1979 55hp vs 1980`s

[Boblester40]

hi..
I have a 1979 55hp johnson wiith two bad pistons , now thw 1979 pistons are very exspensive and i wanted to know what changed between 1979 and around 1980 / 81 as the piston changed but the con rod remained the same as did the bore diameter etc. they are both flat top pistons but the pre 1979 has ports in it where as the post 1979 ones does not, did the style of block change also ?

regards
bob

 

[jay_merrill]

Re: 1979 55hp vs 1980`s

If you are trying to determine whether the pistons in a later motor can be swapped into your engine, you might want to reconsider and see if you can just swap the whole powerhead.

I have no idea if an 80/81 powerhead will fit on your '79, but taking a look at the gasket that goes between the bottom of the powerhead and the adapter plate can be a start in the research. At first glance, the part numbers are different between a '79 and an '80, but that does not necessarily mean that they are different. Over the years, many of the OMC part numbers were superceded, so sometimes you will find a part with a newer equivalent.


PS: I just went back and compared the crankcase halves and the exhaust housing adapters. The crankcase halves are different part numbers between the two years, but the adpaters are not. That at least suggests that the '80 will bolt up to the '79 midsection.



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