The Red Bike


A '79 Yamaha XS650 2FO . I have modified the rear to accept the KZ750B LTD M1 twin 18" disc brake hub . At the moment the front is stock with he the exception of the second brake . The rear is modified only by way of spacers to center the disc in the caliper and turning down the drive hub center to accept more common KZ650 #530 sprockets . The disc itself is a Honda CB200C turned down .200" to fit inside the caliper . The bearings in the rear had to be changed to accept the Yamaha axle .

I found a WM4 2.50" 40 hole rim attached to a Sportster hub and a WM3 2.15 19" 36 hole rim from some dirt bike for the front . Both rims are vintage Akront .The angle of the spoke holes is well within limits for adaptation to the Yamaha and Kawasaki hubs . All I have to do is polish replacement hubs and rims and deliver to the Wheelmaster .

The engine is at present a stock bore XS650 with a 277/83 crank . All else other than a stock XS2 left cylinder decompression valve remains either stock Yamaha or modified Yamaha parts .

That is the red bike as we know it at this time .



I have an alcohol engine in development for the bike . Probably next summer for that project .
Red ? That deserves an explanation . The frame was going to be painted because of 20 years plus of abuse so down to the metal it came . first in a hot tank and then by hand . I'll say this for Yamaha , whatever the paint or process what paint remained was removed by nearly a week in the hot tank . Commercial stripper wouldn't touch it . I had to resort to old fashioned elbow grease to get the remainder.
So where were we ? You wanted to know about red . I had gone the extra mile for a customer several times and he had access to powder coat . The original intended owner wanted red so red it was . A week after it had returned to the shop another customer shows up with the tank , painted rustoleum red .
The rear wheel shows up the next week in the hands of my machinist . The off side caliper was on my lift when I came to work days later .
Yet another customer heard of the project and donated some hoarded engines and goodies like the chrome engine covers and a couple piston sets .
Red it is save for a not very original but appropriate crossed tuning forks logo done in gold leaf destined for the tank . The one other embellishment will be a brass plaque in plain view . So many donated their time effort and parts to this build over the years that I can not in all good conscience let their efforts go unnoticed . Nearly 3/4 of the outside labor was donated . A fair half of the bright work was donated . The rear wheel complete was donated and created untold hours of modification to get it to it's simplest form here . The heavily modified front forks were returned to me after nearly 20 years by a fellow racer . The seat may need replacement even though it looks intact it belongs to a RD250C . A parts bike donated the tapered needle roller bearings for the neck .
An experienced Honda parts guru sifted through seals to get the rear axle assembly finished . A customer taught me 135 x 18 degree split point drill bit sharpening that made going through brake discs near painless . The Wheelmaster has offered to do the wheels . I know the wheels will cost me but just what yet I don't know . For those of you in my corner of the country that know Morrie and Jim I'm sure you'll understand that whatever the cost I'll gladly pay . Having done near daily business with Morrie for 25 of the 40 years I've known him I just don't ask any more .(yes I was part of the tide flat clientèle in the '70's ) I close my eyes , sign the check and have never regretted it . For those of you out here that don't know Morrie it's time you did . All those names and a few more will be on that plaque .
Okay so I avoided it till now I guess I have to answer . Yeah , it's red . Red and chrome to be exact . She wanted it red . Eventually she didn't want me but wanted the bike red . So red it is .


Over 1,000 Posts
Glad to see you around, Kop. I'm looking forward to seeing more.


I was asked elsewhere so ...

The rear caliper is bone stock 2F0 . I was careful to leave as much of the conversion stock as possible . With the un-modified KZ750B LTD M1 twin 18" disc brake hub and rim the Honda disc centers in the caliper once .200" is taken off the diameter . Now one caution , the disc was "marked" CB200C but I did not take it off myself so I won't swear to it . I'm told that the KZ305 is very similar also so ya pays yer money and takes yer chances . I did turn down one side of the rear hub and I believe it was the sprocket side . I'll know more in a week or so . As the project stands the disc is centered in the caliper and the sprockets are so nearly in alignment that I may be able to let it go . I did have to futz with spacers for hours but it fits . I should say almost fits . I'll have to pull the wheel toward the drive side about .250" to put it on center line but with all else falling into place I'm far beyond complaining. I had considered the modification of the front hub to carry sprocket and disc but going without the dampener was more than I or the gearbox and transmission could tolerate .



