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April 14th progress report |
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Some of you may have wondered if I fell off the face of the planet. Let me reassure you that that is not the case. Big things have been happening at my work and my available time has dropped dramatically. I still spend a lot of time thinking about items for the car, so it's not like I haven't been making progress... It's just not the type of progress that gets me closer to finishing the bodywork.
 Once in a while a deal comes along that's too good to pass up, and if you have been through my photo gallery lately you may have noticed that I recently purchased a new engine! Not just any engine, a Yamaha FJR1300 bike engine with 5 speed sequential shift and rear-facing shaft drive output. It's not the hottest engine, but 1.3 liters putting out 150HP, 104Lb/ft torque and weighing around 200Lbs is certainly a sweet piece of kit! I expect that the car will lose several hundred pounds of weight and gain 40Hp over the original Toyota 4AGE drivetrain with nearly identical torque figures. Above is a photo of the Bike that my new engine came from.
I'd like to head off all those people who are certain to express dismay that I am working on such things, rather than finishing the bodywork. The bodywork is still my priority. I simply took advantage of a great deal on a good engine. The current engine and drivetrain will stay in the car until it is finished and past inspections and emissions. It's only after that point that I will re-engineer the rear of the car to accept the bike engine. I will only work on the engine when I am unable to work on the bodywork. Fair enough? Ok, back to the engine. :)
It's a small package, 18" deep, 22" wide and 26" tall. I can pick it up by myself, but just barely which means that it is close to 200Lbs, but that is a guess. I really should put it on the scale to see for certain.
The main question that needs to be answered at this point is; How do I connect a shaft-drive engine to a differential to drive the rear wheels? The shaft of the engine rotates clockwise when looked at from the rear. This is reverse to normal car engine rotation. I spent quite a bit of time debating this problem over on LocostBuilders.co.uk and on this thread too. With many thanks and gratitude to the people that contributed ideas I think I came upon a viable solution that should be relatively inexpensive and transfer the power with the minimal driveline loss. I'll gloss over the details as follows.
 The basic problem with using a shaft driven bike is the reverse rotation of the output shaft. Car differentials use a hypoid ring and pinion gear to transfer rotation 90 degrees to the halfshafts. Although a car differential can be mated to the rear output, some work would have to be done to the diff when it was flipped over. In addition, the power would be traveling through a second set of bevel gears on its way to to the half-shafts. This would reduce the available power to the wheels by a significant amount due to driveline loss. Although this idea seems viable, It may be a bit too long for my packaging requirements and so I decided to continue searching for solutions.
 My next idea was to mate the output shaft of the FJR directly to the input shaft of a Honda FWD transaxle, since the Honda engines of the mid-90's rotate reverse this seemed like an efficient idea. I would retain several of the taller gears in the transaxle including reverse, and rig up a secondary shifting system to choose hi-lo and reverse from the honda gearbox. Thankfully this idea was quickly discarded mainly because I encountered packaging problems, since the bike engine would have to sit behind the driver and that puts all the weight in the wrong place. In addition, there seemed to be a significant weight penalty with this method. And probably quite a bit of driveline loss by using 2 gearboxes with multiple redundant shafts, etc...
 Soon my thoughts were back to chains. (And not the kind from my closet...) Some more digging around the Locostbuilders site and I had my answer. A hybridized combination of Honda driveline parts and chain/sprockets. If you take a close look at the thumbnail (click on it for a lager view) you will see the solution. The engine is turned sideways so the output shaft facing the right side of the car. In this position, the clockwise rotation of the output shaft is correct for the sprocket/chain drive. A sprocket on the output shaft and a sprocket on the differential. The differential assy is attached to a carrier that bolts to the frame and is adjustable for chain slack. The red blob in the center is a car starter motor that will be used as an electric reverse the gear that it drives is a motorcycle started ring gear attached to the intermediate drive-shaft. The entire differential/driveshaft/halfshaft assembly is lifted directly from any Honda FWD drivetrain.
 My neighbor Justin happened to have a differential from a Honda transaxle and was kind enough to give it to me so I can start mocking up the components. The nice thing about this design is that the mass of the engine can be centered to the centerline of the car. The crankshaft is longitudinal to the car centerline. The exhaust ports point to the left side of the engine bay and the entire driveline package is extremely compact. The total distance from the half-shaft centerline to the front of the engine is less than 26".
Current technical issues that need resolving. (Maybe I can get some feedback from the crowd on these items?)
- Attaching a sprocket to the output shaft of the bike. Output shaft is 1" diameter with 14 splines. See photo gallery for detail photo. I do have the original shaftie u-joint with the proper spline/shaft. I was thinking cutting this down and welding a sprocket onto the end of it. It's probably not going to be strong enough and more than likely impossible to make perfectly concentric to the shaft. In all likelyhood I will need to modify an existing bike sprocket to match the spline and shaft. How to attach the resulting sprocket to the output shaft? Will machinework need to be done to the output shaft to thread it for a nut? Ideas please.
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