• Engine starter on the MLW M420

  • Discussion of products from the American Locomotive Company. A web site with current Alco 251 information can be found here: Fairbanks-Morse/Alco 251.
Discussion of products from the American Locomotive Company. A web site with current Alco 251 information can be found here: Fairbanks-Morse/Alco 251.

Moderator: Alcoman

  by JohnR
Hello All,

I have a question regarding what type of engine starter is used on the 12-251 of the MLW M420. On Alcos with AC alternators, such as the C430 and C630, an air starter was used and it appears that MLW continued this practice on their M630 and M636 locomotives. This explains the presence of the third air tank on these locomotives.

The references I've seen state that the M420 uses a GE GTA-17 AC alternator but they make no mention what type of starter it uses. Since there isn't a third air tank on the M420 I would say that it uses an electric starter. My question is whether it is like the arrangement that GE uses on their AC locomotives where the auxiliary generator and field exciter act as starter motors or did MLW do something different?


  by urrengr2003
Can tell you without doubt; C-420 used battery power to motor the Main Generator for starting. Engine had two Starting Contactors (Alco parlance GS Contactors) one positive battery & one negative battery. Note I said C-420 not M-420; during this period (late 60's) believe both models were similar

As an aside; can tell you the first time I tried to start a C-430 almost jumped off the running board when that starter cranked. Sounded like an air raid siren when it started turning...was not prepared for that.

  by JohnR

Thanks for your reply. I was beginning to wonder if my post would set a record for the highest number of views without any reply, even ones telling me that I've asked a really dumb question.

Based upon a number of text and photographic sources I've located subsequently, I believe that I can say with at least 95% certainty that an MLW M420 uses the same method to start the diesel as do GE locomotives with AC generators. If anyone is interested I can provide URLs to the sources that I used to come to this conclusion.

I have some other questions about of the equipment, specifications and CN modifications of the M420 but based upon my experience with this question it does not appear that this is the forum in which to get answers to them. Would any member here know of an active forum somewhere that is more oriented towards MLW locomotives?

With regard to your comment about starting the C430, I can only imagine what that would sound like in person. On the Pentrex Incredible Alcos Volume 3 I remember there being at least one short segment where they videoed a Cartier C636 being started. The sound of the air starter was similar to, but somehow different, to the sound of my air impact wrench. It would not be difficult to see how that sound would be startling, especially if you were expecting a sound more like an electric starter.


  by BrianM
There is a Yahoo news group devoted to the M420 series units. You might be able to get some answers there.


  by bystander
doesnt the SNJ h ave some of these units?

  by *istDS
M420 is set up to motor the aux gen and exiter for starting via some additional contactors and relays. Recall that both machines are identical, GY-27?

Note that the earlier GE AC/DC units used two Leece-Neville truck starters to motor the alternator via a large ring gear ( a la EMD). In contrast, Alco used air starters-of IR manufacture driving the camshaft gear train on their AC/DC units. As has been mentioned before, this is SOP in marine and stationary applications.

  by BrianM
bystander wrote:doesnt the SNJ h ave some of these units?

Yes, they have 4 M420's and 3 M420R's. I do not know the ins and outs but I will ask when I am at the yard on Saturday.


  by N. Todd
Some buses using Cummins L10 or M11 (I don't know jack about buses/trucks, just told by a friend) have air starters... they sound similar to Alcos'.

  by Luther Brefo
N. Todd wrote:Some buses using Cummins L10 or M11 (I don't know jack about buses/trucks, just told by a friend) have air starters... they sound similar to Alcos'.
I think some of the New York City (MTA) buses have air starters. Not all of them but I distinictly hearing a loud whining/whirring sound before some of the busses would start at the 125th Street Bus Depot which was shut down a few years ago. Th e building still stands however.

  by alcodoc
Alco locomotives equipped with AC generators with electric start employ the exciter and aux. generator (GE GY27s) as starter motors.


  by JohnR
Thank you *istDS and alcodoc for providing the answer to my question. And thanks to everyone else for your replies.

For those that may be interested while searching on the Internet for some other information on Alco/MLW locomotives I found the US patent MLW-Worthington held on the ZWT truck used on the M420 series of locomotives. It's US patent # 3713397. I was curious as to how this truck is constructed and functions and this patent answered those questions.

I also found the US patents that GM and GE hold for their respective radial trucks. They are for GM, US patent # 4765250 and for GE US patent # 5746135. The GE patent has quite a number of very detailed drawings of their truck.

If you have never viewed patents on the US Patent Office web site before, you will need to follow the link on the help page to install a TIFF plugin for your browser. The US Patent Office uses the TIFF file format for the patent images.

This may be old news to the members of this forum but I'd thought I'd share it in case it's not.

  by N. Todd
On the ZWT truck the US and Canadian patent #s are stamped on the side of the truck. Searching the Canadian database, you'll eventually find the short six-axle truck, too. I had no luck finding any of the HiAd trucks, so I assume they were registered only in the US.

  by Clyde
This topic brings back good memories. Starting a 16-251 equiped with air starter one time stays in your mind for the rest of your life believe me :-)

I invite you to read my articles in this group in Shop Notes titled Try by Fire and Waking up a Monster.


Claude Gaudet

  by Luther Brefo
So hwo exactly does the air starter work?

Is it just pressuirized air being used to turn the engine over? If the engine has been off where would the instantaneous burst of air come from?

  by Clyde
Air starters are still widely used on passenger transit locomotives for Head End Power engines. Both the CAT 3406 and Cummins KTA19G2 HEP diesel are equipped with similar air starting systems.

By analogy with automotive electric starter, an air reservoir (approx. 30,000 c.i.) is used for air storage (the battery). A check valve on the reservoir feeding line prevents air loss during locomotive shutdown period. The starting relay (solenoid) is piped between the reservoir and the starter. The staring relay is an air piloted high output valve (large air flow) allowing a heavy air discharge from the reservoir through a 2 inches (IPS) pipe to the starter. The relay can be piloted using a mushroom type pneumatic push button valve, or an electric starting switch connected to a magnet valve.

Diesel engine air starters (motor) are in two types: vane (like an impact wrench) or turbine type. In both cases the motor output shaft spins a pinion gear through a gear train. The gear train allow for high breakaway torque at high motor speed.

The pinion gear can be driven on the engine ring gear like an automotive electric starter using a Bendix mechanism, or the pinion is first pushed on the ring gear by a pneumatic device which in turn opens a pilot line to the relay, allowing air to flow to the motor.

I will strongly recommend to wear ear plugs prior to start a 16-251 equipped with air starter, and advise people around prior engine start up. Since the starting button was about 36 inches above the starter on CN 2100 units, even if equipped with silencer, people walking on the running board when the starter is kicked in may jump on the ground like crazy.

Hoping your questions answered.