Bad Harmonic Balancer?
06-27-2006, 12:00 PM
#11
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It absorbs vibrations in the crankshaft created when each cylinder fires
The crank does not rotate smootly because as each cylinder fires it accelerates. This acceleration causes a vibration through the crankshaft. The balancer has a center hub that is hard bolted to the crank then there is an elastic rubber section and the heavy outer ring is connected to the inner hub only through the rubber section. As the crank accelerates the rubber stretches a little and the outer ring cancels out most of the vibration because it is moving in the opposite direction of the crank.
Think of it as a counter weight connected to the crank by a rubber band. Every movement of the crank is counter acted by the counter weight and the rubber absorbs the shock of the vibration and allows the counter weight to move somewhat independent of the crank.
This could effect the timing of the CPS if the sensor reads off a magnet mounted in the outer ring of the balancer. If the rubber had deteriorated and allowed the outer ring to slip in relation to the center hub then the alignment of the CPS sensor magnet to the actual crank postion will be off and could cause a no start. I don't know if the CPS reads off the balancer or not, but I know that some engines have the CPS mounted there.
Think of it as a counter weight connected to the crank by a rubber band. Every movement of the crank is counter acted by the counter weight and the rubber absorbs the shock of the vibration and allows the counter weight to move somewhat independent of the crank.
This could effect the timing of the CPS if the sensor reads off a magnet mounted in the outer ring of the balancer. If the rubber had deteriorated and allowed the outer ring to slip in relation to the center hub then the alignment of the CPS sensor magnet to the actual crank postion will be off and could cause a no start. I don't know if the CPS reads off the balancer or not, but I know that some engines have the CPS mounted there.
06-27-2006, 01:15 PM
#12
Well, if that is the case...
...and the balancer is bad but the crank sprocket/pulley key is OK, then it's easy to guess what happened:
CPS fails and Dave has car towed in. Tech rotates engine to TDC to remove belt from cam sprocket and replace sensor Tech pays no attention to the crank, but uses the timing mark on the cam sprocket to find TDC. After changing the sensor, the tech lines up the marks on the cam and crank and reinstalls the belt. Since the timing mark on the crank has shifted (unbeknownst to him) the cam timing is off and the car won't start. Some valve damage may have occurred depending on how far the mark is off.
However, given the parts diagram Dave posted, I'm not sure how the mark could shift. It is located on the inner most lip on the serp belt pulley which, from the diagram looks separate from the balancer.
As an aside, the "wandering timing mark" is common the Miata's. The balancer fails and the timing mark walks all over.
CPS fails and Dave has car towed in. Tech rotates engine to TDC to remove belt from cam sprocket and replace sensor Tech pays no attention to the crank, but uses the timing mark on the cam sprocket to find TDC. After changing the sensor, the tech lines up the marks on the cam and crank and reinstalls the belt. Since the timing mark on the crank has shifted (unbeknownst to him) the cam timing is off and the car won't start. Some valve damage may have occurred depending on how far the mark is off.
However, given the parts diagram Dave posted, I'm not sure how the mark could shift. It is located on the inner most lip on the serp belt pulley which, from the diagram looks separate from the balancer.
As an aside, the "wandering timing mark" is common the Miata's. The balancer fails and the timing mark walks all over.
06-27-2006, 01:27 PM
#13
Dave, in reading all this and the stuff from the list, I think that there are two basic questions...
...that you need to answer:
Is the CPS really bad?
Has the balancer failure resulted in a shift of the timing mark?
If the CPS is bad, then chances are that's what caused the initial problem. IMHO, it is extremely unlikely that the CPS failed AND the cam timing got screwed up at the exact same moment. That means something else may have messed up the cam timing.
I have no doubt that the balancer is bad (given your posts), but this alone would not cause a problem with the cam timing...unless it was reset using a shifted mark.
I'd bet my lunch money that the cam sprocket is OK.
Is the CPS really bad?
Has the balancer failure resulted in a shift of the timing mark?
If the CPS is bad, then chances are that's what caused the initial problem. IMHO, it is extremely unlikely that the CPS failed AND the cam timing got screwed up at the exact same moment. That means something else may have messed up the cam timing.
I have no doubt that the balancer is bad (given your posts), but this alone would not cause a problem with the cam timing...unless it was reset using a shifted mark.
I'd bet my lunch money that the cam sprocket is OK.
06-27-2006, 01:57 PM
#15
Re: Ding!
It reads well, and AW loves a dealer villain, but look at the pic Dave posted:<ul><li><a href="https://forums.audiworld.com/s4s6/msgs/124645.phtml">Timing mark is on the inner lip of the serp pulley. Could it really move?</a></li></ul>
06-27-2006, 02:11 PM
#16
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It has been awhile since I did my timing belt/Sorry Tom I posted in the wrong place.
But now that you mention it I think the mark was on the serpentine belt pulley which is bolted directly to the crank sprocket. So are you thinking the keyway has slipped? That would suck.
And actually I hate to hear of villain mechanics, dealer or independent. Its bad for the trade which unfortunately already has a bad enough reputation. I usually hate those aftermarket insurance policies but in this case hopefully it will pay off for him.
And actually I hate to hear of villain mechanics, dealer or independent. Its bad for the trade which unfortunately already has a bad enough reputation. I usually hate those aftermarket insurance policies but in this case hopefully it will pay off for him.
06-27-2006, 02:17 PM
#17
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No, not unless the keyway broke on the crank gear/sprocket.
and it slipped. I kept thinking that the mark was on the vibration damper but I think you are correct it is on the serpentine belt pulley.
06-27-2006, 04:32 PM
#19
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They say...
That the CPS was actually good. How can they check if they can't get the engine to run?
Since they didn't pull the crank sprocket or balancer I don't think we will actually know exactly until they get those off. My money is on the sprocket/pulley key (#5 in the diagram).
The car did vibrate some at idle and more so with the a/c on.
Since they didn't pull the crank sprocket or balancer I don't think we will actually know exactly until they get those off. My money is on the sprocket/pulley key (#5 in the diagram).
The car did vibrate some at idle and more so with the a/c on.
