Custom Racer with Aluminium Frame and Sportster Engine

SF said:
Look at the 2004 ZX10R frame...cast head and bottom mounts welded to boxed sheet in between.


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That's actually pretty common with modern frames...

Our machined head stock is stronger than a comparable cast unit, as our raw material is stronger and it does not loose attributes during the machining.
 
Cool, you seem to have done your homework. If you say billet is up to the job then carry-on. Wasn't being picky, I just genuinely know little about such metallurgical matters.

Looking good, can't wait to see the progress.
 
This is very cool!

Take the criticisms with a grain of salt and a smile. A lot of bright folks around here, but in the end it's your project do what you want to do, but don't exclude good advice if you can avoid doing so.

I like it, the hard mount engine is slightly concerning but the mounts look nice and beefy and I don't think you'll have a problem, or at least not a catastrophic failure.

Agreed on the powder, this things going to be too cool looking to cover up. Go clear on the powder.
 
Then let's do an update again.

First we made some spacers to mock up the swingarm mounts in their final place.

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We mainly wanted to check at this point if the frame tubes clear the engine nicely.
As we don't have a proper 3D model of the engine, that clearance/fitment really need to be checked on the actual engine.

So we proceeded and mocked up the tubes for the rear section of the frame.

Note that the top tube has also already been shortened.

That looks then like this.
Everything is roughly in place and a few tack welds hold the parts together...

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The the frame went to our welders.

They made a small jig out of some steel tubes which we still had laying around and then TIG welded the complete assembly.

After they did their magic, I put the frame back on the engine to check the distorsion.

That's the result...

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While there's of course some distorsion, it's actuall all better then expected.
We don't need to mechanically straighten the frame, it can be used as it.

But that's also due to a small trick!

The swingarm mounts are so far not bored to size, they're still 4mm smaller in diameter.

Once the frame is completly finished and all the small parts are welded on, we'll put the frame on one of our machines and drill out both axle mounts to size, all in one go.

In this way we can make sure they're straight and that the position and angle are correct.

The top tube will also be the oil tank for the engine.

So we had to add a filler neck as well as flanges for the hoses.

The oil feed is down at the left, lower frame rail. It has been internally broken through to the main tube.

The oil return is the long tube, which we weld into the bottom of the main tube.

It's long enough to end over the oil level, when the tank is filled.

At last there's still the cam-cover vent hose.

We used an 8mm tube which goes into the tank on the bottom end and then inside the tank to the filler.

I asked my welder to take some pictures this time...

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And that's the current state of affairs...

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Check out the Irving Vincent with a similar frame made from 4130 steel. Looks like a stock Vincent or an Egli but much stiffer. Admittedly they had a different use for their bikes in mind when they designed them.
 
We've been busy again and made a swingarm.

The adjusters on the end and the shock mount are CNC cut billet, the rest is the same tubing we used for the rear of the frame.

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Also we've done some more work to the frame.
Added a shock mount and closed the bottom of the main tube.

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A first mock up of frame, swingarm and rear shock.

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Two observations - please ignore if they are the result of seeing it as a mock up. 1) There looks to be a lot of unloaded drop in the swing arm angle. Generally, you'd want the loaded ride height to result in a straight line for the drive sprocket center, arm pivot center and driven sprocket center to maintain minimum chain issues. 2) The angle between the pivot to shock mount and the shock looks large (hard to tell from the pics). Generally, you'd like this to see this angle move toward 90o as the travel moves toward full compression. This obviously yields an increasing rate for the damping and spring. Moving away from 90o results in the opposite of course - just curious if you have a design intent here. Looks like a great job so far - looking forward to more progress!
 
That looks fantactic! Really stoked to see where this is going. Impressive work to say the least.


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Man I don't know anything about ride geometry or swing arm angles or anything like that, and so it's really interesting to watch an actual frame being built like this. It gives me a really unique perspective on the actual mechanics involved - I'm especially intrigued by the swingarm/monoshock/frame linkage.

Thanks for taking the time to document all this, it's an education.
 
jpmobius said:
There looks to be a lot of unloaded drop in the swing arm angle. Generally, you'd want the loaded ride height to result in a straight line for the drive sprocket center, arm pivot center and driven sprocket center to maintain minimum chain issues.

Are you just saying random things that come into your head? Clearly there is no load therefore there will be drop, it’s call suspension movement.


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Karlloss said:
Are you just saying random things that come into your head? Clearly there is no load therefore there will be drop, it’s call suspension movement.


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That thing is going to have to come up a good 6" to be parallel to the ground. Not likely the shock has that much travel. So, no, he isn't just saying shit. He has a very valid concern.
 
J-Rod10 said:
That thing is going to have to come up a good 6" to be parallel to the ground. Not likely the shock has that much travel. So, no, he isn't just saying shit. He has a very valid concern.


6 inches you say, looking at the images I’d say much less that 6 inches, but hey if you think that distance is 6 inches I can see how you bluff your wife


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Here we go. Probably another thread that could be awesome that'll get shut down, or the op won't return because some dude forgot he wasn't in kindergarten anymore.



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Hurco550 said:
Here we go. Probably another thread that could be awesome that'll get shut down, or the op won't return because some dude forgot he wasn't in kindergarten anymore.



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I agree, so many armchair engineers making dubious statements about angles and picking fault with an awesome build.


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Karlloss said:
I agree, so many armchair engineers making dubious statements about angles and picking fault with an awesome build.


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Yep, described yourself perfectly. Good job.

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