1970 mercruiser 120 lower unit oil leak (Pre-Alpha)

[kd6nem]

1970 mercruiser 120 lower unit oil leak (Pre-Alpha)

Got my dad-in-laws pre-Alpha lower unit off to change water pump. For the most part going better than expected, but have 90 wt dripping from the upper housing. I drained lower unit, not upper. Don't have manual (yeah, I know... ), though do have section on pump replacement. Was I supposed to drain upper instead? Am guessing we have a bad seal probably from the shift selector shaft??? Is this likely/common? Is the seal hard to change without major disassembly? Time & finances badly limited, but we don't have time to screw it up either.<br /><br />Also- am I supposed to use sealer on the water pump assy gaskets? Instructions do not say. Will a very thin application of blue water pump silicone be OK, or will the exhaust temps or other issue cause problem requiring different sealer? And is marine wheel bearing grease OK for assembly lube?<br />Thanks for helping!!!

 

[itstim]

Re: 1970 mercruiser 120 lower unit oil leak (Pre-Alpha)

Re: 1970 mercruiser 120 lower unit oil leak (Pre-Alpha)

Well, (until the pros get on cuz I'm just like you!) here's some things to think about: Number absolute one,1,won..get a manual! $20.00-30.00 bucks will save you $100-1000.00 easy. You really can't shortcut this one unless merc/mech is standing over your shoulder. # 2: look at your lower unit. See that little circle on the side/top/rim/? About 3/8ths or 1/4" diameter with the little o-ring on it. That is the oil passage to the top unit (by the way, you need to change that o-ring now that you've separated the upper and lower...it's usually with the water pump kit...a little bellows adhesive holds it place nicely when you join upper/lower). When you drain the bottom you drain the top. #3- don't think there is any oil contact at the top shifter...I think that is greased. My guess is that oil coming from the top is coming from the gear housing that is protected by the o-ring on the shaft on the lower unit you removed although you don't specify where the "90wt" is coming from. #3--no sealant required as far as I know on water pump stuff but follow gasket order closely or you'll go to overheat heaven! #4--don't think it's 90wt...I think it's called MARINE gear lube... (I) don't use automotive 90wt or you'll go to outdrive heaven (but what do I know!)

 

[pete42]

Re: 1970 mercruiser 120 lower unit oil leak (Pre-Alpha)

Re: 1970 mercruiser 120 lower unit oil leak (Pre-Alpha)

I agree with itsim..A manual (I have Clymer) for your drive is an excellent reference tool..Has plenty of step by step - pictures...I purchased my at a Searay dealership/marina...good luck!....pete42

 

[Blk-n-Blu]

Re: 1970 mercruiser 120 lower unit oil leak (Pre-Alpha)

Re: 1970 mercruiser 120 lower unit oil leak (Pre-Alpha)

Bear, there is a passage between the upper and lower unit that takes a rubber like O-ring gasket which should be included with your gasket set. if you didn't wait long enough or didn't open the top vent screw ,lube would continue to drip from this passage. Here is a link to help you through the rest of the job.<br /> http://www.mercstuff.com/howdoi.htm <br />make sure you choose the right outdrive on the link. Good Luck

 

[kd6nem]

Re: 1970 mercruiser 120 lower unit oil leak (Pre-Alpha)

Re: 1970 mercruiser 120 lower unit oil leak (Pre-Alpha)

Thank you, all!<br />As to the manual- this will hopefully be the only repair I'll have to do, and Dad will never tear into it himself. Cash is tight for both of us- I'm with all of you in complete agreement about the need for a manual, though circumstances being what they are I'm willing to do just this without- this time. My guess is that I erred in draining it with the LU in the up position. <br /><br />I was already using the the site Blk-n-blu mentioned, though this remided me to go back and look some more which did help. It really is a great reference, isn't it? Sure has helped me this time. <br /><br />Looks like we're in good shape. Hopefully the impeller plate is IDENTICAL, but if not the old one looks reuseable. Need to get a fitting in order to pressure test the bugger before filling with marine 90 wt. or whatever the local boat dealer says is appropriate.<br /><br />Anyway, thanks again!!!