YZ125 1979 Race build

Tdub13
Profile picture for user Tdub13
Posts
209
Joined
4/11/2013
Location
MA US
Tdub13 10/29/2014 9:00am
10/29/2014 9:00am
The shock on the '79 125 is the same as the 250 and 400, but with the addition of a 1/2" spacer between the piston and seal head which limits wheel travel to about 9". So, when I rebuilt the shock I just eliminated that spacer and gained back the lost travel. Forks are from a '79 250, so the bike is balanced very well.

The top of the rear tire is about level with the bottom of the number plates. This is the only way I could tell if my bike has close to the same travel as the #11 bike in the picture. It does look like the #11 bike has shorter forks though. But again, I tried to maiintain the overall pitch and steering geometry. I'm happy with the steering and handling.
domoguchi
Profile picture for user domoguchi
Posts
242
Joined
12/24/2012
Location
PA US
domoguchi 10/29/2014 9:43am
10/29/2014 9:43am
The frame geometry along with the suspension set up made these bike wheelie every time you turned the throttle... Wheelie machines.....I use fox forks and fox rear mono on my 79 250 and my 80 125.... Changed everything about the handling and feel of the bike. Total transformed both into very competitive bikes on the track...I own a bunch of 78 79 and 80 YZ's...pretty decent bike in my opinion..
mad300exc
Profile picture for user mad300exc
Posts
107
Joined
1/18/2013
Location
RI US
mad300exc 10/29/2014 9:54am
10/29/2014 9:54am
Todd, How are you making out with that trick head?
Tdub13
Profile picture for user Tdub13
Posts
209
Joined
4/11/2013
Location
MA US
Tdub13 10/30/2014 7:18am
10/30/2014 7:18am
Most of my time is being spent on the spare cylinder. Bringing it up to 1979 National specs as developed by Moto-X-Fox. I'm using that as a beginning guideline, but doing a little of my own updates.

The head is a side project that I've just begun on. I'm eliminating the bridges and rebuilding the fins in the pipe cutout area. Adding material in certain areas and making the overall pattern for sand casting. This is old school pattern making. Wood, bondo and lots of sanding and filing! She's still butt-ugly but stay tuned. I'm hoping to get a handful of these cast and be able to offer them on Marks VMX as blanks.





The Shop

See All »
Tdub13
Profile picture for user Tdub13
Posts
209
Joined
4/11/2013
Location
MA US
Tdub13 10/31/2014 9:45am
10/31/2014 9:45am
I was looking around for go-fast goodies and found this ad. Turns out I've got an HPBB1A somewhere in my collection and I never knew exactly what bike it was for or who the manufacturer was. Time to dig it out, clean it up and slap a fastguy sticker on it. meh.. I guess the sticker isn't exact, but close enough for a racer.



GIwasB4
Profile picture for user GIwasB4
Posts
2585
Joined
7/24/2008
Location
Beverly Hills, CA US
GIwasB4 10/31/2014 3:47pm
10/31/2014 3:47pm
Tdub13 wrote:
Can anyone identify this reservoir? It didn't come stock, but was attached to the YZ250 shock. [img]https://p.vitalmx.com/photos/forums/2013/10/11/33795/s1200_I.jpg[/img]
Can anyone identify this reservoir? It didn't come stock, but was attached to the YZ250 shock.
I think you have a Al Baker / White Brothers reservoir there. All the Luft reservoir's I've seen are finned like this one. Very nice build you have there.


