GT750 Backwards!

[lamberhurst]

Hi Folks
I am proposing fitting a spare GT750 motor into a little Berkeley T60 three wheeler, and in order to make it fit I need it to run backwards.

Now the starter motor and clutch seem to be no problem to reverse, I'll go for a premix setup, electrionic ignition etc, however:

Will the alternator work backwards?
And will the gearbox work backwards?

Anything else that might not work?

Cheers chaps[/img]

[rngdng]

I don't see any way to make the starter work backwards, but I really don't know about the alternator. It should work. If you change the timing and make it spin the wrong way, it'll run; that I'm sure of.....all two-strokes will do that.
The gearbox doesn't care, but, of course, the final drive will run the wrong way. If that's what you want....I guess it's possible.


Lane

[Coyote]

Hmmmmmm --- sounds like an exhaust problem for sure

[Barry S.]

Several years KTM's were bad to run backwards but they just blubbered and would not run right, it's possible I guess but I don't know what all you would have to do.

[jkevinlilly]

Premix will not lube the crankshaft bearings properly.

Kevin

[tz375]

I'm not sure about that oil pump. I suspect it will pump in either direction. The starter will not spin the right way, but could be wired to run in reverse, but the starter clutch will be a problem.

Timing could be set at 24 ATDC to run the other way. Carburation and exhaust are direction agnostic - they could care less, other than pointing the wrong way of course.

[Suzukidave]

http://www.youtube.com/watch?v=nYIrwEYzcTo

[H2RICK]

Yep, those are the two BIG probs.....Premix and starter clutch.
As Kevin posts, there is no way to run premix short of stripping the crank and modifying a lot of stuff.
As to the starter clutch, you might be able to flop the hub and cover around......but it's been a long time since I've had one apart....

[pjmcburney]

Hi,


I can report with absolute certainty that a GT750 engine will run backwards - mine's done it a couple of times, once in traffic!

I was still experimenting with timing and had it just a little too far advanced. I accidentally stalled the bike and it 'caught' before the engine completely stopped...
The engine ran fine, though, and I didn't really discover what was going on until I let the clutch out and the bike shot backwards a couple of feet.

Yes, the starter clutch doesn't take too kindly to it and locks (obviously) and tries to spin the starter motor, backwards, but only when the revs rise above idle.
And, I'm no too sure how the primary drive would be work in the long-run - the axial thrust would be in the wrong direction and may affect other parts, the torque would be 'pushing' the clutch basket in the opposite direction on the shaft.

I'm with Richard on the oil pump, it's a simple cam-operated device and should work running in either shaft direction.

If might be necessary to machine up a mirror-image starter clutch, and wire the starter motor to run the other way, then I reckon you'd be well on the way to solving the problem.


Good luck
Paul

[H2RICK]

And, I'm no too sure how the primary drive would be work in the long-run - the axial thrust would be in the wrong direction and may affect other parts, the torque would be 'pushing' the clutch basket in the opposite direction on the shaft.

Good catch, Paul.....and a very important factor to consider, IMO. It would take some serious investigating and calculating to figure out how to overcome the problems involved with that whole thing.......if they could be overcome AT ALL.

[tz375]

let's think about that for a moment. The crank is located by the half moon clips, so that really wouldn't change.

The clutch is slightly different and uses a pair of flat thrust washers to take the side loads and that won't be much of an issue. The input shaft is located with half moon clips so the shaft isn't going anywhere in a hurry. In fact, the clutch nut holds the shaft and clutch drum together in position and with the thrusts in the opposite direction, the thrust would tend to pull the clutch out and off the shaft. That would put the thrust forces into one set of gears and would pull on one set. I'll take a look at which gears might be a problem.

The complex solution would be to get a new input shaft made with thread on the other end to put the side thrusts into the left case side through that small bearing.

Or just change to straight cut primaries and the problem goes away.

[lamberhurst]

Hi Chaps
Many thanks for the continued input, it really is useful. I'm happy with the starter clutch as I've stripped one and just put it together backwards and it works.

I tried an oil pump backwards, but that was less keen, maybe I'm try another pump, or run it actually in the cases this time.

Hmm, side loads, my feeling here is that it might just wear out a we bit faster somewhere, as there is a fair load each time you shut the throttle at high speeds, and that happens all the time.

If all else fails, and it's enough fun, I do have a straight cut primary set-up. Cheers All

[lamberhurst]

Oh, and sorry, why does my signature thingy say I'm on the driveway.
My bikes are all prety much on the road?

How do you change it?

[Suzukidave]

It changes the more posts you make

[tz375]

Interesting dave.

You're on the highway and I'm only headed to the on ramp


Maybe I need to post more....