New build, straight line speed attempt...

Reason I ask is I think the jr dragster stuff is all 1-1/4” hollow axle and all the stuff I used fit without any slop.
I never used any 1” solid stuff so I can’t speak to that.
I bought a bunch of extra 1-1/4” hollow steel axle, I can send you a 16” length for free, as I have more than I can ever use.
But then you would have to change your bearings, etc to match but I think the bigger hollow axle weighs the same as solid 1” but is stronger.
I ended up using a splined hollow aluminum 1-1/4” axle for my bike to save weight.
Also maybe look into ceramic bearings, I used them on my build and am very happy with the results. Shop around though since some seem to be really expensive, mine were reasonable.

Again this is just my two cents, ymmv

Sorry I guess you only get 10 min to edit posts


Active Member
Massacre, thanks, but I'm going with the 1" solid. It should be plenty strong & seems to run well the way it is, but I'll keep the 1 1/4" in mind if I decide to change it over. I think I'm ok now with the setup I have, but there's always something to tinker with until it's right.

In the shop again this morning for more fitting. Need to do a seat next, but it's coming together now. Still some little stuff to work on, but it's mostly done. Will need to play with the jetting once it's running again. I've gone from 2,000' to 6,500' so there isn't as much air to work with here.


Bike looks great man! Nice job!

Only reason I said 1-1/4” is because that opens up a lot more choices for parts such as sprocket hubs and brake hubs.
Not knocking your choice of parts at all.
It’s a standing offer, if you ever change your mind let me know.


Active Member
Massacre, no worries & appreciate the input from you & others. It was a PITA getting the right parts to match & go together. You're right about the 1 1/4" availability. For now we'll have to see how it goes. Need to take a few days off to go up to Colorado to "dog sit" for my son & his wife (he's back at Benning for training & she's on the road again), so no more updates for a day or two.

This has been a good learning experience for me. Things I would have done differently will follow, but I'm mostly happy with the outcome.
Around here the quick bikes use 4 disc bully. I use a Polar clutch but that is made for Briggs flatheads.
Before my Polar I used an SMC triple disc that worked pretty well.
What clutch are you using now?
You could put one of those 3D manual clutches on it. It would launch just a motorcycle then.

I thought the frame looked really big until I saw that it was a 212 and not a 420. For some reason I thought it was getting a bigblock.
It's just a plain centrifugal clutch for now which runs into PMR jackshaft, but I'm looking into a 3 or 4 disc setup (Bully or Diablo). Not sure this jackshaft type will take the beating a disc clutch will provide with a 3500-4000 rpm stall speed. It "launches" like a slug now, no launch off the line, but pulls well at higher RPM's, so no problems with this jackshaft. The 3d manual clutch seems to be a problem with some of the posts I've seen. A lot of posts about buying it, then going back to a more conventional setup (disc type), since people don't seem to enjoy it. Not sure why exactly, but a disc seems to be the best bet for reliability & tuning on next one.

The final drive for now is 7.38:1, so with the 19" tall tire, 8000 rpm is just 60 mph. I can change this to increase speed, but I found a road which is lightly traveled (& patrolled) so the real shake-down will need to be chosen carefully. It's a bout a 2 mile long straight with some small hills & decent paving. I'm looking into a better rear tire now & have a line on one which will work better. The Kenda is just rated for 43 mph, but it's been a bit faster than that.

Planning on a VC 460 at some point, when I get around to it ($$$), but for now the modified 212 will have to do. The 460 will require a bunch of changes (3/4" jackshaft or torque converter, different motor mount & location, etc.) so I'm not in a hurry to do that one yet. Still playing around with this for now, but it's coming along.
Do you know what RPM you want to launch at?
My dad runs a world formula with stock clutch, but they make different springs to engage at different RPMs.
Is,your engine turning 8000 RPMs now?
Prob have to find the sweet spot in the powerband of the engine to take advantage of the power it makes. Then it would be gearing and tire size after that.
I think i'm going to end up between 3500 & 4000 for the engagement RPM as I said, but that's just a guess for now, since each engine is different. Without a dyno, the only way is to run a series of pulls against known time & distance to see what works best. I would prefer to be at the lower end of the torque curve as it hooks up, not the upper end. I'm not looking for a violent launch with shredded parts & lots of repairs.

The El Diablo Red Devil clutch looks OK for what I need, due to the progressive-wound springs. Instead of having to change springs to different types & take things apart, a simple screw adjustment will take care of the launch speed & torque.