Reverse Cylinder

[Reid]

Figured this area would get more useful replies than the General forum, if it needs moving then mods, feel free.

I'm looking at starting a project bike, something for my own enjoyment and to test my own skills more than anything else and after coming across a TZR 3MA have been thinking about the complexities and practicalities of reverse cylinder designs. I've seen some RD and RZ conversions and basically have a couple of quick questions about them:

What are the main benefits of a reverse cylinder design?
Why does the 3MA use it?
What are the drawbacks?
Is it practical (for riding more than installation)?

The way I see it, I can have something 'unique and different' (after seeing quite a few streetfighter builds I'm hoping this isn't always synonymous with shit) with a real tidy way of having underseat exhausts (as opposed to a huge plumbing mess). I'm presuming I'll save a little weight with shorter exhausts whilst creating less centralised mass (battery and other bits having to be moved about) an causing a load of other headaches. The build so far is going to be a single or parallel twin engine, four-stroke, between 350-600cc - just in case that's relevant at all.

More than anything - I'd just like some information about the the why of the reverse cylinder design more than the how.

[jjdugen]

Only two little problems. The steering head stem gets right in the way of optimal carb/injector/airbox placement and a row of very hot exhaust pipes contained within the chassis will cook the rider. You can shield the exhausts and probably shoehorn an induction system and it has been done, but with little benefit and major engineering costs.
However.... If you get really radical and use a hub center steered front end, you will have acres of room for a proper airbox, exhaust placment and shielding is not to drastic an engineering excersise.
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[Reid]

Hub centre steering would be way out of my league so I'll have to leave that... for now

So how does the 3MA deal with these issues? I know the carbs are ridiculously low to the ground to deal with headstock issues, the exhausts flow around the actual seat and have a simple shield - is there anything more technical than that (fitting carbs so they don't foul the steering and making sure the exhausts aren't likely to melt you)?

I'm still kind of unsure on the benefits reversing the cylinders achieves. Are there any apart from being unconventional for the sake of it? I don't want to end up with a pure cosmetic showpiece, I want there to be at least a little logic to anything I attempt with it

[Reid]

[Kickstart]

Hi

Useful airbox is probably the hardest part (at least on a 2 stroke you have more flexibility on where you mount the carbs). As Chris says finding a suitable doner engine will be a pain, and then you have the fun of custom camshafts to sort the valve timing out again and have appropriate profiles for them to open / close. Even with something like a GPZ500 (central cam chain) I suspect that the sprockets on the cam shafts are slightly offset for clearance.

Cagiva managed to have under twin seat exhausts on the early C9 Freccia 2 stroke single, and that came out in 1986. Next thing girder forks will come back into fashion .

All the best

Keith
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[Kickstart]

[G]

[Reid]

Okay - in that case I'll ditch the idea, just came to me the other night and I thought "why not?". Thanks for talking me back to reality

Out of curioisty though, I'm still a bit unsure of the benefits it'd pose - is it just the fact it opens it up to induction and cuts a bit of length/weight out of the exhaust?

[G]

Have a look at the YZF - the short exhaust length is actually a problem with the design so they have built in an extra loop to make it longer.

https://www.supermotoaus.com/gallery/d/20621-2/2010_YZF450_1.jpg

[Kickstart]

[Frost]

Most bikes tend to lean the engine forwards making the engine not so tall and allowing it to be move forwards without getting in the way of the front wheel. It also allows the throttle bodies to be closer to vertical.

Honda have gone for a reverse on their moto3 bike, but that requires the engine to lean backwards.
https://www.autonewblog.com/wp-content/uploads/2011/06/nsf250r_engine-sfoglia-la-gallery-336x224.jpg
https://www.motodesign.org/wp-content/uploads/2011/06/Moto3-2012-officially-unveiled-the-Honda-NSF250R.jpg

[kestrel]

Triumph 650cc engines quite often had the heads reversed in the 70's, some as custom mods and others in twin engined drag bikes. Twizzle down in bournemouth reversed the head on a GSX1100 on his bike known as 'The Beast' pic here :-

https://www.myspace.com/twizzlecustoms/photos/31079#%7B%22ImageId%22%3A31079%7D
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