NS Dev
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| posted on 7/2/07 at 10:35 AM |
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Bike engine shaft coupling
I now have a question regarding a good way to couple an extension shaft to a bike engine drive output.
I have reconfigured the drive output layout on my new grasser. For those that don't know, it will be using a pair of Aprilia v twin engines,
mounted just behind the rear axle line. I need to get the drive downwards and forwards to the "diff" (actually a shaft with a cv joint
flange at each end).
The engine casings preclude simply taking the chain drive off at the required angle as they get in the way.
The plan is now to use a short extension driveshaft from each engine's output shaft, with a sprocket on the end, so the chain can run alongside
the engine (alternator/flywheel casing end) and down to the output shaft where the two engine's chains will both be driving to.
This then brings up the question of how to support the shaft. Obviously it will need supporting or it will bend, or trash the gearbox bearings or
both.
The plan was to support the shaft on a self aligning bearing in a bolted on housing with slotted mounts, and link the driveshaft via a 4 bolt flange
to flange coupling, basically tightening the coupling up first to align the shaft, then tightening the bearing mounting.
My worry is if the frame to which it is all mounted flexes under load at all, the output shaft will be under great strain and will load up the gearbox
bearings........
A flexible coupling would be nice but then the shaft will need two bearings to support it, and it is so short that there will not be room for two
bearings on it!
Any ideas or reassurances??
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
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locoboy
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| posted on 7/2/07 at 10:39 AM |
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Just a thought.....
Can the engine be used as a stressed member?
Is it possible to fabricate a bearing mount that will be attached to the engine itself?
ATB
Locoboy
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MikeR
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| posted on 7/2/07 at 11:45 AM |
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obvious question for me, why not move the engine forward a little?
(hmmm, didn't i say that once before????  )
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NS Dev
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| posted on 7/2/07 at 11:57 AM |
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Mike, engine would need to go forward a LOT, I did say before!! You need to get the chain out of the rear of the engine, and you need a long enough
chain for it not to be over loaded. The engines would need to be where I sit!!
Unfortunately there is no suitable "strong bit" of engine casing with suitable bolt locations in the area where the extension would need
to go, otherwise that is a very good idea.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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Peteff
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| posted on 7/2/07 at 12:53 PM |
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the shaft will need two bearings to support it
Would one wide bearing on the shaft do the job? Join the two engine outputs together and run a sprocket in the middle of them. edit that won't
work will it as you can't move them forwards, doh.
[Edited on 7/2/07 by Peteff]
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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NS Dev
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| posted on 7/2/07 at 01:03 PM |
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the engine outputs are on the same side of each engine, so you can't just join them together, that would be far too easy!!
right, here is a REALLY BAD piccy lashed up in 10 secs in paint of the layout and issue, top of the pic is forwards in the car, the engines are
black, the extension shafts are red, chains blue and final cv jointed driveshafts green.
Supporting the red bits without buggering up the gearboxes is the issue.
 
engines1
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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Peteff
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| posted on 7/2/07 at 01:13 PM |
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That's what I meant by join them together but it would mean moving them forwards. What about running your primary chains downwards to a jack
shaft underneath the engines so you don't need to extend the sprockets away from the gearbox
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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russbost
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| posted on 7/2/07 at 01:33 PM |
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Boy, you do like making yourself suffer don't you!?
Could you take the chain drive from both engines backwards to a jack shaft with similar sized sprockets to those on the engines, hence short chain
runs, run the jackshaft in bearings across behind the engines then do your final reduction gearing with a longer chain going down the LHS of both
engines to your driveshaft at the front?
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locoboy
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| posted on 7/2/07 at 02:29 PM |
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Can you make a 'cradle' type affair that utilises the mounting points on the 2 engines and fabricate a bearing mount coming off a suitable
point on the cradle?
How are you planning on holding the engines it the car anyway?
ATB
Locoboy
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NS Dev
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| posted on 7/2/07 at 03:13 PM |
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quote:
Originally posted by locoboy
Can you make a 'cradle' type affair that utilises the mounting points on the 2 engines and fabricate a bearing mount coming off a suitable
point on the cradle?
How are you planning on holding the engines it the car anyway?
Yes, that's pretty much the current plan. Coming off the rear of the main rollcage hoop will be a large "U" of 45mm CDS (same as the
cage) which will loop round the rear of the engines, running in a straight line for the width of the engines + a bit. A second rail will be run
parallel and above the transverse part of the "U", braced to it. The engines will be mounted off their swingarm and mount points, i.e. the
rear when fitted in the car, using laser cut plates welded perpendicular the the cross tubes, and I was planning on using laser cut plates off these
same tubes to mount the extension shaft bearing carriers.
