Archive for the ‘Motor – Head’ Category

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: Rocker Shaft Removal   Leave a comment

Have been cleaning up a couple of SR500 heads. Ready for porting, new valves and rocker shaft bushing. Needed to remove the shafts. Rooted around in the odds’n’sods bin.

  • 2 x pieces 6mm threaded rod
  • 1 x long open ended 6mm joiner
  • 2 x 6mm nuts
  • 1 x 6mm dome nut
  • 12 x large 6.5mm washers
  • 1 x piece duct tape

5 minutes. No cutting. A perfectly good 6mm slide hammer.


Screw into the rocker shaft. Off you go.


Same principle for the XS.


XS650: Tappet Covers   Leave a comment

Was ratting round in my spares shelves/boxes. Found a 3-bolt tappet cover with slots instead of bolt holes – wtf?

Then found three more

Ah so! Early XS1 covers. No O-ring grooves. Gasket pure.


tappet covers outer

tappet covers, outside … early 3-bolt, slotted, gasket, … 4-bolt decompression cover, XS2, holes, gasket … 3- and 4-bolt cover, holes, gasket … 3- and 4-bolt covers with holes and an o-ring groove cut – 1 set alu, 1 set chromed



tapppet covers inside

tapppet covers inside … here you can see the flat gasket faces and the grooved o-ring covers





Posted October 15, 2015 by xscafe in Motor - Head

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XS650: Viton® Valve Seals   Leave a comment

Had in mind to tart up one of the XS1 heads I have lying around. Picked up a set of Viton® valve seals for it. Reputed to outperform the originals. Got sidetracked and they sat on the shelf a while.

Viton® valve seal … metal jacketed


These are available with or without a metal jacket.

unjacketed valve seal


I am now sorting out a head for an extra SR500 motor. To go in the sidecar. Emphasis torque. Early 78/79 crankshaft and cases (larger crankshaft counter-weights), specially ground cam, larger valves, lighter valve springs, thinner spring plates, modified ports, carillo rod, O/S piston, modified/heavier flywheel etc. The XS650 and the SR500 use the same valve seals. No point leaving these sitting. Collecting dust.

Wonder how they will work.

Viton®. Flouroelastomer (FKM/FPM). A fluorocarbon based synthetic rubber. These contain 5% Teflon for reduced friction and wear.


  • have a wide and stable Temperature Range -30°C to 225°C (-10°F to 400°F)
  • resist hydrocarbons (fuel/oil)
  • excellent oxygen, ozone and weather resistance
  • incombustible
  • have excellent dynamic properties (coeff. of friction, tensile strength, range of hardness and resistance to compression set etc) – good abrasion resistance
  • have low permeation rates (esp. relevant to alcohols, hydrocarbons and biofuels (biodiesel, ethanol)
  • be solvent, mineral acid resistant (don’t really like ketones, amines or low mw esters,)
  • show low compression set


  • low alkali resistance
  • relatively poor mechanical properties
  • limited elasticity at low temperatures
  • the tensile strength decreases substantially at elevated temperatures
  • high price

The fluorocarbon rubbers are used for special applications that require good heat, oxygen or corrosion resistance and hot solvent and oil resistance.


  • car and airplane seals and hoses
  • fire-resistant coverings
  • heat-resistant insulators
  • o-rings, shaft seals
  • gaskets, fuel hoses, valve-stem seals

Note: Viton® is a registered trademark of DuPont. It is often misleadingly used as a generic term for FKM/FPM flouroelastomers.

For the chemically-minded FKM’s thermal and fluid resistance are a function of 3 main features

  • Extremely strong bonding between the polymer backbone carbon atoms and the pendant (attached) fluorine atoms
  • High ratio of fluorine to hydrogen atoms bonding to the carbons (high fluorination levels tend to create stable compounds)
  • Full saturation of the carbon backbone .. no covalent double bonds between carbons minimizes attackable sites

Structures of fluorocarbon rubbers

Monomers Structural unit Type designation Commercial types
VF 2 + HFP


Viton A, AHV, A-35, E-60,
Fluorel 2140, 2141, 2143, 2146


Tecnoflon SL, SH
VF 2 + HFP + TFE


Viton B, B-50


Tecnoflon T


KEL-F 3700, 5500, SKF-32


ECD 006


Typical FKM structure … flourocarbon rubber


An example of a structure of the fluorocarbon rubbers, VF2 / HPTFP / TFE -copolymer.


Posted March 23, 2014 by xscafe in Motor - Head, SR500

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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.


A1 .. finned tappet covers

finned tappet covers


Found on

Look good mounted.


A2 .. finned tappet covers

cast fins – mounted quickly


A3 .. front left

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: Fork Co Timing Covers   Leave a comment

ForkCo. Japan. Nice timing covers. Black or Plain. Hand cast. Fins are designed to match the engine.


1 .. plain alu

plain alu



2 .. Black




3 .. XS black

XS black



4 .. 650 plain

650 plain


Make some tasty oil pump covers for the SR500 too.

Posted October 12, 2012 by xscafe in Frame - Design, Motor - Head

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