info on alpha one gen 1? water pump base..

[76SeaRay]

I have found that sometimes on EBay and even Amazon, sell items that they show as compatible with the Mercruiser part numbers but have subtle differences. Sierra sometimes does that too (based upon my experience with cooling hoses). Other sellers don't send what the picture shows. Best to talk to a OE supplier that is in the know and with whom you are placing the order. Even when you deal with Mercruiser OE parts you have to watch the revision letter and number at the end of the part number (ex. 18-12345A14). Also, "replaced by" does not mean "equivalent to". I experienced a problem with that on replacing my lower unit. The seller thought it was compatible but the difference in the letter revision showed them not compatible. At least the site that is in the link above defines their parts as with hole and without hole with great pictures so if you don't get the right one, easy to return for a refund.

 

[achris]

To simplify.

There are 3 water pump bases (for drives 1967 to 1990).
1. Early MC-1 drive, will be WITH a flusher hole, 46-48748A1
2. Later MC-1 and R, will be WITHOUT flusher hole, 46-57234A1
3. MR and Alpha One, 46-44292A3

The serial number of the drive is only stamped on the drive shaft housing, so if the gear housing is replaced at any stage, only inspection for key points will determine which gear housing it is.

If it has a flusher hole on the (I think) port side, then it's an early MC-1 (and should have a preload pin. I say 'should' because I have seen them cut off when someone was putting an MC-1 gear housing onto an MR/Alpha One drive shaft housing. )
If it has a preload pin, and no flusher hole, it's later MC-1 or R drive.
If it has no preload pin, then it's an MR or Alpha One gear housing.

If you're not sure of its preload pin status (you think someone may have been a moron and cut it off), as Scott said, look at the bearing under the water pump base. You see tapered roller, it's an MC-1/R. You see a four-slot locking collar, it's MR/Alpha One.

Another way you could use it to push down and pull up on the drive shaft and try to move it side ways.
If it's an MC-1/R, it will move (sideways) when pulled up and be solid when pushed down. If it's an MR/Alpha One, it will be solid when pulled up, and move sideways when pushed down.

Chris.........