1981 yz125 build!!

seanalex538
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seanalex538
Edited Date/Time 11/22/2014 9:45am
Here she is. picked the bike up for $500 with brand new engine but the elctrical all screwed up. I got the new stator coils and cdi should be in anyday. Also had a really bad antifreeze leak and opened it up and the bearings and seals are gone it it. Gonna prder the bearings tmmr. Ant tips and tricks i should know about this bike?also are the rims made of aluminum or magnesium? Gonna get it welded on the crack.....






















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skidmarkz
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skidmarkz 12/8/2013 12:17pm
12/8/2013 12:17pm Edited Date/Time 12/8/2013 5:26pm
I had an H model back in the day and loved it. I never could get used to the front number plate though...replaced it with a flat square shaped (preston petty?) with hexagonal holes in it. My rear rim cracked right at the seam. I had a G (1980)model at the same time and just swapped wheels with it though they were not the gold anodized alumn rims. Mine would dribble water at the seals by the triple clamps too. Just clean everything up and replace the seals and it should be good.
Using distilled water and antifreeze in the system will help keep things in order throughout the entire cooling system. Also check the primary gear on the left side of the engine. It has a stairstep shaped woodruff key that also drives the water pump impeller...mine was loose and it took a chip out of the end of the crank. Had to split the cases and have a machine shop weld up the end of the crank and grind a new groove for the woodruff key. Just make sure the bolt at the end of the crank is tight. I bought another one a few years ago to restore as well....just too busy to get on it right now. Good luck with the restore!
1
motoXman9995
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motoXman9995 12/10/2013 8:08pm
12/10/2013 8:08pm Edited Date/Time 12/10/2013 8:08pm
Good luck with the restoration! Here is a pic of my 81 YZ I restored last year. Let me know if you have any questions. I didn't go too crazy but it turned out pretty well.
rob.boucher.547 12/11/2013 9:25am
12/11/2013 9:25am
Buy a factory yamaha service manual, for service on the steering stem,
and proper timing specs for sure if you had the stator
offl

They are a fantastic performing bike, durable, light, lots of parts
available if set up right
the 81 yz125 was the dominate bike in dist 23 expert class in 81
hands down
1
rob.boucher.547 12/11/2013 9:29am
12/11/2013 9:29am
The stem needs to been pressed down about a1/8 or so to remove the snap ring
then back the other way to dissassemble

The Shop

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BigAl
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BigAl 12/11/2013 10:05am
12/11/2013 10:05am
Here is mine when I found it -




It's finished but I haven't put it back together. I have a fortune in the damn thing.
1
seanalex538
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seanalex538 12/11/2013 12:31pm
12/11/2013 12:31pm
motoXman9995 wrote:
Good luck with the restoration! Here is a pic of my 81 YZ I restored last year. Let me know if you have any questions. I...
Good luck with the restoration! Here is a pic of my 81 YZ I restored last year. Let me know if you have any questions. I didn't go too crazy but it turned out pretty well.
hey man actually i do have a few questions about it. Can you get that crack on the rim welded? and also have you had any experience with the antifreeze leaks at the stem? Will getting the new steering bearings and seals stop the leak? I'm also going to put as many seals as possible i've read you can squeeze 2 in, in some places.

Thanks
rob.boucher.547 12/11/2013 12:57pm
12/11/2013 12:57pm
top seal area will fit 2 seals stacked if you have corrosion on your stem
use honda 8mm tall seals . the part numbers are
in the other 81 yamaha post
they are 6.00. each or buy the overpriced yamaha seals, yamaha of erie penn
charges 80.00!
Napa also , or metric seals online
1
rob.boucher.547 12/11/2013 1:00pm
12/11/2013 1:00pm
Yamaha lists the upper seal dimensions in the service manual
you also need the correct o rings and washers fit with the correct
cbore position, or the upper will leak also
1
CamP
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CamP 12/11/2013 1:20pm
12/11/2013 1:20pm
The 81 YZ125 was the fastest bike on the track, until it got rough.

