1986 Yamaha yz125 restoration

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11/17/2017 1:15 PM

Yes, that's right...yet another yz restoration project for your perusal.

See my last effort here http://www.vitalmx.com/forums/Bike-Builds,46/1988-yz-125-build,1316015

This one I bought a couple of years ago in bits and in boxes from a chap in Manchester (uk) who dismantled it and started a restoration but lost interest.

Here's a few pics of how I got it. Parts acquired and What has been done so far.

I'll update the thread as I go as I've only just started refurbishing parts.

Hope you enjoy... let me know your thoughts.




11/17/2017 1:23 PM

This is what I'm aiming for. Or somewhere very close to


11/17/2017 2:14 PM
Edited Date/Time: 11/17/2017 2:25 PM

So, the guy I bought the bike from (owen) who will probably be following this thread had stripped it down and started the restoration process, He'd already carried out the following so I can't take all the credit for the end result!
Wheels refubed, rims anodized gold, hubs painted and relaced with stainless spokes... topped off with a nice set of new Dunlops.

Frame blasted and painted cherry red... I'm almost certain that the 86 yz was more of a postbox red and the 85 had the cherry red frame? Can anyone clarify?

New plastics including a new pair of nos genuine yamaha red rad scoops (rare as rocking horse poop).

So today I stripped down the motor, I was surprised to find the cylinder bore is 56.6mm, it was only 56mm when new, small amount of play in the big end/con rod... This is by the by as they'll both be replaced in keeping with the standard I'm aiming for.

Cleaned the casings ready for paint. Replaced the bearings in the gearbox with nos Yamaha items.

Replaced the con rod, crankshaft bearings and oil seals, again with nos Yamaha parts.

Crank cases primed and painted satin black.

I'll update the thread as I go.


11/20/2017 2:02 PM

I'll be following this build closely. I picked up a very low hour, mostly original bike a few months ago. Original tires, bars, grips, sprockets, but.....the engine totally disassembled and in boxes mixed with other bikes parts dizzy I think its all there. Im starting the process of acquiring NOS parts, and probably a couple extra '86-'88 parts bikes by time its all said and done.

I have a soft spot in my heart for the 1986 YZ125, as it was my first "real" dirt bike. I absolutely love the '86-'88s, and the '89-'92 generations. I could care less about the prior or later generations. I like the 250's from those era's too, especially the '88-'90 YZ250's.


11/20/2017 2:12 PM

"Frame blasted and painted cherry red... I'm almost certain that the 86 yz was more of a postbox red and the 85 had the cherry red frame? Can anyone clarify?"

I agree that your frame is the wrong shade of red. It looks a couple shades too dark. It definitely looks a darker shade than your shock spring in the pic above.

12/29/2017 3:35 PM


That's exactly what I thought, frame was too dark.
I always wanted this model when I was in my early teens but I couldn't afford a bike.
The engine and box is now done. Pics taken but I've been too busy to update the thread.
I'll get it updated asap. If you get stuck with anything in the meantime just drop me a message. Always happy to help.


12/29/2017 4:54 PM

Ok, so... the engine is now done, I replaced every bearing with nos genuine yamaha items and oil seals.
Casings painted satin black and all new genuine yamaha nuts/bolts and washers fitted (cost for fixing and fasteners around £230
The crankshaft was split, checked and new con rod + big & small end bearings fitted.
Gears, selectors and shafts all in good order.

Cylinder rebored to 1.25os as the bore was quite worn. The power valve had to be dressed up to clear the piston.


12/29/2017 5:11 PM

New wossner piston and ring fitted.


12/29/2017 5:48 PM

I checked the clutch basket, dressed the fingers (evenly) to remove the serrated edge to ensure the clutch plates move correctly.
Fitted New clutch plates (friction and steel) as well as nos springs and bolts

New old stock intake boot, all new gaskets.

Kick start stripped, checked, New spring and ball bearing fitted, greased ( also have a nos rubber boot to go over it.

New panels, seat cover and graphics

That's all for now folks. I'll add some more as I go.


12/29/2017 6:30 PM

Looks great so far, following along for the finished product.


