YZ125K Rebuild

[FourstrokeForever]

Looking good Alex. It's such a great feeling to have a better than new old bike that you build yourself. And the confidence to know that everything is done right. Top job mate.

[suzuki59]

Looking great mate !

[alexbrown64]

Thanks for the positive comments fellas.  Well, i have had a bit of a play and got the clutch cover on. Its a bit of a rub your belly and pat your head at the same time type of job.  Insert the power valve governor into the side cover lining up the power valve linkage and governor groove.  Make sure you have gasket and dowels on case and all water pump gears in.  Put side cover on and align water pump shaft with white plastic gear by twisting the pump shaft.  Then make sure governor gears mesh by gently moving kick start while pushing clutch cover into final position.  Then it was time to bolt up the power valve linkage and adjust it as per the manual and fit linkage and water pump covers. 

GPI Racing silicon hoses:  I sent GPI a set of old hoses, photos, diagrams and the like and they made me up a set of custom hoses for the YZ125K.  They now sell them on Ebay.  I asked for them to be made in yellow as i have never seen any like that before.  I used my existing clamps to fix them on and all i had to do was trim them down an inch or so as GPI leaves a bit of green on the ends.  Better to be longer than too short. 

Below is a pic of everything fitted up.  You can also see the airbox mod i did which is specified in the Yamaha tech report.  Drill 4 x 25mm holes in the airbox for better breathing.

Cheers,
Alex

[smed]

Looking good Alex, top job mate I used VHT clear on my head & cylinder on my aircooled CR250 after it was blasted, I cured the paint in the oven but found every time the bike was ridden the paint softened up & dirt stuck to it & made a horrible mess,exactly the reason I had done the clear in the first place,to stop dirt sticking , I had to rebuild the top end after a seizure so paint stripped the stuff off, Now it's all good & easy to clean, you may be OK with a water cooled bike as the temp may not be as high

Your gonna love riding this bike,nothing like an old flame

Here's mine

Circa 1985

 


Not the same bike from back in the day but near enough,same year model





A couple of years back at the Broadford Bonanza on the above

[alexbrown64]

Nice pics smed... i see your still running the same number.  Good looking bike, do you still have it?  I had the 81 CR125 -  first watercooled one.  What a turkey... it put me off Honda for a long time... so i bought a YZ125J then next year.... what an unremarkable bike.  The K i am doing up was the first bike i really gelled with so i'm hoping for the same again.  I will see how i go with the clear coat.  This cylinder is only temporary until my new ported Eric Gorr cylinder arrives and they just bead blast them and leave them bare.
Anyway, ive got some time up my sleeve so jumped into the shed again and had a go at fitting the carb.  The Yamaha Tech Report called for an upgrade to a 36mm from a 34mm.  Ive got some info in the thread about jetting etc.. so this new VM36 was jetted as per Race Report.  I had already bevelled the inside of the air filter boot to help with installation and ive trial fitted it before.  But there was no way it was going on today.  I wrapped the carb up and cut 15mm of the large end with a dremmel.  I then bevelled the intake to make it easier to get on the boot.  This worked a treat and i was able to get it on and get a good fit up.  I then got the cone pipe re-fitted the engine and hooked up some wiring.  The pic below shows the new VM36 connected as well as the PVL system and a new hour meter.
While i am waiting on the suspension and wheels, its just doing all the nitty gritty.  I will repack the muffler and get all the plastics fitted up properly.  Also, check for spark and maybe kick it over and get it running.
On another note... i tried to fit the gear shifter that you can still buy as a Yamaha genuine part.  What a con.  They are made of cheap pressed steel and are not the correct shape anyway.  They sit too low and dont have the correct bend thus hit the clutch cover.  I tried bending it out and it cracked... I just chucked it in my scrap pile in disgust.  Ive had my eye on an aluminium OEM one for a while and it was still on Ebay so i grabbed it.  I will give it a good polish and i know it will fit well and look the part and be stronger than those things that Yamaha are trying to pass off.

Cheers,
Alex

[smed]

Nice pics smed... i see your still running the same number.  Good looking bike, do you still have it?

Yeah just dropped off the 3 from the early days to make 45, Still got it, It's a keeper

[alexbrown64]

This one will be a keeper too Smed. The boy can have it when he is bigger.

Got stuck in tonight and did 5 hours straight to try and get through the punch list.  Radiator shrouds were fitted properly and the radiators filled with glycol.  Muffler was repacked and refitted.  Side number plates were heated and fitted properly to clear muffler and sit better.  A bunch of works washers were used all over the bike to give it a factory look.  Front brake cable guide and sprocket cover were fitted.  Special washer made for swingarm bolt and then torqued up to 60 lbs.  New OEM pins fitted to footpegs.  A mounting plate was made for the PVL CDI unit and then siliconed and bolted together and then mounted to the frame. The new UNI airfilter was oiled and greased and remounted. 

