water pump base

[tbird175]

I am replacing the water pump base on my 175 hp blackmax (78). The threaded hole in the base was stripped out (1/4-20). The new base is not threaded. After searching the parts listing I have found that it is designed to use a 14-8 screw. I do not have a screw this size. Should I tap the hole for my bolt or order the screw? I wonder why this design change was made by Mercury? What do you engine gurus do when this comes up?

 

[Chris1956]

Re: water pump base

Are you referencing the screw in the rear of the pump? My '77 IL6 used a screw, as does my '93 V6. I think they come with some of the repair kits, along with the key, gaskets etc. Are you sure the original was supposed to be a bolt?

 

[tbird175]

Re: water pump base

This is the OEM base that is stripped out. It came with a bolt from the factory. I overtighened it after installing a new impeller. I am going to contact a Mercury tech tomorrow for advice. I will post my findings.

 

[Faztbullet]

Re: water pump base

The new and aftermart base use a self tapping screw and make sure you have the correct base(OEM#46-96146A6 or Sierra 18-3416) as the lower base is different size on most pre 86 motors...

 

[tbird175]

Re: water pump base

The new and aftermart base use a self tapping screw and make sure you have the correct base(OEM#46-96146A6 or Sierra 18-3416) as the lower base is different size on most pre 86 motors...

Thanks, I do have the correct base. Would you recommend tapping the base for my bolt or ordering the proper screw?

 

[rodbolt]

Re: water pump base

the proper screw always works and it comes with the upper housing kit.
your rig was rigged.
from the factory it did NOT have a 1/4-20 screw.

 

[tbird175]

Re: water pump base

I contacted a Mercury tech today about my problem. His literature did not go back to my serial no. but he did find a shop drawing of the screw that was designed for the pump in 1980. This 14-8 X 2.25 replaced the earlier design (mine is a 1978 model) that used a 1/4-20 bolt. The top housing and base are much lighter in construction now than originally for my engine. Some of the drill passages have been replaced with slots. These changes were most likely to reduce manufacturing cost (threading hole, driling passages, less and cheaper material, etc.). He sent me the drawing of the screw. I was able to find a suitable replacement at a local fastener supply house.

I thank every one for their response to my post. Have fun before cold weather interferes with our boating.

 

[tbird175]

Re: water pump base

I have run into another problem with my new sierra water pump base. The bottom side that goes in to the bore above the drive shaft bearing will not seat. I can remove the o-ring and it will bottom out but with the o-ring in place and well lubricated it lacks about 3/16" seating in the the bearing housing. I tried with the old o-ring and it still would not seat. I tried reinstalling the old base and it worked fine. Is there a trick to installing a new base with new o-ring. Has anyone had this problem with a sierra base?

 

[Chris1956]

Re: water pump base

Normally there are several Orings with different thicknesses, supplied with the impeller kits. Do any of them work? Did you install a gasket on the base as well?

 

[tbird175]

Re: water pump base

Normally there are several Orings with different thicknesses, supplied with the impeller kits. Do any of them work? Did you install a gasket on the base as well?

Yes I tried all the Orings that would fit and the gasket is in place. Even using the old Oring from the old base on the new base would not work. I am going to try it again this afternoon. I may wind up using my old base but I don't like using the old seals and Orings. The old seals look good and are still flexible so they probably would be okay other than being 32 years old. But, the rest of the engine is is the same age so it may be a safe decision. I am going to verify that the OD of the bottom of the Oring groove is the same on both bases, if not this could be the problem.

 

[tbird175]

Re: water pump base

Finally got the new base installed. It just took a lot of pressure, used a pipe over the shaft and tapped with a hammer. Now if I can just figure out how to set the shift slide block on the powerhead to either forward or neutral to match the LU I will install the LU. The shift cable is off the engine so I have no way to determine the correct position of the shift slide block. I welcome any suggestions.

 

[Chris1956]

Re: water pump base

I responded to your other post on this issue. I hope it worked...