The 59 cubic inch models came out in 1998. There are 2 different midsections and gearcases depending on the model year. They did manufacture both short and long shaft versions. The biggest weakness is the bolts that hold the gearcase carrier in place backing out and causing serious damage to the gearcase. That problem can be solved using studs/bolts with locking tabs. A good motor will have approximately 120 compression. Replacement parts from mercury are very costly.
There are 2 different crankshafts. The only difference is the spline. There are 2 different diameter driveshafts. The 60 hp will have the larger diameter driveshaft. You will see both big foot gearcases and the smaller gearcases on different models.
The 59 cubic inch models on a TBoat are noticeably better than the 52 cubic inch models with better acceleration and top end capabilities. You can modify the 59 by using Jeff Dunn high compression pistons and they will produce 90 plus hp. Because the 40 and 50 hp short shaft versions are more common than the 60 hp models and because they are basically the same as the 60 hp, those models are modified more often.
Many say the 1998-9 blocks flow better than the later models.... true?? Maybe?? Generally the early castings are better when the same castings are used for multiple years of production. I think a good cleanup of any block is necessary and the result is equal.
It’s difficult sometimes to tell the difference between a 52 and 59 block. Check the exhaust cover. Normally the 59 will have a sticker there stating it’s a 59 cubic inch.
Here’s a short video of what a 59 powerhead looks like.
https://www.youtube.com/watch?v=dSsL-bZ909U
