CX500 Kubota

[Eddy Wane]

Hi Stephen.
Love the build. It is interesting to see how you have shoehorned the motor into the frame. I have one question. What did you use to mate the driveshaft to the engine? Is it the original Honda part from the CX or custom built?
I am still on with my build using the CX and a Kubota twin but work has stagnated on the bike at the moment. I just realised there is only 24 hours in a day.
Eddy.

[coachgeo]

Thanks for those detailed pics. Always helpful to study how someone else puzzles through the design process. Again, an excellent piece of engineering. Which then leads to the question - and what form will your chain drive take? Do you plan to use a CVT? A gearbox? And the engine - transverse? North/south orientation?

A previous post answers your questions as does his initial pictures of his running shaft drive diesel Honda bike w/north south engine. He finished the bike before he posted his build report so the build report is sorta back assward from what is usually posted Finished bike posted first and detail following.

The drive system is fairly complicated.

An 80 tooth htd pulley mated to flywheel drives up to a 40 tooth htd pulley. On the 40 tooth pulley shaft is a comet 40 series primary which drives down to the secondary. On this secondary's shaft is a 10 tooth sprocket which drives over to a 16 tooth sprocket on a shaft which is mated to the shaft drive through the stock u joint. I didnt drive the cvt right off the crank because I didnt have enough room to fit a cvt large enough to handle the torque of the engine. This is the reasoning behind the 2:1 ratio of the htd pulleys, the torque is reduced by 50% allowing me to use the smallish 40 series comet. The sprockets after the cvt are used to get the correct final ratio as the ratio in the shaft drive rear end is fixed. ....

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Coachgeo: Pietenpol was not asking about my first bike. He was asking about my second build. He knows my first bike was shaft drive and as I have mentioned I plan to build the second bike using chain drive. I mentioned how I had to removed this engine for use in my second chain drive build so he asked " Which then leads to the question - and what form will your chain drive take?"


Pietenpol: The second bike will have the engine mounted transverse driving a double v belt up to a jackshaft 1:1 ratio high behind the engine. The primary clutch of a cvt will be on this jackshaft driving down to the secondary on another jack shaft which will be connected to the rear wheel via chain. Reason for doing it this way is:
My engine is already long and will stick out each side. I determined that two 3v narrow v belts can take the power and be quite narrow compared to a primary clutch mounted on the engine 2" vs 5"-6".The secondary will be tucked within the frame and away from my foot area. Im not a huge fan of the look of clutches being mounted on the side with a big cover, I know it works well and many bikes have been built using this mountig that are very nice, its just not for me. I will be using a comet 94c duster and an appropriate secondary which are much bigger than the comet 40 series clone I used for the first bike. The second bike is being built using a goldwing frame. That plus having the engine sideways, means the secondary should just fit behind the engine. The picture shows the layout with the mockup I bult for the 40 series. The reefer oil pan will be replaced with a regular pan.

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Eddy: I am very fortunate to know a very skilled machinist. I took the whole driveshaft unit to him together (long shaft from diff, u joint and short shaft to engine). The u joints are part of the shafts and are not removable. I didnt want to screw around with the joint as it looked to be in very good working order. He was able to cut the shaft off of the engine side joint, then hollow the joint out for a 4" long 1" shaft to be pressed in. A hole was machined through both and a stainless steel press fit pin pushed through and finally the ends of it were crushed out to hold the pin in. This was all done while the joint was still connected to rest of the driveshaft unit.

The shaft has to slide into the transmission as it is the whole engine tranny unit is pushed into place. This is a HUGE pain in the ass but manageable.

[coachgeo]

Coachgeo: Pietenpol was not asking about my first bike. He was asking about my second build. He knows my first bike was shaft drive and as I have mentioned I plan to build the second bike using chain drive. I mentioned how I had to removed this engine for use in my second chain drive build so he asked " Which then leads to the question - and what form will your chain drive take?"

thanks for clarification. Apparently I was comfuzed .

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I figured it was time to update my build thread. Since my last posts here I have done a bunch of work on a chain drive converted honda goldwing project (put on hold for now). I then went back to this build and swapped the 3 cylinder out for a two cylinder z482 engine allowing me to relocate the radiator up front and allow greater access for maintenance, repairs, and adjustments. My new engine has a normal style oil pan which is much lighter and frees up even more room on the sides of the engine. I also went for a stock manifold into a single straight pipe for the exhaust as opposed to the three pipes I had before. The transmission has for the most part remained the same in design but has definitely been refined/simplified from the original. Since these pictures it has been updated again, I will get pictures of that soon. The great thing about kubotas engines is that the super mini series share the same engine block architecture so all of the custom bits I made for the three cylinder, bolted right onto the two cylinder. Feel free to ask any questions about it, I will do my best to get back with answers promptly.

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Pics of the refined transmission

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I am currently rebuilding my bike with a 3 cylinder Kubota as was originally used. Basically the same design as the original build (back to rad under the seat) but everything has been refined to be lighter/smaller/easier to service. Here are some pictures of the new parts I will be using and some of the ones I had modified/redone. I will be glad to answer any questions.

