So my not so quickly coming along Starlet build has changed direction something like 5 times. I am not thinking about coming almost back to where I started, Bike engine Car. However, my original plan of mounting the engine up front with a drive shaft to the rear (stock or Miata) was scrapped for gearing issues. Now I am thinking about mounting the engine just aft of the front seats and running a short chain drive to a Miata IRS. The engine is a 2001 Triumph ST that I have waffled on what to do with and I have a Miata parts car (90 courtesy of psteav) to donate the ass end. I like this idea because I can change sprockets and chains easily depending on driving conditions and don't have to deal with regearing a differential. The motor is pretty short and makes solid power (108hp and 72 ft) and weighs basically nothing.
Anyone see any problems with this? Things to watch for? Cries of encouragement? Screams of insanity? 
build an armord shield for the chain. other than that, go for it!!
Just lots of friction losses as you run the power through all those gyrations.
What is the whole car going to weigh at the end of this? While that is a healthy motor it will be a lot less so if the car weighs too much.
What about noise? The motor will now be right behind your shoulder.
What gyrations? Run the chain straight to the ring and pinion and the power never actually has to change directions. It'll be as efficient as on a motorcycle. Similar things have been done with Minis and Smart cars before.
I'm not sure how you'll keep the diff lubricated, though. I've run through the same idea in my head, but it's all going to come down to weight loss.
I think it's a great idea. I assume you're talking of having the output of the bike in the same plane as the input to the Miata so it's just a single chain with a tensioner to a sprocket on the Miata rear end. Dumb Q, but do you need to go through a second sprocket to get the rotation in the correct direction to prevent an Italian Army reverse monster with 6 reverse and one forward gears?
I think one of Denis Palatov 4WD monsters had a mid mounted bike derived engine with chains going forwards AND backwards to diff units.
yamaha
UltimaDork
8/11/14 9:41 a.m.
Use a carrier bearing on the front of a driveshaft so you can still keep it north/south
Use the lemons 2-stroke snowmobile powered miata as a guide but substitute the belt for a chain.
Which of these are you talking about?
Adrian_Thompson wrote:
Which of these are you talking about?
One on the Left. I don't want to build a stand alone and deal with the lub issues that Keith mentioned. I know this thing isn't going to be super fast but it should be pretty light for a hack job and fun, which is the main and only concern. If it stays cheap, then I will try and bring it to one of the challenges.
KyAllroad wrote:
Just lots of friction losses as you run the power through all those gyrations.
What is the whole car going to weigh at the end of this? While that is a healthy motor it will be a lot less so if the car weighs too much.
What about noise? The motor will now be right behind your shoulder.
There will be some losses as it turns right and then splits to the wheels but this is mainly a proof of concept. I already have the parts and just want to see how it goes.
Also, this isn't a DD so it will be loud. Not too worried about that. I will of course try and mitigate noise as best I can. The exhaust will be directly behind me so heat is more of a concern, initially.
So a quick search puts the motor just as Adrian placed it. There may be some clearance issues with the output and chain at that angle but I am sure that I can make it a bit passenger mounted without too many issues.
The MEV Atomic (Same people who designed the Exocet) is similar, but uses a short driveshaft and has the engine alongside the drivers legs rather than behind like you are talking about.
I still like your concept and think it's a great idea.
Why not get a driveshaft adapter and make the world's shortest driveshaft to the diff?
In reply to DaveEstey:
Gear ratios my friend. The Triumph has an internal reduction ratio of 1.75 and the desired final drive for a car built is something like a 2.90 rear gear. That is totally not an option on anything with an IRS. The ford diffs get close but still too high in the end and then I have a huge diff and have to make custom axles like the v8 Miata guys do. Again, not idea.
In reply to Adrian_Thompson:
Got any details on the engine to diff connection. I am searching all over without any luck.
Small problem with passenger offset. There isn't much space between the coolant port and the shift lever. Looks like I might have to say screw you to balance and put it behind the driver.
DaveEstey wrote:
Why not get a driveshaft adapter and make the world's shortest driveshaft to the diff?
There's a guy over on the Locost forums, look in the 'non traditional builds' section. He's building a mini LMP type car with a bike engine basicaly bolted directly to a Miata LSD final drive unit.
Semi Ninja edit Here is the link http://www.locostusa.com/forums/viewtopic.php?f=36&t=2142 Look at page 8 for some engine install pics 
Drive shaft page 10 
Then read all 42 pages and come away depressed at his absolutly amazing design skills and level of detail and fab and realize just how insignificant you (me actuly) are. Current status
singleslammer wrote:
In reply to Adrian_Thompson:
Got any details on the engine to diff connection. I am searching all over without any luck.
