Tohatsu M8b 3B2...lower unit cracked?

Canaan

Cadet
Joined
Apr 4, 2011
Messages
11
So, awhile back my dad bought a 14ft boat and trailer w/ a M8B 3B2 8hp outboard as a 'stump jumper' to fish around the house. It set up for the last 2 yrs and I went out to see if I could get it running the other day. Found that it would not turn over and would not shift from gear to gear.

So, to tore down the lower unit...found NO OIL at all and the gearing in the foot was was rusted to hell and locked up. After pulling the foot, the engine would turn over fine, so the cylinders are not locked. I tried to oil the gears up and let them sit in hopes of getting them loose and just replacing the seals and bearings. The water pump looked fine.

But, after spraying some penetrating oil down in the foot, it starting leaking out the side. It has a ~2" crack in the lower unit. So, I'm guessing the foot had not oil and got full of water, then froze over the winter and busted the foot.


I found the parts catalog online and know the part #'s i will need. Gear case, prop shaft housing, bevel gears, bearings, etc.

So, does anyone know where I can get a new foot and other parts for this outboard? Or is it a lost cause? Possibly weld the crack up and just replace the gears, bearings and seals?

Thanks for any help you can give.
 

pvanv

Admiral
Joined
Apr 20, 2008
Messages
6,500
Re: Tohatsu M8b 3B2...lower unit cracked?

Tough spot. You must replace the rusted gears, as any pitting on them will cause them to deteriorate rapidly. Welding the gearcase is sometimes possible, IF you get the right guy to do it, but usually not cheap. Replacing gears requires setting backlash, which requires a special tool and a dial indicator, so it's labor-intensive.

Assuming you have a short shaft, the whole lower unit (driveshaft and all), already set up, is 3B2S873014 LOWER UNIT ASSY SHORT 8B-9.8B $579.20, which is presently out of stock, or for the long shaft, 3B2S873024 LOWER UNIT ASSY LONG 8B-9.8B $627.45. You can interchange driveshafts as you wish, as long as your old one isn't too bad.

Bang for the buck, you are probably better off getting a used 8 or 9.8 with a blown powerhead, and doing a mix-and-match.
 
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