Bike is now ready for suspension and wheels.... Ash's Spoked wheels is getting my nipples anodized gold and ready for the new Excel Takasago gold rims.
Im still waiting on Race Tech as they sent the shock body away for hard anodizing.  Next pics should be of the bike completed....

Cheers,
Alex

[alexbrown64]

Put 850cc of MTX 80 gearbox oil in her,  a litre of premix at 25/1 and tried to lower the bike down on the hydraulic bike stand.  The hydraulic part is knackered but it has a locking bar.  I took the weight a little and removed the locking bar.  My first crash on the bike.  It came down so  fast and it nearly took my fingers with it.  Result... bike on the ground with bent front brake lever and two bloody and bruised fingers.  After some ice, panadol, setting the bike back up and straightening the front brake lever and checking it all over i kicked it in the guts.  Started 4th kick.  Lots of smoke coming out the muffler and black splooge coming out between the pipe and cylinder.  Bike is idling well and revving well.  It does seem to vibrate a bit more but im not sure if its because it has no wheels and tyres on.  Also sounds a little deeper and at the moment is not revving entirely clearly and freely.  Still only first 5 minutes of running from a total rebuild so not sure what to expect.

Phoned Shock Treatment today and the anodizers will not anodize the shock body.  Something about the design and how they cant guarantee the work.  I cant seem to get a break.  He said the shock body only has signs of polishing inside and is not worn.  Not sure what to do... they said they are looking into a race tech full shock.  They can also rebuild the good shock  without hard anodizing and they said it could last 10 years or 10 minutes.   I may also contact Wasp about a shock... 
Cheers,
Alex

[mick25]

I have the same Yamaha bike stand as yours I got it cheap second hand it's a bit worn out because it's made out of alloy but it's not as good as my red steel ballards one that looks and works the same but better ?
Nothing worst than a bike falling off a stand .

[smalls717]

Looks good Alex... What was the time frame between sending your radiators to GPI and getting them back?
I'm trying to get a set for my 84 KX250. One model only radiators and no one makes them.
 

[alexbrown64]

Smalls, it took about 4 1/2 months from when i sent the drawings and radiators/hoses until i got the new ones back.  Long time and not sure what happened but its done.  You will need to find a knackered set to send them.  I have provided the contact details below.  If you want to take that route, then contact them by email first and ask if they are willing, giving all model details.  Best thing to do is find an old shonky set on Ebay, and get them sent directly to GPI and then wait.......
Cheers,
Alex

To: [email protected], [email protected]

our address:
sheng hua shang du 2404# ,wen shao lu 19#
zibo linzi shandong 255400
china
receiver: wang yu ping
phone number : 13011631781 (very importance)
you can find  a little bigger box ,so  you can ship the radiators and hose with one box .
pls write parcel value is 30usd .
thanks
gpi

[alexbrown64]

Can see the light at the end of the tunnel now.  Takasago wheel set arrived today.  Got the bike shop to fit new tubes and rim locks together with the nearly new Dunlop tyres.  Managed to fit the rear up with a 50T alloy sprocket and a Regina non - o'ring gold chain.  I also whipped of the short tubes that came with the VM36 and put extended yellow tubes on.
The suspension has been built and is in the post.....
Cheers,
Alex

[alexbrown64]

Getting to the nitty gritty side of things now.  Bike should be up and running next week so it will time to tune the donk and setup the suspension.  For anyone interested, i thought i would post up the articles that i have been basing the rebuild on.  Besides the Lechien look, i used the April 83 edition of MXA for idea's as they printed a hop up page for the 125K.  This was updated with the May edition of the Yamaha Tech Report which refined the hop ups and specs...




Cheers,
Alex

[alexbrown64]

The Lechien bike had a Dual Leading Shoe (DLS) front brake, but the 83 125 didnt come standard with one.  They cost a small fortune on Ebay.  While keeping an eye out for one, a YZ125K popped up, which is rare.  It also had the DLS front brake on it.  Anyway, apparently it is a good runner.  I purchased the bike and it is on its way to Perth next week.  I will swap the DLS front brake onto my Lechien tribute 125.  The Euro model will be cleaned up and used as a practice/fun bike.  Hopefully, it just needs a good clean up, decals, fork boots and the like. 
Cheers,
Alex

[Rossvickicampbell]

as big as I am I had the opportunity to ride a fully restored YZ125K - I bought if for my sons - and it was a dream of a bike - loved it.