# Broken timing belt: worst case scenario?



## eskimocounselor (Aug 28, 2005)

Here is what happened to my friend's 2002 New Beetle 2.0:
She drove it home just fine and the next morning it wouldn't start. Had it towed to a shop who said that the timing belt was no longer turning the sprocket. Either it was too loose or teeth were too worn. It didn't start, but could the power of the starter alone cause enough damage to the head that it would need a rebuild? Is there any way to know without pulling the head? Please offer your 2 cents. 
*UPDATE Jan. 18*
I spent all day learning how and changing the timing belt. I got the timing marks on the cam gear and crank gear both perfect and it ran/drove, but a little rough. I drove around the block and the check engine light started flashing. Smelled like burnt rotten egg farts too. I hear some clatter in the #1 cylinder too. Looks like I'm in the market for a new/used head. 


_Modified by eskimocounselor at 11:10 PM 1-18-2010_


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## Jay-Bee (Sep 22, 2007)

*FV-QR*

Damage is possible, check compression first, it's a 20$ tool.
I would question the shops diagnosis.
So she drove home and shut the car off, and it didn't start the next morning?
Unless someone cut the timing belt I don't follow their story... unless it was badly damaged and got home under it's own power to never turn again, usually they break while the engine is ON, not OFF.


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## eskimocounselor (Aug 28, 2005)

*Re: Broken timing belt: worst case scenario? (eskimocounselor)*

Can you check compression when it doesn't start?


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## TMTuned99.5Golf (Jan 27, 2004)

*Re: Broken timing belt: worst case scenario? (eskimocounselor)*

No you can't. But as Jay-Bee said, question the diagnostics method of the shop. 
If the timing belt snapped, it might have sounded like a machine gun going off under the hood and then the motor would have stopped. 
Do you know if there was any check engine lights present on the car? Ask her, not the shop.


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## drracing07 (Nov 5, 2007)

*Re: FV-QR (Jay-Bee)*

had a friend with a ford focus, and a ladie (figures







) that parked at my house. middle of winter and the car drive fine there. went to start it again and it wouldnt run. no compression on 2 cyl. the took it to the shop and they said it was the timing belt. they ended up replacing the entire motor. so its possible


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## drracing07 (Nov 5, 2007)

*FV-QR*


_Quote, originally posted by *eskimocounselor* »_Can you check compression when it doesn't start?


yes you can, slap the compression tester in the spark plug hole and crank it over, that is if it can crank. get a new timing belt and tripple check your marks, then run a compression test.


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## ABA Scirocco (May 30, 2001)

*Re: Broken timing belt: worst case scenario? (eskimocounselor)*


_Quote, originally posted by *eskimocounselor* »_Can you check compression when it doesn't start?

It doesn't need to start but it does need to have the camsahft turning and properly timed so doing a compression test would require that you first replace the timing belt. What you want to have done is a leak down test not a compression test, you can do a leak down test without having to do any repairs first. Basically, you make sure the valves on the cylinder you're testing are closed then pump compressed air into the cylinder through the spark plug hole and see how fast it leaks out. 
BTW, the torque from the starter alone is sufficient to do damage, the worst case scenario is a bent valve (or valves), a leak down test will detect that.


_Modified by ABA Scirocco at 8:57 PM 1-12-2010_


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## germancarnut51 (Mar 23, 2008)

*Re: Broken timing belt: worst case scenario? (eskimocounselor)*

Timing belts work until they don't (at which time they break, or strip teeth, or because they stretch, the camshaft and intermediate shaft can jump and skip teeth).
Yes, the simple act of spinning the engine with the starter can cause damage. And, a compression test requires spinning the engine, and if the timing belt is not intact, and timed correctly, you can cause damage. A leakdown test requires the engine to be turned. If the timing belt has broken or skipped, damage can be caused even when rotating the engine by hand.
Best bet it to have the timing belt checked to see if it's intact, and timed correctly. If the timing needs replacement, replace the timing belt, then compression check, and leakdown check to get an idea of whether there is damage, and how much, before teardown for repair. 
Could very well be cheaper to locate, buy, and install a used engine, than to fix a high mileage engine with valve/cylinder head damage.


