So, we have just another AF conversion, as I noted in my previous posting.
So Far.
Engine re-location - yes - 05 /13 YZ250 chassis to current model (?) YZF250 chassis.
Going by what you've said, the CS centre replicates the CS location of the original YZF engine.
You might have just been able to fit it straight in, with the centred hole case inserts. Perhaps, you may have had to make eccentric case inserts to achieve the CS location.
That might have resulted in the crank centre height being higher, or lower than it was on the 05 /13 frame. Certainly, the crank centre could be much lower than the OEM 4t engine.
With, or without a modified SA case insert, adjust ability for raising / lowering, the crank centre, could be achieved by 'slotted' lower forward engine mounts, and the front engine mounts - but that would be dodgy engineering, even with 'top hat' type insert washers. Better would be eccentric spacers into the cases - if you had enough meat / clearance to fit them. By machining the case insert hole larger, if the cases allow it, at the SA pivot point, you could possibly go to a larger eccentric 'difference'. All these adjustable mount points, could give you, at a rough guess, 4 x 4, to perhaps a 10 x 10mm (a very optimistic range) 'square' to move the engine around in. Off course, the head steady, would require adjustment potential , or a few different plates. From what little I can see, the lower and forward engine mounts, are 'plain' mounts, with no adjust ability - correct?
Something you could / should consider, is the use of engine mount plates - combined with a set of adjustable SA pivot case inserts. This would give much better engine placement adjustment potential, Plus, the ability to tune the feel of the chassis. Look to the variety of materials / thickness's of many mount plates used on a lot of the modern 4ts.
The last 2 AFs I made, were Gen 5 frames. A big improvement over the 4s. With those, I made the new, full cradle, to take removable plates. These were made for 2 friends of mine, who are / were Pro Level riders, that I've worked with for many years. So, they know how to develop / evaluate changes. And I know how to decipher their 'impressions and descriptions' of what a bike / each modification is doing. All up, I think we went through 10 sets of plates, in various materials, in various thickness's, and in various shapes. Each rider picked a different combination, as their 'best' setting. But, each rider gave me an equal rating of another set up as being their second pick. Engine mounting, can deliver considerable changes in the 'feel' and handling of a bike.
Something to be aware of, is to make the head stay mounts, so the top spars can still flex as intended - when viewed from above, the flex would be the spars widening. This is one of the major things that has been part of the evolution of previously far too rigid aluminium twin spar frames. This may be an improvement over the original aluminium back bone frame. You can right royally stuff up the handling with overly rigid head stay plates, and, indeed, create stress raisers, that will lead to spar cracking / breakage, if the bike is ridden Hard.
The fuel will be carried higher than the original 'saddle' type tank on the 05/13, with the existing YZF tank. Especially if you go to an aftermarket tank, to match the capacity of the original bike. You could, make a tank to make use of all that airspace that is available now that the 4t engine has been given the flick. Of course, the lower 2t engine, with no cams and valves, will have the advantage that the loss of those items (giro effect gone from those parts too), and engine height will deliver - plus the much lower carb, that will be a fair bit lighter than the 4ts FCR. The machined Smartcarb though, I'm pretty sure, will be heavier than the OEM carb. But, the , what I believe will be considerable benefits / improvements in the carburetion, will far outweigh a few ounces of added weight. I'm very impressed with the Smartcarb. Yes, without having used one - yet. With 'DFI' you could have a chance of fabricating a tank, to go into the area the carb currently sits - as a simple throttle valve / body, could be much smaller, and require little access.
I doubt that much weight savings will come from the engine swap , I think I've read that the YZ engine is a 54 / 56lb item. No effort has been put into the YZ engine to lighten it significantly in at least a decade, perhaps many more years than that. And, a conventional material chamber,and muffler, are often heavier than a full Ti 4t system. And, it would take the use of much thinner section / gauge aluminium frame parts, for the twin spar frame to be appreciably lighter than the incredibly simple / minimal parts count, 05 /13 back bone frame. There are far more sections / items to the twin spar frame, than the back bone frame. Perhaps, any real weight saving, may come from the swing arm, linkage and rear hub - the fitment of previous model YZF parts, has long been used to remove approximately 1.5 / 2lbs from the YZ250 2t. Plus the smaller tank / thinner plastics that 4ts have gone to.
Radiator re-location? Many would know of the Dubach Racing Radiator lowering kits - perhaps you might do that?
Or, relocating the radiators, better still, using a smaller single radiator, with a light weight fan, could offer a weight saving / useful weight re-distribution. Trials bikes use smaller radiators, some with fans, and believe me, that they are not moving through a stream of fresh air, and they can be under serious load, means they can get hotter than an MXer that is going relatively fast, with a good fresh air feed.
Perhaps you intend to eventually make use of the air space created by the lower engine, and put the exhaust in that spot? As noted on another thread here, 2ts Do Not require the stinger to be at the end of the convergent cone. Use of a long known technique for the stinger exit, could give you the room to have part of the chamber in the newly available air space above the 2t engine. The old 'Snake Pipe' build , at least part of it, could be put to use. And, you may minimise the 2t bugbear of easily damaged exhaust pipes.
You've currently used the logical idea of making the pipe and muffler mounts, to suit the OEM items - which should enable you to use existed aftermarket parts. That, I assume, would be the modifications to the subframe that I think I saw mentioned, though, you may also be considering the now common subframe lowering modifications that many do. A simple cut, shut and weld. Or, eventually, a monocoque construction subframe / airbox, in any number of materials
A mate of mine, early this year, put an YZ 2t into a 2012 YZF chassis - like what has been done here. And I'm sure there are quite a few around. His reportage of the difference between his expertly set up and fettled run of aluminium back bone framed YZs, has been "it's pretty much, much of a muchness". The key benefit, is he had something a bit different to what he had before, and even now, with a lot of development and set up, he feels that the original chassis, is in no way overshadowed by the YZF chassis. He, has, for quite a few years, run the YZF parts I mentioned above, that gave a useful weight loss.
Which brings me to the whole AF thing. An AF, can be made with tools as basic as a hacksaw, some files, and a drill and bits, with a TIG Machine to hand, or a TIG Welder that you can pay to do the 12 to say, 20 inches of welding. It's the most basic of 'engineering', and plenty of blokes in their garages do it - many, do a far better job than the companies that charge a small fortune for an AF conversion. Better tools and equipment, can make it easier to do, and, I favour replacement of the entire cradle over the cut and insert method, that is still done by 'noted' AF builders.
As for DFI - might I suggest you contact Athena, to see if they are intending to / have produced, one of their 'DFI" kits for the YZ. The upwardly pointed injector, high on the side of the barrel, is an elegant solution / alternative to the 'conventional DFI' set ups that 4ts and, I think, Evinrude / BRP - Rotax use - much of it licensed from Orbital. Athena's 'DFI' makes use of a 2ts flow patterns, without the need for complicated, heavy , expensive set ups that have been the norm. It also, is the sort of thing, that a competent engineer, could do themselves. That some regard a 'from above / in head DFI' as the Only DFI, is only through the fact that that has been the most common DFI 'solution'. And their lack imagination.
But, to repeat, we've an AF conversion here.
So Far.
I hope to see the results of further development, that will set this bike apart from a 'run of the mill' AF conversion.
Good luck to TCR in their / his endeavour.