sjsingle1
Profile picture for user sjsingle1
Posts
47
Joined
1/15/2014
Location
Fort Worth, TX US
sjsingle1 10/31/2014 3:52pm
10/31/2014 3:52pm
did DG have a head for the 125 back in the day? they had heads for everything else..........
domoguchi
Profile picture for user domoguchi
Posts
242
Joined
12/24/2012
Location
PA US
domoguchi 10/31/2014 4:30pm
10/31/2014 4:30pm
sjsingle1 wrote:
did DG have a head for the 125 back in the day? they had heads for everything else..........
DG did make a head for this model. They are rare to find. The cool factor is high but they never transferred heat well.
78rm125
Profile picture for user 78rm125
Posts
36
Joined
10/24/2014
Location
CA
78rm125 10/31/2014 5:06pm
10/31/2014 5:06pm
Very nice build !
Domoguchi, whats the key to keeping the front wheel down? A softer setting ? I have a 79 250. Thanks.
sjsingle1
Profile picture for user sjsingle1
Posts
47
Joined
1/15/2014
Location
Fort Worth, TX US
sjsingle1 10/31/2014 5:22pm
10/31/2014 5:22pm
sjsingle1 wrote:
did DG have a head for the 125 back in the day? they had heads for everything else..........
domoguchi wrote:
DG did make a head for this model. They are rare to find. The cool factor is high but they never transferred heat well.
how could it not transfer heat......DG heads always had like double the amount of fins over the stockers
GIwasB4
Profile picture for user GIwasB4
Posts
2585
Joined
7/24/2008
Location
Beverly Hills, CA US
GIwasB4 10/31/2014 5:43pm
10/31/2014 5:43pm
sjsingle1 wrote:
did DG have a head for the 125 back in the day? they had heads for everything else..........
domoguchi wrote:
DG did make a head for this model. They are rare to find. The cool factor is high but they never transferred heat well.
sjsingle1 wrote:
how could it not transfer heat......DG heads always had like double the amount of fins over the stockers
Yes, actually they did a very good job of running cooler. The issue is they are a lot heavier than the stock heads.



sjsingle1
Profile picture for user sjsingle1
Posts
47
Joined
1/15/2014
Location
Fort Worth, TX US
sjsingle1 10/31/2014 11:33pm
10/31/2014 11:33pm
whats a few extra ounces over the stocker......the real question is was the squish any better ?
domoguchi
Profile picture for user domoguchi
Posts
242
Joined
12/24/2012
Location
PA US
domoguchi 11/1/2014 12:14am
11/1/2014 12:14am Edited Date/Time 11/1/2014 12:15am
I read a study many years back where they tested each aftermarket head and said at the end of the day , only Webco , I think it was transferred heat away from the motor better than a stock head. I beleive the Honda Elsinore was used as a bench mark. Surely you don't think I meant it didn't transfer any heat away...just not a huge improvement , or any improvement over stock.
sjsingle1
Profile picture for user sjsingle1
Posts
47
Joined
1/15/2014
Location
Fort Worth, TX US
sjsingle1 11/1/2014 9:27am
11/1/2014 9:27am
is heat a real issue that the main point of an aftermarket head is heat transfer?
domoguchi
Profile picture for user domoguchi
Posts
242
Joined
12/24/2012
Location
PA US
domoguchi 11/2/2014 1:44am
11/2/2014 1:44am
Transferring heat away from the motor is the job of any air cooled head. The fins are there strictly for that purpose....
Tdub13
Profile picture for user Tdub13
Posts
209
Joined
4/11/2013
Location
MA US
Tdub13 11/2/2014 2:01pm
11/2/2014 2:01pm
Tdub13 wrote:
Can anyone identify this reservoir? It didn't come stock, but was attached to the YZ250 shock. [img]https://p.vitalmx.com/photos/forums/2013/10/11/33795/s1200_I.jpg[/img]
Can anyone identify this reservoir? It didn't come stock, but was attached to the YZ250 shock.
GIwasB4 wrote:
I think you have a Al Baker / White Brothers reservoir there. All the Luft reservoir's I've seen are finned like this one. Very nice build...
I think you have a Al Baker / White Brothers reservoir there. All the Luft reservoir's I've seen are finned like this one. Very nice build you have there.


Thanks for the info Glwasb4. I think there may have been one manufacturer and many distributors who put their sticker on that reservoir. Maybe it's time to peel off the LUFT and stick a WB one on! Most of the LUFT's I've seen are finned too, so yeah, I'm really not 100% positive either way.

domoguchi: Yes there were aftermarket heads for this bike. The cheapect I've seen was a webco (You're correct on the technical as well, that they were superior in cooling and combustion chamber design). I lost the webco auction at $250, but I'm willing to bet the other guy would have kept going to at least $400. The DG's go for that much and the really rare stuff like FMF porcupine's go for way more.

In general, Power makes heat and heat kills power. So the objective is to get as much power out of your motor as the cooling system can handle. Any more than that and it becomes counterproductive. and expensive too!