1/1/2018 1:29 PM

Looking good! I'm so jealous of those NOS rad shrouds.


1/1/2018 7:40 PM

Nice job... And you can't go wrong with a Wossner piston and ring set.
Their rods are also very reliable...


1/2/2018 11:31 AM
Edited Date/Time: 1/2/2018 11:37 AM

Just a quick update.

Stock white Clarke fuel tank arrived from the us. Looks good but for those of you in the uk thinking about purchasing one be very careful as the customs and import duties are steep.
I bought 2 of the same tanks, 1 for this build and the other for the 1988 yz125 I built last year... tanks were $229 each, combined shipping $125, customs & import duties in the uk $205 (£149) total for both tanks all in $800 (£650).
I knew the costs before I ordered them, just to give you an idea of extra charges if you do order one.
Quality and fit of the tank is good.

Exhaust painted

@ khi guy, yeah those nos rad shrouds were a hell of a find by owen (previous owner) they're like rocking horse shit to find, I believe he found them in the Netherlands and paid quite a bit for them... really nice to have them.

@sandblaster yeah, the mitaka piston and rod were half the price but I wasn't convinced at the quality, I figured if I'm going to do it, do it properly and spend a little extra to make it the best I can.


1/2/2018 5:39 PM

This is awesome, I love it!


1/3/2018 7:18 AM

I'm curious to see how different white shades of plastic look when all done. I am assuming the fenders will be OEM since they are still available. I've heard of the Clarke tank white being a little bit off. What side panels are you using? Those don't appear to be NOS. Or are they?


1/3/2018 1:33 PM

Yeah there is a noticeable difference in the shades of white. See pics of the 88 yz below

It's not quite as obvious in natural (day) light.

The plastics came with the bike. I think the side panels, mud guards and front panel are ufo, I'll keep these for now and replace with nos as I go, I've spent a fortune in the last few weeks.


1/3/2018 3:28 PM

KHI Guy wrote: "Frame blasted and painted cherry red... I'm almost certain that the 86 yz was more of a postbox red and the 85 had the cherry red frame? Can anyone clarify?"

I agree that your frame is the wrong shade of red. It looks a couple shades too dark. It definitely looks a darker shade than your shock spring in the pic above.

x2. By the way, I don't think the '85 and '86 had different reds. As you are probably aware, '85 was the first year of red/white YZs in the USA. I don't think they made a color change until the pink '01s.


Braaapin' aint easy.

1/3/2018 10:01 PM

Looking fantastic!



1/4/2018 2:47 AM

Looking Really Fantastic.
Thanks for sharing.


1/5/2018 7:24 PM

I bought a white ufo rear fender for my kx450f. I then bought acerbis white rear side panels. The ufo white is alot cleaner brighter more white. I think the acerbis white might look better with the white tank you have. Just a thought. I had a 86 yz125 growing up. I remember our middle school library had an archived dirt bike test of it . I used to check it out of the library like at least ounce a month!


1/9/2018 11:24 AM

The acerbis thing might be a good shout as the oem plastics aren't available in the uk anymore, thanks for the info, I'll look into it.

The frame has been blasted and power coated red.


1/9/2018 1:16 PM

This place has pattern parts. Bought from them before and it looks like they import the DC made plastics.



1/10/2018 10:25 AM

That red looks much, much better. cool


1/12/2018 7:04 AM

Keep up the good work!


5/30/2018 12:06 PM

Time for an update, been so busy at work that I haven't had time to get anything done.
It begins, started assembling the frame. Will keep updating as I go.


5/30/2018 12:12 PM


5/30/2018 12:20 PM

You're getting there.


5/30/2018 12:33 PM

Indeed. A mixture of busy and stalling interest put it on a back burner temporarily.
My mojo is back now so I'm raring to go.
Still so much to do, wheel/rear suspension bearings, forks to strip, re-seal paint, brakes, electrics ect... looking forward to it all ?


5/30/2018 1:01 PM

Its like eating an elephant, you do it one bite at a time. smile Good luck!


5/31/2018 6:25 AM

Looking good!