PRR M1a vs M1b

Hi Ron, 

From what I have read in Al Staufer's Pennsy Power the main difference between a M1a and M1b is the boiler pressure. The M1b had 300 psi I believe up from 260 psi. Numbers are most likely not exact but close enough for now haha. 

-Cody

Ron:

I’ve read the primary spotting feature to discern an M1 from an M1a is the outside steam delivery pipes to the cylinders.  M1’s had the outside pipes; M1a’s (and b’s, for that matter) did not.

The solid versus slotted pilot becomes problematic after WW2 when PRR converted most of the M series to solid pilots.

Curt

Cody and Ron, thanks.

FYI: Another spotting feature between the M1 and M1a/b is the M1a/b had two air pumps on the left while the M1 only had one.  However, you need to be on the left side to see it.  I've also noticed in some photos foot board pilots (freight type) on both M1 and M1a engines.

I was just wondering if there was something externally done to the M1b to get the increase from 250lbs BP to 270lbs BP, but it doesn't look like it unless the circulars in the M1b fireboxes were noticeable.  May just have to go by cab numbers.

Again, thanks.

The fire box external washdown plugs were "b" .  Continual firebox Boiler rebuild eventually they all would have them. 

Railroad Museum of Pennsylvania Strasburg, PA 

One of the fire box clean out plugs I mentioned. 

Three clean-outs  pictured. These are on the Weaver M1a/b model.   As are the lower fire box clean-out plugs. 

The two air pumps, mentioned, left side. 

There was a pre-heater on this locomotive that tempered the cold water from the tender before it was added to the boiler.  Super heater also on this locomotive.   Water pre-heat and super heat were probably both "a" and "b"  Another interesting appliance was the Nathan oiler. 

Note the frame extension ?? the larger streamline pilot?? Add may be 15"   

Mike CT posted:

The fire box external washdown plugs were "b" .  Continual firebox Boiler rebuild eventually they all would have them. 

One of the fire box clean out plugs I mentioned. 

Three clean-outs  pictured. These are on the Weaver M1a/b model.   As are the lower fire box clean-out plugs. 

Mike, thanks.

I think in the second photo you mean 4, not three.  Or I'm not seeing the correct item.

I just went though my Staufer books as well as a couple of others, and it seems the M1a has similar protrusions along the top edge of the firebox. I may be looking at the wrong things.  Need to go to the museum again.

Yep  four.  The Weaver model also has four. 

CAPPilot posted:

Mike CT posted:

The fire box external washdown plugs were "b" .  Continual firebox Boiler rebuild eventually they all would have them. 

One of the fire box clean out plugs I mentioned. 

Three clean-outs  pictured. These are on the Weaver M1a/b model.   As are the lower fire box clean-out plugs. 

Mike, thanks.

I think in the second photo you mean 4, not three. 

No, there are indeed 4 washout plugs/caps. The first/top photo shows a close-up of the one on the far right, located between the two turret mounting brackets.

Or I'm not seeing the correct item.

I just went though my Staufer books as well as a couple of others, and it seems the M1a has similar protrusions along the top edge of the firebox. I may be looking at the wrong things.  Need to go to the museum again.

Hot Water posted:

CAPPilot posted:

Mike CT posted:

The fire box external washdown plugs were "b" .  Continual firebox Boiler rebuild eventually they all would have them. 

One of the fire box clean out plugs I mentioned. 

Three clean-outs  pictured. These are on the Weaver M1a/b model.   As are the lower fire box clean-out plugs. 

Mike, thanks.

I think in the second photo you mean 4, not three. 

No, there are indeed 4 washout plugs/caps. The first/top photo shows a close-up of the one on the far right, located between the two turret mounting brackets.   Excuse the foggy head,  I am now able to count to four.   Somewhere in the many rebuilds of this fire box the stay bolt spacing and sheet thickness would determine max boiler pressure, IMO.   There are a lot of stay bolts pictured, very close together. 

Or I'm not seeing the correct item.

I just went though my Staufer books as well as a couple of others, and it seems the M1a has similar protrusions along the top edge of the firebox. I may be looking at the wrong things.  Need to go to the museum again.

 

The M1b had siphons added inside the boiler for improved water circulation.  The cleanout plugs for these siphons appear in a diagonal line rising along the side of the firebox toward the cab on both sides of the locomotive.  Due to the angle of sunlight, you can clearly see these plugs in this photo of M1b #6751.

The spotting difference is not the pilot or anything like that, it's the siphon plugs.  M1b's have them while M1a's do not.

Bob,

If they were on the sides of the firebox like that, I believe they were referred to as "Circulators". The siphons, i.e. Thermic Siphons, were generally from the firebox throat sheet, rearwards and upwards to the crown sheet.

Guys,

Thanks for the education about this great Pennsy steamer.

Norm

The three clean out plugs were detailed on the Weaver model.     "b"

I think I found some of my issue with determining a M1a vs M1b.

Most of the pictures I reference are out of Staufer's books plus a couple of others.  I pulled up my PRR numerical steam roster and found some errors in Staufer's books.

Book 3: One example is #6788, which he listed under the picture as an M1b but the roster shows it never was upgraded.  The pictures shows, based on data provided above, it to be a M1a.

Book 3: Another example is #6715, which he lists under the 1955 picture as a M1a.  The roster states it was upgraded to a M1b, and the picture clearly shows the M1b mods.

Book 2: Here #6779 is listed under the picture as a M1a, but you can see the M1b mod.  The roster confirms it was upgraded.

Book 2: #6738 is listed as M1a in a 1954 photo but is a M1b.  This engine, and #6715 above, were identified in the roster as engines that were upgraded in 1948.  Since the photos were mid-50s it seems like he should not have made the mistake.

Anyway, I need to be more careful about using only one reference.

So do the Lionel and MTH versions have these plugs?

Sorry, I googled it and it appears the Lionel M1b does have the plugs:

My early MTH M1b, 20-3084-1, seems to be a correct "b".

The plugs on the postwar detailed (prewar M's did not have cast drop coupler pilots) 6750 above appear to be slightly undersized, but do identify it as a M1b model.  To my eye the Weaver model's plugs are better sized. 

A disappointing detail on the model are the smokebox mounted green classification lights.  In 1939 the PRR ceased using class lights (the green or white lens ones) on locomotives.  As locomotives were shopped in the postwar era the PRR relocated the former cast metal "clawfoot" pilot beam mounted front marker lights (red lens forward - amber lens to the outboard side) to the smokebox using either oval "tombstone) fixtures or the later smaller round "bullseye" fixtures.  Correct O scale postwar marker light castings were offered in the CalScale line by Bowser.  

The tender lettering on the tender is also incorrect for the postwar era - in the 1941 time frame the PRR applied wider spaced  P E N N S Y L V A N I A lettering on steam locomotive tenders.  Nicely done pre and postwar PRR dry transfer lettering sets are offered by Clover House. 

Here is a not so great photo of my MTH M1b (now that it is on display, I need to take better photos of it).  You can just barely see the plugs.

I noticed that MTH's RK M1a also has the plugs.