It's a xs650 limited by it's combustion chamber and center crank pin .
The best thing about the over bore was gaining room for quench area and even at that some careful welding to fill in some obvious voids in the chamber .
Some facts .
Alcohol has approximately half the BTU's by volume than that of good gas (not pump)
Alcohol has a greater latent heat of evaporation
Alcohol has a stoichiometric mix 6.5:1 as opposed to 14.7 for gasoline .
Most CV diaphragms and rubber parts as well as the carb bodies won't put up with straight alcohol.Even intake port erosion can be a problem .
The combustion chamber is steel on top and sides while the piston top is aluminum .
Alcohol burns much slower and it's behavior near relatively cool combustion surfaces is way different than gasoline .
So ...
toss the BS36-38's
Drop a significant sum on carbs and jets from Sudco (real good people)
Use an old Axtel mag or equivalent
Be prepared to get it wrong a bunch of times possibly torching a piston or two and get used to tearing into it on a weekly basis .
Fixed advance as much as 40 degrees
Jets you can see big screen TV through
Pistons running so close to the deck that at temperatures below 40 degrees the engine has to be heated just to provide enough deck clearance so it will turn over .
Over advancing the timing without enough fuel and "banging" the tune up and having the rod bearings "peen" the crank .
Having to carefully start the bike on gasoline then switch to alcohol .
Freezing the carbs in high humidity .
Having to nearly redesign the clutch or just spend the bucks at Heiden tuning . Might as well change the primary ratio while you're at it .
Adapt XV 700-750 valves , Buy Manley stainless valves or keep an eye out for the titanium valve guy on fleabay .
Hoos racing for the exhaust . They just get it .
Fishead brakes .
A stack of rear tires ,
And on ...
About 75 miles on a tank which drops drastically if you wrist it .
About 78 hp and nearly as much torque in one of the most sensitive to state of tune compilations I've ever owned .
I couldn't keep the thing together as a 360 degree crank . I had to twist the crank and cam . Crank is 277 degrees , You do the math for the cam I'm tired .
This was an outgrowth of the 70's Yamaha ,Shell Thuet , race program with the same caveat as then . Even with the odd crank (the object was to have one piston at or near max acceleration while the other was at minimum ) The center crank pin and it's fit to the counter weights becomes a loose pin in a hand grenade waiting for a place to happen at power levels over 80 hp . Shock load it a lower levels and see the same result .

Was it smart ? No,
Was it fun ? Not really the engine development was a drain on my time and resources .
Was it difficult ? Not really , it's just nutz and boltz .
How close was I at first get ? Left field ( more like Landsdown Street . If you savvy baseball if not nevermind )
Was it worth it ? heh heh heh . Well ok some days yes . Other days it's wtf was I thinking
So here we go again ....


so ...
8.1" = 205.740 mm half the stroke = 37mm Cr 500 rod = 144mm MTC-K1327H compression height = 24.8793 205.740 mm deck -205.8793 assembled height +0.1393 mm or 0.0054" Think I'm close enough to worry it into spec with head and base gaskets ? :)
8.1" is the distance frome crank centerline to top of the XS650 cylinder
The 1/2 kit price is $255.73 as these pistons were originally meant for a big arsed 1300+cc over bore of the Z1/KZ 903/1015
I think that beats the hell out of $400/pr don't you ?
Then again it took me countless hours to track down the information on the interwebz and on the phone
I am not soon going to forget that brain dead 20's something at Wiseco that told me the compression height was "proprietary"
Or Ross and J&E both wanting minimum orders of 8
Or the nameless ID10T that kept telling me " they have different pin diameters it won't work " no matter how many times I told him it was a CR500 rod with a different small end diameter " That's a two stroke rod " , well yeah , sooooo ...
So my machinist answers the email with the dimensions with " And what was so hard about that ?"
I get him on the phone and the voice of reason tells me " Dennis , not a whole lot of people think like you do . You're just going to have to accept that fact and learn to live with it . I have "

Get it from Mike or do it yourself the price difference isn't enough to quibble about . Any real savings will be from your machine shop of choice and or your assembling the pieces . I will stress for the novice that these discussions are all hypothetical until the assembly is trial fitted and the dimensions/clearances verified .
many thanks to Brett ,Greg , Dick , Bubba , LarryC , APE , Cliff @ MTC and Google Calc for the conversions . the original thread .

