Question about marine engines

[dicer]

Specifically fabricated crankcases.

1 With in a medium speed range, what are the cost comparisons between fabricated steel and cast iron?

2 Are they stress relieved before machining?

3 How about ridgidity comparison between the two?

4 Long term ownership comparisons, especially with catastrophic failures.

5 Is there considerable weight savings due to the higher strength of the all steel construction?

6 What grade of steel is used in construction?

7 In your opinion which is the best?

 

[L4189]

First of all there hasn't been a new engine design using fabricated crankcases in over 50 years. The EMD 710 is a rehash of the 645 which in turn is a rehash of the 567 going back to 1954.

1. I would expect that a fabricated crankcase is more expensive than cast iron especially if the manufacturer hasn't done it before. One of the few things EMD actually fabricates in house is the crankcase. Fairbanks Morse is the other with both to OP engine and the Alco 251.
2. After welding they are stress relieved in an oven.
3. Rigid enough. Light weight was an original consideration.
4. Long term; definitely with the fabricated crankcase. Several firms specialize in repairs after any failure or just wear. Just weld it up and machine back to standard dimensions. Cast crankcases are supposed to be repairable, but....
5.There is a weight savings but that may only be that most of the engines with welded crankcases are 2 stroke.
6. Grade of steel? Weldable.
7. Engine manufactures are in the business of selling new engines so if the owner throws it away after 20 years the cast crankcase will last long enough. In the situation where service life is 50 plus years the fabricated crankcase is the easiest to live with