XS650 Crankshaft - ideas needed.

A friend of mine died recently, and before he left us, he mentioned building a fast Commando. His ideas were the same old - short stroke, extreme cams, big ports. I refuted that approach straight away because of the need for billet crank and strong cases etc. I've recently been thinking about the XS650 Yamaha crank with it's centre bearing, and had a close look at my spare set of crankcases. I think it might be possible to hang a bearing support from a 5mm chrome moly plate inserted between the crankcase halves. All it would effectively do would be to eliminate the movement outwards of the centre of the crank. My problem is that I don't know what machine is needed to profile cut the support plate without heating it, and I've cut that sort of plate before with an angle grinder , and it is very hard to machine. I don't know whether the XS650 crank centre shaft is indexed in the flywheels, however I believe it is possible to rotate the flywheels to make a 270 degree crank. I also believe that cams are available for motors with 270 degree cranks. Modified Triumph 650 valve gear will cop 10,500 revs, so it should be possible get a commando train to do likewise.
I'd be interested in any constructive comments, especially on how to machine the 2.5mm off the faces of the crankcase halves.

The XS crank is splined in the middle, 13 splines If i recall correctly. 277 degree rephase on stock parts. There is a bloke making a 270 degree phased spline shaft that utilizes 2 female center flywheels. Go to xs650.com forums and research to nausium about them. I went thru this years ago. Hughs HAnd Built in south carolina does rephased cranks to whole motors for the xs crowd.

I built the center supports in the two center main motors I did out of 7075. Jim

The regular hi end thin stem valves and race springs on 2S cam valve train can stay in control over 10.5 grand, so Cdo racy valve train ain't the weakest link rpm wise. Youtube xs650 staggered crank or such to see and hear a hand full of em. I really thought XS650 looked good in the ole Brit era style and thought that's what I'd get when I lost the P!!. Drove one around Houston a while to realize it was too clunky wimpy mundane numb handler so got into fun boats instead.

Theres some hot XS thread / link somewhere , to a race prep / tweek XS thingo , on Google . Somewhere . Threw a link on here ( Acces N ) once . in one of our great ' Debates ' .

Canae have it shuffling , Laddie .

Thanks for your help, found this interesting :

http://www.xs650.com/forum/showthread.p ... crankshaft

Jim, when you made the centre supports out of 7075 they must have been fairly thick. How were they attached to the crankcases ? On the link that I've attached there is a video of a 270 deg. crank XS650 running. A Norton commando done that way would not be all bad ? I haven't calculated what bore would be needed to make a 750 twin with a 74mm stroke yet, however I believe there was a Triumph Thunderbird 650 which had a 75mm stroke. I think that a 79mm bore with a 74mm stroke gives 725cc , and the piston diameter would still be limited by the cylinder spacing? When you did this exercise , was it successful or down on performance when compared with a normal 750 commando engine ? I believe a motor done this way, should have the potential to accept extremely radical cams without destroying itself.

http://api.viglink.com/api/click?format ... 7374725676

http://www.youtube.com/watch?v=KBUDG4T1 ... =endscreen

Another non 270' to compare, engine wise

http://www.youtube.com/watch?v=4t0R086BLyQ

Acotrel, is the point of this thread a desire to build a 270 degree center bearing supported commando motor?
If so it has been done before, by several people. Ans several different approaches.
And from what I remember, not worth the effort.
Something is always sacrificed in the effort, and it ends up being half hearted.

some rephasing shops

http://offsetcrank.com/index.html
http://victorylibrary.com/brit/offset-c.htm


https://www.google.com/search?q=norton+ ... 4APwqoGQAw

bwolfie said:

And from what I remember, not worth the effort.

Click to expand...

+1

It gets back to problem definition. Is there a problem, well no.

Much better to address crankshaft durability with a billet crank of superior material. All this discussion of re-phasing is a solution hunting for a problem.

If vibration is an issue with a solid mount frame then compromise and raise the balance factor to where the vibration is not so bad; use light weight reciprocating components.

Going down the path of adapting an XS650 crankshaft is pure folly. Introducing a crank phased differently than a 360 degree and introducing a middle bearing causes more problems - DAMHIK.

'Something is always sacrificed in the effort, and it ends up being half hearted.'