So the included valve angle of the Kawasaki 900-1100 up to 83 was 63 degrees . The included valve angle of the XS was 76 degrees for all but the OW72 head . This results in a 6.5 degree difference . The relative importance of this is that it allows for a continuous increase leading from the limited squish area into the combustion chamber . With the bore increase more area is exposed for modification . One of the things the Stock 650 lacked was little if any squish/quench area .

Just a little information on squish/quench area . It has been said that squish/quench area is a band-aid for poor combustion chamber design . On the other hand moderate but effective squish/quench area increases flame front turbulance during ignition cycle turn around through TDC and promotes slightly better scavenging during exhaust cycle turn around tdc at the expense of a short sharp pressure rise as the intake valve is opening . Originally thought to be an impediment to low lift intake flow further experimentation fount that the restance to the inertia of the the resonant intake charge tended to compress the charge prior to entry into the combustion chamber .
This eventually leads to a discussion in inlet valve/seat venturi/geometry at low lift and does not pertain to the present thought .
I just wanted to include that little bit of information as I'm sure most are aware that the intake valve is open a significant amount as the piston turns around during overlap .



Mostly for Matt because we have/had some of the same issues .

The original bore for the XS is 75mm . The KZ bore originally was 72.5 .
So there is only a difference of 2.5 mm between the two or 1.25 mm between the dome of the KZ and the combustion chamber of the XS . That is considering that the clearance between the original pistons and their respective chambers is for now unknown . I still don't have the pistons in my hand . Just these photos offered with an apology by Cliff @ MTC . This after he found them on a shelf , while I was on the phone , taken with the only thing he had and sent via email before we got off the phone . (I will never pass up an opportunity for a shameless plug when someone steps up and outside the norm . Cliff not only represents MTC he , well , he just gets it. )

Looks like I'll be doing a bit of chamber work also . As you can see from the pistons there is a significant squish band that is fortunately tilted several degrees. So from the previous post the angle leading to the top of the chamber created by the valve faces is 6.5 degrees . It should be relatively easy to blend the squish band on the piston to the squish band in the head . What will take a bit of advanced modification will be matching the dome of the MTC to the chamber of the XS , they are bound to be different .

Fortune smiles on the bold , or foolish . The valve sizes are similar to the point where .5 mm isn't going to make much of a difference . I may have made mention of this before . The slope of the back side of the intake valve needs to lead smoothly over the top of the edge of the valve cut out in the piston for as long as possible . The intake valve is opening well before TDC , on the order of .040" @ 30 degrees before TDC and well up on the ramp . Another 30 degrees (15 degrees camshaft) and the piston is dwelling at or near TDC for nearly 15 degrees ,7.5 degrees either side of TDC .

Okay where does this bit of esoteric information come from ? Experience , trust me here , the volume of the combustion chamber changes very little across these 15 degrees because it shrinks to a minimum just after TDC because of centrifugal and inertial forces . It averages out over this rule of thumb 15 degrees in practice .
Again , trust me . The only reason I mention here is as a prelude to the combustion process I'll mention later . Simply , max cylinder pressure needs to occur anywhere after minimum combustion volume . Think on that until we get there .

Now We're at or just after TDC and the valve is well onto the ramp . The object is to "dwell" the valve just slightly inside the the valve cut out in the piston for as long as possible . Initial valve opening may temporarily bury the valve in the pocket but the mean portion of the lobe lift should allow the valve head to track the piston down the hole as closely as possible for as long as possible . This creates problems . The intake can only be open just so long before a late closing point allows the inertia of the intake charge to escape . You can only open the valve just so soon because the combination of exhaust scavenging and the overlap quench spike begin to revert unburned and combustion byproducts back into the intake and poison the incoming charge . These two factors determine the intake duration far more than mechanical interference . Now we add to the confusion , total lobe lift / rocker arm ratio .
I'll not reproduce the math here and now but again , trust me . The inertia of a SOHC /rocker arm/valve assembly easily reaches into the several tons of force region . What determines how fast the valve can open is the limits of how well the assembly can track the camshaft without departing the cam lobe .
I've chosen titanium valves not just to say I have titanium bits in my engine but to allow steeper ramps without prohibitively heavy valve springs . To extend the valve and keep it near the surface of the piston as long as possible the last bit of lift has to happen fairly quickly as the piston begins it's acceleration away from TDC . Now those of you capable of visualizing these demands on the profile of a camshaft I commend you because It took me months to realize that what I've described is nearly square with the exception of the base circle and corners leading to and away from max lift . Fortunately one of the cam grinders I know and has been dealing with me for years understands that I'm a bit "different" and is working with me to provide a modification to an existing cam so that a completely new profile isn't needed . The work continues as I try and get the funds together for the pistons .

