mc-1 failed vacuum test

[ziggy]

so i've been doing a little prep on my drive.
R&Red the impeller
R&Red top brg and race in upper driven gear shaft

things looked respectable so i put her back together again. pressure tested at 14 psi for 24 hrs. rotated drive shaft, prop shaft engaged in fwd. no loss of pressure.

did a vac. test. initially it held at 5hg. but tended to drop off. down to 4 or 3hg. rotated drive shaft, prop shaft engaged. fell off to 2-3 hg. wouldn't hold for 15 min. started seeing a drop pretty much right away.

so i separate the upper and lower again. vac. tested the upper by itself. 1.5 hrs later it was still steady at 5gh. right where i put it. did rotate shaft. so i think to my self, must not be the upper.
vac. test the lower. well, it's now been holding for 2.5 hrs at 5hg.. rotated shaft, tried to wobble drive shaft. still holding.

yes, the quad ring was in place.

upper
very bottom seal (the easy one) of upper was replaced 2 years ago, looks serviceable
oring replaced on top cover
perfect seal on retainer nut
lower
no service at all to the lower other than the impeller. to include not doing the water pump base seal...

any one got any ideas as to why it failed a vac. test when assembled? i figured when i tested the upper and lower separately that it'd lead me to the leak..

have not tried pressure testing separately..

 

[ziggy]

Re: mc-1 failed vacuum test

reply from Don S from another thread http://forums.iboats.com/showthread.php?t=456307&p=3106378#post3106378

The input shaft seal is probably where you are loosing your vacuum. Merc doesn't even recommend it because of the input shaft seal design, it was not meant to hold any vacuum. If you are real lucky, you can sometimes get them to hold 4-6 inches of vac, but that's about it.

i have in the past (not that that means anything though i guess). generally i can hold 4 or 5hg. but not this time. i do understand what your saying about the seal (input shaft) is not designed to hold vac.

so i shouldn't be concerned? and should not be performing a vac. test?

 

[Don S]

Re: mc-1 failed vacuum test

What I do if it fails a vacuum test around the labrinth seal (That is what Merc calls it) is turn the drive up so the ujoints are facing up. Then fill the area around the seal with gear lube and then vacuum test the drive. It will probably hold until it sucks all the oil out of the cavity. But, if you held pressure for 24 hours and it held while you turned the shafts and shifter, I sure wouldn't worry about it.

 

[ziggy]

Re: mc-1 failed vacuum test

turn the drive up so the ujoints are facing up. Then fill the area around the seal with gear lube and then vacuum test the drive.

whew, it took me till just now to fig. out what you said. fill it from the outside, ujoints up... thanks. i'll try that. after i turn the shifter... i forgot to do that even though i considered that as a possible leak point. appreciate the help..

 

[ziggy]

Re: mc-1 failed vacuum test

well, i'm done with it imho.
i vac. tested the halves. neither leaked down.
i reassembled the haves. pressure tested for 3 or 4 hrs @13.5psi and has now been holding 5hg for 5 hrs.
drive shafts turned, shifted fwd to reverse... it's holding pressure and vac.

no idea why it's holding vac. this time. but i'll take it...

time to put my lub in and wait for the next step..

thanks

 

[fat fanny]

Re: mc-1 failed vacuum test

Good to hear Zig. My next step is the thaw!!!!!!