Replacing the rear engine cover dowels and water pipe O-rings – Honda CX500, GL500, CX650, GL650

The water passage O-rings are often quite mangled now that the bikes are 30+ years old and have perhaps seem several engine openings; they’re one way that coolant can enter the crankcase and contaminate your oil so it’s cheap insurance to replace them unless you know they have been done recently. There are two O-rings around the water passage dowels, located here:

Here is how to replace the coolant passageway O-rings and the two sets of dowels in the rear cover of a Honda CX500, GL500, CX650 or GL650 motorcycle as shown on MotoFaction.org.

A closeup of these:

Here is how to replace the coolant passageway O-rings and the two sets of dowels in the rear cover of a Honda CX500, GL500, CX650 or GL650 motorcycle as shown on MotoFaction.org.

These ones are in dire need of replacement – they don’t even slightly look like they have a round section any more. Replacements are available new (on eBay, often for US$0.99ea) and are part number 94608-50000:

Here is how to replace the coolant passageway O-rings and the two sets of dowels in the rear cover of a Honda CX500, GL500, CX650 or GL650 motorcycle as shown on MotoFaction.org.

Given the price it doesn’t make much sense to me not to replace them if they haven’t been done recently; given that you have to remove the engine from the bike and then the rear engine cover to access them, it’s a lot of effort for ~$2 of O-rings. They’re 23×2.8:

Here is how to replace the coolant passageway O-rings and the two sets of dowels in the rear cover of a Honda CX500, GL500, CX650 or GL650 motorcycle as shown on MotoFaction.org.

Dig the old O-rings out, remove the dowels, clean them up if necessary and place the new O-ring around them:

Here is how to replace the coolant passageway O-rings and the two sets of dowels in the rear cover of a Honda CX500, GL500, CX650 or GL650 motorcycle as shown on MotoFaction.org.

Clean out the block where the dowels and O-rings sit, then put the dowel and new O-ring in place:

Here is how to replace the coolant passageway O-rings and the two sets of dowels in the rear cover of a Honda CX500, GL500, CX650 or GL650 motorcycle as shown on MotoFaction.org.

Now for the locating dowels. There are two of these, circled in red (upper left, lower right):

Here is how to replace the coolant passageway O-rings and the two sets of dowels in the rear cover of a Honda CX500, GL500, CX650 or GL650 motorcycle as shown on MotoFaction.org.

If yours are corroded beyond use or missing, a replacement part is available new and is part number 94301-10160 (also available on eBay):

Here is how to replace the coolant passageway O-rings and the two sets of dowels in the rear cover of a Honda CX500, GL500, CX650 or GL650 motorcycle as shown on MotoFaction.org.

Here’s what a new one looks like:

Here is how to replace the coolant passageway O-rings and the two sets of dowels in the rear cover of a Honda CX500, GL500, CX650 or GL650 motorcycle as shown on MotoFaction.org.

Clean the holes out of gunk and insert the new dowels:

Here is how to replace the coolant passageway O-rings and the two sets of dowels in the rear cover of a Honda CX500, GL500, CX650 or GL650 motorcycle as shown on MotoFaction.org.

Here is how to replace the coolant passageway O-rings and the two sets of dowels in the rear cover of a Honda CX500, GL500, CX650 or GL650 motorcycle as shown on MotoFaction.org.

If you are doing this as part of a triple or quadruple bypass, click here to go back to that page.

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