a bit confused on lower unit prop size?????

flyweed · **Posted:** Wed Aug 12, 2015 5:49 pm

Hey guys,

Ok, I finally ordered up, received and had installed by my local boat mechanic a new outdrive that came off of a 1990 180 Horizon that had the 3.0 OMC Cobra engine.

Shop mechanic installed the new lower unit, said everything went just fine and all checked out A-OK...but they had to charge me for a new prop, as my old prop a 14.5 x 19 prop WOULD NOT fit the output shaft on the new outdrive. the new unit they put on had a shaft size for a 13 3/8 x 19

Shop guy was actually surprised, he said he thought they'd all be 14.5 x 19 for the 3.0 OMC units.

Anyone have any insight on this?? I just want to be SURE I haven't put on a outdrive that isn't "correct" for my boat. again, it came off the same year and same engine that my boat had. I've had the boat out twice, and it runs just fine, but I am still stumped as to why it would use a different diameter prop.

Dan

DougT01 · **Joined:** Wed May 20, 2015 6:44 pm **Posts:** 121

I thought those 2 numbers represented pitch and diameter.

I would think spline size would be the same if same engines.

If not, I thought you could get a range of pitch and diameters for a specific spline.

Doug

flyweed · **Posted:** Wed Aug 12, 2015 9:55 pm

yeah Doug..I wish I knew more about these Outdrives.....all I know is the tag on the side of my new outdrive does INDEED say it is off a 3.0, just like my old outdrive..but my old outdrive used a 14.5 x 19 prop and this new outdrive, my 14.5 x 19 will NOT fit, so I had to buy a 13.875 x 19 prop for it.

DougT01 · **Joined:** Wed May 20, 2015 6:44 pm **Posts:** 121

If it's running good and correct Rpm's at WOT, you're good.
I just don't understand their explanation.

I am not a prop expert :-)

. I also have only owned OB's.

GottWhat · **Posted:** Thu Aug 13, 2015 9:02 am

Did the spline have a different number of teeth? You can always sell the other prop.

Regardless, I bet you are happy to be back on the water!

LouC · **Posted:** Thu Aug 13, 2015 10:18 am

Apparently there were 2 different size lower units for the 4 cyl models. Before a certain year (could have been '90 or '91) the 4 cyl models used a smaller lower unit than the V6/V8 gearcase. The later ones got the same lower as the V6/V8 gearcase. The prop shafts and the props that can fit are different.
It may be that your OE unit was the larger lower unit and the one they got you is the smaller one.

rpengr · **Posted:** Thu Aug 13, 2015 11:51 am

LouC wrote:

Apparently there were 2 different size lower units for the 4 cyl models. Before a certain year (could have been '90 or '91) the 4 cyl models used a smaller lower unit than the V6/V8 gearcase. The later ones got the same lower as the V6/V8 gearcase. The prop shafts and the props that can fit are different.
It may be that your OE unit was the larger lower unit and the one they got you is the smaller one.

Yes, I have heard of that. I have a friend with a late '80s boat that had a 4 cyl and the smaller lower unit. The diameter of the prop hub (and "bullet") seemed to be a 1/4" smaller than my cobra 4.3L He is now planning to put in a V6 engine, and is concerned if this smaller lower unit could handle the larger engine.

flyweed · **Posted:** Thu Aug 13, 2015 12:37 pm

GottWhat..you are correct, I am HAPPY to be on the water once more...It's very nice.

Otherwise, I'll have to count the splines on both my old output shaft and the new one. I am just stumped..as BOTH my boat, and the replacement drive boat were 1990 Four Winn Boats..both had OMC 3.0 (4 cyl) engines in them....yet my new outdrive has a smaller output shaft.

Lou, my understanding was that a small unit, gearcase, whatever was used until 1989..and then from 1990 until 1993 everything was the SAME.

flyweed · **Posted:** Thu Aug 13, 2015 12:41 pm

Ok...just checked my old output shaft on my old drive..it has the 15 tooth spline. I'll have to check my new one, when I get back up north where my boat is at the moment, at our camper. I can only assume it is a 13 tooth????

rpengr · **Posted:** Thu Aug 13, 2015 3:03 pm

flyweed wrote:

Ok...just checked my old output shaft on my old drive..it has the 15 tooth spline. I'll have to check my new one, when I get back up north where my boat is at the moment, at our camper. I can only assume it is a 13 tooth????

The spline may or may not be different. It sounds like there is less clearance for prop diameter on the smaller one. The lower gear chamber "bullet" may be a smaller diameter as well. So the prop hub would be smaller diameter to match.

flyweed · **Posted:** Thu Aug 13, 2015 6:00 pm

well, while pondering on this issue today, I came across some info on the OMC Cobra drives. I guess there was a Four Winns OMC Cobra 3.0 (cobra 400) drive that was built from 1968-1991..which was a 13 spline, and used a 13.xxx diameter prop. THEN came in the (cobra 800) which is also for the 3.0 OMC Cobra, and it used the 15 tooth spline and 14.5 diam. prop..this OMC 800 according to what I was reading started being built in 1990 - ????

So there IS a year of overlap between the Cobra 400 and Cobra 800, if I am understanding what I read correctly. Again, I KNOW my new drive came off a 1990 boat, so this could be the case ??????

Dan

GottWhat · **Posted:** Fri Aug 14, 2015 9:10 am

A lot of times boat builders make changes mid-year as they run out of old supply and move to new.

LouC · **Posted:** Fri Aug 14, 2015 12:17 pm

And sometimes a 1990 boat could have a 1989 drivetrain. The only way to make sure is to look at ID numbers and find someone who can decipher them. In this case it doesn't really make a difference as long as your gear ratio is right and you have the correct pitch prop. When it would matter is if you tried to use a drive with the smaller lower on one of the V6 or V8 engines, it might not take the torque of that.
They did something similar but in the opposite direction with the 460 King Cobra. This came with the 460 Ford V8. They determined that the normal V6/V8 lower gearcase was not strong enough for this big block application. So OMC used the V8 outboard gearcase on the 460 King Cobra, with the normal Cobra upper gearcase which was plenty strong. Yes OMC did make an Evinrude V8 outboard. It was a beast.

GottWhat · **Posted:** Fri Aug 14, 2015 1:09 pm

LouC wrote:

Yes OMC did make an Evinrude V8 outboard. It was a beast.

I had to look this up. Not only was it a V8, but it was a two-stroke! Here is a link to more info and some videos: http://www.roadandtrack.com/car-culture ... 8-startup/

flyweed · **Posted:** Fri Aug 14, 2015 3:57 pm

Yeah..I don't care as long as it works right..which it does. At first I was like...WHAT? Smaller prop....DAMN, now I can't go as fast. But I don't think that's the case

Dan

www.iFourWinns.com

a bit confused on lower unit prop size?????

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