V4 and V6 Lower Unit Compatability... (2024)

Wondering if a lu from a 1993 115 will swap into a 1988 150. Looking at brp's parts diagrams they both have the same length shift rod, but I'm not sure if the gear ratios are the same.

Thanks for any help,
Hunter

Re: V4 and V6 Lower Unit Compatability...

read this: http://forums.iboats.com/showthread.php?t=359907

Re: V4 and V6 Lower Unit Compatability...

Horsepower--------------------------------------Years that interchange

40/48/50/55/60..... (small diameter housing)..................1976-1988
40/48/50................................................ .................1989-1992
40/48/50................................................ .................1993-2005
70/75............................(20 inch shaft)......................1978-late 1981
60/65/70/75................................................ .............1982-1988
50/60/70................................................ ..................1989-2001
85-140.............(crossflow 13 spline prop shaft).............1978-1991
88-140.............(crossflow 13 spline prop shaft)..............1992-1998
120-140 Looper V-4... (15 spline prop shaft)...................1985-1991
75-115 60 degree........(bat wing unit 13 spline)...............1995-2006
150-235 & 2.6.................(crossflow V-6)......................1979-1991
185-225.........................(Looper V-6).........................1986-1991
185-225....................(Looper V-6 & Ficht)....................1991-2005
150-250.......................( Magnum Series).....................2002-2007
150-250........................(Lighting Series)......................1997-2001

Thanks TD. I know a v4 lower will bolt on to a v6 as long as the shift rod is the same height, so this list isn't quite correct, correct? I'm pretty sure the two will interchange, but aren't identical (different prop splines or gear ratios, etc..)

Re: V4 and V6 Lower Unit Compatability...

The V4 will bolt up and work. The V6 is a 1.86:1 while the V4 is a 2:1. The props will not interchange but the gear ratio difference will dictate a different pitch anyway. The V6 torque will be pretty hard on the smaller V4 gears. We use V4 gearcases on V6s on performance boats for less gearcase drag (smaller units).

Why exactly do you want to do this anyway? What type boat do you have? What type boating will you be doing?

Re: V4 and V6 Lower Unit Compatability...

List is correct and for direct interchange. The 1993 will not bolt up due to driveshaft and crankshaft lenght differences. It will work with some slight mod's but this is good for "hot rodding"only as stated. You will also have to get another prop due to gearcase diameter difference and gears wont last long under a heavy boat. Below is list of shaft lenghts:

1979-91 V4/V6 crossflow and loopers: 21 3/4
1992-up V4/V6 crossflow and loopers: 22 1/8
1991- up 60 degree V6...................: 21 5/16
1985-1994 V8...............................: 21 3/4
All measurements from top of driveshaft to underside of water pump wear plate. All rounded to nearest 1/16. All measurements for 20" shaft models. Add 5 inches for 25" models Old style cranks are longer so driveshaft will be shorter. It depends on year of gearcase also. I use the attached chart when swapping cranks to get correct d.s. length. Also here are crank measurements for V6 loopers:
Old (91 & back) from bearing seat to end of crank=2.397
New ( 91 &up) from bearing seat to end of crank= 2.121
Old (91 & back) from bearing to d.s. end=1.425
New (91 & up) from bearing to d.s end= 1.228
Measurement may be off couple of thousands due to machining but close

Re: V4 and V6 Lower Unit Compatability...

I am thinking there are at least two different V4 small gear case LU's.. and then there is a large gear case V4.

now because the gear cases are different, I guess doesnt mean they wont bolt up...

also I recently looked up on the brp site and they listed a gear housing and bearing assembly that fir my motor as also fitting the FITCH motors in 4 cylinder

are the fitch motors 60 degree blocks??

but the BRP interchange is kinda funny....youd think if they list something as interchangable with another motor, they are saying it was part of that motor...that isnt true, because they list 90 hp and 115 hp carbs on the same year and model blocks..

same goes for 9.9 and 15 hp carbs

also the heads for 90 hp and 115 hp s on the 60 degree blocks have different part numbers, but are said to be used on all 90 and 115 hp motors in 60 degree from 95-99!!!! but!!we know they only came on their respective hps

so interchange and "came on" are two different meanings

I have a link at work that shows the different heights of the lower units...and some are VERY close to being the same length...small fractions of an inch different!!

actually I just found it:

http://www.sterndrive.info/outboardmotor/help_identifying_lower_units.html

pretty good info

even the dia of the hub is very close.

I would think that if the water tubes fits and the splines match...a lower unit that is 1/16th " different in length would still work!!

bob

Re: V4 and V6 Lower Unit Compatability...

Dhadley said:

The V4 will bolt up and work. The V6 is a 1.86:1 while the V4 is a 2:1. The props will not interchange but the gear ratio difference will dictate a different pitch anyway. The V6 torque will be pretty hard on the smaller V4 gears. We use V4 gearcases on V6s on performance boats for less gearcase drag (smaller units).

Why exactly do you want to do this anyway? What type boat do you have? What type boating will you be doing?

Click to expand...

Well, I have a good lower unit for a '93 150 sitting in my garage. A friend has an '88 115 with a locked up lower unit. If the swap will work I'm going to buy the 150 and put it on my 17' Stratos F&S. It will definitely be an upgrade from the '77 115 I have on there now.

Thanks,
Hunter

Re: V4 and V6 Lower Unit Compatability...

bob johnson said:

I have a link at work that shows the different heights of the lower units...and some are VERY close to being the same length...small fractions of an inch different!!

actually I just found it:

http://www.sterndrive.info/outboardmotor/help_identifying_lower_units.html

pretty good info

even the dia of the hub is very close.

I would think that if the water tubes fits and the splines match...a lower unit that is 1/16th " different in length would still work!!

bob

Click to expand...

I just checked your link and I definitely have the fourth one listed. v4 90* small gearcase. 1978 thru 1998.

Re: V4 and V6 Lower Unit Compatability...

Thats good information on the housings but it tells nothing of gear ratio and interchange.The housing are almost the same on the V-4's it the driveshaft lenght, install a unit with to long a shaft and it will bind up the power head or break the bearing race retaining pins in block. Good Luck...

Re: V4 and V6 Lower Unit Compatability...

Thanks FZB. I'm sure that if the driveshaft is too long I could machine a little off of it...but I don't want to start too big of a headache with lots of modifying. I'm gonna go look at the motor and old lower and see just how far they are off, and if it would be worth my time and potential wear and tear on the lower to make this work.

Thanks again,
Hunter