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## ABA Scirocco (May 30, 2001)

*Re: Broken timing belt: worst case scenario? (germancarnut51)*

Replacing the timing belt first is potentially wasted effort and expense. It's quick, simple and easy to do a leak down test first. It's very easy to make sure you don't do any damage when turning the engine over by hand, you just make sure the valves are closed on the cylinders where the pistons are coming up to TDC, any competent mechanic would have no trouble at all doing this. A leak down test will tell you everything you need to know about the condition of the head before beginning any repairs and the only parts you need to remove to get that done are the spark plugs and upper timing cover.


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## germancarnut51 (Mar 23, 2008)

*Re: Broken timing belt: worst case scenario? (ABA Scirocco)*

So how do you turn the crankshaft on an interference engine without bending valves?
You're supposed to turn the engine in the normal direction for any sort of timing check or compression check. Yet turning the valves in the normal direction will bend valves unless you remove the camshaft, or the timing belt is still timed correctly (belt not broken or skipped), in which case why would you be checking the compression if the engine simply won't start? You could remove the camshaft, but that's going to cost way more than simply replacing the timing belt, and if the timing belt is bad, is going to have to come off whether the valves are damaged or not.
Whether your a "professional" mechanic, or a "shadetree" does not alter physics.


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## ABA Scirocco (May 30, 2001)

*Re: Broken timing belt: worst case scenario? (germancarnut51)*


_Quote, originally posted by *germancarnut51* »_So how do you turn the crankshaft on an interference engine without bending valves?


Easy, you just need to be careful about it. Valves can contact pistons only when the pistons are within a few millimeters of TDC AND when the valves are close to maximum lift, that means for most of each crank rotation, there's no risk. So, if the crank and camshaft can turn independently i.e. the timing belt is off or broken, you pull off the upper timing cover so you can see the position of the camshaft, then you check to see where the crank is positioned so that you can determine which pistons will be the next to come to TDC, then you turn the camshaft so that the valves on those cylinders are closed, then you turn the crank to bring those pistons to TDC, do the leak down test on the cylinder that's at TDC on it's compression stroke and repeat the process on the remaining 3 cylinders. 


_Quote, originally posted by *germancarnut51* »_ and if the timing belt is bad, is going to have to come off whether the valves are damaged or not.
Whether your a "professional" mechanic, or a "shadetree" does not alter physics.


Very true, but why risk going through the bother of replacing the timing belt only to find out you have bent valves? If valves are bent, that would mean you'll have to do the work of replacing the timing belt twice and if you're paying someone to fix the car, you'd be spending money you didn't need to. And, if bent valves mean that you'd elect to replace the engine rather than repair the head, then you'd have spent time and money on a timing belt replacement you may not need. 
The whole process of doing a leak down test on all 4 cylinders shouldn't take much more then about 15 minutes, time well spent imho. That's why I recommended a leak down test before commencing repairs so that you know exactly what you're in for and you don't waste time and money doing stuff twice or doing unnecessary stuff. 


_Modified by ABA Scirocco at 1:54 PM 1-13-2010_


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## germancarnut51 (Mar 23, 2008)

*Re: Broken timing belt: worst case scenario? (ABA Scirocco)*

When the belt has broken or jumped, and needs replacement, and or the head needs to come off, the prep is the same. 
You have to remove the accessory drive belts (serpentine and v-belt), remove the timing cover parts, and remove the waterpump pulley.
The at that point, all you're going to do is index/confirm indexing of the crankshaft, camshaft, and distributor, and slip a timing belt on.
And what if it turns out that the valves are damaged? Slip the timing belt off, remove the lower intake and exhaust manifolds, and the head bolts, and the cylinder head is off the car.
Where the excess unnecessary expense? The only action you did was slip on a new timing belt.
Much easier in my opinion that removing the UIM, valve cover, ignition wires, spark plugs, and timing cover, then watch the pistons through the spark plug holes to see which one is coming up next, and turning the camshaft by hand to avoid damage. After this effort and inspection you still have to do everything done to slip on a new timing belt or to remove the cylinder head for repair.


