Yamaha Lower Unit

[Marc Gershel]

Hi, I've been looking to replace one of my engines, and I found one at a very reasonable price. The only problem is it has a short shaft. Would my old lower unit work if, I swapped it with the short one?
Thanks, Marc 36021

[Allezcat]

Yep!
You will have to also change the water feed tube. I think the shift rod on the old lower unit will match up ok.

Chet
Allezcat 36010

[Marc Gershel]

Hi Chet, thanks for replying. I have another question. The long shaft is 20',and the extra long shaft is 25". My ex-long lower unit has a 3" sleeve/spacer. It seems to me that I would be 2" short. What am I missing? The new engine is about 3 hours away, and I wanted to try and figure this out before picking it up.
Chet, I hope everythings' been good with you,
Thanks, Marc

[Allezcat]

Mark

Good question. I have no answer!
I checked the upper & lower casing part numbers on the L model vs the X model. They are the same which tells me that the 3" extension, longer driveshaft and longer watertube are the only difference. I don't know how you get a 5" higher transom dimension with a 3" extension. I did look in the general specifications of the service manual. It gives a 3 " difference in overall height between the L & X models. The swivel bracket and bracket clamps part numbers all match also. I have attached a page from the maintenance manual which shows the transom height dimension (H4). It appears the height difference between the "L" model and "UL or X" model is really only 3".

Yamaha Specs.jpg (145.85 KiB) Viewed 16283 times

Chet

[Marc Gershel]

How strange is that ? Page 2.2 shows 15", 20", 25", and 9 pages later it's 17",22",25". I guess I'll have to take some careful measurments in case there are some model changes before I commit to the new engine.
Thanks Chet
Marc

[amytom]

Hmmm...
so with a spare lower unit in the locker I could keep a whole spare 9.9 on the dink? Kind of heavy to move around but with the main halyard as a hoist...?

Is the shorter lower unit geared higher or is it still the high thrust?

[Marc Gershel]

I think, if the lower unit has the large prop, that would show it's high-thrust.

[Allezcat]

I believe that if the model number has a T in it, then the lower unit is a hi-thrust (2.92 ratio). If not, it is a standard 2.08 ratio. I do not know if a hi-thrust lower unit will fit a standard engine.

Chet
Allezcat 36010

[amytom]

Marc,

It would be interesting to know what model number your new engine is and how well your old lower unit matches up.

I have a spare 9.9 or two and my dink engine is only 4hp so I'm thinking I might be able to carry a spare and re-power the dink at the same time. Of course long shaft high thrust would be silly on the dink but if the "F" model lower unit will fit...


Tom

[Marc Gershel]

Tom; I also have several 9.9 around, and decided to switch a good lower on one , with a good upper from another, instead of buying the new engine with a shorter shaft. Good thing I did, because it tuned out that hardest part ( almost impossible) was trying to remove the 3" extention sleeve without destroying it completely. As hard as it is to drop the lower unit, I could not budge the extention.
I'm hoping my new "solution" will work, while I look for a newer extra long engine.
Marc

P.S. Does it help to use Never-Seize to make things easier for future disassembly?

[amytom]

I looked up the extension peice at Boats.net $111.72. Not too bad as long as the main casing isn't damaged trying to pull the studs out. That casing is $271.80.

For the antiseize; I'm not sure. I've had luck with it but a marine mechanic I talked to said it washes away and jams up the works.

[Allezcat]

I've had pretty good luck with Lanacote.

Chet

[Marc Gershel]

Chet & Tom, Thanks for the input. Thought I'd get everything put back together today, but I just got done shoveling out from a 20" snowstorm. You remember snow, right.
Thanks, Marc

[amytom]

The only snow that we get down here will get you 5 years.