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PostPosted: March 14, 2019, 11:47 pm 
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Yikes! Toobusy is that an aluminum hub? Either way I guess that's a thumbs down on the keyed shaft.

Maybe I can get the 1.25 shaft, use a weld-on-hub for the inner sprocket. Then have the outer end's spline cut.

My other thought was just get a used output shaft from the engine. Unfortunately they all seem to come with a whole bunch of gears, shafts etc :lol: . Seems a waste. Well there is one on Ebay now for $99 (including a transmission :lol: ) Hmmm...I think it should be long enough, just looking at the outside of the engine.

I don't have plans for any shock absorption in the drivetrain. I think the stock sprocket has some sort of rubber coupler built in. I'm aware of the huge cush/crush? drive in the rear wheel. Maybe something can be done when mounting the rear sprocket to the diff.


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sprocket.png
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PostPosted: March 15, 2019, 11:02 am 
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Splines do not replace clamps/bolts. A splined area where the parts are free to rock back forth wears rapidly. Custom made splined shafts can cost a fortune. Broaching to match the spline requires finding a shop with the required broach. Post-machining heat treat is a given.

However, to eliminate special, costly procedures, splines and keys, with a small lathe and index table drill, you can make a spool and use plain sprockets to bore and drill for bolts. Use as large a sprocket as you can to fit hardened allen bolts to allow a larger bolt shank and still clear the inside edge of the chain with margin for sprocket wear. Also need a concentric support ring. Bearings are shielded/sealed. No room for cush and bolts. Probably need to start with a 3 od x 5 block/rod of low carbon steel to have room for everything. Use very large od, thick wall tube to mount the plates.
You could integrate a cush drive between the sprockets but that would be a lot more work and a couple more bearings, essentially two spools that interlock with male/female bits and rubber/poly between them. Six round holes equally spaced in the female spool and thin wall rubber dowels over thick pins in the male spool would be the easiest to make imho. Consider the cush material does deform and eventually wear out so fairly high durometer.

This isn’t that different from endure bike rear hubs that fit a brake rotor on one side and the driven sprocket on the other. Warp 9 sells cush drives for these but it is super expensive and you’d need to make adapters to use their product so better to make your own.

Of course, it’s never too late to move the engine over 3.0225” and save all this trouble.


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PostPosted: March 15, 2019, 11:38 am 
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Yes, that used to be the aluminum drive hub to the final drive sprocket.

In it's former life with a CVT, the driven clutch and a drive sprocket were mounted on a layshaft. Then a chain to the final drive.
Easy peasy, worked great with the snowmobile motor.

Then I came along and wanted a bike engine with a 6 speed dogbox. I started breaking things the first event and worked my way from one weak link to another all season long.

Hub, sprocket, one axle, then the other axle, chain tensioner... The car wasn't adequately designed for the hard launches and violence associated with autocross.

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PostPosted: March 15, 2019, 1:33 pm 
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Yea, I may have to slow this up a bit and try to get myself to accept a little offset on the engine and the diff. I'll see how much I can move the engine over.

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PostPosted: March 15, 2019, 2:50 pm 
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Having a jackshaft means having two chains that are even shorter than a one chain system. These short chains tend to heat up a lot and fail much more quickly then in a motorcycle where there is more length to dissipate the heat. Moving the engine over and having a longer chain will help with that as well. If you can get some air directed to your chain, I would recommend that also.


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PostPosted: March 15, 2019, 4:56 pm 
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OK, I think I can move the engine over about 2" and have fair clearance to the frame. Also if I mount the rear sprocket on the other side of the diff flange, that gives me a bit more. And I was thinking of trying to make a cush drive (big grommets?) that the rear sprocket would mount on and that gives another 1/4". And voila, the diff is centered! Yea!

But the bearings don't really line up with the engine mounts anymore, but I think I can deal with that. It moved the CG off center about 1/2" too. I guess mount everything possible on the left side.


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PostPosted: March 16, 2019, 8:12 am 
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For cush, the grommets will allow the sprocket to move out of parallel so you must use something else to keep it running true. Consider a plate that bolts on to the diff with a concentric support ring for the sprocket outside of the diff bc, the grommet cavity, then out near the inside edge of the chain, slots with thrust washers. Take a look at how floating brake rotors mount on high performance bikes. It is for thermal expansion and they tend to be half moons rather than slots but it is just the general idea.

