I wanted to see what the differences are in the 225 EFI / 250 EFI / 250XB / 300PM blocks and cranks?
Also on the 225 and Promax, where there any differences from year to year?
I have a 2000 225 that I currently building up, and I am in the process of buying a 98 PM block for a backup/upgrade to that motor in the future (and it comes without a crank, thus that part of the question).
Welcome to BBC!
Your request is far too broad (there's a myriad of information and variables involved, including multiple engines, multiple models, and a variety of years).
In order to attempt to answer this type of question, it will be necessary to have a SPECIFIC SERIAL NUMBER (or TWO specific serial numbers) for comparison.
You must also remember that we must be comparing identical displacement engines (all 3 liter or all 2.5 liter).
Two engines max for comparison, preferably.
Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
Still consider myself a "Marine Apprentice" after 48 years (learn something new every day).
Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor
Sorry for the broadness, but I guess that is also how I was trying to shape the answer, but maybe that isn't pragmatic.
What I am trying to determine, is on the fuel injected 3L series, from say 1996-2001, in general terms what the differences are block wise. Are there significant years for changing in porting, internal improvements, etc... and in general terms are there porting differences between the 225/250/300 across the years... end result is to determine what years and displacement blocks would be most desireable as a starting point for a motor build up.
In terms of cranks (for 3L 225/250/300), I see references to loose style center mains, and new style center mains. Are these interchangeable within the blocks, or do the bearing raceways dictate that they can only be used in their respective cutoff years?
Here's a little info to get you started (keep in mind please- part numbers are referenced to SERIAL NUMBERS.... Mercury does NOT use "year models"). For accurate information, we need to compare two specific serial numbers....\
<u>
CRANKSHAFTS (225/250)</u>:
Serial Number 0T325116 and BELOW use #9784A4 Crankshaft (or one of several part numbers superceeding to 9784A4).
Serial Number 0T325117 and UP use #9784A11 (also used in the 250 XB).
<u>Blocks</u>:
Prior to Serial Number 0G960499, the 225/250 engines use the same BLOCK.
Serial Number 0G960500 and UP: 225, 250, and 250 XB use DIFFERENT BLOCK PART NUMBERS (with different porting).
<u>300 Series Engines</u>:
These are different of and unto themselves.
Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
Still consider myself a "Marine Apprentice" after 48 years (learn something new every day).
Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor
Thank you for the additional information... It all helps in painting the big picture.
Find a 250XB block. It has none relieved exhaust ports which makes the compression higher to start with. Best way to explain crank differences is that older cranks have loose bearings with a two piece sleeve that fits over roller bearings and new style has a caged bearing assembly which is waaay easier to deal with. Crank with cages is found in 2002 250XB.
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