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Old 10-25-2010, 01:33 PM   #1 (permalink)
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Default 2001 broken timing belt

Hi all,
I have a dilemma. The A/C pully disintegrated at 3500 rpm, busted a hole in the timing belt cover, and broke the belt. It's an '01 with 112k miles on it. The mechanic says he can only determine if theres internal engine damage by replacing the belt, and even with that he can't guarantee it will work after he replaces it (bc of possible valve damage).

What's my best bet here. Should I just hedge my bet and look for a whole new used engine? The car still has the original head gasket, so that's a lingering problem as well. Thanks for your thoughts.
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Old 10-25-2010, 01:46 PM   #2 (permalink)
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Leak down test. no starting of the engine required. Takes less time then putting the new belt on and in my opinion is a better method for telling if there is any internal damage(bent valves).

Here is a youtube vid(first Subaru one I found) of a leak down test.

Leak Down Testing
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Old 10-25-2010, 01:51 PM   #3 (permalink)
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That's what I originally thought of, but the mechanic is worried about doing it without the timing belt. His worry is rotating the cam to close the valves with the crank position unknown. What's the best way aroudn this?
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Old 10-25-2010, 03:00 PM   #4 (permalink)
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Ir it broke at 3500 rpm your valves are likely bent. Here's hoping you are lucky.
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Old 10-25-2010, 03:05 PM   #5 (permalink)
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He can verify the crank position by remove the crank pulley to see the timing mark on the cog for the timing belt. Then by knowing where the crank/pistons are know where to set the cams.

Or pull the valve covers off(6 bolts a side) and remove the rocker arms(8 bolts total each side, 4 intake, 4 exhaust(assuming this is a SOHC)). This will allow all the valves to close that are not bent and allow the crank to be turned as needed with no fear of wrecking any thing that is not already damaged. All in all it should only take an hour to pull the valve covers and remove the rocker arms and do a leak down test, maybe two hours.

I am not a fan of the method of install a new belt and go for broke by trying to start it as it has the potential to cause far more damage if a valve head completely separates from the stem.
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Old 10-25-2010, 03:09 PM   #6 (permalink)
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That's what I'm fearing. I threw it in neutral pretty quickly, but i imagine a few impacts are enough to bend the valves. The mechanic is going to take the cover off tomorrow. He did say he could see the belt on the crank though the hole in the cover.

There's a chance the belt just skipped a few teeth and messed up the timing. If only a few teeth maybe theres a chance the valves didnt hit the pistons.
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Old 10-25-2010, 03:37 PM   #7 (permalink)
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Thanks flstffxe. Those are really good ideas. I thought you could carefully rotate the crank and cams, but wasn't sure exactly how you'd go about it. He wanted to take the timing cover off to look and see what kind of damage was done to the belt.

I think the money would be better spent on checking the valves. If the leak down test checks out, can I be confident the internals are ok?
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Old 10-25-2010, 04:12 PM   #8 (permalink)
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99% yes. If it passes the leak down test, the piston rings are good and valves are sealing. If it fails the leak down test he has to check where the air is going, out a valve or past the rings. Fairly easy to do for a mechanic, look and listen.

I use a couple of tricks of my own to help in this. I add a concentrated liquid air freshener for automotive use to the intake air of my air compressor. When I run the leak down test I disconnect the PCV and plug the port on the intake and any others that go from the intake to the crank case. There is always going to be blow by past the rings, thus filling the crank case with the smell of the air freshener and the reason for plugging every thing that goes from the intake to the crank case. Run the leak down test, if the intake valves in a cylinder you will smell the air freshener in the intake, if it the exhaust valves leak you will smell the sent coming out the tail pipe. Stupid simple trick but saves so much time.

I say 99% chance it is good, just because a valve can be tweaked a tiny bit, when the valve closes the head of the valve rests on the seat and can flex the valve stem enough to let the valve to seal and pass a test or even run with out issue. However this flexing will eventually lead to the valve head breaking off the valve stem and destroying that cylinder. The chances of this are slim, generally when a timing belt lets go and valves get bent they get really bent.
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Old 10-26-2010, 07:23 AM   #9 (permalink)
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Turns out the shattered a/c belt got in behind the crank sprocket and make the timimg belt skip. Mechanic removed the belt, retimed it, and there's no compression.

Where should I go from here? Is it worth the trouble of putting new heads on it without reconditioning the bottom half? Should I part it out?
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Old 10-26-2010, 02:29 PM   #10 (permalink)
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For me I would pull the heads see if they are repairable, if they are repairable get them redone and put it back together.

If the heads are not repairable( in my book it takes a lot to ruin a head), look for a used set of heads, maybe freshen them up and go from there.

Now if the engine used a lot of oil or had some knocking going on I may look for a replacement engine.
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Old 10-26-2010, 02:38 PM   #11 (permalink)
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Not to be a vulture, but where are you located? I'm looking for a foz with a blown motor for my swap.
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Old 10-26-2010, 04:07 PM   #12 (permalink)
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The engine was well taken care of and functioned well before this incident. How hard is taking the heads out. From some other threads it looks possible to remove the engine mounts and trans mounts and jack it up to get enough clearance to take the heads out while in the car. I've rebuilt an engine, but it was an old chevy engine outside of the car.

I suspect gaskets, head bolts, and fixing the heads would be around $600?

In case it doesn't work out, I'm located outside Philly.
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Old 10-26-2010, 05:57 PM   #13 (permalink)
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the exact same thing happened to my daughters car. I installed 6 new valves, lapped all the valves. new head gaskets. timing belt etc, the car is running perfect. I bought the valve spring compressor from sears. It was cheap. I removed the heads in the car but if doing it again I would pull the engine out.
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Old 10-26-2010, 06:22 PM   #14 (permalink)
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I'm glad it worked out so well. Are those nicks in the piston from the valve? Are you worried about that?

Do you recall how much the gasket, valves, and bolts ran?
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Old 10-26-2010, 06:34 PM   #15 (permalink)
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the head gaskets were from 1stSubaru com about
$70, you don't need to replace bolts they are all reusable. The valves removed were osvat same as online vendors. $6.22 for intake valve, $8.80 for exhaust valve, the heads and pistons are fine. the valve seats all cleaned up with a light lap. 4 exhaust valves were bent bad, they marked the pistons in the pics. 2 intake valves were bent slightly they did not leave marks on the pistons
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