Gib key broke while running

[2ringers6]

Does anyone have any insight as to what would cause a gib key to break?

I had the shafts, and keyways and the keys clean and dry when I installed them.  I used a 4lb hammer and a punch and I thought that I had them in plenty tight.  They weren't in as far as they were originally, but they were no longer moving as I was driving them in.  I was careful to not hit them off square.  There were no obvious defects in them when I removed them.

This was my first time running the engine.  ( a 6/1 ). I ran it 3 times for no more than a minute as I was balancing it.  The next time as it started, the key broke.  Luckily the flywheel stayed on the shaft and just spun there freely until coming to a stop.

I want to make sure this doesn't happen again.

Thanks

[xyzer]

When you say broke I visualize a piece of the key was left in the keyway but you said the flywheel spun to a stop and stayed on I would say it sheared. Why it sheared is a good question. Was it a new or previously owned listeroid? I don't recall anyone having this problem. Loose or imposable to remove are the common complaints. I suppose  I would rather remove a sheared key than have it broke and not being able to get a hold of it to pull it. Have you pulled the flywheel off yet? Did it damage the crank during the freewheel?

[2ringers6]

It was a new listeroid.  Very minor marking of the crank.  The center of the flywheel has a spot where it looks like it was turned on a lathe. 

I found the largest piece of the key, but not the small piece. I assume it ground up to nothing in the center of the flywheel.

[dieselgman]

A picture would be great...

I have never seen nor heard of a key shearing in this fashion either. If I had to hazard a guess, I would say that the metal had to be compromised or inferior to allow that to happen. When you removed them, how much force was required?

dieselgman

[2ringers6]

I soaked them for a week and had to use the breaker bar on the key puller to get them broke loose.  I will post pictures tomorrow. 

[BruceM]

I don't think the other half of the key was "ground up", it probably just got spun off and is out of sight somewhere.  If it was ground up the crank and ID of the flywheel would be a mess.

This is very strange, a fractured key has never been reported before.  I wonder if it started to come out half way and then got fractured by pounding of the keyway? I'd expect some keyway distortion if so...

[ronmar]

Sheared and spun?   WOW!  Key could have been cracked when removed or re-installed, but that is surely weird.  I have had one work loose as the original keys were not a very good fit as the tapers didn't match that of the keyway.   

Another good argument for 2" clamp on collars inside and outside the flywheel  A flywheel spinning on the crankshaft is way better than walking off the end of the crank...

[millman56]

Whilst working as a fusion engineer ( sounds better than plain welder ) in the 70s,  when due to strikes etc, inferior steel was imported,   this steel in plate, section or bar form often had lamination faults which showed up when manipulating and forming this stee.     
It may well be that this gib head key had a laminar fault coinciding with the shear line on the crank/flywheel slots, it usually takes a dead stop of one or the other to shear a key.
Just my twopennorth.

Mark.

[Schwen]

Just hypothesizing - is it possible that the flywheel was installed back to front so that the tapered keyslot in the hub did not fully engage with the tapered key?

This would explain why the key wouldn't install as deeply as when it was removed, and the mention of a small piece of the key missing makes me think the key has a notch taken out of it rather than being sheared entirely along it's length.

just a thought. A picture of the sheared key would be useful.

[scrapman]

Interesting i've never seen a gib key shear off ,would like to see photos.
When installing keys a old fitter at saw mill showed me how back in 1970 ,filing taper face of key to take high spots off which show up when key is pushed into flywheel or pully on shaft with a coating of engineering blue on taper and draw filing so as not to round the face,blue or black marker pen also works, check bottom and sides for high spots on a piece of glass ,also keyways.
New file +file card (special wire brush for cleaning files) when no high spots left and taper shoes touching along whole length and with ,clean +key ways and install ,google for better description.
Peter

[ronmar]

Thats a very good thought.  Wheel on backwards would not allow full key engagement.  That coupled with a key fault and load concentrated on a smaller section of key could be an answer.  the torque pulses to spin the wheel up to full RPM are pretty impressive...

[2ringers6]

I'm having computer issues, so I can't post pictures for the time being.

The flywheels were not on backwards.  I just tried that and I can't even get the key to start in.  When I said I couldn't get the key in all the way, it was out 1/2 inch from the mark where they were originally.  It's not like they were barely in. 

I pulled the other key to compare the two keys.  There is not as much sheared off as I had thought.  Only the very end is broken off.  I had thought that they keys came out to nearly a point.  Bad memory.

It seems as the key must have come out and as it was coming out, is probably when the end sheared off. 

I put the other one back in and it stopped moving about 1/2 inch from where it was originally.  I then turned the flywheel so the keyway is at the bottom and tried driving it in further.  It did go in farther and is now about 1/8 from the original mark.

[carlb23]

As Ronmar had mentioned above. 

All the more reason to put some 2" collars on the ends of the crankshaft. They are available from McMaster carr for about 10 dollars each

http://www.mcmaster.com/#shaft-collars/=niqchv

Carl

[ronmar]

I got mine thru fastenall for about that same cost, 2 part circular lock in place with allen head bolts. 

The keys should be seated with the keyway pointing down IMO.  The whole process of key insertion is to pull the side of the flywheel opposite the keyway into complete contact with as much of the crankshaft as possible.  The keyway is only partially responsible for securing the flywheel, Contact friction provides much of the flywheel security.  It is easier to achieve this if the wheel bore is already in as much contact with the crank as possible, which naturally occurs with the keyway pointing down..  One thing I noticed with mine was that the key angle and the keyway broached in the wheel were not at the same angle. I determined this by holding the key in the flame of a candle and letting it get covered with soot.  Then with the keyway pointing down I insert the key as hard as I can by hand and remove it and look at the witness marks left in the soot.  I then filed in the area of the witness marks and retested.  I did this repeatedly untill there were witness marks along the entire length of the angled portion of the key. If the angles do not match, it can cause the wheel to not grip the crankshaft evenly as seen in this drawing, as well as concentrating forces in one particular point on the hub instead of spreading them out evenly thru all the hub...   
 

[mobile_bob]

my bet is the key was not fully seated, worked its way nearly out, and sheared the end off just before it came completely out on its own.

it wouldn't take much to shear the last quarter inch of key, just before it came clear out?

or so it would seem to me.

how much is sheared off the end? compared to the other good key?

bob g