CX650 Eurosport

Research / Which 650 engine: GL650, CX650E or CX650C

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Which 650 engine: GL650, CX650E or CX650C

The engine bay of the CX500E line drawing: the V-twin, its cylinder head and the frame around it
Where the 650 goes: the engine bay of the donor, drawn from its real dimensions.

Where it stands

My bike is a 1982 CX500E Eurosport. It came with a 500, and the plan is a 650. I haven’t bought one yet.

The order of preference right now:

  1. GL650 (engine code RC10E). Its base workshop manual is the same one that covers my chassis, it already has the 650 front hangers and electric-fan cooling, and it reportedly already has the 500-type output shaft.
  2. European CX650E Eurosport (RC10E, or RC12E for Canadian bikes). Its own parts list shows the same frame bolts as my bike. The extra job is swapping the output shaft.
  3. CX650C Custom (RC11E, the US engine). Same hangers, cooling and shaft swap, but it came out of a different frame, and I have no parts list for it. Only if it’s very cheap.

The CX650 Turbo (RC16E) and anything seized are out.

Why the GL650 leads

It comes down to the output shaft and the final drive.

  • My CX500E has output shaft 23521-415-000 and a 3-nut final drive, 41300-MC5-000.
  • The CX650E has a different shaft, 23521-MG0-000, and a different damper cam. Its final drive is a 4-nut unit, 41300-MG0-000, which I won’t use.
  • Most GL650s are reported to have the 500-type shaft already. MotoFaction and the forum both say “check first”, because some don’t.

With a CX650E, I’d move the whole final-shaft assembly across from my own engine: the shaft, the damper cam 23722-MA1-000, the lifter and the spring. That’s a known job, but it’s still a job.

All three engines share a final drive ratio of about 3.09, so the gearing doesn’t change.

What has to happen with whatever goes in

The engine will be rebuilt and painted by a shop. That means the “quadruple bypass” every documented swap does: cam chain and tensioner, stator, water pump seal and starter clutch, plus stronger clutch springs. I’ll get the shop quote before I buy the engine.

What would change my mind

  • The engine number. Ask every seller for a photo of the stamping. RC10E is good. RC11E means a CX650C.
  • The output shaft. A 500-type shaft has a lock-bolt groove; a 650-type has a snap ring and spring.
  • Freight and biosecurity. Most of the engines are in Europe or the US. Anything shipped here has to be clean for MPI, and from September to April a European shipment needs stink-bug (BMSB) treatment. A good engine that’s hard to get here loses to an average one that’s easy.
  • Murray’s Carbs’ answer on which engine and carb kit suit the E frame (see carbs).

The mount-by-mount detail is on frame and engine mounts.

History

  1. Compared Honda's own parts lists for the three frames. GL650 confirmed as the closest bolt-in. A US GL650 Interstate engine turned up, but the seller won't ship to New Zealand.
  2. First weekly search run. Added the RC10E engine code to the search terms.
  3. Decided to stay on my CX500E frame rather than buy a whole CX650E. Set up a weekly engine search. A parts-fiche check ranked GL650 first, CX650E second and CX650C last.
  4. Decided a shop will rebuild the engine. On 25 Oct that became rebuilt and painted.
  5. The research library found the 650 swap is easier in the Eurosport's triple-backbone frame than in any other CX500, and that it needs LVV certification.
  6. Decided to build the CX500E chassis and prepare a second, 650 engine off the bike, so it can be rebuilt and tested out of the frame.

Sources

Spotted something wrong? Tell me. Jeff Sutton is building this, not an expert writing it up.