The internet seems to agree that the eye to eye length of the DT100’s rear shocks is 320mm, but my bike has 285mm (approx) shocks. 

Can anyone with a DT100 measure their rear shocks eye to eye to verify the stock size? 

Alternately, can anyone think of anything dire that would affect the bike going up about 40mm in shock length? I know it’ll change the geometry of the bike but I feel like it’s not a huge change. 

The chain top rail might contact the swinging arm around the pivot point ,

Shock length of my US market 1977 DT00D is 280mm centre to centre.

I specify US market because here in the UK we kept the physically larger 1976 model right through to 1983, albeit with minor paint and graphics changes.  Model was discontinued in 83.

We never had the smaller 77 onwards DT100.

I expect the 320mm shocks are from the pre 77 models.

As for fitting the bigger shocks, it will certainly tighten up the steering, but since the 77 onwards DT100 has rubber compliance bushes instead of conventional swingarm bushes, they may not enjoy the longer travel of bigger shocks and may start to spin between the axle and frame tube.  This leads to loose bushes and eventually an egg shaped frame swingarm axle tube if not caught early.

RT100s were notorious for wearing out the axle tubes if not checked daily, admittedly the ones I was in charge of, used commercially, were submitted to extremely harsh conditions and hours of usage.far, far more than the norm.


UK spec DT100 1976 till 1983.  Full size bike.


US spec 1977 DT100.  Kids minibike. The size difference is very evident just in the gap between the cyl.head and the bottom of the tank.  A hoot to ride though, absolutely bonkers.  I love it.  The missus says I look like a circus clown perched on top of it.

It is a pure fun bike.  You are not going to get much more than a 50 mile range from a full tank of fuel ( 1 imp gallon to the brim) and probably much less off road on the more technical trails.

 

Damn Yamaha and their model machinations. So it seems I have the midget model, but per my other thread, it's a 1977 US spec DT100 masquerading as a 1980 because it's Canadian. How's that for specific?

I'm going to attempt to fit the 320mm shocks and see what the swing arm and chain clearance looks like compared to stock. I actually wouldn't mind a bit of height, and I had to fit 2.75 tires on the front because 2.5 doesn't seem to exist in that rim size here anymore, so I have a tiny bit of front end height to compensate for.

You've reminded me to check the swing arm bushings though. This bike is in great shape, but previous owners usually tend to care for the obvious things and ignore the important.

Great info Tinkicker!  

I love the little bikes too and it's always interesting to hear about the variations in other countries!

I wonder how much "culture" influenced the model differences?  And even laws?  Here in the US, at about age 15-16 you were able to own and legally ride any model... even say a Kawasaki triple "widowmaker" as your first (and hopefully not your last!) bike.

Smaller displacement bikes didn't sell well here except as "mini bikes".  They didn't change the frame size, but Yamaha even put a lowering spacer in the rear shock and shorter forks on our 80-81 DT125.  (In 78 and 79 our DT125 and DT175 were the same size, in 80-81 the 125 was lowered here)

8ender wrote "Damn Yamaha and their model machinations. So it seems I have the midget model, but per my other thread, it's a 1977 US spec DT100 masquerading as a 1980 because it's Canadian. How's that for specific?........"

The 1977-1983 US DT100 was basically a 1977 model with color changes, emissions upgrades, and minor spec changes.  

One reason so many parts are still available is because Yamaha made a strong effort to use existing parts as long as possible.  For example a modern YZ85 has the same rubberized pipe mount bracket as my 1988-90 DT50's.  

The US 1980 model DT100 came with CDI.  Canadian model didn't.  That doesn't mean you have a "1977 US spec model" as there may have been other changes between 1977 and 1980 that appear on your Canadian version bike.  

P.S. Curiously, Canada (and other countries) got a CDI on the popular "RD" street models starting in about 1976 or so.   US model RD's never had a CDI.

Well, I learned a lot today.



320mm shocks on and they sure look pretty, but there's problems.



You can see here with the new shocks on the chain clearance to the swing arm 's the clearance with stock shocks for comparison.



However, chain clearance aside, when I hopped on the bike with the new shocks on it almost bucked me back off. There's ZERO dampening happening with the new shocks. I decided to do some investigating.



It's hard to see here, but that's a plastic shell over the "piston" which, as it turns out, hides the fact that there's no real piston at all. Damper free shocks! Immediate return and personal humbling because I should have known better. In my defence, when I was restoring my KZ650 and YDS3 you could actually get halfway decent cheap shocks from eBay and Amazon. I didn't realize things had gotten so bad.

So I'm back to the stock shocks. One dampens with a concerning wheeze, and the other tries it's level best but is clearly fighting for it's life. The springs are rusty too. I plan on taking this bike on real trails, so I need to find a 280mm +/- 10mm shock that won't cost more than the bike.

Anyone have any ideas? My eyes are crossing from endlessly scrolling for 280mm shocks that aren't bright red, or meant for a monoshock setup, or contain an open to air damping setup like my Amazon shock. NOS shocks are wicked expensive, and used ones look like they've been at the bottom of the ocean.

Edit: Apparantly BB code images from Imgur aren't allowed or aren't working, so you'll have to go to this album and figure out what pics are what from my commentary above (remove the space between imgur and .com): http://imgur. com/a/rear-shock-install-AbA0kLn

You need more than a dozen posts to post links...  so should work for you soon.

I'll look and see if I have any shocks in that length range and will let you know what they fit so maybe you can find a decent set.  
 

Treatland.tv has a lot of great stuff for smaller bikes.

Just checked there on a whim and found these.  www.treatland.tv/fully-chrome-adjustable...-shocks-8mm-10mm.htm

They have dozens and dozens of shocks that might work if you search their site...  from cheap like these to fancy ones like YSS for a couple hundred or more for a pair.  

Treatland looks great. Too bad shipping from the US to Canada is brutal right now. Oddly the Honda Z50 shocks seem to be a perfect match but I'm not keen on shiny chrome on chrome. Doesn't suit the bike.