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The new to me D722 engine. The original got swapped into a John Deere Mower

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New oil pan to replace the huge heavy reefer style pan

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Rear exit manifold to replace top exit manifold on engine

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Black valve cover with low profile crankcase breather to match black oil pan

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New high capacity Fan and Oil cooler which I will attempt to use as a radiator

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New sub-frame assembly designed so that the down tubes are easily removable to allow the engine and transmission combo to be slid forward to allow more space for service, repairs, adjustments. The new plates will remain on the frame under the gas tank, the down tube will unbolt at the top and slide off at the bottom. The down tubes are not fully slid on to the aluminum rails in the last picture as there are burs that need to be cleaned up first. Then a hole will be drilled through both and a bolt used to hold them together.

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Making steady progress. Sub-frame pieces are fully assembled, the oil an has been swapped to a normal tin style, the stripped engine was mocked up and the extra pieces were all added, the transmission was assembled, and the gas tank got new front mounts that tie into the new sub-frame design. This is all for mock up and is not final assembly.

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Very glad that the forum is back up and running. Still working away at the bike slowly getting little things done over the winter so it's hopefully finally ready to go on the road this riding season.

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New engine mounts. More angular design, engine lowered 1/4" I believe in order to better align the final shaft output with the u joint cup in the swingarm.

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Remote mount oil filter adapter and remote oil filter mount. There was not enough room for even the shortest filter I could find. The adapter is about 2" deep total and just fits behind the sub-frame vertical tube. Fairly pricey unit but it did the job and looks good. The oil filter mount was very cheap in comparison. Both pieces had different styles of connections so I had to build the brass/silver combos with a fair bit of trial and error to end up with the same size barbed fittings on each. Adapting the remote mount adapter(from jis or an, cant remember) to barbed without buying $40 specialty pieces online was a pain. Luckily my local hydraulic specialty store has very helpful employees. There is just enough room to unthread and remove the oil filter without removing the engine mount under it. I will do the hoses soon.

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New low profile stainless alternator/dynamo mount. Not sure if the dynamo will supply enough power but I hope it does as I'm not sure I have room for anything larger.

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The brass (bronze?) tubes are rigid mounted to the aluminum bracket and will serve as guides/sleeves for my throttle and fuel cut -off cables. They are brake lines that start as straight stock with flares and fitting on each side. Fairly easy to bend without kinking with the correct tool. One starts at the solenoid at top left and goes to the fuel shut off lever. The other starts above the valve cover where the throttle cable will come from the other side and goes to the throttle lever. Both the cables and the normal black sleeve will be fed through the brass tubes together.

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New genuine comet 40 series driven clutch. I originally bought a knock-off set from ebay which worked ok but you get what you pay for. The drive clutch seems fine but I was having problems while trying to dial in my clutch alignment. I could never get it perfect. Then I released that the driven clutch had an enormous amount of run-out. If you spun it by hand you could see it wobbling around id say 1/8" of an inch. Aligning with one side of the wobble would inevitably leave the other side out. I could have aimed for the middle ground but I felt it would never work efficiently or have good belt longevity. The genuine comet part cost 2x more than the knock-off pair but it spins nice and true and is much higher quality.

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With the 3 cylinder engine back in the radiator will be going back under the seat as it was originally with the other 3 cylinder kubota. I could have used the same modified cx500 rad but the fit was rather poor. I was having a hard time finding something with the correct dimensions while trying to maximize cooling capacity. Most rads I found were too wide. I did mock up a very thin rad that could have worked but the cooling capacity was most likely to small. I also tried a transmission oil cooler that might have worked but I was unsure how well it would cool. I eventually went with a heater core out of a 60's chevrolet impala. It is small length and height wise but very deep. It actually has 50% more volume than the stock cx500 rad that I used before. It will need to have mounts brazed to it and I will have to use an inline pressure cap but it fits quite nicely and I will use the same high capacity fan as before.

[pietenpol2002]

Great to see your progress. And can't wait to see it on the road. I do wonder if you could get by with that little dynamo if you went to all LED. Even so, you'd have the load of the radiator fan. Fourteen amps doesn't drive much.

You also have the benefit of mounting your oil filter on either side. Mine came with that option as well, in addition to a right angle oil filter adapter. The beauty of the right angle filter mount is that they can be swiveled 360 degrees to whatever fits your build. I mounted mine on the IP side and tucked it up under the injection pump. Perhaps a moot point as you may well now be committed to the remote arrangement.

https://www.ebay.com/itm/Oil-Filter-Hou ... ctupt=true

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Thanks for the recommendation. I did try that route before buying the adapter. Wish it had worked as it would have been much cheaper and simpler.I tried one on both sides and it was close. My engine also slides forward about 4 1/2" on the lower sub-frame, once the engine and tranny mount bolts are removed, to give access to the transmission for belt changes and general transmission maintenance/adjustment so everything has to fit between the vertical sub frame tubes. They can be removed separately but it requires much more work to do so. The 90 degree mount did fit on the exhaust side, downwards on an angle, and on the IP side horizontally facing the back, but would contacted the frame once the engine was moved forward and the thicker part where the filter spins on tried to go past the tubes. I wasn't willing to sacrifice the serviceability and didn't want to be removing it/doing oil changes every time I had to slide the engine forward.

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Clearance on IP side

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Mount Position. Very limited access to transmission components.