Got a problem....a 1993 Merc XR6 150HP....was running down the lake the other day and the motor started making a terrible knocking sound....the lower unit is messed up and needs to be replaced....was told that the lower unit is a small one (4 1/2 in.) and should be a large one (4 3/4 in.)....does anyone know the difference in these two units and the advantages or disadvantages between them??....thanks for any information.....

Merritt Marine Hillsborough, NC Carl Merritt 919 732 7377 Good man. Smiles, G

The larger unit which is 4 3/4" is standard on your motor.It will bolt right up to your motor.But you have to change the prop because the prop is also larger.

Greg - I also have a 1993 150 Merc XR6 and also have the smaller lower unit. Found this out once when I wanted to change props. So far I have not had problems specifically due to this being a smaller unit, and I really find it hard to believe that the lower unit would run fine for 14 years and then break b/c the small ones are inherently bad. That being said, I guess it is possible you will have to replace it every 14 years - who knows, I've never had a lower unit on my rig last 14 years anyway .

Greg,

Have you torn it apart to see what exactly is wrong it?May be something that can save you big bucks.Just inspect it all when torn apart and whatever looks good,reuse it.Just because it sounded like it tore up heck,doesn't mean it did.