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post #1 of 27 (permalink) Old 10-26-2018 Thread Starter
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Hello again

Hello everyone.

I've been a member that's sort of been hit and miss. More miss than hit, really. A few years ago, I got an X-19, and kept building it up and modifying it to try to keep up with a friend's crf150f that we raced in miniGP. It ended up with a 125cc Lifan motor. I modded the forks, came up with a complete custom brake setup with an oversized rotor, modified the frame, made my own shifter to use GP style shifting, fitted a Honda 954RR rear shock, used the tail fairing from an X1 or X2. It turned into something that handled way better than it really should have. The only problem with it was it's size, and the fact that I'm over 6' tall. I then got a crf150f and started modding it like crazy. During that time, I actually setup a fairly decent home machine shop in my garage. Well, it's time to take on yet another project.

MiniGP Bike, Version 3! I've decided I want something styled like a sport bike again, but sized so that I could feasibly ride it for 30 minutes at a time for the endurance races. I've considered building up a Honda Grom, but there is so much I don't like about those bikes, and so much wrong with the inherent design about getting the type of handling that I want. But, it's about the perfect size. So, I've decided to just build my own. To that end, I have a set of Honda Grom forks on their way. My plan is to potentially make my own triple trees (maybe even with adjustable offset). Make a headstock that will utilize Grom sized tapered roller steering bearings, and weld together my own aluminum perimeter frame and swingarm. I've already had a friend donate an R6 rear shock. I'm still in the process of studying chassis design. I've got a good handle on rake and trail. I need to get diameters of the PMT slicks I plan on using on stock grom wheels so I can start with realistic numbers. I'm now reading up about swingarm angle and anti-squat, moment arms for torque from acceleration and braking and balance between the two. I haven't completely decided on what engine I'm using, but so far I'm leaning towards using a Daytona 190cc engine and qualifying for the supermini class to compete with the new Ohvale bikes that are getting imported. (Speaking of which, if you haven't seen them, check them out at risemoto.com - I'm just not interested because they seem to be the same size as my x-19 and really expensive).

I realize that building my own bike from scratch and being grom sized might put this just outside the realm of pocketbikeplanet, but I also thought you guys might be interested. I also know that some of you really know your stuff and I've learned a lot from some of you. If you'd like, I'd be happy to start a build thread once I actually get started making parts. Or at the very least, start getting a real frame mocked up in Fusion 360 and have anything to share.

Edit: I just found my previous post from August about this, where I was less certain. Since then, I've had shoulder surgery, and I'm still in recovery/PT, which is why I have a lot of time for planning and mocking stuff up in Fusion 360 for now.

Pic of my pocket bike compared with a Grom:

Last edited by ygolohcysp; 10-26-2018 at 10:39 PM.
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post #2 of 27 (permalink) Old 10-27-2018
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How fast does your x19 go
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post #3 of 27 (permalink) Old 10-27-2018 Thread Starter
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Re: Hello again

I'm not sure of the exact top speed, but I think I remember a friend pacing me with their car and it got up to at least 50mph. I've tried different gearing on it, and settled with something that gave me better drive out of the turns.
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post #4 of 27 (permalink) Old 10-27-2018 Thread Starter
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Re: Hello again

Okay, still getting off to a slow start, and honestly, I'm not sure which direction I want to head as far as more purchasing. Really, I need to spend too much on a TIG welder before I get too crazy. I also need to finish a little more of the design aspect, and studying a couple bikes that I know work good. Still, I've gotten the forks, lower triple, new steering bearings, and the R6 rear shock. After looking at the stock lower triple and taking detailed measurements, I'm planning on scrapping that and making my own. For one, it's steel with the stem welded in. Too heavy. I'm going to make a new steel stem and aluminum lower triple. I'm tempted to make it a little big in the center, and mill some tapered oblong pockets, and then make inserts for where the stem goes for the upper and lower triple to make the offset adjustable. But at the same time, I think that's going overboard. I've got manual machines. It'd be easier to just make another set of triples if I need to adjust the offset. I think I will make it easy to undo the lower triple from the stem though. I have enough info to machine the headstock now, but that doesn't really do me any good without being able to weld up the frame.

Anyway, I also got a few drafting supplies so I can do some hand drawn mock ups before programing into Fusion 360. Here's what the bike looks like so far:

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post #5 of 27 (permalink) Old 10-28-2018
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what about getting a YSR then modifying it to your liking

Sounds like that's what you want anyway and would be a lot easier than starting from scratch and they are street legal...
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File Type: jpg 1988 Yamaha YSR50 1_1540746763223.JPG.jpg (36.6 KB, 10 views)

Faster then a speeding E Revo

Last edited by MrKitty; 10-28-2018 at 12:12 PM.
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post #6 of 27 (permalink) Old 10-28-2018
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Re: Hello again

If I was gonna start with any bike it wouldn't be an antiquated YSR besides the frames are steel///.....They have better models almost fully setup that just need minor refinements like the Senda GPR50R...

