1981 Yamaha YZ125 frame

Totally different linkage suspension setup in the rear on the 1982.

What all is damaged on yours? Got pics? And have you asked around on Marks Motorcycle Swapmeet yet? I would think an 81 YZ125 frame would be a fairly easy one to find.

there is an 81 125 frame on CL in monrovia CA right now LA county

I have a spare one if you need one.

VERY IMPORTANT!!!!!

Make sure the seal area on the lower(bottom) is not corroded in any way . In the steering tube area,bottom area.

Strip the frame , dry film moly coat both seal area's -upper, lower . Use 2 Honda seal stacked in the upper
Area(4.00 each), follow the assembly manual exactly, new o ring's etc

Lower seal use stock set-up, or a 2 lip press in frame seal, versus the stem seal,

I just remachined the steering stem for bronze bushing's to prevent rust issue

And new bearing's

$129.00 seal= alek power sports of Erie penn?

Crazy ripoff!

Ok seal info. = ID OD Height. All in mm, or mm x .03937 = inch / decimal size
Yamaha = 28 37 8
Honda part # 91201-ksr-a01 = 28 37 7
SKF. = 28 37 10

Your local Honda deal should have the Honda master seal and bearing catalog, or you can download one
With all the seals and bearings available thru Honda dealers

You can stack a Honda part number 91201-ksr -a01, = is 1 mm less in height than the stock Yamaha seal on top of the
Yamaha seal, there is plenty of room for 2 seals( I just did this about 2months ago)

As far as the sleeving steering stem-easy job, your repair machinist ( not a production machinist, or cnc machinist)
Should know right off the top of his head the thickness of the sleeve, and how to install it, and the best material to use,
Or the best material he has on his shelf., and how much to remove from the stem, if it has corrosion issues.
If he does not know- move on to the next shop.

I had plans of machining new stems from 17-4 ph stainless, but the cost would be about $700.00 each including heat treatment!
They are actually a very complex part, double ID's, pressed in plug(and pinned) in the center, cross drill coolant holes,
And a plug pressed in and welded at the top, then center drilled , and final machined( threads cut) wow!

I made my stem sleeves out of ams 4640, and shrink fit the sleeves to the machined stem's( I made a spare stem assembly)
When I machine custom parts from billet, I always make extra's once the tooling is set-up, and running.
Once on the stem, install in a lathe, and finish to size , and concentric, I finished mine oversize to put more pressure
On the seal lip

Then I coated the stem with a dry film moly lube, and baked

DO NOT WELD UP THE CORROSION ON THE STEM, and machine back to size!


The bottom seal is a little different
You can insert a small spreader ring into the middle slot on the bottom seal( would need to be machined) precisely
ID,OD to fit right thus putting outward pressure on the seal lip= this is if you want to use your old seal

New lip seal for bottom
OD= 1.655 ID 1.2. 43mm 30 x 8 If I remember right my notes are in my shop

I am currently machining out the cast iron bearing liners in the rear hub, and fitting with a 4000 series high strength steel
To properly secure the rear wheel bearing's( weak spot on the hub)

Parts partially complete on the bench- for my personal YZ125H

Aluminum brake pedal's
Billet exhaust dampners
Billet exhaust rings
Billet brake stay
More Titanium bolts
Bronze bushing's for the floating brake assembly

Did you ever finish the bike?

My bike is done, with 9 lb weight reduction
currently.

Remove or replace the steel

handlebars
kickstand /and mount
both bearing hub spacer's (2lbs ) wow!
front, rear axle spacers ,nuts
all the steel washers, spacer's
silencer mount hardware
hose clamps
all the small 10mm head bolts, lock washers
Rear brake pedal, floating brake spacer's
Brake arm
kicker pivot pin( replace with A2 drilled thru tool steel
heat treat)
Foot peg bolts hardware
plus more.......

9 pounds is all? I think the swingarm and shock replacement on my 76 CR125 project adds up to more than that! I don't think the engineers at Honda could have made those items any heavier if they tried. What a turd they built when they "redesigned" that bike for 76.

yes, currently that was the total, The SS spokes, sun rims
were pretty much a wash on the lbs, and hub mods to
strenghten the really only weak link on the bike

I will be swapping a few more items with Titanium

The 79 CR250 I built was about 15 lbs less when i finished the bike

Lots of cheap steel removed .

Lots of good info here Rob Boucher thanks! I'm a machinist / toolmaker by trade and owner / operator of a small six man shop with edm, cnc and conventional machine tools. Your posts here are very informative and inspire confidence if I go ahead with the 'H' model I have lined up semi-locally. Was tempted by an air cooled 125G or 250G at first but I see the H as being sort of an add on works kit for the G haha. Less maintenance once everything is dialed in and I can live with the high rad connection complexity by reworking the whole thing like you did. Mind you I would go with a 250 air cooled G or H if there were any but hard to find. I am going to race it, it will not be a garage queen. Just love the looks, had a YZ125F from new as a teenager. Always wanted the G or H and love the simple monoshock design.

Some parts are getting hard to find, and i know of at least 5 complete resto's being worked on now! find your parts asap
Since you own a shop, you can fab most
parts
You can leave the stem in the triple and turn with no problem to machine sleeve area's
or press out, i have done it both ways
You can also fab up a complete lower stem
seal using o'rings similar to what a submersible pump uses by the impellar
area
or sleeve the frame to use a regular lip seal
link on


water pump impellar
lower seal
front nylon cable guides

feel free to contact me

Thanks Rob, way cool !
Hey I went with the '80 air cooled CR125 after all, got it for 150, pretty complete.
This will be my first resto, we'll see how it goes.
I'll do a YZ later on in time, but in 250 when a deal comes my way locally.
Ideally an F or a G, want to stay in the air cooled class.
But thanks again for the encouragement.
There are lots of Boucher family's in Québec !

yes, My great(x3)grandparents lived in Quebec in the late 1700's, my great grandparents moved to mn in the 1900's

Nice thread. I am restoring my 1981 YZ125H with my son and I have a question. How far down the steering stem do I install the top steering stem seal? I disassembled the bike completely a long time ago and forgot where the top seal is positioned. I saw a pick of a used one on EBay and it was pushed all the way down below the hole drilled in the center of the tubular stem. Is this the correct position?