Do the Mercury Drysump VI have different reduction ratios in the bottom half of drive??
Some are telling me they are all 1. to 1.,others say possibly different ?

Thanks for your relpies !

19/20 tooth for standard
19/21 tooth for "split ratio"
5% more reduction in split ratio, so multiply posted overall ratio by 1.05 to get correct overall ratio.
Example: Upper is marked as 1.35 ratio (this is the overall ratio, upper and standard lower). If you have a standard lower, the total ratio is 1.35. If you have a split ratio lower (stamped on the strut above the propshaft, 1.05), you have a 1.42 overall ratio drive.

Thanks for your help Falcon !
I have this new #6 lower half in the classifieds http://www.offshoreonly.com/classifi...o29393-en.html and the 1st question i get is "What Ratio is it ?"
It doesn't have a stamped ratio on it and all i have are the exposed gear set to ck.35 teeth on each gear.
If i spin the Prop shaft 19 times then the gear set will exactly re-align.One turn of prop shaft it doesn"t.
Is it possible to figure out ratio from that ?

Thanks Ken

What is important is how many turns did the vertical shaft make? If it made 20, it is a standard ratio, 21 it would be the "split" ratio. From the factory the standard ratios are not marked, the split ratio lowers are marked 1.05.
Just as important in selling it is the intended rotation. It should be marked on the back of the strut above the propshaft, just like the ratio on a new one is. Actual rotation of the unit does not change, but the timing of the spur gears is done to have proper gear loading. If it marked with an "R", it should be run only with a RH prop, etc.

Thanks again Falcon !
The vertical turned 20, so the standard 1.35 it is.
I'll have to ck.the history on which side it purchased for
.No L or R stamp on it.

No, there is no such thing as a 1.35 ratio lower! I guess I shouldn't have used the example including the hypothetical upper. The 1.35 ratio I had in the earlier post is an example if you have a listed 1.35 ratio upper.
What you have is a standard ratio lower that is 20:19, for all intents and purposes it is considered a 1.0 ratio lower. The "split" ratio 21:19 is about 5% more reduction than the standard lower, so it is considered and marked as a 1.05 ratio. Multiply this and the listed and marked upper ratio and you get the overall ratio.
This all started because Mercury only offered a single ratio lower at first, so they always sold the upper gears by the overall ratio combined with the standard ratio lower. It was simpler at first, but now it seems if it would have been simpler to mark everything by it's actual ratio.
Sorry for the confusion, sometimes I go too far when answering a simple question.

If forgot to mention in the earlier post, from the picture it should be a RH lower. The nozzle for lubricating the spur gears is on the stbd side, which if nobody made a mistake during a rebuild, should indicate it as a RH rotation lower. If this lower did not have a rotation mark on it, it is an older drive. Just to double check, the rotation should be stamped on the back of the strut just above the propshaft.