Centre of flywheels and lateral centre of weight for a twin engine.

[Monkeypants]

I'm starting to think that perhaps the alignment of the three gyros is not critical.

Terry P tells me that Ken Horner shifted the engine over to get chain clearance with the wide tire on his Daytona bike and managed to win the Battle of the Twins with it. I believe that bike beat a new Ducati 1198 in the most recent Battle of the Twins, so handling must be decent.

I suspect that shifting the engine an inch or so to the right will actually improve the overall balance of the bike. This is just a guess based on the appearance of the Vincent twin engine which looks to have more mass hanging out on the left side than the right.

Howard said
"Why not make the frame/engine fittings wide enough so that you can move the engine off centre to suit various tyre widths including standard. A batch of spacers of varying thicknesses should allow quick adjustment, and if the offset causes problems you can simply go back to a standard wheel/tyre."

this is a great idea. I suppose the only drawback might be the need to make the swing arm in such a way that it can be kept on the frame centre line when the engine is shifted about. This would mean that the swing arm pivot tube would be narrower than full width to allow for the same bushing setup as the motor mounts, so the bearings would not sit out at the full width of the space between the left case and the g50 plate.

 

[Howard]

The swinging arm doesn't have to be central. Just wide enough for the widest wheel, then adjust wheel position with MORE spacers. You'd think I was a spacer salesman.

It's "just" a matter of setting the rear wheel in line with the front one, then moving the engine to align the sprockets. Sounds easy to me And no I don't want to try it first!

Could it be that engine position accross the frame isn't too critical (within limits) and they're only central for aest......... looks

H

 

[Monkeypants]

Howard, I think the swing arm needs to be centred for the rear shocks to sit true.

One other slight complication is the down tubes on the Egli Frame. They also attach to the engine and come off the frame at top. These would also need to be made extra wide and spacers used to allow for different engine postions.

Hearing that Ken Horner's bike has the shifted engine has me thinking "just go ahead and build it that way, it will work just fine."

I've also been rethinking the rear suspension on the Egli and considering using an alternate method similar to a modern bike such as a Suzuki gsxr. In the end I nixxed this idea as it caused the rear wheel to move back and increase wheelbase by about 3"

Here is an interesting set of facts on the subject-

Rear travel on a swing arm Egli- 3.5- 4" depending on rear shock choice
Rear travel on 04 GSXR 750 5.1"
Rear travel on 1949 Vincent Rapide 7"

Hmmmmmm

 

[Tom Gaynor]

I can hear the excuses already - "I'd never have fallen off if that engine had been centred".....

 

[Monkeypants]

I do like the idea of a built in excuse

 

[roy the mechanic]

my standard rapide runs a 130 x18 rear tyre, what's the problem, or are you just a greedy b'stard?

 

[Monkeypants]

I'm using gsxr rims, they are nice and light but the rear rim is 5.5", tire is a 180.

I might be a bit greedy.

 

[roy the mechanic]

with the limited power of a vin the "chosen" tyre will only result in extra friction, not reduced lap times!

 

[Monkeypants]

Power is not going to be all that limited. The engine is 1350CC, 10.5 to one, squish head, 38MM ports.
Terry P has dynoed 140 hp at the rear wheel or about 160 at the crank with the same crank and top ends, mostly the same other components.
The wide tire is necessary, in fact it will probably take much more of a beating from this engine than it would have from a 750GSXR, given that a GSXR only has about 50ft lb torque, this engine should have double that amount easily.

 

[roy the mechanic]

whilst i wish you well with your project- as in the words of the prophet-"dream on" steve hamel was very pleased to make 100 hp, currenty one of the fastest salt racers-check-out vincent 100 hp dyno run on u tube. regards, Roy.