MaxPower
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MaxPower 12/12/2013 4:08am
12/12/2013 4:08am
You guys must have lived through a different 1981 than me. The RM was the only bike to own back then. No matter the track conditions
1
CamP
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CamP 12/12/2013 7:36am
12/12/2013 7:36am
MaxPower wrote:
You guys must have lived through a different 1981 than me. The RM was the only bike to own back then. No matter the track conditions
The YZ was faster than the RM in '81. I was 40lbs heavier than most of the kids on the line and I still got good starts on my YZ, but when the track got rough the full floater was a big advantage.
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BigAl
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BigAl 12/12/2013 11:45am
12/12/2013 11:45am
CamP wrote:
The 81 YZ125 was the fastest bike on the track, until it got rough. [img]https://p.vitalmx.com/photos/users/323/photos/33858/s1600_98529950_1272142851.jpg?1294292005[/img]
The 81 YZ125 was the fastest bike on the track, until it got rough.

Never saw anyone copy the front number plate from a 1981 CR before...
1
BigAl
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BigAl 12/12/2013 11:48am
12/12/2013 11:48am
Here is what I have for the seals

Bottom

KOYO-CR XMHSA 30 42 10 J


Top

KOYO-CR MHSA28 37 BJ
1
seanalex538
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seanalex538 12/12/2013 12:58pm
12/12/2013 12:58pm
thanks alot guys can't belive how big of a help you are! I'm going to be doing alot of trail riding with this bike is it decent on fuel? and hows the low-end power on it?

Thanks
CamP
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CamP 12/12/2013 1:21pm
12/12/2013 1:21pm
CamP wrote:
The 81 YZ125 was the fastest bike on the track, until it got rough. [img]https://p.vitalmx.com/photos/users/323/photos/33858/s1600_98529950_1272142851.jpg?1294292005[/img]
The 81 YZ125 was the fastest bike on the track, until it got rough.

BigAl wrote:
Never saw anyone copy the front number plate from a 1981 CR before...
I think I saw a pic in cycle news of a YZ with a similar modded front number plate during the Florida winter series. I thought it looked cool so I made one for myself. A bunch of guys around here did the same thing after they saw mine.
MXM
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MXM 12/12/2013 1:38pm
12/12/2013 1:38pm
seanalex538 wrote:
thanks alot guys can't belive how big of a help you are! I'm going to be doing alot of trail riding with this bike is it...
thanks alot guys can't belive how big of a help you are! I'm going to be doing alot of trail riding with this bike is it decent on fuel? and hows the low-end power on it?

Thanks
Low end power? You must be joking, it's a 32 year old 125cc 2-stroke. You are a funny guy...hehe
seanalex538
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seanalex538 12/12/2013 2:22pm
12/12/2013 2:22pm
seanalex538 wrote:
thanks alot guys can't belive how big of a help you are! I'm going to be doing alot of trail riding with this bike is it...
thanks alot guys can't belive how big of a help you are! I'm going to be doing alot of trail riding with this bike is it decent on fuel? and hows the low-end power on it?

Thanks
MXM wrote:
Low end power? You must be joking, it's a 32 year old 125cc 2-stroke. You are a funny guy...hehe
From the look of your profile pic you drive an old kx so you wouldnt know what low-end power is hahahahahaGrinning

Pit Row

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rob.boucher.547 12/12/2013 2:39pm
12/12/2013 2:39pm
Those are the seal numbers
looked at my notes
Once you put the 465 spring on the bike
and dialed the preload and dampning
i thought it was great.
Yamaha had the best fork set-up stock
Having time racing
the 81-82 Suzuki full floaters I think
the yamaha was pretty good.

And the quality of the YZ components
and durability overall of the bike was
superior to the Suzukis
The clutches, and actuation set up the
zooks (no bearing in the case for the
pivot arm) really did not hold up well
when new, let alone 30 years later
I had to remachine the case sets for
the Suzuki , the front forks needed help

Having recently been racing a RM465
and really enjoying the ride, after race tech
mods installed One of the
best open bikes ever!
Same mods on my YZ250/YZ125, I still
like the YZ 's better


Magoo raced,(and bought the 81YZ125H)
in 81 and it survived, before Suzuki gave
him the 81 Rm bikes, if i remember his
interview correctly
1
BigAl
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BigAl 12/12/2013 3:48pm
12/12/2013 3:48pm
CamP wrote:
The 81 YZ125 was the fastest bike on the track, until it got rough. [img]https://p.vitalmx.com/photos/users/323/photos/33858/s1600_98529950_1272142851.jpg?1294292005[/img]
The 81 YZ125 was the fastest bike on the track, until it got rough.

