Waterpump Conundrum - 1971 Merc 800

[Moody Blue]

Started out trying to find out why I was getting water in the LU. Dropped the LU and did a pressure test that showed a leak at the base of the waterpump.

So I took the pump apart and pried up the base. What I found shocked me. The wrong base was installed. The collar that fits down inside the housing over the bearing was at least 1/4" too small in diameter. Its P/N is 46-48747 (lower item in photo) The O-ring seal was doing nothing. I have a second complete LU (for parts), so I took that pump assy apart and found a different style waterpump base. Its P/N is 46-58618 (top item in photo) I tried fitting that base into the first LU and it was a TIGHT fit, almost size on size.

Now I have no idea what the proper waterpump base should be. The lower unit of interest has the helical cut gears, preload pin on the driveshaft and tapered roller bearing as the driveshaft bearing. The P/N of the LU casing is 1623-4021 and it has the flush port. See photo.

Anyone know what P/N base I should be looking for? There are SO many P/N's and I have no idea what year this LU actually is.

 

[Moody Blue]

Re: Waterpump Conundrum - 1971 Merc 800

B u m p e d.

 

[Faztbullet]

Re: Waterpump Conundrum - 1971 Merc 800

Should be part # 46-58618 and o-ring 26-33145 as the o-rings are different thicknesses also....

 

[Moody Blue]

Re: Waterpump Conundrum - 1971 Merc 800

Thanks for the confirmation. I realize that the fit needs to be tight between the pump base and LU housing but the part I have (46-58618) barely fits in without any o-ring. Will I be able to force that base into position once the o-ring is in place?

Please confirm the size of the two seals that are required. From the crankshaft, it looks like the bottom seal would be 1" dia., while the top seal would be 7/8" dia. However, the seals that were in the "correct" base were both 1" dia.

On a separate note, I am totally amazed at how well the WRONG pump base did seal despite the fact the O-ring did nothing at all. I mean there was at least a 1/8" gap all around the o-ring. I was ending up with about 1/2 cup of water after 10-12 hours of operation.

 

[Moody Blue]

Re: Waterpump Conundrum - 1971 Merc 800

Checking back.