Honda 600cc Supermono engine build sequence

Honda XL600R meets XBR500 crank cases. I put the left hand case half in the oven on a low heat and crank in the freezer for 24 hours and the hefty left main roller bearing slipped in a treat.

Cases were bead blasted and parafin washed beforehand. Filled the kitchen with a lovely scent of hot aero engines when they were in the oven :oD

A choice of different balancer shafts!! (XBR500, XL600, NX650)


Turning down the XL600 balancer shaft bearing diameters to fit into the smaller XBR500 roller bearings. I did this instead of sourcing more bearings

XL600 balancer shaft with backlash gear removed, mates with crank, double check the timing is right or your engine may go clackety clackety :oD

XBR500 close ratio gearbox

XL600 selector drum and a shifty pawl! The XBR500 runs a reversed selector drum profile to allow the gear change lever to be operated from the opposite direction. I wanted the XL600 style.

XBR500 gearbox slots straight in

XL600 selector drum and centre selector bolted into place

crank case gasket and RHS engine case tapped into place

XBR500 oil pump checked and bolted into place. The drive gear is fitted just before fitting the clutch cover

XBR500 kickstart assembly

Kickstart shaft and idler gear fitted. Gear selector plate and follower fitted

NX650 primary drive gear and new Honda XR600 pulse generator


NX650 clutch basket and bearing slips onto XBR500 gear shaft. The NX650 primary drive gears the highest road gearing possible

New clutch plates soaked in oil overnight and fitted

clutch nut screwed on with tab washer

simple clutch locking tool made form skirting board. One end bolts onto the 4 spring bosses and the other end gets gripped tight in a vice

ready to tighten the nut through the hole in the exquisite clutch tool.

Tool removed. tab washer bent over. Clutch pressure plate fitted

New Kibblewhite race clutch springs read to be squeezed to death

springs fitted

LHS end of crank. Taper ready for generator rotor fitment

XL600 rotor

XL genny vs XBR500 genny. About 8 Kg lighter I guess

big securing bolt tightened to the recommended high torque!!

Wiseco 100mm piston fitted

piston details

A few gasket sets I got at a clearance sale !!

New NX650 100mm cylinder

New cylinder bolts trial fitted to ensure they are'nt going to cross thread or bottom out

simple view showing meshing of crank/balancer gears and acceptable clearance between the gears and cases


XL600 cylinder head dowel holes machined to 12mm to accept the larger (M9!) head bolts fitted to the NX650 cylinder.

XL600 intake work to match with bespoke intake.

intake to be used eventually with Suzuki RGV250 flatslide carbs - but not for starters

dowel holes machined via hand drill!

XL600 generator stator fitted to XR600 Magnesium engine cover repainted and fitted.

XL600 twin carbs rejetted for ramair filters

Vauxhall sealant applied to base gasket face

This is the stuff used

0.5mm copper base gasket cut out by hand (laser cutting was too pricey)

Cylinder fitted

Kibblewhite race valve springs and Ti retainers. Stellite welded cam followers

A new cam follower in place

Top of the XL600 cylinder head showing the 'fifth' valve for decompression

oil seal fitted to decomp valve guide

A valve spring in situ

Fitting the valves with a suitable compressor tool

Valves all in place

Fifth valve fitted. Cylinder head offered up. Cam chain fed up the tunnel

cam chain held up with simple hook

Phil Joy Race cam and OE sprocket fitted. Valve timing ready to be sorted. I slotted the sprocket for fine alterations

lumpy cam

now for the cam chain tensioner...

Tensioner and spring pressed into the head

home made lever tool presses the spring into place

not pretty... but effective

one way tensioner clutch bolt slipped into place


tensioner rotated using suitable allen key and pin locked into place with dowel pin. The valve timing is the re-checked after the cam chain is tensioned.