You can always come back to it after the car is otherwise sorted out.

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PostPosted: March 17, 2019, 3:08 am 
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OK, I got rid of the layshaft, thanks for holding my hand through that. :lol: Here's the plan for a fabricated "diff cage", just two of the new main arms are shown. And yes, the new steel parts will eventually be all one weldment.

The two round "medium grey" tubes are just a representation of the engines rear mount points.

Oh, MV8, Yeah I just realized that a cush drive for this should only flex axially.


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master145.jpg
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PostPosted: March 17, 2019, 8:57 am 
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John
I suggest that you take a look at the design of upper and lower axle attachment tubes. I believe you would have less deflection if you use straight tubes Vs the of leg design. You could use a spacer tube weld to a straight tube to from a Tee, attach at the engine lug, and run it straight back to the axle bracket. Also there is no reason you could not just make separate tabs, one for the engine and 2nd on the lower frame tube, for the torque arm. Consider making the chain adjuster at the top side. It would be much easier to see and quicker to adjust. Pivot on the lower tube, then adjust with the top tube. You could actually go to the rear upper horizonal tube, so you could use a threaded adjusters under tension so you could easily verify that they are equal distance relative to the LH and RH side. Davew


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PostPosted: March 17, 2019, 3:24 pm 
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maybe this can give you some idee . in case you want to have reverse


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PostPosted: March 17, 2019, 5:51 pm 
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Davew, the upper rear left engine mount point is closer to centerline than the lower one. In my previous plate design I did have a spacer in there. I guess I figured since I'm not using a plate anymore, make it go as straight as possible to the mount point. On the lower arm, it's bent to go around the chain. Are you suggesting mounting that arm (a straight version) to the main frame tube? That's not where I had planned to mount the engine, but maybe.

I put the pivot up top because I think that joint will be taking most of the force from the chain. The lower adjustment won't need to take so much stress.

I was thinking about having a starter motor swing down and engage the chain for reverse, that Westgarage system looks nice.

Thanks, for the ideas!

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PostPosted: March 19, 2019, 3:32 am 
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Here's a good chunk of the diff cage fabing. The plates are a version or 2 behind, but they still hold the diff.

I was cutting the top middle angle piece and things just weren't lining up right. When double checking the engineers work I found the problem. I accidentally mounted that 1/4" plate to the engine wrong. So i had the engineer fix that and we moved on.

I normally just scribe cut lines and go to town with a small cuttoff grinder and it's usually right on. Anyway it worked out fine.


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PostPosted: March 19, 2019, 9:42 am 
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davew wrote:
John
I suggest that you take a look at the design of upper and lower axle attachment tubes. I believe you would have less deflection if you use straight tubes Vs the of leg design. You could use a spacer tube weld to a straight tube to from a Tee, attach at the engine lug, and run it straight back to the axle bracket. Also there is no reason you could not just make separate tabs, one for the engine and 2nd on the lower frame tube, for the torque arm. Consider making the chain adjuster at the top side. It would be much easier to see and quicker to adjust. Pivot on the lower tube, then adjust with the top tube. You could actually go to the rear upper horizonal tube, so you could use a threaded adjusters under tension so you could easily verify that they are equal distance relative to the LH and RH side. Davew


One downside to having the adjuster on top is the engine is trying to loosen the chain every time you're putting down power. I can't tell you how many times I threw the chain on the A Mod.

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PostPosted: March 20, 2019, 12:46 am 
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Cush drive idea:

I was thinking about mounting small (3/8" id) radial ball bearing on a ring shaped plate around a radius about 3". Then another larger ring would fit over that to allow the free rotation. Then I looked at it and realized I was just making a big bearing out of smaller bearings.

Then I looked for a big bearing instead, mostly what shows up are "thin section" bearings that start around the $300 range. Bah!

Maybe just a big diameter bushing (greased) would work? Make it V-groove to limit all movement to rotation. Then figure out the paddle/fin/rubber things.

Also, as near as I can measure, the large bolt circle on the diff is 5.800", which makes no sense, it doesn't come out metric either. I guess it is what it is.

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PostPosted: March 20, 2019, 7:00 pm 
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For more ideas, look at a standard automotive clutch hub. They use compression springs instead of bushings but they are for the same thing.

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