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## eskimocounselor (Aug 28, 2005)

*Re: Broken timing belt: worst case scenario? (germancarnut51)*

The missing factor is whether or not I decide to pay a shop to do the work or do it myself. I have never done a timing belt myself, so I will be dealing with a learning curve. At this point I can pay $250 for the shop to throw on a new timing belt with no promises and then risk having to take it right back off, or I can pay $50 to have it towed to my house and start monkeying around with it myself. I know this is not rocket science, but sure can't afford to waste much money. How long would it take a noob like me to walk through the process for the 1st time without causing further damage?


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## ABA Scirocco (May 30, 2001)

*Re: Broken timing belt: worst case scenario? (germancarnut51)*

To do the leak down test as I've described, all you have to do is remove the spark plugs and remove the upper timing cover. If the timing belt is merely stripped and not completely broken, you can just cut it, no additional preparatory work is required.
If your plans are to repair the engine regardless of what damage may have occurred, then you're right, removing all of the other stuff and slipping on a new timing belt is no big deal. But, if your plans are to replace the engine if the valves are bent, any work you do beyond the minimum required to do a leak down test would all be wasted effort if there are bent valves and if you're paying someone to do the work, unnecessary expense.


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## germancarnut51 (Mar 23, 2008)

*Re: Broken timing belt: worst case scenario? (ABA Scirocco)*

How do you determine the position of the valves, so you can turn the crankshaft safely without removing the upper intake manifold (on a crossflow engine) and the valve cover so you can see the position of the camshaft and valves?


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## germancarnut51 (Mar 23, 2008)

*Re: Broken timing belt: worst case scenario? (eskimocounselor)*

$250 is most, if not all that you would pay for a used engine. Why would you pay a shop $250 to replace the timing belt? 
Also consider the total of of replacing the engine. If you buy a used engine, you are still going to have the additional cost of prepping the engine for installation (like replacing the timing belt, waterpump, and the clutch).
Buy the Bentley VW Service Manual, and learn to do the work yourself.


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## ABA Scirocco (May 30, 2001)

*Re: Broken timing belt: worst case scenario? (germancarnut51)*


_Quote, originally posted by *germancarnut51* »_How do you determine the position of the valves, so you can turn the crankshaft safely without removing the upper intake manifold (on a crossflow engine) and the valve cover so you can see the position of the camshaft and valves?

By the timing marks on the cam sprocket, the same way you do when you're setting up the valve timing to replace the timing belt. When the mark is lined up as it normally would be to install a timing belt, the #1 cylinder's valves are closed, then for each 1/4 turn of the camshaft, the valves of the next cylinder in the firing order are closed.


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## urbancynic (Apr 19, 2007)

*FV-QR*

I had the tensioner (hydraulic pos) fail in my aba. 7 bent valves. damage is PROBABLE


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## germancarnut51 (Mar 23, 2008)

*Re: Broken timing belt: worst case scenario? (ABA Scirocco)*

You can't ASSUME that it's safe to turn the crankshaft by guessing at the position of the valves, yeah, every 90 degrees, the valves of one cylinder will be closed with the piston for that cylinder at TDC, BUT what about the other cylinders?
Without removing the valve cover, YOU CANNOT KNOW FOR SURE THE POSITIONS OF ALL THE VALVES, when to turn the camshaft, and how far (to stay out of contact with the pistons) to turn the crankshaft and camshaft.
What are you thinking? After starting with cylinder #1, you're going to turn the camshaft 45 degrees, then turn the crankshaft (how far?), then turn the camshaft another 45 degrees, and then the crankshaft 45 degrees ending up 90 degrees from tdc on the camshaft?
What about the camshaft duration? What if the Owner changed the camshaft? The lift and duration are going to be different, which changes the safe zone from what it would be with a stock camshaft. How do you know how long the valves are open, and when they start to open or start to closed without removing the valve cover? You can't know without taking the time to remove the valve cover.


