Lower Unit model #'s

[SHickey]

Hello,

I was wondering if anyone has a link to identify LU series #'s that are compatible with my '87 2.3 Cobra unit. I am in the market to replace the LU I presently have because it is geared for a 5.0 instead of a 2.3.

I am having a time trying to figure out a decent prop configuration that will get my motor to hit it's recommended RPM's. The two props I have 13.25X17 and 13.25X19 are too much prop for the set-up. I would expect they would work fine with the correct gears 2:1 for a 2.3 motor.

Thanks for any input.

SH

 

[Howard Sterndrive]

Re: Lower Unit model #'s

I think you might be confusing upper with lower or something because 13.25" props don't typically fit a 5.0 lower unit. The 5.0 lower has a large 15 spline propshaft for which props are 14.25 dia.

13.25 props are 13 spline.

 

[SHickey]

Re: Lower Unit model #'s

It has been very frustrating for me to figure out this LU. It was a replacement and not the original. The original boat paperwork said the Blue Fin came with a LU model # 985583. The model of the LU on the boat now is 984540 and it does not have a 2:1 gear ratio. It is more like a 1.59 ratio so I don't know if I should re prop the LU or replace it altogether and keep the one I have as a spare.

I have a guy that has a LU from a Cobra 3.0 and the LU model #985268 and I would imagine that would be compatible with my present set up.

SH

What would you do given this situation??

 

[Howard Sterndrive]

Re: Lower Unit model #'s

What would you do given this situation??

1. learn the terminology- NO Cobra Lower units have model numbers on them - never did ever.
model numbers are only on upper cases

2. ignore those numbers - 20 year old drives can be rebuilt with different gears with tags left on (I don't know why rebuildrs do that but seems almost a given)

3.treat the upper and lower as two separate things. Split the two and turn the input of the upper 10 times, count the output shaft turns, do the same for the lower - get a calculator out and figure out what you have using the charts in the back of the Seloc Cobra manual.

 

[SHickey]

Re: Lower Unit model #'s

Thank you for your response.

The LU on my outdrive has a # stamped on the bottom of the case just below the trim tag. I thought this # was a model # but from your experience these #'s are meaningless considering these cases are 20+ years old and could have been rebuild one or more times.

I will split the two and do some calculations as you advised.

 

[Howard Sterndrive]

Re: Lower Unit model #'s

maybe someone else can chime in if they've ever seen the tag there
I've never seen a tag on a lower. Someone may have fastened it there I suppose. That is the number for a complete 2.3 ratio drive, but not a lower unit. Lower units had no model numbers.
upper:

lower:

 

[SHickey]

Re: Lower Unit model #'s

The # that I see on the bottom of the case (on the LU) is stamped on. It is not a tag that was attached to the LU. It seems to be an part identification # similar to those stamped on other components.

SH

 

[Howard Sterndrive]

Re: Lower Unit model #'s

that seems to indicate that the lower case should have 2.3 gearing in it, or it did originally. So if the upper was from a 5.0, that would explain the goofy overall ratio. You could take the top cover off the upper without removing the drive and have someone bar the engine over (ignition off). Using white out, you can mark a gear tooth of each gear and count teeth to see what gears are in there.

Again- the Seloc is the best resource for all the Cobra tooth counts and ratios.

 

[SHickey]

Re: Lower Unit model #'s

Thank you again Captain, it did not dawn on me that maybe the upper was from a 5.O and the lower was correct for my 2.3. The upper seams to perfectly match the outdrive assembly while the LU was a different color from the rest of the OD.

I will start counting some teeth in the upper and see what I have. Maybe the tooth fairy will replace my whole OD (upper and lower) and I will be done with this mess.

Thanks again Howard, you really know your stuff.