Author Topic: YZ125K Rebuild  (Read 30448 times)

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Offline alexbrown64

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Re: YZ125K Rebuild
« Reply #30 on: January 11, 2015, 01:08:34 PM »
Should be fine Husky.  Thats why i wouldnt mind knowing what sort of arrangement other members have.  The 85-89 Honda CR's have the same brake arm and all they run are two collared bushes (10) and two seals (26). 
Cheers,
Alex
« Last Edit: October 13, 2017, 10:00:28 PM by alexbrown64 »

Offline alexbrown64

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Re: YZ125K Rebuild
« Reply #31 on: January 12, 2015, 12:38:46 AM »
OK, an update.  Quite a few months ago i purchased some GPI radiators for the K.  They advertized them for the K and L model.  Unfortunately, when i got them they didnt fit because the L went to the rad cap on the right side and different plumbing and that is the only ones that they made and sold (although they advertized them for both models).  GPI said no problem, just send us the rads back, together with your original ones and we will reverse engineer some.  Well, my bike was still coming from the states, so i located some cheap OEM ones and some hoses, then sent everything to GPI.  Just had an email back with the first pic.  Apparently, my new rads and hoses are in the post so heres hoping.  Below is a pic of my bike with its bent and twisted OEM rads on it and below that are the new ones that GPI have reverse engineered using some good ones i sent them.  Just hope it all fits :-)



Same should go for anyone else.  If you have some ratty rads and cant get replacements, then ask GPI to knock you up a set.
Cheers,
Alex
« Last Edit: October 13, 2017, 10:03:18 PM by alexbrown64 »

Offline 80-85 husky

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Re: YZ125K Rebuild
« Reply #32 on: January 12, 2015, 10:07:09 AM »
the wr husky's just have a small collar and o rings (swing arm attached) while the cr huskys have a frame mounted torque arm with spherical bushes....I think :)

Offline tony27

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Re: YZ125K Rebuild
« Reply #33 on: January 13, 2015, 08:01:52 AM »
What was the OD of the bearings at the front of your torque arm, the 490 arm I fitted to my 465 & the standard 465 arm used a bearing with 22.5mm OD which isn't available. I had to shorten the arm 19mm to fit the 465 so I remade that end to take a GE12 spherical bearing which is an off the shelf item from any bearing supplier
The bike will certainly be a looker when finished & hopefully it goes as good as it will look

Offline alexbrown64

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Re: YZ125K Rebuild
« Reply #34 on: January 13, 2015, 12:49:43 PM »
Tony, it was 19mm.  I could get a spherical bearing but it was expensive and i would still need a seal each side to stop muck getting in and wearing it out.  I got two 19mm sealed bearings that are 6mm wide each.   They fitted perfectly.
Update: The cases arrived in the post and look good.  I removed the last 3 blind bearings with a combination of techniques including wet wadding packed into the hole to pressure the bearing out, also had to run a small weld on one to loosen it... all worked OK so now ready to blast, paint and install new bearings and seals.

Offline tony27

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Re: YZ125K Rebuild
« Reply #35 on: January 13, 2015, 01:01:09 PM »
I just used thick O-rings as seals, pretty sure that's how my TRP shock in the back of my trials bike is sealed & I've not had a problem with wear even with the amount of water we ride in
I found wear in the brake plate bushes & sleeve, a piece of ejector pin drilled & reamed fixed that, seals were available unlike for the brake pedal which ran steel on steel for it's pivot

Offline D project

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Re: YZ125K Rebuild
« Reply #36 on: January 13, 2015, 06:53:25 PM »
Wouldn't having no spherical bearings affect your floating rear hub. When you apply the brakes it needs to centre itself to get good brake shoe contact in the hub?