This is the website http://www.roadtrackrace.co.uk/rtr.html and these are their forums with some builds in http://www.mevowners.proboards.com/ look under the ATOMIC section.
From this At the front it’s all conventional stuff with urethane bushed MEV round-tube wishbones, Rally Design alloy uprights and Pro-Tech aluminium coilspring damper units. The steering is a rack and pinion with 2.4 turns lock to lock and the pedals comprise an MEV-fabricated, floor-mounted brake and clutch with a pendulum throttle.
At the back, the arrangement is conventional with double wishbones and Pro-Tech alloy coilspring damper units but the source of the other components deserts the Sierra in favour of the Mk2 Mazda MX5 for the LSD differential, driveshafts, hubs, bearings and uprights. The MX5 also supplies the rear discs and callipers while the fronts are Wilwood, the system operated by twin master-cylinders and a balance bar.
it sounds like they are using the Miata rear diff unit with a short drive shaft.
There is a OG mini in my neck of the woods that has miata subframes front and rear and a turbo hyabusa motor running a chain driver to the rear so its absolutely possible.
In reply to Adrian_Thompson:
I went through what little there was on the forums without a ton of luck. I looks like they are running a driveshaft from the diff to right under the motor and then I am guessing a short chain to the driveshaft. I think the directness of what I am thinking might be easier than their setup overall.
Just ran a gear calculator to determine what I need at both ends of the chain. Looks like .7 ratio (19 at the motor and 27 at the diff, or something with a similar ration) would work good for a street driving. 110 top speed and motor is at 5800 (not great but acceptable) at 70 in top gear. A 1 to 1 is great for auto-x but nets a top speed of only 77.
In reply to Adrian_Thompson:
Cool car! That is what I was thinking originally but gave up on doing it cheaply do to the as mentioned ratios.
In reply to wearymicrobe:
That sounds killer! I am guessing you don't have any pictures of that thing floating around... 
singleslammer wrote:
Just ran a gear calculator to determine what I need at both ends of the chain. Looks like .7 ratio (19 at the motor and 27 at the diff, or something with a similar ration) would work good for a street driving. 110 top speed and motor is at 5800 (not great but acceptable) at 70 in top gear. A 1 to 1 is great for auto-x but nets a top speed of only 77.
I'm guessing your engine has a lower rev limet then what he's using or the R1 in the ATOMIC then>?
Having built bike powered a couple different ways I'd say which way to go depends on what your going to do with it.In one used a Miata rear and custom driveshaft,worked perfectly fine with no real reliability issues.It was an autox only toy so the 4.3 rear gear was decent for the task,for the street/tracks with long straits it woulda been to short.
The other used chain drive to custom built diffs from the original car so I could use the cv shafts I had on hand,it also worked well but the chain tensioning was fussy and anytime you had to do anything in the chain case it was pretty damn gooey.
With the location of the drive sprocket on the bike engine and the mounting angle to keep the oil pickup happy(hopefully...another matter to worry about)the engine will need to be fully behind the driver and well and truly in line.Not a great spot for weight distribution and if handling is to be the main goal I'd rather stick that lightweight engine up front and do it the easy/clean way with a standard diff and driveshaft.
I'd suggest going to gearing commander.com and looking up your engine,plug in the tire size you want to use(it works with car based sizes as well)substitute the sprocket teeth for whatever Miata ring and pinion you can get your hands on/available and look at the speeds/rpm in the speed charts it'll spit out and assess it to your needs.Hopefully that helps you decide,mucho easier to go that route than chain drive imo.
Cool project,look forward to seeing how it pans out.
Step 1: remove Miata diff from car.
Step 2: remove and modify rear cover/ mount from diff by cutting off mounts and rear cover
Step 3: remove and discard pinion shaft, gear, and bearings and ring gear. Seal pinion input hole in diff with frost plug.
Step 4: mount motorcycle rear sprocket to differential center section and reinstall in housing.
Step 5: cut flat plate in size and shape to replace rear cover/ mount and locate and support diff installed upside down with the pinion pointing to the rear.
Step 6 mount engine so chain lines up with diff and can enter and exit diff housing through rear opening.
Step 7: fabricate cover for chain that seals to the new front of the diff, enclosing the entire chain and a tensioner so that the differential oil lubes the chain but it mostly all drains back to the diff.
Step 8: profit?
