how can a timing belt jump a tooth?

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baja1

New member
just finished installing a junk yard engine in the '97, by far the hardest thing i've ever tackled....now it won't start.
so today I removed the TB cover, crankshaft mark and both cam sprockets are still aligned but the arrows on the belt are off a tooth! new TB, water pump, thermostat, I checked and double checked before I put it back together, how can the TB arrows now be off????
....and it won't start :ybrick::ybrick:
 
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The marks on the BELT are off? Those are install reference marks. Once the engine spins, the marks on the belt are useless.
 
baja1 said:
I agree....just wondering how that could happen????I assume there's no sense in changing it?
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None whatsoever. The marks on the belt move with every spin of the crank. After install, just look at the hard marks in the metal.
 
baja1 said:
I agree....just wondering how that could happen????I assume there's no sense in changing it?
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The belt rolls around the pulley, cam and crank gears. The marks only line up while you're installing at TDC. They'll eventually line back up but I don't know the math on that. If all your physical marks are lined up correctly, don't worry about the arrows on the belt.
 
baja1 said:
just finished installing a junk yard engine in the '97, by far the hardest thing i've ever tackled....now it won't start.
so today I removed the TB cover, crankshaft mark and both cam sprockets are still aligned but the arrows on the belt are off a tooth! new TB, water pump, thermostat, I checked and double checked before I put it back together, how can the TB arrows now be off????
....and it won't start :ybrick::ybrick:
Click to expand...

Warranty claim?
 
If all the marks were aligned at install, you should be good - even if the belt were off a tooth (which isn't likely) the car would probably start but run badly.

I would check all the basics: fuel, air, spark and check for CEL and any codes.

Good luck and keep us posted.
 
Could be the crankshaft sensor. Since the engine was just installed It's likely something electrical isn't hooked up correctly or a wire is broken.
 
jhfleet said:
Could be the crankshaft sensor. Since the engine was just installed It's likely something electrical isn't hooked up correctly or a wire is broken.
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that would sure make my day, I have the sensors still from the old motor....and I know they work. I did research part numbers from 97 to 02 and they were the same so didn't swap them out, probably should have but figured newer was better?
 
baja1 said:
that would sure make my day, I have the sensors still from the old motor....and I know they work. I did research part numbers from 97 to 02 and they were the same so didn't swap them out, probably should have but figured newer was better?
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what does the engine diagnostics tell you? any codes? (visible or not)
 
There are folks on here who can advise exactly what needs to be done to make an '02 engine compatible with the wiring and electronics of earlier 3.4 T4Rs. As I understand it, the '02 engine essentially needs to be stripped down to a long block and all the removed parts replaced with ones from the earlier engine. I may be all wet so hopefully one of the experts will weigh in. I think there are references somewhere on this forum about swapping a late 3.4 into an earlier 3rd generation. Best of luck to you!
 
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