Archive for the ‘head’ Tag

XS650: Rocker Shafts   Leave a comment

Been building myself a couple of XS motors lately. 277° and 360°. Have had the blocks together for some time – gearbox and crank, new bearings and seals etc.

Got round to stripping down an old XS1 head the other day. Just to check her out. Actually not too bad, some leakage around the top of the inlet valves, guides ok, valve stems straight. Cam ok. Rockers starting to wear a little. Decided to replace them and the shafts as I had a new set lying around and I have a new cam.

First you need to remove the 4 press fit sleeves that seal the outer-headstuds. You can simply bash these out but I wanted to remove the rockers and the shafts sit pretty tight (unlike the SR500) so I popped the rockerbox in the oven for a while.

The sleeves knock out easily with an 8mm socket.





Then you can get to the rocker shafts. These are tight.The puller I had rustled up for the SR500 wasnt up for the job but still had the longest 6mm thread I had on hand so I simply packed the outside with a socket and an old gearbox bearing and wound the shafts out.





Total time, less than 5 minutes once heated (if you heat use the oven and not a torch – no point in risking warping the box).

Slapped her back into the oven for a few minutes before inserting the new shafts and rockers. Dont forget to blow out the oil galleries first, and lube.

If wanting to reuse remember to bag and label: left/right, inlet/outlet



Posted May 29, 2016 by xscafe in Motor - Head, Uncategorized

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XS650: WTF?   2 comments

Can you believe this?

ebay item nr 131068858233 … seller: losser0


This is what he has to say …

very rare Yamaha 69 70 71 xs1 head, this is the one with only three bolts on the triangle valve cover over the left side exhaust valve, not a square cover with four nuts but round with three matching the other three valve covers on the engine, this head is in excellent shape, it has been completely torn down chemically cleaned all tolerances checked, the valve guides are in perfect condition,then the valves were lapped and then cleaned again, reassembled and ready to run, does not come with plug in photo,only used to cc combustion chamber after work was complete…. all, and I mean ALL threads are good and has no broken cooling fins, this is a really really hard to find part, and if your looking for one and you found this one you already know that, only a limited production the first few years so there almost imposible to find, much less one a beautiful as this, make offer option is there, but don’t be a NED! im not accepting 3/4 the asking price, thanks for looking and happy rides.

Very rare? … there were 32,069 officially produced

No broken cooling fins? … well I can see 2

broken cooling fin #1 – top left


broken cooling fin #2 – top right


This is an early one – shown by the oil return dams in front of the intake valves – although one of these has been smashed out.

oil return dam – left intake valve – smahed out


WHERE IS THE COVER? This is useless without the cover – see here

No cam. Or rocker gear.

And all for a $750 bargain.  … hmmm – for who?

What the fuck?

This chart is also listed in the ad …

hmmm – what possible good is this without a cam???????????


Who the hell is this?

??Dont be a NED??

Who’s the fucking NED here?

losser? – or is that loser? – or tosser?

Take a walk through the Hall of Shame.

But wait!! Another head. Same seller. Again no cover.

wow – a ported head, no cover – you are wasting your money buying this without a matching numbers cover … same as the one above


It gets worse. Take a good look. It’s the same head in both pictures. Broken top front cooling fins (left and right). Smashed out left intake valve oil dam.

Posted December 11, 2013 by xscafe in Motor - Head

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XS650: Finned Tappet Covers   Leave a comment

Picked up a set of these the other day. Nice. Sand Cast.

finned tappet covers

Found on

Look good mounted.

cast fins – mounted quickly

front left

2 of these weren’t machined to tolerance. Needed fitting.

Posted October 19, 2012 by xscafe in Frame - Design, Motor - Head

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XS650: Buying Heads or How to Throw Away Your Cash   Leave a comment

Our beloved XS650s have become pretty popular these last few years. They look good. Sound great. Ride well. Classics.

This has driven prices up. And created a market hungry for parts. A market of often inexperienced buyers. Unfamiliar with these machines. Unfamiliar with their idiosyncracies.

Slowly, backyard and enthusiast businesses are beginning to cater for this market. See for example, the Australian XS650 Club here, and JBM Industries. One of the main reasons I started this blog was to promote such endeavours. I have personal experience using most of what you find written about here. The other reason was to provide options to those useless crap new parts as sold by the supplier whose name rarely passes my lips.

Ebay has also provided a ready venue for bike dismantlers (often these bikes are worth a lot more as used parts than as complete machines). Many of these online sellers are straight-up. Others NOT.

One of my pet hates are assholes that sell Heads and Rocker Covers as separate items. If you buy these you are literally wasting your cash. You would do better going downtown and buying some homeless person a meal. Karma rules!

You need to be aware that Heads and Rocker Covers were machined by Yamaha as a matching pair. And stamped with matching numbers.

matching numbers…6198…found behind the oil feed pipe

mismatched cam bearing mount

mismatched numbers… J1954/9450

surfaces dont match

valve inspection port misalignment

single head … €85 wasted … and no cam

single rocker cover … $72.99 thrown down the toilet … at least it has the rockers and inspection covers

These sellers know very well that these should be sold as matching sets. How do I know? I have made it a point to let them know. Does it make a difference? Obviously not!

