Resuming Bike Project

[oilburner]

After a two year delay due to unavoidable circumstances, I've resumed work on my diesel bike project. A picture of the bike can be found on www.dieselbike.net/daihatsu.htm

The bike is powered by the D950 953cc 3 cylinder Daihatsu industrial diesel. The gearbox is a BMW 5 speed with a Kayser 1.42 5th gear. (I'd appreciate knowing where I can get a Kayser 1.35 5th gear set). The final drive is a BMW 2.91. The setup should be good for 68 mph @ 3600 rpm.

I'm currently fabricating an alloy housing for the instrument cluster, which consists of VDO programmable 80 mph speedometer and 4000 rpm tach and 8 VDO warning lights.

+++

Congratulations Stuart on the new forum.

Avery Frail

[Anorak_ian]

Hi Avery, why the gearbox change? BMW better engineered?
Oh dear, looks like your speed has dropped since the swap over.
I was thinking of using a Harley box myself, but as my Sportster box fell apart for the third time, Ill use an Enfield 4 speed, not the best box but different ratios are available (Brit boxes only).
So how did you get a BMW box to work anyway? Presumably this will be shaft drive? Any pics?

Cheers
Ian

[oilburner]

The bike is my own design and was intentionally built to utilize a BMW gearbox and shaft drive and as many other BMW components as possible.The objective is to build a bike that looks good (clean, uncluttered), is extremely reliable, requires minimal maintenance, and provides decent performance. This picture was taken at a bike show 3 years ago, a number of components such as exhaust, seat, fuel tank etc. were for display and development only and will not appear on the finished bike:


Top speed will be limited by governed engine speed which is 3600 rpm. The aftermarket 5th gear provides an extra 5 mph top speed over the stock BMW 5th gear. The overall gear ratios should permit the bike to maintain top speed while operating within the *continuous* power output range (for longest engine life).

The BMW gearbox attaches to the engine using a bellhousing I built myself. The original Daihatsu flywheel has been machined to accept the BMW clutch assembly. I had to retrieve this picture (originally taken by me) from the German website as I have lost the original:
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Hope this helps.

Avery

[Anorak_ian]

Agggh! Sorry I was looking at the wrong bike, the link sent me directly to Terry Martin's green Harley. You must have thought I was going mad.
Now the kids are back to school and the wife is at work, I can take a more leisurely look.
I must say I'm a tad jealous of the gearbox, a modern design and after market ratios is the way to go. Don't BMW make a 6 speed box that you could use?

[oilburner]

Several of the new generation R series boxers and four cylinder K series have 5 and 6 speed gearboxes with overdrive ratios and also have final drives with tall ratios which are very well suited to a diesel application. In my case, I had several of the old style gearboxes in my parts bin and they are considerably easier to mate to the diesel engine than the new style units. No question I would have gone with the more modern setup with better ratios if I had to purchase parts.

Avery

[balboa_71]

Avery,
How do you go about getting a bellhousing built to mate your diesel engine with a BMW gearbox? I've often been curious how people can mate one brand of gearbox with an engine never designed for this application. I addition, there is a clutch to deal with (mating of clutch to engines flywheel, etc....).
I once thought about mating a diesel to my T3 Moto Guzzi, but the Guzzi flywheel is a rather unusual design.
I'd pay for a book written on how to spec. out these conversions!!!

Cris

[LocomotiveBreath]

Avery,
You did a great job on your bell housing, did you cast your own or modify the stock B&S bell housing to accept the BMW Transmission?

Dave

[oilburner]

Hi Cris;

The process of fabricating a bellhousing or other adapter is simple in concept but, depending on skills and tools at one's disposal, can be somewhat harder to actually accomplish. In my case, it was a tough challenge with my modest tools and skill set.

First, I decided on the clutch / flywheel setup. I had the Daihatsu flywheel machined to accept the BMW clutch assembly. The flywheel was also lightened by removing a few pounds of metal from the circumference, to help offset the weight of the BMW clutch assembly.

With the flywheel and BMW clutch assembly in place, I then determined the length of the bell housing. This is the distance between the bellhousing surface that mounts to the engine and the surface that the gearbox bolts to. This was easy - two measurements were required: (1) the distance from the surface of the Daihatsu flywheel to the engine mounting surface and (2) the distance from the surface of the flywheel in a BMW engine to the gearbox mounting surface. These two numbers added together are the length of my bellhousing.

Ideally at this point you create drawings of the mounting flanges of the engine and the gearbox to be used, showing the bolt holes, locating dowel pins, etc. and the centerline (very important!). The gearbox input shaft must line up with the centerline of the engine crankshaft, otherwise the gearbox input shaft will experience rapid wear and/or failure. Then, find a machinist willing to make the bellhousing for you. There are two problems with this (1) it's near impossible these days to find a machinist willing to take on the job and (2) it would probably cost a fortune.

I couldn't afford the luxury of paying someone to build the bellhousing from scatch, so at this point I fabricated the bellhousing by welding plates of aluminum to a 12 inch aluminum ring that I milled out myself on my sloppy Chinese milling machine. Then I took the bellhousing to a machine shop to have the engine and gearbox surfaces machined parallel to each other. I then drilled all the holes and installed the dowel pins on the engine side of the bellhousing.

I came up with an alternate way to ensure the gearbox was perfectly lined up with the crankshaft centerline. I purchased a factory stub accessory shaft that bolts to the flywheel, and checked it was true (perfectly aligned). The accessory shaft is 1 inch in diameter. Using an empty BMW gearbox casing, I had a brass *go no-go* bushing machined that is a push fit into the gearbox input shaft bearing recess. The bushing has a 1 inch hole in it and is push fit over the accessory shaft. I cut a slightly undersize hole in the bellhousing for the gearbox alignment flange, and carefully filed and sanded the hole until, with the gearbox held in place on the bellhousing, the bushing would just slip over the accessory shaft and through the gearbox bearing hole, thus ensuring perfect alignment. I marked the gearbox mounting hole locations onto the bellhousing and drilled the holes. The holes were drilled and tapped oversize and fitted with steel threaded inserts were installed.

So there you have it. Sounds quite straight forward, but it was *very* time consuming.

When I get a chance, I'll post some pics of the bellhousing fabrication.

Avery

[balboa_71]

Avery,
Thanks for the explantion, basically standard tool and die work....kin to alinging upper and lower die sections when positioning into a die set, etc..
I wasn't sure if you were able to spec out a store bought unit to save all the labor and cost involved. With autos, sometimes there are standard SAE bellhousings available.
I've always been weary of someone machining on a flywheel, but I guess it's done hundreds of times each day somewhere..... like you said, finding a good machinist

Cris