Offline alexbrown64

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Re: YZ125K Rebuild
« Reply #37 on: January 13, 2015, 09:42:56 PM »
See pic above.  The Honda does not use spherical bearings.  Also, the front of the brake stay (where the bearings/bushes/seals go) squeezes between two plates in the frame, to which it gets bolted to.  There is no where for the rod to move except up and down, which is what my brake stay does smoothly.  D Project, you are correct that its important to keep the floating free hub "free".  I think a pic is needed so have taken one of the YZ125K brake stay arm and how it is bolted between the two plates on the frame.

From the Race Tech website:
"Floating Rear Brake maintenance is commonly overlooked and can have a significant impact on a bikes suspension and handling. This type of rear brake was common up through the 80s on both dirt and street/road race bikes.

Now you might be thinking, "How would this backing plate have any effect on a bikes suspension?"

Well, since the brake "floats" it moves with respect to the rear axle as the suspension moves. This means that any binding in the backing plate bushing, or stay-arm pivots will inhibit suspension movement. This has a huge effect on both traction and harshness! This means that even the best suspension will work poorly when there is drag.

The main culprit is usually the Backing Plate Bushing itself. This is on the rear axle in the backing plate. These can bind for one of two reasons; first is simply neglect. The bushing is dry and/or corroded. Second, sometimes the dust cap on the outside of the backing plate on the axle gets grooves in it (over-tightening the rear axle or long-term wear) so when the axle is tightened it no longer has clearance.

Maintenance is pretty straight-forward; clean, inspect, grease. On the other hand, if the dust cap is grooved you will either need to replace it or figure out a way to get the clearance back (sometimes machining is required).

Next check the bearings at both ends of the stay-arm. These are all pretty simple; either spherical ball bearings, needle bearings or plain bushings. Take them apart, inspect , replace if needed, and grease 'em up.

You should be able to freely spin the backing plate with the rear axle tight and the stay-arm off. This is commonly overlooked and can reap huge rewards with a little love."
Cheers,
Alex
« Last Edit: October 14, 2017, 11:09:59 AM by alexbrown64 »

Offline alexbrown64

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Re: YZ125K Rebuild
« Reply #38 on: January 16, 2015, 05:10:24 PM »
Well, still going around in circles with some wins and losses.
One loss was the cases i purchased.  I never noticed, but the left case had been rewelded where one of the posts that holds the shift forks fits.  I posted it up in the tech section and got a bunch of good responses but decided to get another set flown over as they were only $35.  Hopefully, with the 6 case halves i will have, two will be good with an interference fit for the mains and no welds or repairs.  You could buy individual case halves from Yamaha so i dont believe there is an issue with "matching".

While i wait for the cases, suspension and new rims, i will pull the old wheels apart and start on the hubs..
Cheers,
Alex
« Last Edit: October 13, 2017, 10:06:31 PM by alexbrown64 »

Offline alexbrown64

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Re: YZ125K Rebuild
« Reply #39 on: January 20, 2015, 10:58:02 PM »
Well, the new GPI radiators arrived so i have given them a trial fit. Let me say, they seem reasonable quality and look great.  All the holes lined up and they fitted well.  The original large rubber grommets that are used to fit the rads to the frame need packing out as the original rads have a 5mm thick tab that the grommets slip into while the new rads are about 2mm thick.  Easy adjustment.  They also made up a yellow silicon hose set from an original set i sent them ( i never got them back ).  They look good and seem to fit well but i cant do the final fit up until i have an engine.  The have added a bit of "green" each end to allow for any inaccuracies.  Below are some pics of the rads fitted to the frame and the new silicon hoses.  I have also trial fitted the plastic scoop/shield things and the shrouds.  They fit well with some minor bending of tabs.  The only downside is that the old rads had prewelded nuts on the back of some of the tabs but the new ones dont.  I'm just glad that after 32 years, there is a replacement available.
Cheers,
Alex
« Last Edit: October 13, 2017, 10:08:41 PM by alexbrown64 »

Offline foxy999

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Re: YZ125K Rebuild
« Reply #40 on: January 22, 2015, 10:42:58 AM »
looking very nice, job well done  ;)
My fastest lap is the first one :)

