are lower mercrusier units interchangeable

[catotdo]

two questions
I have an alpha 1 generation 2 outdrive on a 4.3 v-6...my lower unit needs replacing....can I replace the lower unit with an alpha 1 gen 2 that came off 4 cylinder engine.
question 2 I have the plastic trim tabs on the outdrive and one is cracked....should I replace them or not....do they really help in trimming the boat. Thanks John

 

[sharkin95]

Re: are lower mercrusier units interchangeable

yes ..the lower's are interchangable as long as it's a alpha 1 gen 2. I don't use the bat wings but a better suggestion is trim tabs mounted to the stern.

 

[mercs4mark]

Re: are lower mercrusier units interchangeable

MY Experience with the plastic whaletails is take them off.... I have seen many outdrives cracked because of them.

 

[DaveG55]

Re: are lower mercrusier units interchangeable

yes ..the lower's are interchangable as long as it's a alpha 1 gen 2. I don't use the bat wings but a better suggestion is trim tabs mounted to the stern.

Ummmm, not quite. They are all PHYSICALLY interchangable BUT each motor / stern drive unit will have a different gear ratio and if you do not replace the existing drive with a similar ratio drive you may very well alter the performance charicteristics of the boat for the worse and possably even cause severe engine damage.
If you are replacing the drive, replace it with the same ratio drive. The ratio will be stamped or marked on the drive. Also, used drives are notorious for having defects. You might be better off using one of the SEI units. They are new and have a 3 year no-fault warrranty. I have a friend that just hade one put on this year and has been happy with it so far.

 

[DaveG55]

Re: are lower mercrusier units interchangeable

MY Experience with the plastic whaletails is take them off.... I have seen many outdrives cracked because of them.

Just for a counter point...

I have had one on my 20'6" bowrider with 5.0/A1G2 for 12 years now without a single problem. And yes, it does help with the trim. Not as much or as versitile as stern mount tabs but not nearly the cost or install trouble either.

 

[sharkin95]

Re: are lower mercrusier units interchangeable

I guess you missed the point the question was are the LOWER UNITS the same. I have Nautilus trim tabs which are stationary tabs My boat is 3400 lbs loaded I plane at 2400 rpms with a 4.3 v6 had them for 5 yr's in saltwater cost on sale $150.00.

 

[Don S]

Re: are lower mercrusier units interchangeable

Ummmm, not quite. They are all PHYSICALLY interchangable BUT each motor / stern drive unit will have a different gear ratio and if you do not replace the existing drive with a similar ratio drive you may very well alter the performance charicteristics of the boat for the worse and possably even cause severe engine damage..

Yes you can replace the lower with the one from a 3.0L.
The upper is where the Gear ratio changes, not in the lower unit.

 

[PaulHaig123]

Re: are lower mercrusier units interchangeable

Don S or anyone,
I am looking for some further confirmation that the Mercruiser lower units are in fact interchangeable.
I have Alpha 1 Gen II 2.00R and have managed to destroy my lower unit.
I understand that the actual gears for the ratio are in the upper unit. However some quick internet research shows that there is actually 2 different lower units available depending on the ratio of the drive.

See:

815822A45 GEAR HOUSING ASSEMBLY, Standard Rotation (COMPLETE)
(2.00:1 AND 2.40:1 RATIO)

OR

815822A43 GEAR HOUSING ASSEMBLY, Standard Rotation (COMPLETE)
(1.47, 1.62, 1.81, AND 1.94 RATIO)

What is actually the difference with these 2 part numbers? Are lower units from a 1.47,1.62,1.81 or 1.94 actually interchangeable with a 2.00R Upper ?

Any clarification would be greatly appreciated.

Regards,
Paul Haig

 

[PaulHaig123]

Re: are lower mercrusier units interchangeable

Here is what I have learned through chats with Sterndrive engineering, consulting the Mercruiser Service Manual 14 and counting the teeth on my exploded lower unit.

Not all Alpha 1 Gen2 outdrives share the same lower end.
Thus the ratios are not ONLY in the upper.

- IF you have a 2.00:1 or a 2.40:1 drive the lower unit is geared differently (12 tooth pinion, 24 tooth forwardgear 2:1)
- IF you have a different ratio drive the lower unit is geared with a more common ratio (13 tooth pinion, 21 tooth forwardgear 1.62:1)

Technically the lower ends are interchangeable and you can reprop, but if you want to stick with factory ratios on a 2.00:1 or 2.40:1 drive you will need a lower end with 2:1 ratio.

(I have found out that my lower unit on my 2.00:1 drive that the lower unit was swapped by the previous owner with the other 1.62:1 lower unit, I am curious what will now happen when I reprop with the correct lower unit. )

Paul.