I tend to believe that the major strength of the commando design lies in its torque characteristic, and that moving power up the rev range is not supported by the valve train and port design. I do believe however that it is feasible to adequately support the centre bearing of an XS650 crank in Norton cases. I've previously used a short stroke top end motor in a Triton - it was much more powerful than a longer stroke motor of the same capacity, however much nastier to ride.

Oh My Yes on Norton torque advantage, which is acceleration advantage, that pulls great up to the horse power limits, which can be most pleasing to most disappointing, ie: runing circles around hi hp fat tired cycles and manic pilots when ever any leaning involved, then to be passed [after a good lead] in straights because the Commando just wouldn't pull more rpm in top. Comstock and a few others have revealed the long stroke rpm innate friction limits so even if crank could take 10K rpm the pull would decrease to make it more effective to just shift up. Seriously if you could spend what it'd take I've figured out a way to remove crank shaft limits inside space of Norton cases by complete jump away from anything ever tried outside of RC model engines. The only significant way to increase Norton hp is to increase its torque which means boost and special fuels. Then you need to study up on thermodynamics to dump the waste heat of half again+ more fuel burning in air cooled engine. Then must have some wits about avoiding narrow tire abrading and melting by a new style of ridding that never puts long sustained lean loads in one area of tire patch, which goes completely against the smooth riding philosophy that simply can't keep up with a tamed rubber baby buggy sling shot. Then ya run into the power pulse to tire hysteria big bang principle that big wide damped pulses help and smaller higher freq hits in rigid mounts unhook w/o warning when resonance vibes crescendo. Then need dragster design stance for anti-wheelie planting torque leaps better than the wheelie prone acceleration limited modern black box controlled moderns. Just saw video of Ducati 1199 vs top end Porsche in various contests to see it could only pull 10.25 sec 1/4 miles due to hook up and wheelie limits, but did beat the Porsche after 1/8 th mile neck and neck going 139 mph by 1/4 m. Only takes about 135 hp on 500 lb bike/pilot mass to break under 10 s 1/4 mile if it don't wheelie or just smoke rear. When they strap down a sports bike for drags it cuts about a sec off ET's. So how fast you old farts want to go before ya gone? I want under 10 sec 1/4's @ 140+ mph then more than 160 in opens in a few more secs.

Going by Jim's recent 97 lb/ft 86 hp dyno for base line power reality check, I can safety conservatively add 50% more in future Peel considerations to hook and handle up to 7000, but after that the calculations with drag only cam and exponential boost rise gets ridiculous if projected to 8000, which is well withing Norton proven capacity even w/o using the extra expensive racer upgrades developed last decade.

Sounds like theyre a oncer . http://hughshandbuilt.blogspot.com.au/2 ... d-and.html

Heres the page with the Yamahahahaa tuneing / raceing links / info . commando-crankshaft-porn-t8365-315.html?hilit=crankshaft%20porn

My finking is a steel three bearing crank , out of a Merc or Nissan . Probably a six so as to get a third rather than half a four . Problem is its easier to chop the block ( & fit the Norton Head ? )
than fart around. thouh a water cooled heads more use than a water cooled block . However a pushrod injun , the 711M Ford ( Formular Ford / Capri / Escort 1300 - 1600 ) Block only takes
Two Hours to bufricate by hand , after youve marked it out . Anyone worth their salt can cut it to 1/4 m.m. ( and get some daw* to face it & machine off the thrust bearing retainer :evil: )
never assume anyones brains engauged .
They throw the steel Nissan cranks in the megabuck histeric raceing Lotus Cortinas . The Chateram 7 is abot 168 H.P. on a ' Kent 1835 ' with DCOE 45s , sa a arf is 80 odd .

Now where were we . :lol:

Machineing up say a steel Mercedes crank to mate to the Norton Bearings , and throwing a flywheel into the works ( at the center ) & indulgeing in a bit of welding , could do it .

Probly better to whip down to the dockyard & chop a bit out of the propshaft of one of the Neucear Subs , as it is of high anto osscilatory material , and fairly strong . Machineing could be a problem .
A billet Commando crank with the counterweights in the correct locations , induction hardened ( tuftrided ) might be the cheapest option . If the Counterweights are adjacent the big ends and equal Ea. Side ,
the stress in the crank would be reduced . In fact youd configure the swine so the load osscilations are the most progressive . The Combustion being the greatest force . And to hang with a ' fixed ' Angle .
Set it to get the most progressive rotational loading . So it Spins FASTER .

