1973 Johnson 135hp piston help

[Krakenmama]

Firstly Hi from Australia.
I have a 135hp Johnson that we have been rebuilding and some time ago purchased online 020 sierra pistons.
We were first told that 1973-1976 were the only years for a 135hp and the website we purchased the pistons from showed the part number for 1973-1976 so we thought we were safe. This was some time ago and since then a new computer and a CC hacking the required cancelling means we have no receipt or proof of purchase.

anyway upon reassembly I find out the pistons have a way different gudgeon pin height and subsequent research tells us that in fact there was a different 135hp for 1973 to the ones made in 1974-76. detailed serial numbers etc. are well worn off this engine.

So I have a rebored 020 1973 135hp with matching pistons that I either purchase new pistons for and rebore again to 030.
Or can I search for some 1974 conrods that will fit?

Help please

 

[emdsapmgr]

Re: 1973 Johnson 135hp piston help

I believe the length of the connecting rod changed in the 1974 model year. That changed the height location of the piston pin in the piston. No, they won't interchange. A good thought to consider using the 74 and up connecting rods. However, the crank part number changed also. Possible it's a significant change (could affect the height of the rotation) and may affect what you are trying to do, or perhaps it is not significant. If you could determine if the crank journals were machined the same as the 74 and up, it's worth changing rods.