I just turned 40 and as a long time lurker decided it was time get in the game. My dad raced YZ’s and I remember his 79 and 80 250’s when I was a kid.
I bought this 79 125 last weekend. It apparently has a 78 cylinder head and the pipe was siliconed on. I have the 79 head, would doing the work to replace the top end be to much if your not to mechanicaly inclined? Also the bolts were bad or mismatched when I took the seat and tank off. Does anybody have suggestions for a good bolt kit?
Anybody in Portland know of a good shop for vintage yz’s?
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I have only done top ends on bikes that were more modern, but it has been easy for me. Just take your time and double and triple check everything. Vitalmx, YouTube and Google can be great resources. Its too bad it can be hard to find parts.

I raced a 1980 yz250 in a vintage series. I haven't raced a vintage 125, but I bet it would be fun.

raced a 77 125 in the day, raced a d, e and f 125 in pre 80 mx, love 125 racing..

sorry not m8ch help these days..

good luck

Get a repair manual for your bike. Worth every penny and its what you need if you are not familiar. Cool bike.

Thanks for the advice! I will look into a manual. Did a few things since last weekend, mostly cosmetic.

The problem with these vintage bikes is that you often simply won't know what has been done to it and what parts/cylinders/heads/pistons, etc..are on the bike. So..that makes a normally routine re-build of the top end somewhat of a mystery. For this reason, I suggest you not tackle the first re-build, but instead take it/send it to a professional with a reputation for working with vintage machines. Once that is done, you can have them tell you EXACTLY what you have and you can maintenance (new rings) from there.

Looks like you have a great example of a '79 to work with. They are fun bikes, but have a few challenges, especially since quite a few parts were/are only used for this one year model. Feel free to contact me if you have any questions. I've learned he hard way on a few things and am just now feeling like I've dialed my bike into what I hoped it was when I bought it. (bad CL experience).

Oooo.....nice bike Joe!

wfoyz250 wrote:

Oooo.....nice bike Joe!

wfoyz250 wrote:

Oooo.....nice bike Joe!

Thanks Larry! I've got two rides on it now after a full crank re-build, new rod/piston/rings/cylinder work; along with a full HPI ignition and Boyesen reeds. It's really quick, but only if I make a great effort to keep the revs and momentum up in every corner - it won't allow me to be lazy like I sometimes am on the 250!

Nice bike,would be the bookend to my 250

Yep, I have it's big brother as well.

That’s a sweet 250! Where did you get your pipe and silencer on your 125?

Since73 wrote:

Yep, I have it's big ...more

Since73 wrote:

Yep, I have it's big brother as well.

Where did you get the fork seal dust covers? Great looking bikes!

Tchamberlin wrote:

That’s a sweet 250! Where ...more

Tchamberlin wrote:

That’s a sweet 250! Where did you get your pipe and silencer on your 125?

I bought the 125 with both items already on there; so not sure. Externally, I didn't do much to it other than the
side panels (I have the originals if anyone needs them). What I DID do is rebuild the entire engine, as explained in my post above to wfoyz250. Not what I was planning to do when I bought it, but at least now I know exactly what I have.

Since73 wrote:

Yep, I have it's big ...more

Since73 wrote:

Yep, I have it's big brother as well.

neverwas wrote:

Where did you get the fork ...more

neverwas wrote:

Where did you get the fork seal dust covers? Great looking bikes!

The forks are 43mm from an 81YZ465. Hot Foot Moto should be able to hook you up with any size, including for the 38mm forks that were stock on the '79

I’ll take those side panels off you! I’m new to to posting here so I guess PM we with what you want on those.

Since73 wrote:

Yep, I have it's big ...more

Since73 wrote:

Yep, I have it's big brother as well.

Is the tank plastic or aluminum ? Always preferred the look of how the graphics wrap around the front of the tank. Good look'n bike.

Ledger, the tank is the original plastic; painted. The bike was a garage queen before I got it, so painting the tank and fenders was ok for that purpose. I bought it to race, though, so the fenders didn't last long. The paint on the tank is holding up pretty well, so I'll keep running it for a while (even thought the perfectionist in me doesn't like the fact that it's a lighter shade of yellow than the OEM fenders). I'll eventually have to either strip it and restore what's there or simply buy another nice tank.

Find yourself a manual and take your time. Here's mine after two years of finding parts and going through everything. Now it's time for some vintage racing!