The head I'm building will be heavier than stock. That's not a concern of mine right now. I'm not fast enough to know or feel the difference. Smile
domoguchi
Profile picture for user domoguchi
Posts
242
Joined
12/24/2012
Location
PA US
domoguchi 11/2/2014 4:17pm
11/2/2014 4:17pm Edited Date/Time 11/2/2014 4:19pm

The FMF is the coolest looking for sure...here's mine..
I own a bunch of these for the Honda, Suzuki and Yamaha...I have the DG on my YZ at the moment...
Tdub13
Profile picture for user Tdub13
Posts
209
Joined
4/11/2013
Location
MA US
Tdub13 11/3/2014 6:55am
11/3/2014 6:55am
Those do look crazy-cool. That's why they are the most coveted of aftermarket go-fast stuff. The lack of cooling area (missing fin area) is what makes them look cool, but also run as hot or hotter than stock.
The theory on these is that the cuts in the fins will break up the laminar airflow and get more cool air to flow deeper into the fins. It does work, but the cuts don't need to be that big, only for extremely slow airflow.
Yamaha did the fin-cut on their air cooled TZ's and RD's. Montesa had a different approach with their fin "wiggle".





It's all about getting air to flow deeper into the fin area at low speeds. Higher speeds require less cuts or wiggles and can tolerate closer fins as seen by the RD's.

Pit Row

See All »
mad300exc
Profile picture for user mad300exc
Posts
107
Joined
1/18/2013
Location
RI US
mad300exc 11/3/2014 9:32am
11/3/2014 9:32am
I can't get enough of air cooled dirt bike engines..
Shawbridge Husky 11/4/2014 4:36pm
11/4/2014 4:36pm Edited Date/Time 11/4/2014 4:43pm
Good post ! I owned a '79 YZ125F bought new when in high school in '79-'80 and did one race in '81 with it in Junior 125 in St-Gabriel de Brandon Quebec when there was a GP track there. I sold it the year after when I bought my first truck ( lifted gas guzzeling V8 full sized Blazer ) Took 20 years to get back on a bike, my '99 YZ400F which I still have and am presently reconditioning with the '03-'05 yellow hurricane look and weight saving machining / free mods.

I think the late seventies / early eighties Yamaha make the best vintage race bikes as they were simple well built quality machines that are still well supported. Am sometimes temped to get a Can-Am MX-6 as I sort of dig their looks but the YZ's just make more sense overall, plus its my background as I had a YZ80E before.

I'll be bringing some era pictutes of my YZ125F to work tomorrow and will scan and post them up here for everyone's viewing pleasure. This stuff is great, keeping an eye out for an air cooled YZ in my area !
Tdub13
Profile picture for user Tdub13
Posts
209
Joined
4/11/2013
Location
MA US
Tdub13 11/5/2014 6:25am
11/5/2014 6:25am
Yeah, definitely post up some pics of your 125f on this thread.

Did you have any hot setups on the bike?

Back in '79 I was still riding my Tecumseh powered Sears minibike and dreaming of having a real MX bike to ride, so I don't know as much history on these bikes as other guys on here. Any help, comments, recollections and stories are more than welcome on here!
Shawbridge Husky 11/5/2014 6:43am
11/5/2014 6:43am Edited Date/Time 11/5/2014 6:43am
You're in for a treat, I have the pics here today.
Will scan and post up tonight !

As for set-up I rode stock, the rear shock was horrible in whoops an d got thrown off
in my first race, twisting my forks which ended any racing career visons I could of had.
Money and life situation kept me out for decades after.
At 51 I look back on those times with fondness, MX really did keep me out
of trouble and wrenching my own bikes helped develop skills that I still benefit
from today in my machinist's / business career.
Original 44
Profile picture for user Original 44
Posts
515
Joined
12/4/2008
Location
Chardon, OH US
Original 44 11/5/2014 11:54am
11/5/2014 11:54am
Tdub13 wrote:
This is what she looks like now. [img]http://i13.photobucket.com/albums/a274/beefytorque/September2013_zpsafbf7612.jpg[/img] Oh, and the IT250 has taller suspension and a reservoir on the shock. Also has solid handlebars with...
This is what she looks like now.


Oh, and the IT250 has taller suspension and a reservoir on the shock. Also has solid handlebars with no crossbar! Should I swap suspension????
Nice job on the 79 YZ125! Looks great.