The current Ebay Hall of Shame:

Took me 5 minutes to find these ………

  • thebikebarn … head only, valves and springs, no cam … £60 wasted
  • Impala66k … cover only, no rockers etc … $72.99 blown
  • Impala66k … head only, valves, springs, no cam … $149.99 down the toilet
  • wilto54 … head only, no cam … $125 you may as well have given to a thieving banker
  • independent-cycle … cover only, rockers … C$44.95 don’t you need snow boots?
  • elkhntr6x6 … head only, no cam … $99.95 you should have given to the homeless
  • juan.fernandez … head only, valves, springs, no cam … $99.95 throw a party instead
  • motorcyclesalvation … cover only, no rockers etc … $25.49 you should have spent on new oil
  • bigfootedalien … XS2 cover only, rockers etc … $100 ??wtf??
  • bigfootedalien … cover only, rockers … $57 your ex could have done with
  • bigfootedalien … head only, springs, valves, no cam … $95 do you need a tyre?
  • thecyclebarn1 … head only, no cam … $79.99 worth of BC Buds you missed out on
  • thecyclebarn1 … cover only … $49.99 you paid for scrap metal
  • yourtrashmytreasure … head only, springs, valves, no cam … $195.99 better spent at a brothel
  • yourtrashmytreasure … cover only, rockers … $79.99 worth of condom insurance

Be aware that Engine Cases are likewise machined as a pair. And also stamped.

matching case numbers … 3062 … found behind the clutch pack

look here … 9426

Photos from Terry, Australian XS650 Club.

Posted December 16, 2011 by xscafe in Motor - Cases, Motor - Head

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XS650: OU/OW72 Heads   1 comment

Was discussing XS650 heads earlier. The major limitation to developing horsepower in our beloved engines (developing hp is a different topic to actually reliably and effectively getting it to the rear wheel).

Design limitations are found in exhaust port shape and cross sectional area-too large. Inlet ports could be smaller and would be better inclined downwards. The ‘Yamaha Racing Tips’ manual produced in 73 also recommends pocket porting-careful removal of material around the valve seats.


valve springs


The legendary dirt track battles between Yamaha and HD highlighted these limitations to the extent that for the ’76 season USYamaha brought in Tim Witham. The OW72 (I have seen these called OU72 and OW72-this would indicate 2 separate programmes-as far as I know this was a 1 off so I will, for continuity, use OW72) was developed. Didn’t stop the Harleys. Kenny Roberts lost the AMA Grand National Championship to Gary Scott. Time was short. Frames not properly set up. Shell Thuets eye for detail and reliability was missing too.

Still, from Roberts: ‘Best thing I ever rode’

Surprizingly Yamaha Japan had accepted Withams challenge to produce a new head. Probably as an R&D exercise for future 4 stroke engines. Kept King Kenny happy too. The head was cast totally different to the production ones. To accomodate the steeper valve angles ( racing: 56° production: 76° … inlet: OW72 – 43mm, prod’n – 41mm; exhaust: OW72 – 37mm, prod’n – 35mm) the heads were higher and the rockers shorter, enabling a lower rocker cover. Overall engine height was the same. Interchangeable with production motors.

The heads arrived from Japan in dribs and drabs. No ports, guides, valves, springs, cams. The engines had larger crankpins, improved pistons, rods,  gearboxes, clutches and deeper sumps. I can imagine the stress. Modern business practice could learn a thing or two from this about networked local sourcing for local consumption.



Racing combustion chambers were hemispherical, aluminiun, with steel valve seat inserts. Production heads had a steel cap cast into the alu and valve seats were cut directly into this.


inserts direct in alu head


XS1 heads showing the steel cap containing the combustion chamber … valve seats are cut directly into this


inlet port


exhaust port


Cycle World wrote an article about the development of these motors in their Aug 76 issue.

Original consensus is that 25 of these were produced. AMA homolugation rules required 1 complete bike and 24 engines and transmissions.

‘In order to be approved, a motorcycle must be a standard catalogued production model, one complete motorcycle produced, race ready, and at least 24 identical engines and transmissions must be available for inspection and purchase within the United States.’

There seems to be more (?). There is some confusion about this. It seems that Don Vesco produced some tuned heads back in the 70’s based on production heads and TRD valves. 650 Central sells your production heads CNC machined to tuner Lillies’ racing specs (these are your remanufactured production heads NOT ‘Yamaha’ racing heads).

70 hp motors appear to be relatively reliable. 75 hp motors not so.

I have seen several other attempts to address this problem, including homemade cast heads and machined billet heads. Of course, head modifications increasing available hp will expose shortcomings in other parts of the drive train, namely crankcases, crankshafts, clutches……………..How deep are your pockets?