Alan, if you scroll down to the pictures I posted here,I think this is close to what you are suggesting, although it uses Rotax cranksaft parts instead of XS650.

commando-crankshaft-porn-t8365-45.html?hilit=center%20bearing%20crankshaft

Elsewhere in the same thread, Jim Comstock has posted pictures of the center bearing crank he made from a VW diesel crankshaft, and how he fitted the center bearing plate into the (heavily modified) Commando cases.

Ken

Thanks Ken, I'd seen that thread previously however never investigated it. The idea of using coupled crank assemblies out of two singles is a good idea. I noticed the discussion about crankshaft weight. In 60s unit construction 650 Triumphs, two types of one piece cranks were used. The 650 Saint had the light shaft, and never performed as well as the Bonneville with the heavier shaft. An external flywheel might be necessary ? I've started to think about where I can get to see the internals of modern Japanese 450cc MX bikes. I'm fairly certain that I know an engineering shop capable of remanufacturing/modifying the required splined centre section of the crankshaft. The mounting plate for the centre bearing looks like the major problem. Has Jim Comstock had major successes with his bikes when they've had built-up cranks ?

See this page and scroll down toward the bottom to see the inner workings of a middle bearing and how it is done with a 500cc ultra short stroke. You will also not the middle bearing to support the cam.

http://www.accessnorton.com/commando-crankshaft-porn-t8365-165.html

This is Herb Becker's craftsmanship but we now know that there was no need to go down this path and it caused more problems than what we thought we were going to solve. As an example, going with a 180 degree crank caused unusual cam loading which then caused multiple headaches with the can drive mechanism; oil distribution to the journals was not always successful and crankcase breathing needed some extraordinary work to include a deep sump with a windage tray.

Again, this middle bearing 180 degree crank was a response to a perceived problem but we got the "problem definition" wrong.

Dances with Shrapnel said:

Again, this middle bearing 180 degree crank was a response to a perceived problem but we got the "problem definition" wrong.

Click to expand...

Perhaps we shoud also remember that Matchless thought that parallel twins needed a centre main bearing - and used a bolt-in alloy centre plate.
Caused more trouble than it was worth ?, and eventually went with Norton engines as a complete replacement engine.

Steve Maney engines seem pretty strong. ?

Unless we are going to ohc, or dohc, and ultra short stroke high revving engines ??

Rohan said:

Steve Maney engines seem pretty strong. ?

Click to expand...

Most definitely.

Rohan said:

Unless we are going to ohc, or dohc, and ultra short stroke high revving engines ??

Click to expand...

No, not even with OHC or double OHC. We took a Steve Maney 59.6mm stroke crank up to +10,000 rpm regularly. Want more assurance, go one piece, well designed nitrided billet.

Want more assurance, go with larger diameter main bearings but then you get in to main bearing speed limitations.

A middle bearing and different crank phase angles makes sense if you are building a production bike that will normally live at 9-10,000 rpm but with a Norton twin you are bumping into practical limits of max mean piston speed or valve train speed.

CRIKEY . :shock:



ITS BROKEN in HALF > :evil:



click on one for link / info .http : http://www.google.com.au/search?q=split ... 80&bih=856

MANEY CASES are probably more usefull , then a decent one piece chromemolly crank .

Jegwaw & Aston used to run ' Hares ' at Le Mans . to break the Mercedees / Ferraris etc .
as they couldnt stomache not leading . Jag would build a 4 / 5 bearing six , as theres Less DRAG . So Its FASTER .
After leading the feroaries to distruction it would ordinarrily blow up , with Valve Gear Failure .
Though I think Fairman / Shelby couldnt blow the Hare Aston . :lol: So it WON ! . thus this isnt a bad idea .
Leaveing bearings out .
the torsional considerations vary from the crank supporeted adjacent each rod , though .

Graeme Hill got 198 out of this old barge . on the Mulsane straight . 9 this is a bit like the Albany straight was :evil: :idea: )



not those metric ones , either . Whacking a few cylinders off of a Jag / aston donk wouldnt be to silly . specially if it fitted in the Norton !