n85
Electrical
- Apr 8, 2010
- 17
I am interested in understanding the reasons for failure of a woodruff key joining a crankshaft to the timing belt pulley. This has happened twice on the same engine and I would like to find a reliable solution.
The engine in question is a (late 80's) Japanese 1.3 litre inline four with dohc and direct hydraulic tappets.
The key originally wore asymetrically as if it were taking an abnormal load in only one direction of rotation, that is it was changing into a Z-shape as sketched below. There was corresponding wear on the pulley and shaft where they contacted the worn parts of the key and all corners were rounded since the key was rocking in its seat (with the ensuing cam/ignition timing variation). The pulley inner diameter was enlarged and the pulley could wobble on the shaft but the shaft was not worn significantly. The accessories pulley which bolts onto this pulley was not significantly damaged.
The shaft keyway was enlarged using EDM, a new key was ground and a good pulley fitted.
After less than 20000km we've had to remove the timing belt and the same problem has happened. The key is not as worn as previously but the pulley ID is up by ~0.7mm. Shaft OD is effectively unchanged since flipping the pulley over onto the undamaged side it is tight(the pulley edge protruded slightly more than the shaft). The bolt retaining the pulley onto the shaft was loose and threads were damaged).
When trying to find the cause a local machinist asked about AC but the car doesn't have it. The accessories pulley seems to be a damper with a rubber ring - could this be the culprit? There was an issue with the alternator being slightly misaligned from the drive pulley but this was addressed at the time a new key was fitted.
Did anyone here encounter anything similar? Any suggestions to avoid another failure in a year's worth of driving?
I would try to use threadlock on the shaft-pulley interface but I am not sure whether it is appropriately strong...
I have seen similar damage on two other engines of roughly similar age - an inline three from the same manufacturer (but not the same engine family) and another inline three from another Japanese manufacturer.
N
The engine in question is a (late 80's) Japanese 1.3 litre inline four with dohc and direct hydraulic tappets.
The key originally wore asymetrically as if it were taking an abnormal load in only one direction of rotation, that is it was changing into a Z-shape as sketched below. There was corresponding wear on the pulley and shaft where they contacted the worn parts of the key and all corners were rounded since the key was rocking in its seat (with the ensuing cam/ignition timing variation). The pulley inner diameter was enlarged and the pulley could wobble on the shaft but the shaft was not worn significantly. The accessories pulley which bolts onto this pulley was not significantly damaged.
Code:
________
| /
| /
| /_
|_ |
/ |
/ |
/________|The shaft keyway was enlarged using EDM, a new key was ground and a good pulley fitted.
After less than 20000km we've had to remove the timing belt and the same problem has happened. The key is not as worn as previously but the pulley ID is up by ~0.7mm. Shaft OD is effectively unchanged since flipping the pulley over onto the undamaged side it is tight(the pulley edge protruded slightly more than the shaft). The bolt retaining the pulley onto the shaft was loose and threads were damaged).
When trying to find the cause a local machinist asked about AC but the car doesn't have it. The accessories pulley seems to be a damper with a rubber ring - could this be the culprit? There was an issue with the alternator being slightly misaligned from the drive pulley but this was addressed at the time a new key was fitted.
Did anyone here encounter anything similar? Any suggestions to avoid another failure in a year's worth of driving?
I would try to use threadlock on the shaft-pulley interface but I am not sure whether it is appropriately strong...
I have seen similar damage on two other engines of roughly similar age - an inline three from the same manufacturer (but not the same engine family) and another inline three from another Japanese manufacturer.
N