Posted September 13, 2011 by xscafe in Frame - Design, Manaul - Literature, Manual - Other, Motor - Head

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XS650: XS1 Heads   Leave a comment

Kind of strange how you can do a job dozens of times and one day discover you’ve been missing the art. Blindly bypassing the finer details not directly pertinent to what you’re doing.

I pulled an old NOS XS1 head out of the mothballs the other day. Pretty clean. Next to it sat a used XS1 head. Well used. Started to clean it down. Slowly I became aware of differences. Mostly minor. But functional.


S650-0148## on the left … ???NOS to the left


I found 8 or so differences on the outside alone.

  • thicker, differently formed and more cleanly cast mounts and supports, front and rear on the used head
  • thicker tappet adjustment cover mounting face flange on the used head
  • artful blitz moulded into the unused head where the oil feed pipe passes
  • round cam sprocket tunnel on the used head, blocky cast on the unused head


inside the rocker cover


Multiple casting marks on the unused cover. Rougher casting quality too. What are the other differences?

  • cast ridge inside each tappet adjustment cover opening, used head
  • cast ridge between the bearing supports and the oil inlet cast, directly over the cam, used head
  • round brace for each of the inner stud holes on the used head are replaced on the unused head

They appear inside the cover only. Later models have a thicker wedge shaped form sitting over the cam. I assume these are for better splashed oil control. Seems the ridges above the adjustment openings would reduce oil draining onto the inside of the adjustment cover,lower leak risk. Those above the cam would allow oil to concentate and drip directly onto the cam/rocker mating surfaces.

I’ve seen the blitz on some early models and the blocky sprocket tunnel cast is standard so I assume the unused head is early but later than the used head. Why they were experimenting with lighter top mounts and relaxed oil control I have no idea.


XS1 head


Later models differ too.

a later head


  • Thick wedge above the cam
  • oil inlet node different
  • adjustment opening ridges intact
  • this later head has the 4 bolt front left cover


and outside


  • no blitz, but definite casting mark
  • adjustment cover flange thicker than the unused head
  • has the rectangular casting on the cam sprocket tunnel and the heavier front/rear mounts-cant see here

All the heads have the walling before the inlet valves-presumably to pool oil to the front so it has to drain past the exhaust valves into the cam chain tunnel. As they all have the feed channel to the exhaust valves. The bleeding holes from the breather box are also the same.

I guess there are other differences and other heads.

Apart from these differences the unused head seems to be useable. Wonder how critical those ridges are. Guess if the covers leak and I mark cam lobe surfaces I’ll know.

Posted June 3, 2011 by xscafe in Motor - Head, Motor - Oil

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XS650: Engine Temp. RHS   Leave a comment

A week or so ago CM wrote asking about operating temp differences left and right. Why does the rhs run hotter?


xsjohns, rip, engine temp recording…with cooler…left and right can run up to 30° or so difference


I’ve been out of town. Away from my computer. Exiled. Disconnected. But not deleted. Basically this is the answer I sent him.

Over the years I’ve heard many postulate. From aerodynamics to exhaust placement.

When you look at the engine design you see all the mechanical parts are focused to the right. As is oil flow.

Hot oil is sucked up through the pump. Slowed at the filter.

Mechanical action from the tacho, oil pump, primary and clutch all add frictional heat.

Aluminium is a good conductor. Heat gravitating upwards meets that from the combustion chamber and exhaust ports.

To the left we have the generator. In an air cell. Dry. Different thermal properties.

Allows the left to act more efficiently and effectively as a heat sink.

When Yamaha built the carbs they did so symmetrically. Jetting specs both the same. Each operating in different thermal environments. Built in imbalance. With appropriate feedback loops.

If you have adjustable needles it is possible to richen the right hand carb by raising the needle.


lowering the clip raises the needle…enrichening the mix


XSJohn, rip, ground needles with different tapers as a set. Left and Right. The canadian needles apparently are similar. Replace needle jets and jet needles together as a pair.


xsjohn, rip … on his needles … no grooves here, his production needles were grooved


John also built wings or foils to deflect airflow over the cylinders.


xsjohn’s wings…notice the deflector under the lower clamp


Others install oil coolers.


remote filter and cooler…so positioned the cooler will reduce air flow over the head


heidens side filter-cooler


Today there are many diagnostic techniques. Years ago I had an interesting conversation over too many beers with an Australian Naval NCO. Have never been fond of military types. Too rigid. Thinking actively suppressed. Later I was to learn the corporate world is, in theory, no different. In practise, a lot worse. Establishment meeting punk – the shock was mutual. He was a vibration analyst. Spent his time listening to machines sing. No different really to listening to your motor through a long solid screwdriver. He had a lot to say about the internal workings of Australia’s navy.

I would like to see a series of  Infra Red pictures of an XS650 motor running. Done in a resolution capable of  differentiating temp gradients within the 80-300° range. You would see some definite nodes on the right and fronts associated with temp assymmetry.

I come from the southern hemisphere. Live in the north. Apart from north and south there are other differences too. Here they drive on the wrong side. When you pull the bath plug, flush the toilet, water runs anticlockwise-the coriolis effect. I wonder what this does to other physical gradients Winking smile.