BigAl wrote:
Never saw anyone copy the front number plate from a 1981 CR before...
CamP wrote:
I think I saw a pic in cycle news of a YZ with a similar modded front number plate during the Florida winter series. I thought...
I think I saw a pic in cycle news of a YZ with a similar modded front number plate during the Florida winter series. I thought it looked cool so I made one for myself. A bunch of guys around here did the same thing after they saw mine.
I think DG made a front plate for the bike that looked cool, I'd like to find one in good shape
CamP
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CamP 12/12/2013 4:28pm
12/12/2013 4:28pm
BigAl wrote:
I think DG made a front plate for the bike that looked cool, I'd like to find one in good shape
I remember that someone made a perforated plastic number plate and had individual plastic numbers.

Here's my first design, which was an oversize plate that I cut out the area around the numbers. I zip tied wire mesh in the back to protect the radiator.

rob.boucher.547 12/12/2013 4:37pm
12/12/2013 4:37pm
cool pic, My original plate is busted hanging on the shop wall
I had a stadium plate on my 1980 G
if i remember right
my resto versions i fabbed out of
some DC plates , a plastic mesh,
and painted numbers
1
CamP
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CamP 12/12/2013 4:57pm
12/12/2013 4:57pm
rob.boucher.547 wrote:
cool pic, My original plate is busted hanging on the shop wall I had a stadium plate on my 1980 G if i remember right my...
cool pic, My original plate is busted hanging on the shop wall
I had a stadium plate on my 1980 G
if i remember right
my resto versions i fabbed out of
some DC plates , a plastic mesh,
and painted numbers
That turned out nice. I think I'd experiment with some black contact paper to match the black ovals on the side plates.

rob.boucher.547 12/12/2013 5:07pm
12/12/2013 5:07pm
I did make one like that, it does look better, I took it off , and put that one on ?
I made another with wire mesh too, but
the black was better
-22 degrees yesterday, so bikes are a
6 months out now
lawn mower boy 12/13/2013 5:15pm
12/13/2013 5:15pm
seanalex538 wrote:
Here she is. picked the bike up for $500 with brand new engine but the elctrical all screwed up. I got the new stator coils and...
Here she is. picked the bike up for $500 with brand new engine but the elctrical all screwed up. I got the new stator coils and cdi should be in anyday. Also had a really bad antifreeze leak and opened it up and the bearings and seals are gone it it. Gonna prder the bearings tmmr. Ant tips and tricks i should know about this bike?also are the rims made of aluminum or magnesium? Gonna get it welded on the crack.....






















Your bike blows give it up, I highly recommend getting something with more power like a lawn mower or a ts185
BVS40FL
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BVS40FL 12/14/2013 6:12am
12/14/2013 6:12am
CamP wrote:
The 81 YZ125 was the fastest bike on the track, until it got rough. [img]https://p.vitalmx.com/photos/users/323/photos/33858/s1600_98529950_1272142851.jpg?1294292005[/img]
The 81 YZ125 was the fastest bike on the track, until it got rough.

BigAl wrote:
Never saw anyone copy the front number plate from a 1981 CR before...
CamP wrote:
I think I saw a pic in cycle news of a YZ with a similar modded front number plate during the Florida winter series. I thought...
I think I saw a pic in cycle news of a YZ with a similar modded front number plate during the Florida winter series. I thought it looked cool so I made one for myself. A bunch of guys around here did the same thing after they saw mine.
My profile pic is from Gainsville. Probably Winter - Am like you said. We saw someone with that number plate set-up and the next week EVERY YZ had them. Ha ha.
1
evomx244
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evomx244 12/14/2013 7:07am
12/14/2013 7:07am
I still have my original front number plate from my 81 YZ125 completed with zeronine numbers

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