I now open the floor to your general insanity and specific ignorance . If not for you silly bastiches I wouldn't be attempting this throw back , full silly , irrational , nutjob build .



Split personality, I fake being smart
Interesting thread, glad I found it at last ;)
I was wondering about the big bore KZ pistons, been using modified 84mm XV 750 pistons with my CR500 long rod motors
I haven't bothered with oversize exhaust valves, just did XV inlets


happy I found it too . :)

Pete it will be a week or two before I get the crank and bore sorted then we'll see how the MIC actually fit .
I may get all four and just keep two around for whatever reason .



some crapy pics of the pistons ...



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...I reposted part of the aussie sight somewhere else and it was ready to paste

The late Phil Irving could hardly have wished for a more loyal disciple than Ron Valentine, best known in motorcycling circles as designer of the highly successful Westlake racing engines. More than 30 years ago nobody was quicker than Valentine to recognize the merit of Irving's proposed cure for the engine vibration that, in varying severity, had long plagued Britain's big four-stroke parallel twins, condemning their riders to mobile vibro-massage without the option.

The essence of Irving's brainwave was to replace the standard crankshaft with its crankpins in line, by a shaft with its pins staggered so that when either piston is at top dead centre (where it primary inertia force is greatest) the other is approximately at midstroke and generating no primary force. This arrangement considerably reduces the engine's maximum inertia force, and thus vibration - though not by so much as the 50% one might suppose, as we shall see later.

A second benefit stems from the fact that when either piston is stationary at tdc, the other is moving at or near its maximum speed and thus contributing to the flywheel effect, so that the flywheels themselves can be a bit lighter for the required level of smoothness. It was this consideration that dictated Irving's original choice of 76° for the spacing of the crankpins. For with that angle - given that the centre length of most connecting rods is near enough four times the crank radius - when either piston is at tdc, the "big-end" angle (con-rod to crank) in the other cylinder is a right angle, hence piston speed highest.

To their shame - and perhaps because of an irrational horror of uneven firing intervals? - the manufacturers of even the most vibratory parallel twins showed not the slightest interest in Irving's proposal despite the relative ease with which they could have converted an engine for test by twisting the crankshaft and camshaft, adjusting the spark timing and fitting a second carburetor where necessary to obviate a mixture bias from overlapping induction phases.

Following the demise of the British industry, it eventually fell to Ron Valentine (and his assistants, including mathematician Tom Oliver) to prove the soundness of Irving's scheme when (three or four years ago) they completed their second 76° crankshaft for Steve McFarlane's 952cc (80.5mm x 93.5mm) BSA parallel twin classic racing sidecar outfit. Stretching both bore and stroke of the original A65 engine had aggravated its vibration to the point where the crankcase was in danger of disintegration.

Machined from a solid bar by Dave Nourish, Nourish Racing Engines (NRE), in his Oakham workshop, the new shaft proved to require balancing (to a factor of 50%) as if it were two separate flywheel assemblies joined together. Once that was done, the engines character was transformed. Gone were the frantic shakes. Instead, said McFarlane, there was a slow and lazy throbbing sensation as - to the accompaniment of a pleasant off -beat exhaust lilt, reflecting the 436°/284° firing intervals - the revs soared to 7,000 RPM and the more powerful 1000cc - 1200cc Imp engined outfits were humbled as the BSA won its heat in the Snetterton Race of the Year meeting in 1990.

Encouraged that his and Nourish's sacrifice of valuable time and effort had proved worthwhile, Valentine decided to follow his hunch that a 90° pin spacing would give even better results. True, the instantaneous contribution of the descending piston to flywheel effect, while the other was at tdc, would be slightly reduced because it would be just past its maximum - speed position (big-end angle only76°, not 90°) but there would be two overriding benefits - one to mechanical balance, the other to the smoothness of the flywheel effect.

