EMD SD90MAC;s

[Gary UK]

 but when the demand for a 6000 HP AC locomotive appeared, they basically scaled up their 4 stroke design and the H was born and placed in production.  

Now im realy confused. So the engine in a 90mac is a 4 stroke then?

Whats in a 43/90mac? Is this a 2 stroke 16 cylinder 710G??

Im presuming here, the 90mac was the 4 stroke but later downrated to the 2 stroke 710 to 4300hp, correct?

[oltmannd]

The problem with the H engine is production was VERY rushed.  EMD had been fooling around with a smaller bore 4 stroke, but when the demand for a 6000 HP AC locomotive appeared, they basically scaled up their 4 stroke design and the H was born and placed in production.  Given that unforeseen problems creep up every time even a minor change is made on a proven design  (EMD F engine, anyone?)  that the H engine was headed for trouble shouldn't have been a shock. 

The shock was that UP purchased so many of them right off the bat.

It's also why Conrail purchased their AC units with 20-710Gs (not saying that CR was smarter than UP.  Draw your own conclusion )

[edbenton]

Easy to many TEETHING problems and the fact that it is an ODDBALL engine like a CAT engine would be in the fleet.  Think about it they only have 4 of them TOTAL and parts supply could be hard.

[ArtOfRuin]

The SD90MACs (and GE's AC6000CWs for that matter) have proven to be unreliable and rough-riding, which is why many of them are being withdrawn from service. Some SD90s and AC6000s were designated SD90/43MACs and AC6000CW Convertibles and were given less powerful, more reliable prime movers (approx. 4300hp for the EMD, 4400hp for the GE) when built. The manufacturers gave the railroads an option to upgrade to the 6000hp powerplants at a later date. The SD90/43s and AC6000 Convertibles with the less-powerful prime movers may be less of a target for withdrawl. Most railroads have settled on 4400hp as the upper limit for horsepower ratings as it gives the best amount of operational flexibility.

As for the H-engine, China is considering buying about 300 locos form EMD with the H-engine as their prime mover.

[Moonie]

I just read that CP, like UP some time ago, will remove their four SD90MAC's from active service. Does anyone know why seemingly the experiment with 6000 HP is over? What about the future of the four cycle 265H?