Promised drive pics

[phoenix827]

This is the bike the drive is on.

This is a pic of the comet drive. Very tight.

Here is the drive box we made from 4x4 box tube and the shafts we cut.

Here is the top shaft. You can see the drive pulley from the engine on the back.

Heres the bottom shaft. You can see the sprocket for the chain to the wheel.

We ran it last year and it still runs great. I only took it apart 'cause I promised pictures. We cut the shafts and made the drive box ourselves. The bearings are flange bearings that are rated for 7000rpm. We are planning a full rework after this riding season is over. We have a 5 speed Kawasaki trans to go in. Plan on lowering the seat some more and stretching it.

[pietenpol2002]

Thanks for the pics Ben. Certainly a novel approach to squeezing the Comet into limited space. Are you using a tensioner on the primary belt drive or do you have a means of taking up the slack? Also, can you tell us what kind of top speed you're getting with that arrangement?

[phoenix827]

I do have a tensioner on the primary side. Its a simple pulley mounted on a slide with a lock bolt. Pull it tight, tighten the bolt. We made it using pulleys for idlers off a mower deck. We stepped up the speed on the input to the comet to get it to pull lower in the rpm. The drive pulley on the engine is six inches and the one on the jackshaft is 4.5 inches. We have a large rear sprocket, 60 teeth. It runs great 45 to 50mph easy. I have seen 60mph out of it on a downhill. We geared for in town, I hate freeways. Its my cheap college transportation. I get about 110 miles to a gallon. I run cooking oil in it.

[IgorVigor]

Looks good

Its the sort of basic idea I am thinking about...

Still dont like the colour though, sorry

[albertaphil]

Nicely done, phoenix. So that is how you fit a CVT into a smaller space. The extra shafts would add a bit of weight, but I think you might have just made possible another project with an engine and comet 94c I have lying around.

Shall I assume that you don't care for the CVT, hence your plan to install a gearbox?

Why did you "gear up" your primary drive between the crankshaft and primary CVT shaft, and "gear down" with such a huge sprocket on the rear wheel?

Anything you would do differently next time besides not use a CVT?

Once again, great job!

Phil

[phoenix827]

We sped the drive up to "tune" where the clutch engaged. Normally those drives don't engage till around 1600rpm. This one pulls in around 1000rpm. The large rear sprocket was 'cause I hate freeways,. We geared for in town. I like the comet, but we are on a quest to see just how much mileage we can get. Seems like the comet is costing some in parasitic drag. The five speed has a wider ratio spread and the clutch locks, so no loss. Right now, I average 110mpg in town. Pretty good considering I'm 280 pounds. There is also the custom view, it'll never really be done. There will always be something to improve.

[coachgeo]

...I like the comet, but we are on a quest to see just how much mileage we can get. Seems like the comet is costing some in parasitic drag...

Do believe the loss from parasitic drag is more than made up for my keeping the engine at its most efficient point in its bandwidth. This is the beaty of CVT. Not to mention that CVT is a third to two thirds lighter than a gearbox.

The five speed has a wider ratio spread ....

Not sure how you can claim wider ratio spread with a 5speed compared to CVT. CVT are tunable well into overdrive ranges and near infinant number ratios below that.

[phoenix827]

The kaw trans we are going to use has an aluminum case and weights about 10 pounds less than the current unit. (the case we built is heavy.) I checked the ratios in the trans. First is lower and fifth is higher than the comet can get. The range is broader than the comet. We have several rear sprockets, we can tune for optimum rpm that way. We played with different pulleys and different rear gears, If we put too tall gear in, the drive compensated and did not go all the way to the top ratio. It cut its own legs off. this is about maxed out considering how much weight its haulin' around. . One real issue with the comet is that take off is limited to whatever the rpm it comes in at. I do all my riding in town. Sometimes you need more acceleration, People drive like maniacs around here. I could bring the clutch in at a higher rpm to get out of the way faster.
We are going to built a scooter with the drive and probably a 6.5hp diesel. Classic scooter style, seat over the engine, floor board, and step through. We plan on mounting the jackshfts and comet on the swingarm, so the engine will be right in front of the swingarm.

[IgorVigor]

CVTs do offer a wider range of gear ratios, but they do get hot...

Heat is lost energy to the back wheel...
A local bike mechanic reckons that a CVT can lose as much as 30% of the power from the engine in heat....

How true that is I dont know, but he does seem to know what hes talking about...

[albertaphil]

I suppose this is turning into a pretty specific thread but...I don't know what to think about the whole CVT/power loss/powerband issue. I'm using the 6 spd trans that came with my Honda Superdream because I can't get a CVT to go onto the crankshaft of my ruggerini. I'm still happy because I'll have 6 gears. But the setup is going to be pretty heavy. Add up the lbs of weight for the primary sprocket (a double #40 which is still undersized according to Marting sprockets) the chain, the secondary sprocket to be welded onto my original clutch, the chain tensioner, and the sealed aluminum case to enclose the primary drive.

With a CVT (depending on the setup) all you need is a sheet metal (or plastic or fibreglass) enclosure for the belt.

As for parasitic loss, that can be gauged by heat generated by the belt(s) as IgorVigor stated. A little 5 spd box likely won't generate much heat. But the power available at the rear wheel may still be more with a CVT due to the engine always operating at its optimum RPM. That is, if the CVT is tuned properly for the hp/torque/rpm of the engine, and that can be a bit tedious, I understand.

What model of Comet are you using? I know that the 94C can be tuned by changing pucks (weights) and springs for RPM at engagement, and then the secondary pulleys can be adjusted to "gear up" at higher or lower RPM and depending on the torque output of the engine.

The beauty of your 2 shaft setup is how narrow it is, and the drawback is the weight of the extra shaft, bearings, pulleys, belt and frame to hold it all.

How heavy is your bike, Phoenix? My 1980 CB400 presumably had a curb weight of 400lbs, and I doubt that your CM started much different. Where are you at now?

Phil

[phoenix827]

The plan is to make everything we can before cutting. We are enjoying riding season. We are actually turning the crankshaft from the kawasaki engine into a jackshaft to correct rotation. We are making a plate to seal where the cylinders where. The trans has five speeds. We know we will have to stretch the frame some. The plan is to take the lower back half of the kawasaki frame and mount the trans, then extend the lower frame forward and make mounts for the diesel. Once the engine/trans mounts are completed, we will take this subframe and mount it place of the current bolt out lower frame. After that we will cut/stretch to ensure clearances for everything else.We believe we really only need about 4 inches of stretch. Because of the way we plan on setting everything up, we can set the seat almost right on top of the trans. The bike weights around 450-500 pounds. If all goes we should lose some weight. We will only need one gaurd and it will be much smaller, so less metal. The five speed is 10 pounds lighter than the current drive box, so more weight loss. We are going to use the kawasaki clutch. There is a large heavy plate in the frame that we put in to hold the drive in alignment, we will not be needing it. Its going away.We hope to bring it closer to factory weight. When the trans work is done I'll post pics.I'm planning on documenting the rebuild as well.