Is a cracked engine sprocket a common occurance or more likely a faulty part ? it was relatively new. Crack is at the bottom, starting at the keyway
dan
Fairly new...
- Log in to post comments
Should have bought a Massey…
Should have bought a Massey Ferguson! This was from a supplier I regularly use, I'll contact them on Tuesday before I mention their name, I cant help thinking that the thread on the crank should strip before the sprocket cracks.
- Log in to post comments
Not something I have ever…
Not something I have ever come accross, However with several different and reversing forces acting on the stress raiser that is the woodruff key slot , I am surprised we have not seen more as fatigue and old age increases. Wear pattern suggests alignment worth checking along with taper engagement.
- Log in to post comments
Robert It was a new sprocket…
Robert It was a new sprocket - the alignment is slightly off but the best I can do with the 3 available offsets. I'll double check the taper (and key) when I get a replacement
Dan
- Log in to post comments
Speculation
Perhaps the wrong steel spec? Was the original case-hardened? Perhaps this sprocket is through-hardened, lower grade steel and objected to being forced up a taper?
If the sprocket teeth are not hard, (don't really need to be), poor steel spec choice?
Many years ago I worked in a university metallurgy department, we were always on the look out for just this type of failure for students to study and determine how and why the failure occurred. Quite a few failed motorcycle components found their way through the laboratory!
- Log in to post comments
Keyway a bit shallow in this…
Keyway a bit shallow in this sprocket?
Typical failure I would expect to see if key is too tall. Something has to give if the sprocket is held off the taper by the key.
Peter
- Log in to post comments
My guess......
....would be keyway machined without proper radius at the bottom.
- Log in to post comments
Yes, I have seen it before…
Yes, I have seen it before with an aftermarket part. It destroyed the primary drive.
- Log in to post comments
A suggestion for installing new sprockets on a taper......
... would be to use some fine lapping paste to check for good contact/seating of the sprocket to the shaft. I'm still very suspicious of the quality of the keyway machining process here with the crack running right out of the keyway.
- Log in to post comments
Never mind all that...
Never mind all that, Dan, I just want to know how you found it?
I don't take the primary cover off from one year to the next, and I wouldn't be looking that closely at the sprocket if I did.
Don Anson
Melbourne
- Log in to post comments
Don, I had checked the…
Don,
I had checked the timing with a disc and was re tightening the nut - I noticed that the chain was sticking on the engine sprocket and it opened up. The new one arrived, I lapped it onto the crank and measured the distance from the end of the crank to the sprocket then did the same with the key, I needed to take a little off the flat side to get it to sit firmly on the taper. Hopefully that will be it all sorted!
Dan
- Log in to post comments
Following Michael's suggestion...
... I found with my Electra starter motor sprocket that lapping the tapers then omitting the key has worked for many starts. I think that often the key prevents the tapers from mating correctly.
- Log in to post comments
I have never heard of an original sprocket cracking. I do wonder if this is an aftermarket one and perhaps not to the original specification.
I did have an original sprocket break clean in half on my New Holland 276 baler. A replacement from New Holland was £1200 + VAT. The second hand one at £120 seems like a bargain by comparison. And you thought bike spares were expensive...