There is a post on the moto-related forum about the 79 Yamaha YZ125. I just finished my friend 79. He is the original owner. And it is now in his family room.



1
Original 44
Profile picture for user Original 44
Posts
515
Joined
12/4/2008
Location
Chardon, OH US
Original 44 11/5/2014 12:02pm
11/5/2014 12:02pm
I do have so trick part for sale. I have a Fox head that is in great shape and a Fox shock that needs rebuilt, but is in great shape. Also have a NOS seat complete( cover, foam and base ). NOS right side number plate. Please PM me if you are interested.
Shawbridge Husky 11/5/2014 12:15pm
11/5/2014 12:15pm
Wow, bike above is perfect ! The rims are not period correct however, they were regular silver, at least in Canada. I ran stock bars and they were lower I think. After my crash I went to an even lower bend, but at 17 YO I was still a small kid. Late bloomer hehe. I bought the bike for 1500 new at Daytona in downtown Montreal, same place the 80 came from. I resold in spring '82 for 800.00 with a new cylinder and top end. But was still immaculate as I tended to be OCD about my stuff. A little better now, the 426 is not nearly as maintenance intensive.
Original 44
Profile picture for user Original 44
Posts
515
Joined
12/4/2008
Location
Chardon, OH US
Original 44 11/5/2014 12:25pm
11/5/2014 12:25pm
Shawbridge Husky wrote:
Wow, bike above is perfect ! The rims are not period correct however, they were regular silver, at least in Canada. I ran stock bars and...
Wow, bike above is perfect ! The rims are not period correct however, they were regular silver, at least in Canada. I ran stock bars and they were lower I think. After my crash I went to an even lower bend, but at 17 YO I was still a small kid. Late bloomer hehe. I bought the bike for 1500 new at Daytona in downtown Montreal, same place the 80 came from. I resold in spring '82 for 800.00 with a new cylinder and top end. But was still immaculate as I tended to be OCD about my stuff. A little better now, the 426 is not nearly as maintenance intensive.
A local pro had gold rims on his bike back in the day and we were so jealous of him. When I did the restoration I put gold rim on it. Better late then never. The bar are NOS bars, not as high as they looks.
Shawbridge Husky 11/5/2014 5:20pm
11/5/2014 5:20pm Edited Date/Time 11/5/2014 5:25pm
Here are some pics. I know of a few taken back at St-Gabriel de Brandon Qc. summer '80 by my cousin at the big race. I will have to get back in touch with him and try and to get the negatives. These here are grainy black and white by a buddy but at least it gives an idea as to a stock bike in use back in the day. The color one is nice and I was wearing a Bell Moto2 and some M. Robert plastic boots. The boots were not stiff at all like Scott's and I loved them, they fit great and could easily feel the controls. The backgrounds were white, so these were taken the year after my race as they are dated June '81. The cops came to that riding area soon after and escorted me through town to the police station. Cost me a few hundred in fines and that was the end of the line for me. Still bugs me just thinking about it. This was how I spent my childhood while most of my friends were into screwing, smoking pot and drinking beer.











Tdub13
Profile picture for user Tdub13
Posts
209
Joined
4/11/2013
Location
MA US
Tdub13 11/5/2014 5:37pm
11/5/2014 5:37pm
Beautiful resto O44. Too nice to ride! I've only made one bike too nice to ride and I can't do that again. Smile

Thanks for posting the pics Husky. Good times!
450exc115
Profile picture for user 450exc115
Posts
664
Joined
11/6/2014
Location
Hebron, CT US
450exc115 11/6/2014 9:30am
11/6/2014 9:30am
Todd is that still an emulsion shock with that ressy or does it have a separator pistion/bladder in it? I'm reworking my YZ 400 shock and may add a bladder to it from a fox atv shock.
Tdub13
Profile picture for user Tdub13
Posts
209
Joined
4/11/2013
Location
MA US
Tdub13 11/6/2014 9:38am
11/6/2014 9:38am
Mine has a piston in it, so not an emulsion rez. A bladder or piston rez from any other shock will work in theory, but keep in mind that the volume of the rod is what's being buffered. The YZ shocks had a lot of piston travel compared to newer designs, so make sure the bladder you're considering has enough volume to do it's job. (This is why the YZ's had such big external reservoirs for the earlier Mono's).
1

Post a reply to: YZ125 1979 Race build