Balance would be enhanced because the top and bottom dead - centre positions of either piston (where the secondary inertia forces act upward) would coincide with the midstroke positions of the other, where the secondaries act downward. Thus those forces would counterbalance one another at the cost of a small rocking couple.

As to the moving piston's contribution to the flywheel effect, this would be the same whether the stationary piston was at tdc or bdc (the big-end angle being 76° in both cases). With the earlier 76° pin spacing the ideal "big-end" angle of 90° was achieved only when the stationary piston was at tdc. When it was at bdc and the moving piston was rising, not descending, the angle was only 62°, so the effect was not constant but fluctuated at high frequency. Of these two benefits in favour of 90° pin spacing, the absence of unbalanced secondary forces is clearly the more significant.

When the subject of "cranky cranks" was discussed in Motorcycle Sport three years ago Charles Bulmer suggested that a 180° crankshaft would be even better provided its primary rocking couple were eliminated by means of a crankshaft-driven contra-rotating balance shaft. Quite so, for an engine so designed from scratch by a manufacturer, as with some Hondas.

But what Phil Irving was proposing was the least possible alteration to already established mass-production lines to overcome a serious deficiency in British parallel twins. Given a clean sheet of paper, he had long since shown his own preferences for twin cylinder four strokes: designed just before the second world war, his 600cc Velocette Model 0 vertical twin was a model of smoothness; like its racing stable mate, Harold Willis' 500cc super-charged "Roarer", it had contra-rotating geared crankshafts and shaft drive. Later, his postwar 50° V-twin Vincent Rapide ranks as one of the industries greatest designs.

Again drawn by Ron Valentine and machined by Dave Nourish, the 90° crankshaft has four flywheel discs and is a replacement for the conventional (360°) shaft in one of Nourish's Westlake powered classic racing 500cc NRE Triumph based pushrod parallel twins. Since the total upward inertia force with the standard crankshaft occurs when both pistons are at tdc together, it might be supposed that separating the tdc positions by means of staggered crankpins would halve the force and double its frequency, regardless of whether the stagger is 76° or 90°. Not so as Mr. A Archdale was at pains to confirm in the original "cranky cranks" discussion, although the individual tdc forces in each cylinder remain one half of the total for the 360° shaft, the total upward force occurs when both pistons are level and their cranks equally disposed each side of tdc, i.e., 38° before and after tdc for the 76° stagger and 45° for the other. The point one must grasp here is that - although one piston is moving upward and the other downward when they are level - their inertia forces are both upward, as can be seen in the accompanying curves, where both points are above the base line. Note too that the 45° points are slightly lower on the curves than the 38s, indicating a slightly lower force in favour of the 90° pin spacing.



The net result, as calculated by Valentine and confirmed by Bulmer, was that whereas the 76° shaft reduces the maximum upward inertia force by a useful 32%, the 90° shaft is an altogether better proposition with a reduction of almost 45% (see Tom Oliver's graphs)

The first tentative outing for the "90" was at Mallory Park last May, when Martin Smith found the engine considerably smoother than standard. It was also 4-5 bhp up in power as a result of new cam profiles - Valentine had replaced the Triumph type radiused tappets by experimental roller cam followers, since they are less dependant on copious lubrication, and had taken the opportunity to up rate the cams.

In the Classic TT Robbie Allen was in the hot seat and finished 10th in the 500cc race, eighth in the unlimited. However, in common with most classic racing participants, Robbie is well over the win-or-bust age range and the object of the exercise was not to win but to compare the modified crank with the standard one. Riding apart, the fact that Robbie's bike finished well ahead of a brace of standard NRE's reflected the cam changes rather than the pin spacing. Subsequent bench tests at Oakham gave a repeatable 57-58 bhp at 9,000 RPM and a one off flash reading of 62.5 bhp at 9,800 RPM.

Since riders with an analytical flair of a Geoff Duke, John Surtees or Peter Williams are as rare as elephants teeth, Nourish had intended to try the machine himself at Jurby airfield but was foiled by atrocious weather. Before the final outing (to the Manx GP) however, he took it to East Kirby airfield, in Lincolnshire, for assessment and was delighted by the extent of improvement. A few other invited riders were equally impressed. Alas in the Island, Allen was troubled by a few unrelated problems - valve float and missed gears - before an ignition failure in one cylinder brought about his retirement in the third lap. But Nourish is now so hooked on the new crankshaft that he is planning to market complete 90° NRE engines.

