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I won this powerhead [long block] in a British auction. It is 50 hp, 3 cylinders ,but, it is not 43 cubic inches like the normal 40 and 50 horsepower Yamahas we see over here. It has a serial number 100189 on the block. It looks a lot like a 70 6H3 or 6H1 block. The papers I got with it say it had a 14:24 gearcase, a 11 3/8 x 12 pitch prop, 4500 to 5500 rpm operating range and a compression of 6.30. The documents look totally yamaha. I am at a loss with the 62F code. It doesn't match the normal Yamaha outboard codes. They go "number","letter", "number" [example 6H3] This motor is 62F! Anyone know what I have here?
thanks
Don

Looking online it looks like a 1993-1994 powerhead for a model 50G. Just seems to be next generation of the 6H powerhead.

http://continuouswave.com/whaler/refere ... Guide.html

Yep...what andrew said...

There are some differences too...they don't interchange easily with the older block. I can't remember why right now....

Thanks Guys, so it is 1993... 50hp.. With the low 4500 to 5500 rpm range I thought it was a commercial motor. But, the Compression is higher than a 70 hp. It likely had a small nitro foot like the 55 hp 2 cylinder model. I am afraid to take it apart because there could be parts I can't replace. I posted on Ron Hill's site. Someone overseas should know more.
Thanks it is a good start.
I may have a Thunder Cat Motor.

I'm amazed actuallly... LOL

I went on British ebay and was able to buy YAMAHA OUTBOARDS PARTS CATALOGUE FOR 1993 3 CYLINDER MODELS

COVERS- 25J/30D, 40H, 25Q/50G, 60F/70B, 80A/90A, ALTERNATE PARTS , NUMERICAL INDEX

A4 IN SIZE , 1993

Now I will be able to see what fits and what parts are interchangeable so I can try this powerhead. With a 4500 to 5500 rpm operating range I don't think it would be much of a performance motor. I just hope a lot of the parts are common.

Now this is really starting to get interesting!
I was e-mailed this link......Thunder Duck Motor?

http://www.marineengine.com/boat-forum/ ... Shortshaft

you can use any motor on a thundercat, but the main engine of choice is Tohatsu and Yamaha some guys run the merc seapro mainly in the states, on the tohatsu most guys knock the rev limiter off and weld the crank thats about it.

They made some 50's outside of NA that I think were detuned 60's...so it may well look A LOT like the 60/70 lol. I don't have much info on engines that didn't come here....

There are 2 versions of the 43ci Pro50 as well...but given the location I would bet that it's an 850 motor...

Looking at the picture, the cowl seems to be a 60 or 70 hp manually start. The mid looks to be a 70 short. The clamp brackets look totally different. Maybe it is just the angle of the picture and this is actually a 43 cubic inch short shaft. I am amazed at the number of different motor combinations Yamaha sold in different parts of the world.

Rick if it is a detuned version of the 6H3 powerhead. Then the difference would be the reed stops, jetting and 2 to 4 more degrees of timing. That would explain them running it in a 50 hp Thunder Cat class. The motor would produce in the 60 horsepower range and be competitive until it raced against a 50D Tohatsu which is lighter and produces the same 60 hp.
So it may not be a top Thunder Cat 50 hp motor, but? maybe T750???