Honda XR500 big bore 591 cc

Full on power


The journey down the road of building several trick XR500 had to lead me to the mother of all motors. As the saying goes, "if you need power, there is no substitute for displacement".

So, on an expensive day of 2013, I decided to request from Engine Dynamics to provide a 591cc big bore kit for the XR500.

These things are not exactly sitting on shelves waiting for the next customer of the day. So I had to be patient.

From my stock of parts I selected a nice cylinder jug, a good strong cylinder head that I fitted with helicoils all around, a rockers cover, a good inlet pipe.

I sand&soda blasted everything nice and clean and shipped to EdCo in Petaluma, CA.

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Carillo rod and balanced crankshaft

     A big piston.      97 mm diameter for 591 cc.

And the nicely prepared cylinder-head.


My instructions to EdCo were:

  • On cylinder: 591cc kit including sleeve, piston, rings, pin, gaskets, clips

  • On cylinder head

    • full race porting (exhaust at 29mm to match exhaust pipe please)

    • valve spring kit inc. guides and titanium top retainers

    • 1mm oversize stainless valves

    • new valve guide seals

    • high lift Megacycle cam

    • (Please remove the bolt that is still there, I did not manage to extract it, thanks)

  • On cam cover: please confirm what happens here

  • On inlet pipe: port as per inlet for a 38mm Mikuni carburetor


But there was more

My project was more than just making a 600cc out of a 500cc.

While EdCo was building the top end, I turned to my stock of parts to build the bottom part of the business. I intended to go for the full enchilada.

  • XR (PE01) cases

  • Tight innards from a low mileage XL500S

  • Removed the balancers and chain (1.74 kg less)

  • Carillo rod fitted to balanced crank

  • Billet aluminum clutch basket

  • New Barnett clutch plates and springs

  • NOS cam chain and guides

  • Flywheel from a XL250S (700g lighter)

  • And a whole bag of new bits and pieces.

Before the assembly can begin, I need to replace the now-absent rear balancer wheel with a suitable spacer.


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