Lower unit pressure test question

[zorak]

Hi all.I have an 88 merc classic 50 that has water in the Lu oil ( AKA biscuit gravy). I have ran a pressure test on it.It started leaking around the gear shift shaft at 7 psi but would hold 5 psi overnight. i can put LU in FWD and hold prop shaft and as the drive shaft is turned the pressure would drop from15 psi down to about 8 psi I definetly have water in the oil per the spatter test and have a lower unit seal kit on order. Would these pressure readings be typical.I haven't had this motor on the water yet so the water showed up on muffs after only about 10 minutes running time.Thanks in advance

 

[achris]

Re: Lower unit pressure test question

Hi all.I have an 88 merc classic 50 that has water in the Lu oil ( AKA biscuit gravy). I have ran a pressure test on it.It started leaking around the gear shift shaft at 7 psi but would hold 5 psi overnight. i can put LU in FWD and hold prop shaft and as the drive shaft is turned the pressure would drop from15 psi down to about 8 psi I definetly have water in the oil per the spatter test and have a lower unit seal kit on order. Would these pressure readings be typical.I haven't had this motor on the water yet so the water showed up on muffs after only about 10 minutes running time.Thanks in advance

If you have a kit on the way, do all of them. If you have the pressure at 15psi and you turn the shaft and it drops to 8.... there is a seal failure on one of the seals in the water pump base. If the shift shaft won't hold 7 psi, replace the seal.

Chris.......

 

[zorak]

Re: Lower unit pressure test question

Thought i would post pics of the gadget i cobbled together to do the aforementioned pressure test. It consists of a brass tee ,a brass 90,2 brass nipples,a schrader valve a pressure gauge and the aluminum piece i turned on my lathe to screw into the lower unit. This was hooked up to a regulated air supply with a clamp on tire chuck. I was able to put the LU under water to test for leaks and visibly see where my leaks are. Of course i could have done something easier but i had everything except the aluminum piece. I thought this might give somebody else an idea what would be required if they had to come up with something to test their lower unit.

 

[achris]

Re: Lower unit pressure test question

In the I/O section there is a thread on different pressure and vacuum test units people have built.... He's mine...

 

[zorak]

Re: Lower unit pressure test question

Chris.Upon looking at yours,perhaps i made it more complicated than i had to.I was going to use the plastic fill adapter from my lu pump oil bottle but didn't think it would hold up. I wanted to ask,my LU held 5 psi all night but it definetly had water in the oil. i am going to replace the seals on the top of the LU and wait on the prop shaft seals. My prop shaft is slightly bent and i am unsure i could remove it from the carrier.The shaft has .014" of runout and if it doesn't leak i will attempt a proper repair at the end of the season. I will be making a spanner to remove the plastic nut. The manual says to replace the nut no matter how good it looks. What is your opinion? Thanks for the help. I appreciate it.

 

[achris]

Re: Lower unit pressure test question

Chris.Upon looking at yours,perhaps i made it more complicated than i had to.I was going to use the plastic fill adapter from my lu pump oil bottle but didn't think it would hold up. I wanted to ask,my LU held 5 psi all night but it definetly had water in the oil. i am going to replace the seals on the top of the LU and wait on the prop shaft seals. My prop shaft is slightly bent and i am unsure i could remove it from the carrier.The shaft has .014" of runout and if it doesn't leak i will attempt a proper repair at the end of the season. I will be making a spanner to remove the plastic nut. The manual says to replace the nut no matter how good it looks. What is your opinion? Thanks for the help. I appreciate it.

Ok... a few things...

14 thou is WAY too much. It may not leak statically, but I can almost guarantee it will leak when it run under load. Book spec on the shaft is 6 thou. You can straighten them with a press, a couple of Vee blocks and a dial gauge. I get mine within 3 thou.

Put a new nut (11-87763) in... they're not expensive ($5.19) and not worth the risk of a major failure for the cost...

The plastic fill adapter should be ok, it's not a lot of pressure.

Chris..........