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Tohatsu

1962 OB2B
Early OB2 sell-sheet

I owe a tremendous debt of thanks to the fine people at Tohatsu America who helped me get information about this 1962 Tohatsu OB2B outboard. Tohatsu is Japan's oldest manufacturer of outboard motors tracing their roots back to 1922. They were a maker of motorcycles, mopeds and small engines for a variety of applications. The little OB2B seen here can trace its design back to 1956, the powerhead previously used on a motorized sprayer. They had built a small number of outboards prior to 1956, but the need for a small motor to be used by Japan's many fisherman led to the development and eventual success of the OB2. The first versions were 58cc and 1.5ps (ps x 1.014=1.521hp) at 4,000rpm and had a generating coil that produced 6-8v and 8 watts. For additional information on Tohatsu's history, I refer you to their website: Tohatsu company website and be sure to check out the free eBook link at the bottom of their site called Tohatsu History of Reliability.

None of the technical publications in the OJM library cover this motor and there is only a small photo and mention on the Tohatsu site. (Theirs has the addition of a recoil starter. This one doesn't appear to have ever had that feature) Stamped on the back of the leg where it meets the powerhead is the build date of DEC 3 1962. It appears to be rated at 2.5ps. (2.535hp) I did find a 1/2 page ad in a trade publication BOATING INDUSTRY MARINE BUYER'S GUIDE from November 1963 - so they were offered for sale in the USA at that time.

People with a keen eye will note the similarity in the leg to that of an HD-25 Johnson. The tiller arm even has the mounting hole used on the old HS gas tank! The paint and colors are all original and appear to be inspired by the Smurfs, the paint is good enough that I won't change it. The powerhead is air cooled - we doubt there is also a waterpump since there is a muffler on the starboard side. The motor appears to be piston ported though it has not been disassembled since it runs well - it is, however, a loop charged design. (This is the oldest loop charged outboard motor that I've come across) This example also has the generating coil producing 6-8 volts and 8 watts - two thumb screws are provided on the front to attach the wires.

A friend in the AOMCI found my Yamaha P-35 interesting and offered to trade this to me for some other motors in my collection. If you have any information you can share regarding these early Tohatsu outboards, please contact me.

I was really impressed with the customer service at Tohatsu. They promptly answered my email and were able to dig up quite a bit of information on this motor. (Most of it came all the way from Japan!) This type of good olde fashioned customer service means a lot, if they are this good with a 50-year old outboard, I'll bet they are exceptional with their new products! In my opinion, more companies should model themselves after Tohatsu.

1962 Tohatsu OB2B 2.5ps

Year & Model: 1962 OB2B
Horsepower: 2.5ps (2.535hp) @ 5,000 rpm
Cylinders:
1

Bore: 42mm (1.65")
Stroke: 42mm (1.65")
CC: 58 (3.53CID)
Ignition: Magneto
Point Gap: 035mm (.014")
Cooling: Air
Condition: Unrestored
Retail price when new:
Weight: 17kg (37.5lbs)
Oil/Gas Mix: 16:1 aircooled
Spark Plug: NGK B6 (Now B6S)

Comments:
This little guy runs well in the test tank, it is relatively quite and smooth for an aircooled motor. I hope to offer a full report soon!

 

(Click on the images to the left for a larger version)

 

 

 

 

 

Had a chance to make a short video of the Tohatsu running on the boat. It moved the old Duranautic 12' along very well for a 2.5ps motor, I was impressed! It is very smooth but quite noisy at full throttle, my decibel meter said 103 at the skipper's ear - ear plugs are a must for long voyages.

 

 

Here are a few additional photos of the motor:

Missing the carb cover
Note retainer for gas cap on the outside of the tank!
Note drain petcock on bottom of crankcase. Appears original, I've never seen anything like it before. Nice beefy grab-handles on the back & front of the motor.
The ID tag indicates it is a model OB2B and 2.5ps (2.535hp) I would be interested to know what the Japanese writing says.

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