Got a question.... I have not seen it mentioned anywhere, but maybe I missed it.

Does anyone with a counter-rotating sport master lower unit have a very slow drain of the fluid when compared to the other normal rotating lower unit? This has happened on 2 different sets of 300XS's we've had. First we noticed this on the original motors from 10 years ago, and we initially thought it was just a fluke with our lower unit. Now those motors have been replaced with new 300's, and again we experience the same thing. The counter rotating lower unit seems to drain very slowly, and takes longer to fill too. It eventually drains, but it takes much longer than the other one. Is this typical?

Thanks in advance, Gary.

Yes it does seem to drain slower. Also holds less oil than a RH rotation. You should always make sure you fill it a little extra after the vent plug is in.

Thanks. If I remember correctly, we get about 8 oz less out of the counter rotating unit than the RH unit. I think we measured only 18 oz out of the LH, and 26 oz for the RH lower unit. Does that sound about right?

Also, filling the LH one takes a bit longer too, and many air bubbles take time to work themselves out. (Yes, we fill them from the bottom).

I've never had these lower units apart. Does the gearset of a LH unit take up more volume???

The merc manual calls for 28oz. in either one. If you squeeze it in from the bottom the std. rotation will take a little over 32 oz. from bottom to top.
To have enough expansion room, you need to let some spill out when putting the bottom plug in. If you catch it in a measured cup, you can be fairly accurate.
The counter unit is a little different, all of the oil has to drain thru the special Timkin thrust bearing (slooooooow) I'm in the habit of letting them drain overnight and part of the second day. If you let it go for a couple of hours then turn the shaft a few times it seems to drain better (pita) I have been successful in cramming 28oz. into a counter rot. lower by pumping it until it comes out the hole, letting it set for a while, then finishing it off.

p.s. I drain my lowers into a measured container so I know how many oz. was in them.

The special carrier and thrust system take up some extra space in the counter unit.

Nice Pair - Thanks for that info, appreciate it. We didn't think about spinning the shaft a little to help drain, good idea.

We were probably not waiting long enough for it to drain. Usually we start to drain the LH first, let it drip while moving over to the draining and filling the RH unit. Then we go back to the LH unit again. Maybe total elapsed time for letting drain was an hour. I think we'll have to wait longer to help ensure a total drain.

What we've been doing is as we fill the LH unit, we continue to fill and let it overflow, watching for clear fresh fluid (no air bubbles or old fluid in the clear hose that we use in the vent) and continue to pump some more, for good measure. Gear lube is cheap, lower units are not!

Thanks again! Gary.

I've always been told too much oil causes seals/oil to be pushed out. (no room for expansion) I always as a last precaution leave the top plug out long enough for it to level off and stop running out to leave a little room. If your running an expansion tank then it's not a worry. :-)

I do the opposite. I fill mine using a large pressurized can with quick disconnect and give them an extra shot before putting the plug. But I do not run stock seals. I run the 4 seal drive shaft/and dual shift shaft from Todd D on here. They are billet aluminum and have ZERO issues with water intrusion and have been doing it for years. Just my .02 cents.

Double Rigged - I'm not familiar with that set up? Any more details? Is the can pressurized with gear lube, or what am I missing? Thanks in advance....

Here is the link for it.

Gearcase Testers, Fillers