_Modified by germancarnut51 at 8:25 PM 1-13-2010_


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## onewiper (Aug 29, 2002)

_How do you determine the position of the valves, so you can turn the crankshaft safely without removing the upper intake manifold (on a crossflow engine) and the valve cover so you can see the position of the camshaft and valves?_
A lot of arguing for nothing, if I were to do a leakdown test I would just remove the camshaft, an easy job.
The thing is these are a non interferance engine and the chance of damage is minimal. Also these are one of the easiest engines to do a timing belt change, do the belt start it up and see how it runs, no need to waste your time on compression testing or leakdown testing. If it runs good, fine, if it runs like crap( assuming your timing is right on) then you know there is valve damage and you will need to pull your head


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## Jay-Bee (Sep 22, 2007)

*FV-QR*


_Quote, originally posted by *onewiper* »_
The thing is these are a *non interferance engine* and the chance of damage is minimal. 


Not true, MK3/ABA MK4/AEG+ are indeed interference, I don't see why they would state in the Bentley to not turn the crankshaft without the camshaft attached as damage can occur, if it wasn't the case.
But it is true that with only 2 timed valves per cylinder, chances are you can walk away without damage.


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## ABA Scirocco (May 30, 2001)

*Re: FV-QR (Jay-Bee)*

There are plenty of examples of people breaking timing belts on Mk3 and Mk4 who have bend valves and also lots of examples of people that have not. Probably the worst thing that can happen is what urbancynic described, slippage or loss of tension, that pretty much guarantees extensive damage. 
BTW, last season we broke a timing belt on our 13:1 ABA racing engine without sustaining any damage, with the high lift, high duration cam we run, that almost classifies as a miracle.


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## eskimocounselor (Aug 28, 2005)

*Re: FV-QR (ABA Scirocco)*

I will pick up a timing belt kit this weekend and pray that I will have no damage.


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## ABA Scirocco (May 30, 2001)

*Re: FV-QR (eskimocounselor)*

I'm not sure what the actual odds are but, if it's just a simple broken belt, there's a reasonable chance it'll be okay. 
Good Luck


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## FL 2.0L (Aug 1, 2002)

MKIV? My money is on head damage.
The belt went on my MKIII at 63K as my wife pulled into the parking lot at her work. Clutch was in and it was a low rpm failure. Shop slapped a new belt on (well, a couple teeth off) and it ran.


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## sipediesel (Nov 7, 2009)

*Re: (FL 2.0L)*

I bent all four intake valves on my AEG and ate the top of the pistons. Happy times!


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## eskimocounselor (Aug 28, 2005)

*Re: (sipediesel)*

I spent all day learning how and changing the timing belt. I got the timing marks on the cam gear and crank gear both perfect and it ran/drove, but a little rough. I drove around the block and the check engine light started flashing. Smelled like burnt rotten egg farts too. I hear some clatter in the #1 cylinder too. Looks like I'm in the market for a new/used head.


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## TMTuned99.5Golf (Jan 27, 2004)

*Re: (eskimocounselor)*

If you didn't live so damned far away I might be able to take a gander.... then again, I am driving a Chevy Metro until I get my engine rebuilt so I do have great gas milege.
Maybe one a weekend I could swing out your direction and take a look at it for ya if you'd like... (I live in Troutdale)
BTW, mk4's are starting to appear in the junk yard around Portland. I just pulled some engine parts off an '01 Jetta on Sunday morning.


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## 91redjetta (Aug 28, 2006)

*Re: (eskimocounselor)*

so the aeg 2.0l are interference? i didn't think the aba's were in stock form?


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## ABA Scirocco (May 30, 2001)

*Re: (91redjetta)*

There have been lots of reports of bent valves on stock ABA's so apparently, they are interference. I think the AEG are the same but I'm not sure personally, I'd treat them as though they are, just to be on the safe side.


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## eskimocounselor (Aug 28, 2005)

*Re: (ABA Scirocco)*

Yes, ABA and AEG are both interference.


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