This is from the Yamaha Racing Tips Manual.

447 rods came slotted from factory … 533 rods didn’t – Heiden sells them now

 

interesting about the bearings

 

 

256 cranks … 135mm rod … XS1, XS1B, XS2, TX650 … 22mm piston hole … 26mm crank pin

447 cranks … 130mm rod … TXA on, US and 447 Euro motors … 20mm piston hole … 26mm crank pin

533 cranks … 140mm rod … European 533 motors … 20mm piston hole, scooped crank pin 29mm

I first heard whispers about rephasing listening to my older cousins discuss how they could improve their old Triumph race bikes. There are long discussions over at the brit forums.

Then I forgot all about it.

Some years ago I bought an old Special from a bloke in the Hunsrück. Don’t really know why. On a whim. An ebay joke-bid. Low kms. Clean. Been sitting for some years . MMM. As usual. The missus wasn’t happy. As usual.. And it sat. As usual.

Then I put my back out. Time on my hands. Found the aussie 650 site. Yes Terry, I know. You didn’t force me to read. And it got me off my arse. Actually I like the Yamahas. The only new bike I’ve ever bought was a ’77 XT500. My daily rides are my SR500 and SRX600. Growing up with British bikes you learn to think that‘s all there is. Later I was introduced to Italian bikes, falling in love with a ’75 Ducati 750. And with Guzzi Le Mans. They all, however, share one thing in common. They’re Thumpers.

Anyway reading that site opened my eyes to the versatilty of these bikes, and reintroduced me to rephasing. This little gif said it all.

 

XS Standard 360° Crank – Parallel Twin

 

XS .. 270° Rehased Crank

 

Changing the crank set up so the pistons dont travel together. Rephasing doesn’t so much give a power increase. Rather it uses the existing power more efficiently. The torque wasted overcoming the inertia of having both pistons stationary at TDC and BDC is made useable

• power saving
• less vibration, the motor runs smoother
• better responsiveness
• slightly torquier
• if you do this weld the pins to the flywheels…balancing helps too

 

 

split crank…you want another #2 disc

 

 

and one of these 90° offset centre pins

 

 

#2 disc modified…dont forget to renotch for the cam chain gear locator … this is only necessary when doing a 277° rephase as the sprocket is relocated onto the splined rephasing shaft for a 270° and is positioned properly when re installed

 

 

to be assembled so

 

 

and so

 

 

to look like this

 

 

so right leads left…makes timing easier as you can use the original marks

 

Tolerances

 

Tolerances

 

Mmm

 

There are 2 ways of doing this
277°

• split the crank at the centrepin-rotate the right hand side 3 splines and press back together…277° rephase

270°

• split the crank, replace the 2nd flywheel from the right with a slightly modified 3rd flywheel (remove 7mm from the pin boss where the cam sprocket seats … Distance between centre flywheels is 54mm, unmodified flywheel is 25mm cam sprocket is 11mm leaving 18mm for the modified flywheel therefore 7mm is removed. This just happens to be from the end of the bearing mounting section to the bottom of the circlip groove.), use a 270° pin and press together 90° out of phase…270° rephase.

Was talking with Heiden a while ago. They were tying to explain their new method. I couldn’t exactly understand what was being said. What I did get was that they use an offset pin…do the 277° swap and a 3° offset pin to get the rest. Saves sourcing and machining the other crank disc.

These require a suitably modified camshaft and ignition system…a good time to consider installing a permanant magnet alternator. Originally I used a modified points plate

Yamaha missed a golden opportunity to produce a truly extraordinary motor by turning this idea down. Todays TDM.

Anyone interested in spending the effort wont be disappointed. Virtually all modern-day parallel twins are built this way.

Last time I went home I took with me the bits necessary to do this. Airport security and check-in were not happy. Complete 533 crank. Already set-up. Back home we get 447 motors. Rephased 256 cam. That hurt, I had around 8 or 9 of these. All got destroyed trying to weld them together. Except for that last one. What a waste. And a modified points plate. Fortunately I had my 2 year old with me and got to use his baggage allowance too.

My initial test ride was the Scenic Drive. This winds its’ way along the Waitakere Ranges west of Auckland, separating it from the west coast. A nice ride. Couldn’t get the smile off my face. Had to turn around and run again. This time taking the Piha Kare Kare road. To the beaches. In the old days this used to be gravel. Great for testing. What a blast. Couldn’t stop. Back. To Huia and Whatipu. Then. Shot across the city. South and East. Through Kawakawa Bay, Orere, down the Kaiaua Coast road, stopping for fish and chips at my cousins. And along the Coromandel Coast Road to the commune at Coro. There I changed the oil, got super wasted and spent the night. Next day across the Hauraki Plains, out to Port Waikato and down the back way to Raglan. Then time to go home. Had forgotten my poor son. Although he was with my family he doesn’t speak english. He was not happy. Ouch.

I was converted. My son was concerned.

Bits can be sourced from Daryl promctun@bigpond.net.au ph: aus 03-9330-4909 …  and Heiden -not on their site-u need to ask for these

Webcam will regrind your stock cam to any of their profiles, and for a rephase motor. Megacycle will do this too, they need to know which piston you lead with & what profile you want. See Heiden also for billet cams. If anyone in kiwiland is reading, contact orb, he will point you to a grinder.

The crank was split and reassembled using a press. Safe. Controlled. I have seen photos where this has been done on the garage floor. It can be done. I’ve seen similar in Africa, Sth America, Asia, India etc.

Don’t know about you. But. I like my eyes.

 

 

if these get loose i dont want to be in the way

 

 

parts of me wish i’d never seen these 2 photos..hugh says ..’The 2 picture you posted of a crank being split and pressed together are mine. I did that several years ago when no one else in the US was willing to build a crank for me, nor had anyone had any real experience doing so that they wanted to share. Low budget, and not a highly recommended method, but it worked and has worked for over 10,000 miles now. I do recommend welding the crank at all pressed joints though, as they tend to seperate at high rpm’s.’

 

Vibration was noticeably less. Was not an XS any more. Neither sounded nor responded the same.  Begged to be cut loose. Yamaduc.

Generally crank vibration depends on such-like: balance factor, stroke and rod ratio. She will run smoother the closer you get to a balance factor of 50 to 53%. I didn’t balance mine. Pressed her together. Mic’d her up and slammed her gently into the cases. Ride.

I want to do this to my ride here too. Wont tell the wife unless she notices. Time to start collecting the bits again. This will complement the 750 well.

Interesting. Was talking to Jerry Heiden this morning. Was saying he doesnt like, or more to the point, is not as fond of the 270° conversion. Too time consuming for the extra gain? Says he has been having problems matching crank parts. Seems there are variations in castings and machining between the years. Puts the balance out. To minimise the problems you need to get the extra crank parts from a machine as close as possible to your production run/engine nr. All for only a 2% gain. Or stick to a 277° rephase. He welds them up. But not fully. 2 x 1cm tab welds. Makes it easier to resplit.