CS Crank Keyway: 14mm not 9/16"

[MAK]

Hello everyone,

I have been doing research on this site concerning fitting Gib keys and acceptable tolerances of key/keyways for the flywheel and things have become confusing, so I figured I post it to the group for comments.  Maybe I am over thinking it too much for a 1930's design, but a poorly fitted key on a large spinning mass is scary, even with shaft collars installed. I have read and understand how to fit the taper. The post here is concerning the keyway fit and acceptable tolerances there.

Looking at the various handbooks that specify tapered key design, the recommended tolerance for the width of the shaft keyway is around (- 0.001" to 0.002" ) and the for the hub except (+ 0.001 to 0.002). However when I look at the lister design, things get confusing.

The nominal key width for the lister is supposed to be 9/16" but the keyway on CS British crank is 14mm. How can this be? In addition, when I measure my original British made key, it is indeed 14mm wide.  So not close to 9/16", but correct for the handbook specs for shaft keyway tolerance. The hub keyway on the other hand is 0.565, which seems to make sense for a 9/16".  So the original key has a gap between the key and hub keyway of 0.01".  This is 5x the recommended handbook spec

here are some questions:

1)  does the above make any sense to others that have looked at the CS engine or is mine a one off ? I think I saw another post referring to 14mm keyway as well.

2) If the above is correct, there will always be some slop in the system since the shaft keyway is smaller than the hub keyway. As pointed out by Quinn in one of his posts, this slop can result in a knocking sound. I have this in my engine and I have been trying to determine where it comes from for years. I suspect the keyway slop in the hub has been the issue. A recommendation was made to use brass shims to take away the slop. Is brass the right choice or is steel a bette one given the forces involved? I would appreciate some advice here.

3) The India made keys I purchased from Gary are 0.545" which means I need to shim the crank keyway to get close to the 0.001" spec and also shim the hub keyway. Am I being too picky here for a 1930's engine?

Thank you all.

[mihit]

I don't think I've measured a key or a keyway in my life!

I Just hand-fit (file and emery paper) and there should be no discenable slop. This goes for everything from high-torque (like large flywheel) applications to fast electric motors.

[sirpedrosa]

Hi MAK and Gentles

See here: https://listerengine.com/smf/index.php?topic=8320.msg101273#msg101273

After here: https://listerengine.com/smf/index.php?topic=8320.msg102563#msg102563

CS keyway is really 9/16.

Cheers
VP

[mikenash]

I don't think I've measured a key or a keyway in my life!

I Just hand-fit (file and emery paper) and there should be no discenable slop. This goes for everything from high-torque (like large flywheel) applications to fast electric motors.

Mihit, these tapered Gib Keys are potentially different to what you might see in motors & drives?  In that they aren't held "down" by a grub screw but by the taper.  So some of the "fit" is in the force needed to hammer them home until they are "tight enough"  If you watch a vid or two of the Indian blokes assembling them with a big whack from a big sledgehammer - you'll see what I mean.  It wouldn't surprise me if they are expanding in two dimensions under that force

Just a thought.  Cheers

[MAK]

Thank you sirpedrosa.

Thanks for looking into this. I agree that It makes no sense for Lister to be making a metric keyway in the 1930's given the imperial system was widely used. My engine was built in 1939 based on the serial number information. The only parts on the mine that have metric components (as far as I have seen) are the fuel pumps that have a metric banjo. However, I have seen other folks mention the confusion around the crank keyway and 14mm.  It appears you were able to machine your own keys and fit them accurately using the 9/16" stock you purchased. So at least I have one other person that has done this  

I have come to the conclusion that the Keys that I purchased are useless paper weights given how far below 9/16" they are. I placed a new order to get a set from the UK. They are actually 9/16". It may be helpful for those CS owners who are looking to replace their Gib Keys to ask for the measurement of width before purchasing. 

The specifications for tapered key design are clear and a wide gap in the keyway is not acceptable. I have cross checked this across many references including DIN, British and US standards of the past and present.  A key without correct tolerances on the width will be problematic independent of how well the taper is matched. Any forces that arise due to slightest flywheel imbalances will cause the key to come loose unless it was driven in by excessive force which caused deformation to the hub.

Moe

[mikenash]

Thank you sirpedrosa.

Thanks for looking into this. I agree that It makes no sense for Lister to be making a metric keyway in the 1930's given the imperial system was widely used. My engine was built in 1939 based on the serial number information. The only parts on the mine that have metric components (as far as I have seen) are the fuel pumps that have a metric banjo. However, I have seen other folks mention the confusion around the crank keyway and 14mm.  It appears you were able to machine your own keys and fit them accurately using the 9/16" stock you purchased. So at least I have one other person that has done this  

I have come to the conclusion that the Keys that I purchased are useless paper weights given how far below 9/16" they are. I placed a new order to get a set from the UK. They are actually 9/16". It may be helpful for those CS owners who are looking to replace their Gib Keys to ask for the measurement of width before purchasing. 

The specifications for tapered key design are clear and a wide gap in the keyway is not acceptable. I have cross checked this across many references including DIN, British and US standards of the past and present.  A key without correct tolerances on the width will be problematic independent of how well the taper is matched. Any forces that arise due to slightest flywheel imbalances will cause the key to come loose unless it was driven in by excessive force which caused deformation to the hub.

Moe

Hey Moe

I guess any new Gib keys are mostly ex-India

Certainly excessive force & distortion of the hub is their normal method when it comes to installing.  Have a look at a vid or two lol

[sirpedrosa]

Gentles

Adding some "rice", take a look at this sites:

https://www.keysandpins.com/products/gib-head-keys

https://www.mcmaster.com/gib-keys/

https://www.grainger.com/category/fasteners/key-stock/machine-key?attrs=Type%7CTapered+Gib+Head&filters=attrs

https://www.huyett.com/

Be safe
VP

[MAK]

Thank you for the information. I keep reading about the excessive of use of force on Indian made machines and I hear there are videos Please point me to some as this has me very curious to see

[mihit]

Mihit, these tapered Gib Keys are potentially different to what you might see in motors & drives?  In that they aren't held "down" by a grub screw but by the taper.  So some of the "fit" is in the force needed to hammer them home until they are "tight enough"  If you watch a vid or two of the Indian blokes assembling them with a big whack from a big sledgehammer - you'll see what I mean.  It wouldn't surprise me if they are expanding in two dimensions under that force

Just a thought.  Cheers

Yeah I know what he's referring to. I've pulled and refitted lister flywheels that probably hadn't been off for at least half a century.
But that's where the engineer's blue comes in. Good bearing surface, no excessive force required.