1988 90hp 3-Cyl ELTPO -- lower unit replacement?

I need info on a replacement lower unit for my 1988 Mercury 90hp 3-Cyl ELPTO outboard.... serial #B374250...

I know there has to be other model year engines in different horsepowers that have a compatible lower unit that I could use..... Can anyone tell me what's compatible for a swap.... or point me to a good website/information that I could use as a reference.

Boat is 25 miles away, so I don't know exact shaft length, but my guess is either 20" or 25".

I also need some info on how to properly take the lower unit off the motor.... Does anyone have a link to a website with good instructions and/or a YouTube movie that demonstates how to do this.

Any information or advice would be greatly appreciated. I am fairly mechanical with car engines, but no expert by any means. I know only the very basics when it comes to outboards.

Thanks in advance.

Re: 1988 90hp 3-Cyl ELTPO -- lower unit replacement?

I'd start with an appropriate service manual from Merc. Answers most of the questions you asked including part numbers for parts you are seeking in the IPD (Illustrated Parts Diagrams).
Mark

Re: 1988 90hp 3-Cyl ELTPO -- lower unit replacement?

Ok. Any idea where I can find a decent manual for this model motor?

Re: 1988 90hp 3-Cyl ELTPO -- lower unit replacement?

You can use a 70-90 hp large diameter lower unit in the 1987-97 year models. The earlier units use a 3 jaw clutch dog and after 1998 they went to a 6 jaw design. You can use the 98 and later but will have to change shift rod and bracket. I suggest a factory manual from Ebay or other site as the Seloc is not up to par for the price.

Re: 1988 90hp 3-Cyl ELTPO -- lower unit replacement?

Done. Went to eBay and had a Merc-brand manual. Its in the mail. You mention a "large hub"..... I take that to mean that there's also a "small hub" for the 70 - 90 hp range for those years?

Would a lower unit from a 4 or 6 cylinder also work?

Re: 1988 90hp 3-Cyl ELTPO -- lower unit replacement?

There where some early model 70 3 cylinders that had a small diameter gearcase that you see on Ebay but these will not fit. A 4 & 6 cylinders will not work do to gear ratio's and the driveshafts are different. You have what we call the L3 engine.