Walschaert Eccentric Key

This forum is dedicated to the Live Steam Hobbyist Community.

Moderators: Harold_V, WJH, cbrew

Post Reply
User avatar
dnevil
Posts: 270
Joined: Fri Aug 03, 2012 10:19 am
Location: Springtown, Texas
Contact:

Walschaert Eccentric Key

Post by dnevil » Wed Aug 21, 2019 9:05 am

I am working on the design of a 4-4-0 based on Bill Van Brocklin's No 28. It will use Walschaert valve gear. I plan on keying the eccentric to the crank pin.

My question is as follows. Is it common to also key the crank pin to the wheel to prevent the pin from rotating and throwing the valve timing off?

Thanks,
Daris
Daris Nevil
IBLS Secretary
North American Region
http://www.ibls.org

Soot n' Cinders
Posts: 803
Joined: Wed Jun 27, 2012 5:24 pm
Location: Marietta, Georgia

Re: Walschaert Eccentric Key

Post by Soot n' Cinders » Wed Aug 21, 2019 12:50 pm

I would. I’ve seen the main pin work loose and begin rotating on a friends LE Atlantic
-Tristan

Projects
-2.5" scale Class A 20 Ton Shay

User avatar
cbrew
Posts: 2841
Joined: Sat Jan 04, 2003 12:17 pm
Location: Vancouver Wa

Re: Walschaert Eccentric Key

Post by cbrew » Wed Aug 21, 2019 1:06 pm

dnevil wrote:
Wed Aug 21, 2019 9:05 am
My question is as follows. Is it common to also key the crank pin to the wheel to prevent the pin from rotating and throwing the valve timing off?
Thanks,
Daris
I would be say YES.
this is more important than keying the eccentric crank to the pin,
If it is not live steam. its not worth it.

User avatar
pat1027
Posts: 224
Joined: Sat Oct 09, 2004 3:45 pm
Location: Michigan

Re: Walschaert Eccentric Key

Post by pat1027 » Thu Aug 22, 2019 1:56 pm

My drivers are keyed, the eccentric is not.

User avatar
Bill Shields
Posts: 5553
Joined: Fri Dec 21, 2007 4:57 am
Location: Somewhere in the World
Contact:

Re: Walschaert Eccentric Key

Post by Bill Shields » Thu Aug 22, 2019 8:09 pm

is this new, being assembled..or already partially together? I am guessing that it is new based on your description.

I ask because of a recent experience with a BvB chassis and things that should have been tight press fits that were not..and basically the chassis had to be disassembled and new axles and crank pins fitted...since there is no way that it would have stayed together.

I have seen valve gear run practically forever with no keys holding the crank pin to the wheel...and others that didn't last 3 years...

The only realistic answer is that if it was fit properly, it is most likely OK if it is already together..however if it is not a good, tight fit...it may well come loose..

Keys are nice... but small square keys on 3/4" loco crank pins are tough to get to fit well.

a recommended thought would be press fit round 'key' pin in from the back...put in the crank pin, then drill / ream / press fit a small 'pin key', then assemble the driver to the axle
Too many things going on to bother listing them.

User avatar
Fred_V
Posts: 4338
Joined: Sun Jan 12, 2003 3:26 pm

Re: Walschaert Eccentric Key

Post by Fred_V » Fri Aug 23, 2019 7:40 am

Taper pins work nicely too. Whatever you do, don't drive a pin into a blind hole. I had to fix that for someone that did and it was a real pain to get it apart.
Fred
Fred V
Pensacola, Fl.

User avatar
ccvstmr
Posts: 1649
Joined: Sat Jan 04, 2003 10:37 am
Location: New Lenox, IL

Re: Walschaert Eccentric Key

Post by ccvstmr » Fri Aug 23, 2019 10:04 am

In 2016, a "dutchman" on the Rutland main crank pin fell out while on a road trip. Was hell trying to move the loco up a long grade back to the yard. When the loco was up on a steaming bay, the main and side rods were removed. Had a crank pin in my hand...and a hole in the driver...
IMG_7661.JPG
Where did the dutchman go? DOWN...into the ballast...never to be found again! Had no measuring tools to determine the pin size. Made a trip to the corner hardware store to get several drill bits in the 1/8" diameter +/- range and some Permatex thread locker products. Ground off the butt end of an 1/8" drill bit and made a temporary repair for the loose crankpin. Enough or a repair to finish the weekend running no-load.