Its already got 17" rims/tires yet handles tighter and out brakes a YSR...

But I saw you also wanted to build an aluminum perimeter frame ...Aluminum is a tough gig to tigweld up....cleanliness is a #1 priority..

The Aprilla RS125cc is the perfect candidate to getting you on the track a lot faster.........The perimeter frame below too...

Good Luck
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File Type: jpg perimeter frame.jpg (55.9 KB, 16 views)

Cut
Up
Stuff
To
Obtain
Masterpiece

Last edited by CAM2; 10-28-2018 at 02:37 PM.
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post #7 of 27 (permalink) Old 10-28-2018
Re: Hello again

I am still ****ed at myself for selling my YSR. It had 5 speed trans and did 55 MPH cause I only weigh 145 lbs.

Buying a bike that don't run and needs a lot of parts is not good, cause you will spend way more than the bike is worth on Junk. I learned the hard way with a $750 Cag, and $1200 X18 Nitro.
Attached Images
File Type: jpg X18.JPG (498.8 KB, 9 views)
File Type: jpg X18-1.JPG (505.6 KB, 8 views)

Empty Pockets Racing: The difficult we do, the impossible takes longer.....
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post #8 of 27 (permalink) Old 10-28-2018
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Re: Hello again

Quote:
Originally Posted by EPR View Post
I am still ****ed at myself for selling my YSR. It had 5 speed trans and did 55 MPH cause I only weigh 145 lbs.

Buying a bike that don't run and needs a lot of parts is not good, cause you will spend way more than the bike is worth on Junk. I learned the hard way with a $750 Cag, and $1200 X18 Nitro.
Yeah but this guys building a GP style racing bike to race with...When you do a build for that purpose you want to put every ounce of detail into everything because once youre out on the track the only blame for poor performance after getting the bike dialed-in is just basically yourself or in your mind the things you failed to modify.....LOL

When I raced karts as a kid 80% of the people I competed against in the outlaw class were machinists and mechanics who made their own parts....My dad owned a machine shop too....LOL

When you build for racing you want the best of the best...That costs loot but youre more certain to win or place high every race......

When I built my 1600lb 29 A altered chassis railcar I spent $40k on it back in 1998....After I raced it through the mill I couldn't even get $10k for it so I cut off the frontend and re-engineered it with a front and rear suspension aswell as provisions for a BBC with a radiator to take out on the streets on weekends to take the crackdealers money on Friday and Saturday nights til it got confiscated....lol

Cut
Up
Stuff
To
Obtain
Masterpiece

Last edited by CAM2; 10-28-2018 at 03:04 PM.
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post #9 of 27 (permalink) Old 10-28-2018 Thread Starter
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Re: Hello again

Quote:
Originally Posted by CAM2 View Post
Yeah but this guys building a GP style racing bike to race with...When you do a build for that purpose you want to put every ounce of detail into everything because once youre out on the track the only blame for poor performance after getting the bike dialed-in is just basically yourself or in your mind the things you failed to modify.....LOL

When I raced karts as a kid 80% of the people I competed against in the outlaw class were machinists and mechanics who made their own parts....My dad owned a machine shop too....LOL

When you build for racing you want the best of the best...That costs loot but youre more certain to win or place high every race......

When I built my 1600lb 29 A altered chassis railcar I spent $40k on it back in 1998....After I raced it through the mill I couldn't even get $10k for it so I cut off the frontend and re-engineered it with a front and rear suspension aswell as provisions for a BBC with a radiator to take out on the streets on weekends to take the crackdealers money on Friday and Saturday nights til it got confiscated....lol

This exchange is great! But yeah, Cam2 is right. I've been leaning towards trying this just because. It's a natural progression for upping my fabrication/machining skills. And, I can test out my understanding of how the bike works. I can dial in the right rake angle, the right fork offset, and swingarm angle. I can try to get the best weight distribution, and size it to fit me. I've always sort of faced an uphill battle with racing because I couldn't afford to spend $2000 on just the suspension, and $5000 rebuilding the engine and using ceramic bearings. But instead, I slowly built up my own hobby machine shop. Last year, I placed third in a 4 hour endurance race. My friend's bike died in practice, so we just used my bike. Rather than replace the whole suspension with CR85 forks and shock, I redid my forks with RaceTech stuff, tweaked and tuned that, made my own fork spring preload adjuster caps, modded the rear shock. For the engine I lightened my own crank, flywheel, and cam, milled the head, did the port work. Modified the brakes, even down to replacing the rubber bushing that ride on the alignment pin with brass for more precision and feel. We were only 4 laps behind the sponsored teams that didn't lose time refueling, on top of the 6 laps he cost us with a pit lane violation, and another time he wasn't ready for rider change.

