1986 YZ125 - bringing her back

[Brian Bowles]

I also got this YZ125 for free. The plastic had a lot of discoloration from being outside the last 6 months. I used soft scrub and the discoloration disappeared. I did not even scrub it much. I am waiting on a Kickstarter to see if I have fire.

 

[Brian Bowles]

Well I have a new problem. I see why the kick starter was missing. The bolt that holds it on has sheared off in the shaft. I guess we can try to drill it out. Any one else have any other suggestions or recommendations about doing that? If that fails I may have to buy a new shaft. That would mean draining the fluids, taking the side cover off, and buying new gaskets. 

[mlatour]

Even before attempting to kick over the engine, considering it's age and the outdoor storage,

I'd have a peak at the cylinder's condition, check for a stuck piston ring etc.

 

Replacement parts are going to be a challenge for a 32 year old dirt bike, no use risking damage to the cylinder by trying to start it

without first fully inspecting the top end, cleaning the carb clean & fuel system etc.

Inspect rubber intake components for cracks, air boot, inlet / reed boot, debris ingested thru there can mess up your engine.

 

Easy-Out type extractor might work in getting the broken bolt out,

if you take off the RH side cover off, you can bring that small starter gear assy to a machine shop to extract/re-thread.

Edited December 3, 2018 by mlatour

[mlatour]

Bike looks complete / not butchered, you are very lucky to have found one in this condition,

moreso that it was FREE!

 

Take your time, perhaps not considered a 'classic' but well worth investing a bit of money (and lots of time) into it.

IMO the best method is to tear it down to the bare frame and carefully inspect EVERYTHING as you rebuild it,

many 4-5 year old bikes suffer from neglect, imagine this 32 years old one.

 

Myself typically not a fan of older/out-of-production/hard to find parts for bikes but,

would no doubt jump on the occasion if something like this came my way.

I had a brand new 1986 Honda CR125R at the time so this era bikes are always of interest to me.

 

Edited December 3, 2018 by mlatour

[Brian Bowles]

Mlatour, thank you very much for all of your suggestions. I will proceed cautiously. I also got a 1986 CR125 for free as well. I have it running now. It is in my other thread. 

The suggestion of the machine shop is a good one. That might be cheaper than buying a new shaft which would be $40 for an after market and $64 for an OEM shaft.

 

[rob the snail]

great little period racer.

mine has been rebuilt, parts were no problem

[mlatour]

Man how I wish I had kept my old '86 CR ('best 125' of 1986 according to all shoot outs)

but now an old YZ would complement my 2010 just fine, you guys are lucky to have such clean examples. 

 

Market size / popularity in Canada makes used parts a challenge here.

Ebay / shipping / currency exchange rates make cross border shopping very cost prohibitive.

[Brian Bowles]

Here is my CR125 that I am also working on. 

[Brian Bowles]

Rob, your YZ125 looks great! How do you like riding it and what did you have to do to it?

[Singletrack_rider]

Now you need a 86 kx125 and a rm125 then you can have the 86 125 collection. 

[rob the snail]

10 hours ago, Brian Bowles said:

Rob, your YZ125 looks great! How do you like riding it and what did you have to do to it?

it goes great actually, is my favourite bike to ride in vinduros as well as classicmx...

my buddy and I won a 4 hour pony express, me on the yz and him on a 86 cr125 and we were the only 125s, plenty of open class bikes and 250s

the bike was a pain in the ass when I go it...I replaced just about everything, all the elecrics, carb, new pipe, rebored and rebuilt powervalve ...it was still slow....then I discovered the cdi was from a yz490..now it really pulls, is a great bike. is my fave

[prandalljackson]

To get the broken bolt out you might try a product called Aero Kroil. It is remarkable at loosening up stuck fasteners. If you can heat the shaft up slightly, apply the Kroil and let it set for several hours to work. The manufacturer claims it will penetrate up to .000001 of an inch.

[Brian Bowles]

Thanks for your story of your YZ125. It is motivating for me.

 

i will look into the Kroil stuff thanks!

[Brian Bowles]

For some reason I cannot get her to start. Any ideas?

I cleaned the carburetor 

i have a very good spark on the plug

i did notice that at first the head did not want to  move when first kicked but it broke free. I figure tomorrow I will take the head off. 

[Brian Bowles]

I used a compression tester and it said it has 150lbs. 

Here is what the piston looks like: 

Here is a video of the piston:

https://youtu.be/vhRSm9v1A70

 

 

Edited December 5, 2018 by Brian Bowles

[Brian Bowles]

She is alive!!!

https://www.youtube.com/watch?v=xbwTL4HynXA

Hear her roar back to life!

https://www.youtube.com/watch?v=KbV3nULjm4s

[76xtdrvr]

I owned and raced a '86 yz250. That cylinder was sleeved and Yamaha offered oversize pistons. Sure enough, there are (3) different oversize pistons and ring sets still available for your 125 if you ever have to do a replacement. My guess is that it also has a sleeved, not plated, cylinder that can be bored.

[Into the sunset]

1 hour ago, Brian Bowles said:

She is alive!!!

https://www.youtube.com/watch?v=xbwTL4HynXA

Hear her roar back to life!

https://www.youtube.com/watch?v=KbV3nULjm4s

That’s quite impressive. I take it you fixed the kick starter? How did you finally get it to fire?

[Brian Bowles]

I slide a new kick starter lever on. I have ordered a new shaft. I only put just a little more gas in the cylinder. The bike runs great and now starts on the first kick. It took a little running to get stuff blown out. To do this we took the air filter out, opened the throttle, and misted gas through the carburetor. It first sputtered and then came to life. Previously we cleaned the carburetor to make sure the jets and internal pathways were clear. We used carburetor cleaner and compressed air to blow them out. 

I have a brand new set of tires going on tomorrow and a new seat cover on the way along with the kick starter shaft. 

Edited December 9, 2018 by Brian Bowles

[Brian Bowles]

On 12/8/2018 at 7:43 PM, 76xtdrvr said:

I owned and raced a '86 yz250. That cylinder was sleeved and Yamaha offered oversize pistons. Sure enough, there are (3) different oversize pistons and ring sets still available for your 125 if you ever have to do a replacement. My guess is that it also has a sleeved, not plated, cylinder that can be bored.

Thanks for the info. I saw a video online saying that it could be bored if needed. That is good news for the future.