Back home, the loco was blocked up. All the drivers were dropped. The crank pins pushed out. A light bore cut was made in the drivers for each of the crank pins. New crank pins and hub cabs were machined, heat treated and ground to size.
IMG_7905.JPG
The original eccentric was "locked" in place with a set screw. Was convinced this was not necessary with a proper fit.
IMG_7703.JPG
The new crank pins were pressed into their respective drivers. Don't believe the eccentric was bored. There was just enough play on the crank pin for a snug fit to allow adjustment before tightening the bolt.
IMG_7971.JPG
End result...no more set screws, dutchmen or other means of locking the eccentric in place were harmed in this procedure. The eccentric has held tight for several years without slipping. Just saying... Carl B.
Life is like a sewer...what you get out of it depends on what you put into it!
I don't walk on water...I just learned where some of the stepping stones are!
I love mankind...it's some of the people I can't stand!

User avatar
dnevil
Posts: 270
Joined: Fri Aug 03, 2012 10:19 am
Location: Springtown, Texas
Contact:

Re: Walschaert Eccentric Key

Post by dnevil » Thu Aug 29, 2019 4:28 pm

Thanks to all who replied.

Bill Shields, this design is based on Billy Van Brocklin's drawings I obtained from John Kurdzionak of Friends Models. Billy's drawings do not specify keys. However, I'm machining the parts on a Haas VF-0E CNC mill, and want to use the accuracy of the mill to place the keys so that there is no guesswork when pressing the crankpin and fitting the eccentric. Keying the eccentric is suggested by Joe Nelson in his book "So You Want To Build A Live Steam Locomotive." I read somewhere else (perhaps in Nelson's book) that crank pins can rotate after time as well.

Carl B, how did you properly adjust the eccentric location without the aid of keys?

Did I mention this is a 1.5 inch scale model? Here are photo's of Billy's version:

http://ibls.org/mediawiki/index.php?tit ... in#Loco_28

Regards,
Daris
Daris Nevil
IBLS Secretary
North American Region
http://www.ibls.org

User avatar
Bill Shields
Posts: 5553
Joined: Fri Dec 21, 2007 4:57 am
Location: Somewhere in the World
Contact:

Re: Walschaert Eccentric Key

Post by Bill Shields » Thu Aug 29, 2019 5:14 pm

Just because BvB did not use keys does not mean that they are not needed.

Like many people, I have locos that have run for years without them and have fixed a dozen or so for people that should have had them. I even have a 1-1/2" loco with the drive wheels glued on to the axles...no keys...works a charm...others say that I am crazy and should do things the 'better way' and press fit them...

irrespective of how anyone mills parts, I would recommend they check everything after assembly prior to fitting keys...

Please don't get me started on JFN's book...

there are a lot of good ideas in there...and there are some really not-so-good ideas.

A book is a lot like today's internet...

Just because it is in a book does not mean it is necessarily a good idea.

However...the idea of using keys is difficult to argue with.

The Brits had an interesting idea where they made the end of the crankpin 'square' and broached a square hole in the eccentric crank..so it could only go on one way..

of course, if the pin was not true to the driver...then there you are.

I fixed one like this a few years ago where I put the driver assembly in the mill and RECUT the square so that it was truly at the correct position WRT to the axle and remade the eccentric crank...all this because the pin was 'pinned' to the driver with a hardened roll pin that was a real bear to consider removing....

the person who had built it had never considered the need for 'future maintanance'...
Too many things going on to bother listing them.

User avatar
ccvstmr
Posts: 1649
Joined: Sat Jan 04, 2003 10:37 am
Location: New Lenox, IL

Re: Walschaert Eccentric Key

Post by ccvstmr » Thu Aug 29, 2019 9:45 pm

dnevil wrote:
Thu Aug 29, 2019 4:28 pm

Carl B, how did you properly adjust the eccentric location without the aid of keys?
Well Daris...don't burn me at the stake for this (or anybody else for that matter). Having photos of the eccentric locations before the drivers were dropped and the old crank pins pushed out provided a starting reference point. Once the new crank pins were pressed in place, no longer had the old set screw "key" hole to use for a reference.

Used a Sharpie to draw a line on the end of the crank pin to coincide with the eccentric slit at the approximate setting. This was the starting point. Based on the locomotive performance and sound, would loosen the clamping screw, shift the eccentric forward or back in small increments and re-tighten the clamping screw. Continued to do this until the locomotive "sounded" best. Wasn't any more qualitative than that.

So far...so good! Carl B.
Life is like a sewer...what you get out of it depends on what you put into it!
I don't walk on water...I just learned where some of the stepping stones are!
I love mankind...it's some of the people I can't stand!

Post Reply