Besides that, I just love racing. I've pushed my pocket bike to the point of having knee down, almost have elbow/shoulder down, and leaving black marks on turn exit and not being able to tell whether it was the front tire or rear cause both tires were pushing. I like building and modding the bikes just as much. And now with the Ohvale bikes coming out, I have a new target to shoot for.
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post #10 of 27 (permalink) Old 11-25-2018 Thread Starter
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Re: Hello again

Well, I've made a small bit of progress. More with making detailed measurements of a full superbike race class R6, and coming up with a drawing for the frame. So far what I've come up with is a 30" seat height, approximately 5" longer between front edge of the seat and steering stem when compared with my x-19 (already has a longer than stock measurement by putting an x-1 or x-2 tail fairing on it). Front edge of the seat and rearsets in the correct relationship for height and front/rear balance. I've mildly started working on building parts for the triple trees. Because this bike is an experiment, I'm making the fork offset adjustable to be able to adjust the trail. I'm aiming the rake for an angle of 24 degrees.

I'm not yet done with the upper triple, but close enough that you can see how it'll pan out. The oval hole and oval piece are how I'll make the offset adjustable by using different inserts with the hole offset. Centered would be the same offset as the grom, but less trail because I'm going with a steeper rake angle. The lower triple will have the same oval, and the stem will have a nut on the bottom as well. Different offsets will need matched inserts for top and bottom.





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Re: Hello again

Killer work dude.

Empty Pockets Racing: The difficult we do, the impossible takes longer.....
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post #12 of 27 (permalink) Old 11-26-2018 Thread Starter
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Re: Hello again

Thank you. I got that mostly finished up yesterday. It fits really well. Now I just have to make the lower triple, stem, etc. I think this piece took the most milling though. Emulating full race bikes with the cutouts so the top triple may let the forks deflect sideways a little so the tire can follow bumps better when leaned over. Start with the hardest piece, right? I might still smooth corners a bit more, but it is as it sits so far.

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Re: Hello again

Nothing better than good front forks.

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post #14 of 27 (permalink) Old 11-28-2018 Thread Starter
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Re: Hello again

I'm starting to wonder if aluminum is too heavy. Thinking about just using cardboard fiber! Well, for mock up, anyway.





Not entirely sure yet on all those angles for the top part, but so far it's not looking too bad. Of course I'd make the vertical sections more parallel.
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post #15 of 27 (permalink) Old 02-19-2019 Thread Starter
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Re: Hello again

I've been doing more work on this. Finally got back to work after shoulder surgery as well. I've been a bit busy. Anyway, here it is at the moment. Motor isn't mounted at all. It's just sitting on scraps of I-beam for a very loose approximation.

By the end of this coming weekend, I hope to have made adjustable mounts for R6 rearsets, mounted the motor, and potentially weld on tabs for mounting a rear subframe and at least start on building it. This is all in progress so far. I still plan on cleaning up some of the welds, adding more reinforcements here and there, but I'm stoked that I at least have a rolling chassis at this point.

Does anyone happen to know of any good exhaust headers for the larger displacement motors like this Daytona 190? If I have to make the whole exhaust I will, but if I could buy at least a header premade, it would make life easier.

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Re: Hello again

Wow. I'm a bit of a machine tool/fabricator myself, but I'm taking a backseat to you!
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post #17 of 27 (permalink) Old 02-19-2019 Thread Starter
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Re: Hello again

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Originally Posted by pntrbl View Post
Wow. I'm a bit of a machine tool/fabricator myself, but I'm taking a backseat to you!
Eh, I just buy tools, watch youtube videos, do some reading, and then act like I know what I'm doing.
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What typ of alu did you use for the frame?

Get your kick with 2 stroke mix
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post #19 of 27 (permalink) Old 02-19-2019 Thread Starter
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Re: Hello again

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What typ of alu did you use for the frame?
6061 Tubing, 1"x3", .125" wall thickness. Machined the head stock out of solid bar. So far, almost everything aluminum is 6061. The exceptions are the steering stem, all 3 nuts for the steering stem, and the nut for the swing arm pivot are 7075 aluminum. Swingarm pivot is steel. I did the swingarm pivot with needle roller bearings, and thrust bearings, which is why I emulated the threaded sleeve from a full size sport bike to preload the thrust bearings.

For welding the aluminum, I chose the filler rod in the 5000 series so that if I get things anodized, it shows up correctly. I think 5356 maybe? But it's been a while since I bought that, so I'd need to look it up again.
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Re: Hello again

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Originally Posted by ygolohcysp View Post
Eh, I just buy tools, watch youtube videos, do some reading, and then act like I know what I'm doing.
I fool people all the time too. I must like not knowing what I'm doing. I do it all the time.
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