New member, Mercury 55 powerhead question

[Boatingfun]

Hello

I have recently bought a Mercury outboard motor and I'm a new member here in this Mercury forum. I have been a member in the Yamaha forum for many years and have received a lot of help there and thank for that. Good to be here also.

I decided to open a thread because my friend's 2-stroke 55 (1994) blew a piston. He then got a brand new powerhead but that is year 1997. The seller did not tell him that it is different. Can this 97 model powerhead be used with the 1994 mid-section? How about the hole in the block? Shouldn't that be blocked?

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I have here pictures of different mid-sections and the old one on the left is the one that needs to be used because only that fits into the outer housing.

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I was going to test if cooling water flows right using the old mid section but can someone tell whether I'm worrying for no reason.

Thanks JJ/Europe

[boats.net]

Can you obtain the serial numbers from both motors? There is a freeze plug on the blocks with the serial number. With this information I can obtain more accurate information.

[Boatingfun]

Codes

Hi, the old blown powerhead was 0D054302. The new one is 0G642533.

What motor is that new one, is it 55 or 60hp?

Thank you, JJ

[boats.net]

Well the original powerhead is actually a 1991 50HP, the new powerhead is actually a 1998 Mariner 55HP. The blocks are not interchangable. There is no discription as to what the differences are.

[Faztbullet]

The difference is the 1991 block is a small bore 51 ci and the 1998 is a 58 ci..