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Merc 260 questions...

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What year did Merc switch from the small upper bearing to the large upper bearing? Is there a difference in the crank journal or just the OD of the bearing and the bearing cap?

What year did they change from the big rods to the small rods?

Any other changes to the motors as they grew up from the early 90's?

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Some of this is from memory and the years may be a bit off:

Crankshaft - The small bearing cranks were used in the early 260's and Drag engines. The big bearing cranks arrived sometime in mid '98 as the small bearing cranks were used up in production.

The early cranks used a pressed on sleeve to hold the bearing in place. In extreme conditions this sleeve can work its way loose and damage the top crank seal on the block.

Pistons/pins - The early Mahle pistons had a slightly higher ring pack that gave slightly more compression than the later Wiseco pistons, and had a slighlty lighter weight wrist pin. The change-over occured in '96 - I believe (I don't remember for sure).

Connecting Rods - The 260's used large bottom guided rods with the Mahle pistons. With the change to Wiseco pistons, the engines used the top guided small rods. The 280's used the large top guided rods (as did the later drag engines). In 2001 the Drag engines changed to single ring pistons and large rods.

Port height - The early 260's had lower port height that got a bit higher each year until '97 when the Drag engine was introduced mid year - I believe as an early '98 engine. The '97 Offshore 260 engines seem to have the best (and most accurate) port height and chamfers. I believe they were actually rated with a bit more power than 260.

I hope this helps.

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