Offline alexbrown64

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Re: YZ125K Rebuild
« Reply #41 on: January 31, 2015, 02:42:15 PM »
Thanks Foxy, its getting there... slowly.  Bit of a head f*ck this week.  Two steps backward.  1984 yz125 cases arrived in perfect condition.  Only thing is, they are slightly different.  I have another set of 83 cases coming so i will have a lot to choose from and keep some for spares.  I will sell the 84 ones as they have both cases in good condition, clutch cover and power valve linkages. 
Called RaceTech and they reckon one of my shocks i sent them is ok and they will send it to get hard anodized but they are really slow at the moment.
Have not heard back from Eric Gorr about my cylinder yet.
I have a bunch of stuff coming from the states. OEM front guard, Maier rear guard, seals, etc...
Local bike shop tried to order me some gold Excel Takasago rims for the YZ but struggling to get any.  I called Ash's spoked wheels and talked to Ash.  He said he has a front but they all need to be drilled to suit the drum front hub.  He is going to try get me a 18 x 185 rear but if he cant he will get me a 2.15 as he said you can still put a skinny rear tyre on it to suit the 125's.  That will also need drilling.  Both ends will also need bigger nipples to suit.  I have decided to send him the hubs and spokes so he can build them up and make sure they all fit up nicely.
I have blasted and painted the hubs and installed new bearings.  Wheel sets should last another 30 years if i do it right the first time.
I have fitted new Reed/Windham bend Renthal bars in black.  I fitted up the original perches and added new OEM levers.  Then i added new cables and pillow top grips.  I have always liked the Renthals.
So far i have gone through 8 case halves, 3 rear shocks, 2 sets of plastics, 3 sets of bars, 2 cylinders and tonnes of parts to try and get the bike race worthy and mechanically good enough to last another 30 years.
Pics soon when i have something to take a picture of!!

Offline Tomas

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Re: YZ125K Rebuild
« Reply #42 on: January 31, 2015, 10:29:01 PM »
Like your thread Alex. It looks like you have already spend fortune on this bike. I am sure that you are going to keep this one for a long time. Any more pictures?

Offline alexbrown64

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Re: YZ125K Rebuild
« Reply #43 on: February 20, 2015, 12:30:48 AM »
Tomas, as promised, some more pics.  As usual, the bike is fighting me all the way.  I finally put together a decent set of case halves.  When i chose the two best ones i had out of the 8, i removed all the bearings and seals.  I then used paint stripper to strip away 98% of the paint.  When i was happy, i put them in my Bunnings home sand blaster and cleaned them right up.  Then i washed them in detergent and used a compressor to blast away any remaining grit and to dry them.  I then put them in the oven at 100C for an hour.  During this time i got all my bearings ready for each side.  I then inserted all the bearings using a combination of G clamps as presses and sockets to gently knock some into place.  I used all my pictures of where each bearing goes as described previously in this post.  Righto, all bearings in, so i put both case halves together, clean them with wax and grease remover then use my aluminum engine paint to give them a nice coat of silver as per the Lechien OW125. (i also had to do a lot of prepping and taping up).  The cases looked great but to cure them they need to go in an oven at 100C for an hour.  So, back into the oven to cure it all up... pic below...



Now there is a thousand ways to skin a cat and this is just the way i had decided to do it.  When it was all cooled down, i took off all the masking tape and spent some time inserting the main seals.  I will leave the other seals until i get it together.  You can see the pics and manuals i used to make sure i was getting it right.



OK, now down to the nitty gritty.  I checked all my pics, the manual etc, and installed my gearbox. I could run it through the various gears from 1st to 6th so i was happy it all went in OK.  The next part i picked up on YouTube.  To install the crank, i heated a socket on the stove and then put it in the main bearing.  The heat transfer expands the bearing and the crank just falls into place.  This went well and it just fell into position, no hammers, pullers or anything.  When i was happy with the crank and gearbox, seals and everything, i prepared to join the halves.  I used the same trick to heat the bearings in the opposite case so that it would just fall together.  While the bearings were being heated, i slapped Three Bond on the cases as the gasket material.  I then positioned everything up, made sure the dowels were in and then popped it all together... pic below of it all happening...



