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Discussion Starter #1
Hi Grom fans of the interwebs! I'm not usually big into forums and the like, but I'm pretty excited about my two stroke Grom conversion that I have slowly made progress on. With virtually no extra money, 2 job changes, and two very wild two year old twin baby girls that always come first, progress has been extremely hard to come by at times. I'm a CNC machinist and programmer by profession, and I have most definitely leveraged my skills, abilities, and access to virtually any machine tool to my advantage to get it this far. Where there is a will, there is a way my friends!

I'm going to start by posting some current pics and then I'll go back and get more into the details if you guys seem interested. Yes I already know I'm not the first, but I'll say that I do in fact believe I'm the first to do this properly snd not create an unrideable gimmick like what I have seen elsewhere out there. I used to race A Superbike in WERA, and grew up on the pegs of a 2 stroke dirtbike so I was extremely careful and methodical in my approach and I believe the current state of the bike reflects that. Anyway, without further a do, I give you my best efforts to create a totally mad Grom! Enjoy.


As a side note, the frame is only tacked at the moment, and this is still what I call a final mockup stage before the final details are worked out, but it's scary close to beibg exactly how I want it. Just need to fab the rads and mounts and work out the lighting/stator/coil issues and I'll be firing this thing up and riding it. HARD.
 

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Sweet, I can't wait to see more of it. welcome to the forums.
 

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Oh my gawd.... hats off to you sir!

Welcome, and looking forward to seeing more of this project. I thought about trying to sandwich a CR80 or 85 engine into one. This is way cooler though!
 

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Very cool!
 

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Please Please Please share more! I've considered doing a very similar swap with a 65 2smoke to stay in a cc'd class I want to race. Would love to see your approach and any tips you might have!
 

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Very good job! I would like more detailed pictures and explanations on the frame job to install that engine.

Enviat des del meu LG-H870 usant Tapatalk
 

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I had a Yamaha YSR-50 way back in the good days and it did real 70mph with all the race parts I installed on it and with all the mods I did to it. I use to ride from San Jose to San Francisco on it and up and down many back roads in San Jose. It was one of the best 2 stroke mini-motorcycle I ever owned and wish I never sold it. I like the power band of the 2 stroke engine and the sound of the high revving engine but my neighbors never liked the loud noise of the 2-stroke.

Good luck in your build.
 

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Discussion Starter #10
Thanks for warm welcome and comments...I'm still digging through my pics that I've taken along the way, still trying to find some of them. One of the keys to my success was cutting up a portion of a '97 CR125 frame and fusing it to the existing frame. Only a few stock Grom gussets, wire loom posts, and random mounting provisions had to suffer the zizz wheel. And only a small portion of the stock Grom backbone was operated on for clearance of the CR125's PJ15LA Keihin carb. It's obnoxiously tall and falls almost directly under the Grom's top tube. Also you'll see in these pics the temporary aluminum motor mounts that were easily adjustable/movable while I wiggled the motor all over the place until I was content and things were exactly where they needed to be. First photo is without the front downtube in place. You can see it sitting on the ground. Second photo shows how I kinda go overboard on projects like this. This is my idea of tube notching, which actually far more complex than you might usually see when frame tubes come together. I modelled the oval top tube and the 4130 chromoloy DOM tubing to be notched in my CAM software and then generated the 3 dimensional surfaces using a Boolean subtraction of the two solids at their intersection. I then programmed a few tool paths, loaded a couple endmills, fixtured the tube vertically in a chuck mounted to a plate on the machine table and machined the complex 3d geometry. I can't tell you how satusfied I was with the initialy test fit. Shown here in picture 3. Looks tits, right? Next photo is that tube tacked in place. Then another shot from a different angle with the frame now a closed loop cradling the engine exactly as Honda originally intended. Also able to check the pipe's fitment for the first time at this point. Once I had the frame mostly finalized geometry wise I decided it was gonna need some trick gussets for the additional rigidity. So I got busy modelling some ideas in CAM, save the parasolid, converted it to a 2d dxf, found some extra 4130 .098 plate we had laying around and fired up the waterjet. How you like these for unobtanium? And lastly, at least for tonight, a shot looking downward from the front, you can see how the cases are almost perfect centered on the frame. There were quite a few almost too perfect to be coincidence discoveries like this as I went along. It's almost like Honda knew somebody out there was gonna get it done and made sure to make it doable! Food for thought at least. I'll keep digging for the rest of my pics, I know I'll find them. Anyway enjoy these, and goodnight. Also if any of you cats are on Instagram, my username name is @automaticman1984 if you wanna see a ton more of my work and lots of really trick CNC machining. I've been at it just shy if 15 years now and I've taken pics of nearly the whole thing.
 

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That is a perfect fitting. I really enjoy warching custom works like yours.
Very well executed.

Enviat des del meu LG-H870 usant Tapatalk
 

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......and then generated the 3 dimensional surfaces using a Boolean subtraction of the two solids at their intersection......
I will not claim to fully understand *what* that phrase actually means, but it sounds so cool, that I just had to quote it!

You have great technical skills, and your workmanship is beyond impressive. You are -- in my opinion -- building the ultimate Grom. By using (a) a two-stroke, (b) liquid-cooled, (c) a carburetor, you are preemptively addressing most of the changes others try to resolve [get more power, heat management , endless EFI issues]. I look forward to your final product. Thanks for sharing this.
 
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