Conversion kits for other engines, however, would not be a commercial proposition. Each 90° shaft, says Dave, is suitable only for the precise reciprocating weights of its particular engine - and con-rod weights, for example, vary enormously (the top portion is the critical end), so the balance holes in the flywheel discs must vary too. There are other relevant variations and the net result is that machining a shaft to suit a particular engine would take too much costly time.

Engine vibration is unpleasant in touring machines as well as racers. Some tourists may dismiss a mild case as inevitable provided they don't make day long trips - or try a BMW boxer and realize what they are missing. In racing, however, it is unforgivable, especially in long distance events such as TT races. It can cause not only metal fatigue - breaking anything from brackets to engine plates - but also rider fatigue. It can impair engine performance by seriously upsetting carburetion. And, at best, it must absorb a modicum of power. Phil Irving now has another disciple in Dave Nourish. Only 10 more to go for a full apostolic set!


And a hearty thanks to the xs 650 club of Australia for the info as it was lifted directly from their site
a great resource and I highly recommend you all visit and contribute .



The rephase distributes rather than concentrates forces . With the exception of side thrust near all of the 360 degree cranks forces are in a vertical plane . There is a secondary rocking couple induced by the alternating left right firing sequence but that is actually an order beneath the primary forces .
The rephase was initially used to increase available traction , in steam locomotives . A timing arrangement that allowed for application of force to one side of the locomotive and then delaying the other side for 90 degrees with respect to the primary and then allowing for 270 degrees "rest" to allow recovery of traction .
Fast forward to the English and their venerable vertical twin . Their cranks were almost exclusively bolt together although tapered fit and key'd . As modern fuels crept in to the mix higher and higher compression engines became possible due to advanced alloys . The crank became not only the weak link but a source of annoying vibration .
Enter an old idea with a new purpose . I'll spare you the force diagrams .gif and leave those as a homework assignment or for some member to post following this monologue . To reduce the inherent vertical impulses one piston was to be at TDC whilst the other was to be at maximum acceleration which is when the connecting rod and piston are perpendicular to the stroke (90 degrees) . This happens to be near our 277 degrees . With the reduction of vertical forces by way of distributing them throughout the cycle and consequently having portions of those forces happily cancel each other out we have by subjective definition a "smoother" rotating and reciprocating mass .
Does it make more HP and Ft/Lbs ? Not necessarily . The bore and stroke have not changed nor have the combustion chamber dimensions . So what is the real performance benefit ?
Honestly it accelerates quicker because it isn't acting against itself throughout its cycle . It acts like a much lighter crankshaft and well it should .
Longevity . It isn't beating itself to death just to idle . It isn't prone to the wild imbalances of a secondary rocking couple that is at the mercy of combustion processes rather than mechanical timing .
Mean repeatable maximum BEMP . meaning the ultimate breaking strain of a rephased engine is much greater than that of a 360 or even 180 degree engine .
Specifically the limiting factor in our engines is the center crank pin . Anything we can do to keep stresses off this one area will add to the longevity of the rotating and reciprocating mass .
Traction . Back to the original reason for the phasing . The reason I used it was specifically to keep up with a well known 45 degree V-twin. There were tire sizes and sprocket ratios unavailable to us with a 360 degree crank because we were hitting on the same spot on the tire every time around !
This uneven firing order also allowed the tire and chassis to recover in between power impulses allowing subsequent impulses to gain traction .

Since I'm sure you have all had enough of this ...
More Ft/Lbs ? maybe a little
More HP ? Again maybe a little
But both due to the reduction in vertical forces
A fair impersonation of a lighter crank ? Absolutely
More reliable ? Apples to Apples , yes
Able to leap tall buildings in a single bound ? YMMV



Split personality, I fake being smart
The 76 degree Triumph was to lose most of the rotating mass, less vibration was only a happy consequence
90 degree crank is better to reduce vibration (Yamaha used it on TDM850)
The 277 XS 650 crank is close to optimum for lighter flywheel.
It was a major thread at XS650 Garage about 7~8 yrs ago
If I ever get back to it I stripped my 840 re-phased motor and started lightening individual flywheels
BTW, I used to work with a guy from Yamaha, Kenny Roberts works OW motors made 100HP but center pin would either separate or fracture if welded

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