It will be pretty robust, but was worried that 0.3mm flex could be enough to start damaging the bike gearbox........... I guess maybe I am worrying
too much!!!
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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NS Dev
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| posted on 7/2/07 at 03:19 PM |
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quote:
Originally posted by russbost
Boy, you do like making yourself suffer don't you!?
Could you take the chain drive from both engines backwards to a jack shaft with similar sized sprockets to those on the engines, hence short chain
runs, run the jackshaft in bearings across behind the engines then do your final reduction gearing with a longer chain going down the LHS of both
engines to your driveshaft at the front?
Almost exactly what I WAS going to do, and have seen done here:
however apparently the short chains expire on a daily basis during racing season, they just overheat and trash the bushings. Also the final drive
chain needs to be drag race chain, as it will have 310hp going through it with very high traction off the rev limiter starts in every race.
I was talked out of that idea by geoff berrisford at the autosport show, he says he has done both and the short shafts work best.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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Minicooper
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| posted on 7/2/07 at 03:38 PM |
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NS Dev,
Are your jackshafts going to be solid to the gearbox? there is a different type available that will allow a tiny bit of movement taking the strain of
the gearbox
 
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Bob C
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| posted on 7/2/07 at 04:32 PM |
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Nat, I've seen folk do the 'slight misalignment' thing by using a duplex chain - one on the gearbox output cog, t'other on a
cog on the jackshaft. The chain is the same size as the cogs & transmits the torque by shear rather than tension.
Bob
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NS Dev
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| posted on 7/2/07 at 04:59 PM |
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quote:
Originally posted by Minicooper
NS Dev,
Are your jackshafts going to be solid to the gearbox? there is a different type available that will allow a tiny bit of movement taking the strain of
the gearbox
Yep, that's what Geoff Berrisford makes, I suppose it might be the answer, but I don't like the 2 side by side bearings much, and I
don't like the £65 for just the cup that sits on the sprocket, especially as its a 14t one which I will then need to get specially made for my
engines by the same company that can make me a drive flange for a rigid coupling.
The force distribution is a bit weird with that setup too, the side by side bearings can't take all the load off the sprocket end, so that cup
must end up taking some side load, which seems a bit odd to me! must work as loads of grassers use them, but I was hoping a solid flange connection
would do the trick.
I don't mind paying up if its a better solution than mine, but if mine is ok alignment wise then I think its better........
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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NS Dev
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| posted on 7/2/07 at 05:01 PM |
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quote:
Originally posted by Bob C
Nat, I've seen folk do the 'slight misalignment' thing by using a duplex chain - one on the gearbox output cog, t'other on a
cog on the jackshaft. The chain is the same size as the cogs & transmits the torque by shear rather than tension.
Bob
Hi Bob,
was looking at that idea earlier, makes a lot of sense, as I can use a std output sprocket.
Only prob then is I would need 2 bearings spaced out a bit on the shaft to avoid the chain coupler taking the shaft side load (imparted by the output
chain at the other end) and there is no space on the short shaft for 2 spaced bearings.
2 side by side like on the other pic I can't see taking the load very well.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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dmac
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| posted on 7/2/07 at 06:56 PM |
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If you're planning to build it Engine-coupling-bearing-sprocket and you make the sprocket the same distance from the bearing as the coupling
flange then aren't the forces on the gearbox going to be the same as a normal chain puts on it? If that is correct you can reduce the forces by
moving the sprocket nearer to the bearing than the coupling flange, or have I misunderstood your design?
Duncan
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Minicooper
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| posted on 7/2/07 at 06:58 PM |
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Weird loads? what sort of side loads do you think a solid coupling will give you, it will given time snap your drive sprockets off.
An engine or engines will always move no matter how you try and restrain them, you just need a little give
David
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NS Dev
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| posted on 8/2/07 at 08:17 AM |
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yea, I guess you're right, that was really my concern, that the mounts will flex to some, very minor, extent, so I guess a larger cheque for
more off the shelf bits it is then! 
My £3500 budget is going to get stretched, I can feel it now!!!
Oh well, will still be one of the cheapest twins out there!
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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MikeRJ
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| posted on 8/2/07 at 08:24 AM |
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Nat, would it be possible to slightly stagger the height of the two engines so the shaft on the RH engine can run under the LH one? It could be made
long enough to have two reasonably spaced bearings then.
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NS Dev
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| posted on 8/2/07 at 09:47 AM |
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thats a good idea Mike, think I am going with the berrisford route now though, I have come to the "spend the money and follow the herd"
conclusion, too much work in not enough time to try and improve it!
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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