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Timing belt jumped after lose pulley


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2 replies to this topic

#1 nmos

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Posted 28 June 2008 - 02:20 AM

About 2 months ago I noticed the crankshaft pulley was wobbling and found that the bolt was just barely finger tight. I tightened it down to 120ft-lb and everything seemed fine until about 2 weeks ago when the timing belt jumped several teeth on just the right (passenger) side. When I removed the pulley I found that the keyway on the pulley was worn (about 1 key worth) but otherwise it looked ok. I needed to get the car back on the road so I filled the gouge in the keyway, re-installed the timing belt, and pully using blue loctite on the bolt threads and the inside of the pulley where it contacts the crankshaft. At this point the engine seemed to be running great but I was getting the occasional P0325 (knock sensor) CEL. That made me nervous so I ordered a new pulley and key which I'll be swapping in tomorrow (if I can get my loctited pulley off).

Any thoughts on what caused the timing belt to jump? The belt is only about a year (15000mi) old, didn't show any problems, and the tensioner seemed fine (required plenty of force to compress). I just don't see how that gouge in the pulley keyway could have caused the belt to jump like that once the pulley bolt was tightened but I also don't see anything else wrong.

Added: BTW this is a 97 Impreza OBS with 139,000mi

#2 hohieu

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Posted 28 June 2008 - 06:26 AM

The torque on the crankshaft pulley bolt presses the t-belt gear against the snout of of the cranshaft. This torque holds the gear in place while the woodruff key is merely a guide for installing. If your crankshaft pulley bolt was that loose, it's possible that the pulley was shifting along the snout and not making full contact with with the belt, which could, in turn, cause the belt to slip.

Knock sensor code is really no big deal. Disconnect and unbolt the connecter and inspect the sensor. If it's cracked, you'll need to replace it in the near future. Otherwise just clean the contact surfaces and reinstall.

Check the idlers while you're in there. The toothed one is most highly loaded and tends to be the one to go. If you're not replacing them, it's also possible to regrease them.

The hydraulic tensioner should be compressed very slowly, otherwise you could blow out the seal. I put mine in a vise and crank down little by little as I'm doing the work.

BTW, year, model, and mileage would help.

Good luck.

#3 stumpy

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Posted 28 June 2008 - 11:44 AM

I'm no authority on all possible causes but can tell you about my experience with an ej22 timing belt jumping.

My first subie, 90 Legacy with 201K miles.
Bought as a runner with suspension issues.
Fixed the suspension and off I go. 300 miles latter it dies on the highway.
I decide the timing belt needs checked (Basics first) and it's off a few teeth. Reset the belt with no success.
End up taking it to a shop who gets it running and tells me the t-belt needed reseting and thats it.
I show up at the shop with my trailer to pack her home. Take a test drive around the block and all seems fine. Go to load on trailer and she dies.
Shop takes her back in and a week later I get a call telling me it's some thing internal, she's toast.
I pack her home and promptly tear down the timing set up. It's out of time again.
Did some checking and one of the idlers is missing a number of bearings allowing it to make quick moves when it jumps on/off the remaining bearings.
Replaced that idler and have put 18K miles on her sence then.
Also the shop (Subaru dealer) reimbearsed me 100% of my money.




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