PMA (kick only) + Rephase + Big Bore = Practical? (Cheney rigid project).

[Jeeter]

My daily rider is a kick-only XS and I've never, even once, wished that it had electric start. They are easy to kick and, if tuned right, will always fire on the first or second kick. I do not have a big bore or high compression so your mileage may vary.

I also have run a 277 re-phase and found it far more "buzzy" than the 360 when going down the road. The 360 crank I'm running now is smooth by comparison. That's not to say that it is actually smooth, because there is no way to make a non-counterbalanced parallel twin run smooth. To me, the 360 has a rhythmic vibration where the 277 had a harsh buzzy vibration. That said, I still prefer a 277 motor to a 360 just because it sounds better.

I have never run big-fin jugs and I've never had the motor overheat. So, it's kind of like the solution to a problem that doesn't exist. I also don't live in the desert so, again, your mileage may vary.

Excellent information, thank you very much.

I've watched a number of videos of people kicking over XS650s. They seem to be (dare I say it?) pretty easy to kick over, as long as they are properly tuned. Even though I stand at a towering 5'6" and come in at a massive buck-seventy, I don't think I'll have much problem.

NOW, AS TO THE PRACTICALITY OF THIS CONFIGURATION:

Ok, I've read a bunch of tech stuff in the tech section by this point. It's funny, half of everyone that had an opnion on the 750 (or other larger bores) said that it increased vibrations (offensive vibes, that is). And half of them said it decreased offensive vibes.

What seemed to make the most sense to me (being as ignorant as I am on the XS650 package) was to retain the 650cc displacement, keep the static compression down to "91 octane friendly" levels, and properly tune the engine (jetting, ignition timing, carb syncing, and so on). Do a clean-up on the ports (simply matching the ports to the gaskets .. aka "gasket matching" .. is usually enough), pipes, carbs, cams, ignition, call it done. Oh, and the PMA/Kick-only setup.

My guess is that increasing the power-to-weight ratio will be a far more effective way of going faster with this engine package, unless reliability is of no concern. Hopefully I can get this bike below 350 pounds soakin' wet. If Mert Lawwill could get his iron cylinder, steel side cased Harley down to 309 pounds (wow!), I should hope that I can get this thing down to at least 350.

 

[TwoManyXS1Bs]

Great! Sounds like a plan. Go with the 650, iron it out, find the weaknesses (as only personal experience can reveal), then plan the 750 upgrade knowing what you're after and what you're getting...

 

[scabber]

That is a good way to go the stock 650 is a good motor. I'm putting a stock compression 650 together for my other bike. I got to go with a Shell #1 cam and new RD springs.

 

[Jeeter]

Yea, I think that the "baby steps approach" is the best path here. To be honest I think I'm going to have so much fun on this thing that I'd be pleased with the warmed-over 650cc engine I described above for a good while. At least enough time to figure out what it is I actually want out of this thing. This bike is going to be a little unique, there are some unknowns ahead. So engine mods that work for (whomever) may be total crap for my application (power delivery and such being taken into consideration here).

I just had to go through the learning pains with this engine. Admittedly there is a LOT of drool-worthy trickage out there for the 650. It's all too easy to go nuts with the engine mods with the massive availability of tech and aftermarket goodies for it. It took me a few weeks to get over the "Holy Shit!" affect once I dove into this engine package and I discovered the amount of support it has.

I may not even opt for more displacement, in the end. I've read testimonies from folks about how the large bore setups do not provide the expected torque or top end increases. Question then becomes one of return on investment. It seems some people insist that a well tweaked 650cc can actually perform almost as well as the 750cc units. There's no more top speed since the engine's rev limits have not been improved. It's more about accelleration, sound/feel, and of course almighty bragging rights.

So I think I'll attempt to stay at 650cc and sane compression levels at first. Cams, pipes, carbs, some gentle port-matching, ignition should be a great place to start.

This leaves more money to put towards oiling system issues (I'm still working out how exactly I want to set up the oil filtering system, external? - internal? - Both? I have some ideas as well as some interesting gear by a company called Canton that I'd like to try to apply to this engine). The clutch seems like it can become a project all on it's own, as well. The stuff in the TECH section on the clutch is very informative and inspiring. So there's other stuff (oiling, clutch, other?) rather than just power production that needs looking after.

Rephasing is still on the table. That sound! I mean, talk about taking me back to 1976 at any given Friday night at Ascot! That snarling, pissed off "Jap bike" sound that punched through the other engine's roar as the bikes lined up at the line. It sounded like a roaring predator amongst unwitting prey. The look on the Triumph rider's face as a rephased XS pulled up on the line next to him, as if he's saying inside of his helmet "what the hell is THAT thing?" as it roars and snarls, it's rider calmly looking straight ahead. The Triumph rider attempts to respond with a few blips of his own throttle, attempting to reply with his own intimidating roar. The overwhelming feeling of "You ain't got none!" sweeps over the stands as the Triumph rider revs his seemingly anemic powerplant. The XS rider tosses in a few more blips, and the Triumph runs away like a frightened puppy leaving a trail of piss in his wake.

Er something like that....

So I don't know how much I would need rephasing, I suppose it all depends on how one defines "need" ...