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Post by pitobread on Sept 5, 2018 11:04:45 GMT -5
A few years ago I Almost bought a Derbi GPR 50... this started a landslide of me wanting a 2 stroke streetbike that was small bore I found one, then another one of these 1974 (or are they 75, I should look at the regis) RS-100. Both rough, both non running, both without papers. So I started a paper search and started tearing them apart. After tearing them apart I saw a bunch of things I hated, terrible brakes, spindly frames with poor welds, 18 wheels so no real modern sticky rubber. So I fixed all that, I put on some GSXR750 forks, laced up some modern wide 17" wheels to stock rear hub, and a GT550 front hub, used some CBR1100XX rotors and a Suzuki Savage caliper along with a bunch of machining for spacers and bearings. I also re welded the frame, stripped all the brackets that weren't needed, added new braces in weak areas and prepped it for paint. So I have a few more brackets to weld up for seat and exhaust, make a pipe and build a motor. I have some plans for the engine, it shares some similarities to the DT and MX engines of the same era and it looks like I can put a MX cylinder on it pretty easily. I happen to have a spare MX100 engine here. It has a bigger carb, bigger reed block from OEM and electronic ignition, but uses a cast iron jug. The RS has an aluminum jug. I also have a DT125 engine here as well, perhaps some sort of stroker engine can be built..... currently in the daydreaming plan for the engine, nothing solid. If anyone around here has played with one of these engines i'm all ears!
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Post by 190mech on Sept 5, 2018 11:57:35 GMT -5
COOL!!!
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Post by 90GTVert on Sept 5, 2018 12:51:59 GMT -5
That's gonna be a fun ride! Great work so far.
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Post by aeroxbud on Sept 5, 2018 16:36:26 GMT -5
Used to see these everywhere when they were new. Those and the Suzuki GP100. Thousands were brought as cheap transport to work. Interesting build 👍
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Post by pitobread on Sept 5, 2018 18:49:59 GMT -5
Yeah one of the cheapest bikes you could buy at the time.
This one will hopefully be a little 20hp monster.
I've been doing some research and the MX 100 motor I have here is 16hp stock, and the cylinder is the same bolt pattern. And they are the same 45.6mm stroke. These rs100 are 11 hp from the factory.
Or I want to source a 76 YZ100 basket case engine and steal the barrel and crank out of that it is a 50x50.
I'm really excited to make the pipe. I started the calculations today. May start that next
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Post by 190mech on Sept 6, 2018 4:20:20 GMT -5
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Post by ryan_ott on Sept 6, 2018 5:13:47 GMT -5
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Post by pitobread on Sept 6, 2018 11:25:42 GMT -5
^^^ Thats a beaut! I have to stay under 110cc for the cheap insurance. I have a DT125 engine here, 2 of the 3 bolt holes line up for the engine. It is neat the CT1 bolts in. The cases are similar but slightly different. I was heavy into the fiche last night, So the MX100 and the DT100 both use the same cylinder yet the DT is rated at 10HP at 7500 RPM and the MX is 16 at 10500! Different pipe and carb, and electronic ignition make all the difference If I wanted to as well it seems I can increase the stroke to 50mm by using various TY175 YZ100 and YZ125 cranks from certain years. It may require cutting the cases a bit. Got the rear wheel on, made a few pieces, trying to get the correct placement for the rear set I have to make.
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Post by ryan_ott on Sept 6, 2018 13:04:50 GMT -5
That front end and wheels are really going to make that bike! Now I’m looking at classic Yamaha’s again... great
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Post by 190mech on Sept 6, 2018 17:19:13 GMT -5
RS100 has a super long pin to crown height; www.mitaka.co.uk/CATALOGUE/PISTON_DIMS_ALL.htmNot a good setup for a high revving build,longer rod,50X50 would be the go to..Now perhaps finding a decent/more modern cylinder layout to graft to a 50 stroke,6 speed tranny build to make this a screamer...
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Post by pitobread on Sept 6, 2018 20:54:35 GMT -5
Now now, 190Mech. You know I don't let stock specs keep me down. I have torn down all my parts engines and have them scattered throughout various parts washers. Soon I will be making up a battle plan.
I have a 50mm crank at home out of the DT125.
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Post by pitobread on Sept 7, 2018 11:49:52 GMT -5
Well I made some dummy bearings last night so I can install the crank and check the timings to see where I am at with what cylinders.
I also hate the head designs, there is no real squish band, just a big cascading dome. So the machinist in me wants to make a better head.
Rod/Stroke ratio ain't bad. I do need to replace the rod and bearing. I am currently trying to find a longer rod (110mm) that has a 28mm big end and 18mm small end. Then I could possibly use a KX100 Wiseco piston kit, which would also have the benefit of a lower compression height, but would require extensive cylinder modification to get the port timing back to normal.
Also going make a crank pin stuffer and possibly stuff the cutouts
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Post by 190mech on Sept 7, 2018 14:47:01 GMT -5
Here is a good rod dimension list; www.mitaka.co.uk/MDP.htmEdit;Looks like the old Kawasaki KE175A/B fits the bill,14/18 small end,22mm big end pin,P/N 03.4260 Mitaka
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Post by pitobread on Sept 7, 2018 22:24:47 GMT -5
I need a 28mm big end unfortunately
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Post by 190mech on Sept 8, 2018 16:35:24 GMT -5
The 28mm is the big end eye right?You need a 22mm crank pin and 14mm piston pin?I found a KTM rod (Pro-X p/n 03.6226),its got a 19mm small end but they make a bearing that fits a 14mm pin,p/n 21.1103,21.3205.. www.pro-x.com/wp-content/uploads/2018/01/2018_TECNICAL_online.pdfSorry for dragging this on,I love to track down parts for odd ball builds and this fits the bill!!
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