Tilt/trim pump O-ring rebuild????

**69MyWay** · 05-27-2020, 07:29 AM

I have a 1979 Merc 115 on my 84 Viper. Last year I rebuilt and replaced the hydraulic rams and replaced the lines. I also replaced the relays and wiring for the pump assembly. This is the kind that has the pump in the boat.

It has always leaked down. I'm told this can often be fixed with O-rings. Since I assume the O-rings in my unit are well out of size, I didn't want to pull then try to match them up so I found a fellow that has the correct size. They should be here soon.

Hoping it goes smooth. The hardest part my just be getting access to it and doing it without making a mess all over the floor.

Anybody here every replace those O-rings and have success?

**Dave Strong** · 05-27-2020, 10:53 AM

Is this the square pump with the square metal reservoir ?

Dave

**69MyWay** · 05-27-2020, 11:16 AM

Originally Posted by Dave Strong

Is this the square pump with the square metal reservoir ?

Dave

Yes

**Dave Strong** · 05-27-2020, 11:47 AM

Originally Posted by 69MyWay

Yes

Sierra used to hVe an o-ring kit, can't remember the number and no longer in the catalog.

Dave

**69MyWay** · 05-27-2020, 11:53 AM

Originally Posted by Dave Strong

Sierra used to hVe an o-ring kit, can't remember the number and no longer in the catalog.

Dave

Yep I looked and looked for that - but found this fellow that claims he has all the sizes in a kit for $10.

**wellcraft17** · 05-27-2020, 09:52 PM

I’ve found that the port ram gets some trash in the Check valve seat and that will cause the leak down.

**69MyWay** · 05-28-2020, 06:52 AM

I might get my son to run the go-pro when I pull this apart form a pure amateur perspective and create a repair video. We will see. I may pull the pump out over the weekend and get it all set up on the bench.

**XstreamVking** · 05-28-2020, 07:00 AM

The manual by pass screw o-ring's could be the leak down problem. Do it 1st and check operation b4 you tear it apart.

**69MyWay** · 05-28-2020, 07:14 AM

Originally Posted by XstreamVking

The manual by pass screw o-ring's could be the leak down problem. Do it 1st and check operation b4 you tear it apart.

I agree with you on that. Question - can I replace that one without taking the unit apart? That knob/handle runs counter clockwise to operate the lock/release of the mechanism...Can I just totally unscrew it to replace the o-ring, or does it require the removal of the housing?

**XstreamVking** · 05-28-2020, 08:08 AM

Been a few years since I messed with one. Seems just screws out? Has tapered shaft with 2 rings?

**69MyWay** · 05-28-2020, 08:24 AM

Originally Posted by XstreamVking

Been a few years since I messed with one. Seems just screws out? Has tapered shaft with 2 rings?

This just got interesting....really - I didn't think about doing that. Easy peasy except for the mess and doesn't have to come out of the boat to do this.

**69MyWay** · 06-02-2020, 08:19 AM

Update - I took the pump assembly out last night. Got the valve all torn down and soaking in cleaner. Still don't have the O-rings, but I called the fellow this morning and he confirmed only the side body O-rings are coming. Hopefully I can put it back together (springs/check balls) in the order removed. I did find there are three O-rings in the bypass valve. These are not coming with the kit. I'll have to go to NAPA I assume. Will give that a shot Wednesday. Overall it is a simple unit. I'm super impressed that at its age I was able to unscrew all the caps and parts without a problem. Amazing over-engineered metals they used/use in these. Nothing like automotive parts.

**69MyWay** · 06-04-2020, 07:27 AM

Got the O-rings day before yesterday and tore the valve all the way down. There was only one part I couldn't get out right on the other side of the manual release. I assume it is pressed in the valve body so I sprayed plenty of cleaner around it but left it there. Got all he check balls, springs, and parts out...cleaned the snot out of it. Went to Napa and lined up new o-rings for the piston/valve on the other side of the manual release mechanism. Put it back in the boat and cycled it for air bubbles. When I raise it all the way up it will fall a bit (fairly quickly) but when it gets to 3/4 or so full up it stops and sits there. It has been holding in place all night long. I don't know if that is air that is causing the initial fall - but prior to this it would NEVER stay up this long. It is possible - every so slightly possible that it is fixed. I'm cautiously optimistic. Will pull the boat out of the workshop today and hook it up to water and light it up for the first time since last year...and if all goes smooth fuel it up and take it to the lake this weekend! FINALLY! I opted NOT to put a water pump in it yet...as I just replaced it later last year and really haven't had that much run time. But I may do that soon as well.

**69MyWay** · 06-08-2020, 08:08 AM

Well - it was a FAIL. UGH. It worked great - we had an excellent time at the Lake over the weekend...but when we pulled the boat out the tilt sagged and is now consistently falling after raising it. There are no external leaks. I'm positive that the springs must just be worn out in the valve assembly from sitting loaded in one spot for decades.

I hate to do it, but I'm going to hunt down that aftermarket pump/valve assembly and give it a go.

**XstreamVking** · 06-08-2020, 08:12 AM

Check out db electrical. They have a lot of replacement merc pumps and trim motors, alternators etc. I have had no problems with the parts from them. 4+ yrs customer. No failures yet.