It all slipped together easily... and i nipped everything up with the new engine bolt kit that i had bought.
This is where it all went wrong.............

When i nipped it all up and the cases were tight.... so was the crank.  I loosened off the bolts and the crank loosened up.  I tapped everything and had a play all to no avail.  It all had to come apart again.  I have another post in the forum on this subject, but what had happened was that when i had the crank rebuilt, it was rebuilt 1mm wider.  This meant that it would get tight in the cases when you did the final nip up.

I took the crank back to the shop and they pulled it apart.  It had been damaged previously so they were not able to use the thinner shims that had been supplied with the ProX rod kit.  The shop machined the crank and put it all back together using Yamaha crank specs.  Thanks to Witch Cycles for fixing the problem and not charging me any extra for machining etc.. 
Also, when i tried to remove the crank, it was really stuck in the cases.  I *ucked up and belted it out and bent the tip of the shaft and damaged the threads where the rotor goes on.  Before i gave it to the shop, i straightened the tip up and cut off the damaged threads.  It came up like new so i got away with it just this once.

And that is it for now... tomorrow, i clean up the case halves and go through the process again and hopefully this time it will all be OK.  I hope to get it all together and in the bike soon.

On another note, Eric Gorr has completed the cylinder sleeving and porting and has sent it all with the new 56mm Wossner piston kit.  But for now it is going back together with my 58mm Wiseco kit and my original cylinder.

Cheers,
Alex

« Last Edit: October 13, 2017, 10:13:15 PM by alexbrown64 »

Offline alexbrown64

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Re: YZ125K Rebuild
« Reply #44 on: February 23, 2015, 12:06:26 AM »
Got stuck in and managed to get a bit done.  This time, the case halves went together easy and i buttoned it up with my new SS bolts. 


Next up i fit the clutch arm shaft.  This take an hour because it would not go in.  I sanded the internal shaft, cleaned it all up and it fitted.  There is a new bearing in there and i put the seal in before i fitted the shaft and tapped the retaining pin back in.  I forgot to put the spring on but managed to work it over the shaft arm and into position because i could not get that retaining pin out again.  When that was done, i fitted some gears and things and put the clutch back together with new springs and plates.  I also put a new gear shift shaft in and tested it.  Gears work well.  Also fitted the 58mm Wiseco piston with a new small end bearing, ring and piston clips.

The cylinder, head, power valve and PVL ignition were fitted and torqued to the correct specs and then the timing was set on the bench using my home made dial gauge set at 1.2mm BTDC.



I used the old grommet from the original ignition and fitted to the new cable coming out of the right side case.  I had to split it, then reseal the split with rubber cement.  I then fitted the kick start and sprocket shaft seals.  Next up was the new 12 tooth JT sprocket which was torqued up to spec and a new washer with a tab bent into place for safety.  The engine is now ready for fitting.

I cleaned up some engine mounting threads and filed some paint off the frame in preparation for engine fitment.  The engine went straight in with no problems and i fitted up the polished engine bracket with new bolts.  I then fitted up the ignition cover and clutch cable.  I had to leave the clutch cover off before fitting the engine because you have to fit the clutch cable and then undo the lock nut on the clutch center and play around with the clutch centre rod and clutch shaft arm position.  Thats all explained in the manual, which i constantly referred to in conjunction with all my pics i took.
After adjusting the clutch and doing a few other bits and pieces it was time to call it a day.  Below is a pic of the fully rebuilt engine finally fitted into place...



The YZ125K engine was originally black, but the Lechien works bike had a magnesium coloured engine which is what i painted mine.  The cylinder and head have been blasted and clear coated with VHT engine clear coat.

Cheers,
Alex
« Last Edit: October 13, 2017, 10:17:46 PM by alexbrown64 »