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Engine swap compatibility for Honda CX500, GL500, CX650, GL650

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This page is very incomplete and is being added to over time.

CX650ED or GL650 engine into a CX500 frame

CX650C engine mounts are different to the above; if you have a CX650C engine it will fit, but you'll have to find/make different mounts. Swapping a 650 motor into a CX500 is possible; an incomplete list of what you will have to address is:

• New front engine hanger - thermostat outlet differs between the two motors, which has an impact
• Use the 650 or TI CX500/GL500 wiring harness
• Use the 650 coils
• Check the output shaft; may have to swap the 500 one in
• Use 650 exhaust headers
• Carbs - need info (500 carbs won't run a 650 without changes, 650 carbs don't fit the center spine frame)

CX650ED or GL650 engine into GL500 frame

Same with the CX650C; the engine mounts are different, so if you have a C you'll need to make/source GL650/CX650ED engine hangers. This is easier;

• Use 650 carburetors
• The 650 engine hanger bolts up to the 500 frame
• Use 650 radiator

TI motor in a single-spine frame

Examples of this would include a 500EC, GL500, 1982 Shadow or 1982 Custom motor being used in the older, single-spine frames.

You need the engine hanger for the single-spine frame as shown below:

The engine mounts from a triple-backbone frame will not mount to a single-backbone frame.

The radiator overflow tank is a consideration - the stock CDI one may not fit, and the one from a triple-backbone frame has different mount points. You need to use an overflow bottle from a 1982 Shadow or Custom - i.e. from a bike whick had the single-spine frame and a TI motor from the factory, which came with an overflow bottle to suit. Those bottles aren't particularly common. Alternately, you could relocate the bottle and use something else entirely.

The engine final output shaft is also a consideration - there have been some reports on the internet that the 500EC came with a four-bolt final drive instead of a three-bolt final drive, which would mean that the output shaft (and driveshaft) was different - make sure that you have the same type to match the swingarm/driveshaft of the frame you are installing the motor into. To change the output shaft you have to remove the rear engine cover.

The engine mounts at the top of the rear cover were deleted in 1982 and are not present on TI motors. On a CDI bike these form part of where the ignition coils mount, though it's quite easy to make a basic bracket out of metal for them. The mounts are not necessary.

You will also probably want the wiring loom from the TI motor, and the controls can be different - the killswitch at the very least functions differently.

The radiator is different between the two frames, too - you will need to use the radiator and thermostat housing to match the frame, so for moving a TI motor from a triple backbone to a single backbone frame you need to use a thermostat housing from a motor which came out of a single spine frame.

The carb intake boots - also known as the carb insulators, or just intakes - are also different between the triple backbone and single spine frames, so you will need to use single spine (e.g. CDI) intakes if you put a TI motor in a single spine frame.

The carbs are angled quite differently to fit each of the frame types - you will need carbs from a motor that came in a triple backbone frame to run the TI motor in a single spine frame.

Know of any other considerations? Please let us know - shoot us a message.