those bikes.

The X also had the dual chamber air forks shared with the 250C and 400C, with a big black cannister on the top of each fork leg. That was the easiest way to tell the X from the C. Hannah's '76 racebike did not have the air fork.
 
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SMMWest

Mod Ban
Dec 7, 2008
160
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What cylinder would fit on this 1976 Yamaha YZ 125 bottom end that would possibly have 2 Spark Plugs?
 
S

SMMWest

Mod Ban
Dec 7, 2008
160
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This bike is a Frankenstein Monster. I guess the cylinder head is of a 1974 or 1975 Yamaha MX125. Crazy beast this is.
 
2

2strokerfun

Member
May 19, 2006
1,500
1
dirt bike dave said:
FWIW, the water cooled OW works bike that Hannah rode to the title in '76 had little to nothing in common with the two air cooled '76 YZ125 production models, which were the 125C and the 125X.
Click to expand...

But remember, Hannah only ran the OW27 part of the year. After a bike was claimed, Yamaha pulled the water cooled engine and stuck an air-cooled unit back on the bike, much to Hannah's dismay........
 
S

SMMWest

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Dec 7, 2008
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Think that I will put the 1974/75 Yamaha MX125 Cylinder (yeah it is the entire cylinder) and Head up for sale and then search out a 1976 Yamaha YZ125 Cylinder and Head with those monies.
 
S

SMMWest

Mod Ban
Dec 7, 2008
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So I am cleaning up the Cylinder so that I can sell it and low and behold on the side it says 171cc.

It is a 1975 MX 175B Cylinder. I can't believe what I have gotten myself into, ha ha ha ha. But it is still fun. Gotta laugh at myself. I am to old to have jumped into grabbing a project like this, but I will enjoy it.
 
S

SMMWest

Mod Ban
Dec 7, 2008
160
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whenfoxforks-ruled said:
They used to run that bike in the 100cc class, well the cheaters tried anyways.
Click to expand...


Yeah I had no idea it was a MX 175cc Cylinder and Head. That would of been an easy cheat back in the day.

Thank You for that information. Restoring this bike with all of its mismatched parts isn't going to be as easy as Restoring my 1985 Honda CR125 but it is going to be fun and I can't wait to get it all sorted out and finished. I am up for the long process.
 
S

SMMWest

Mod Ban
Dec 7, 2008
160
0
Project has stalled as I don't want to paint the frame and try to let it cure in this freezing cold weather.
 
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madmurph

Member
Dec 30, 2024
1
0
Hi from UK, it would appear I fell into a similar hole. I bought (via eBay) a project what I was told was a Euro model (white tank) 1976 YZ125X. Once I got it home and check frame and engine numbers it turned into a YZ125X with a DT175 engine. Oh joy.
 
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