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Go Back   TDIClub Forums > TDI Model Specific Discussions Areas > VW MKIV-A4 TDIs (VE and PD)

VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old November 27th, 2001, 01:04   #1
Mike Jeremy
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Default How much can a timing belt slip before damaging engine?

The timing belt on my Passat has apparently jumped one or more teeth. I drove the vehicle to a garage in this condition for about 20 miles at low revs, where they are recommending a new engine, despite not having inspected further to see if there is more damage to the valves,pistons etc. My question is: When the belt jumps,throwing the timing out, is damage inevitable? Should I pay for an inspection ($250) or accept their view that engine replacement is necessary? The car DID make it to the garage, despite heavy smoke, missing, and a rattling sound.

Many thanks any feedback, Mike.
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Old November 27th, 2001, 01:18   #2
mickey
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Default Re: How much can a timing belt slip before damaging engine?

I'm not sure. One...maybe two...but certainly no more than that. The clearance is VERY close!

Have them install a timing belt, fix the broken pulley key you mentioned in the other thread, and start the engine. You might get lucky.

-mickey
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Old November 27th, 2001, 01:19   #3
mickey
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Default Re: How much can a timing belt slip before damaging engine?

Better yet, have it towed to a COMPETENT and HONEST garage! If these guys are telling you the engine needs to be "replaced" when they haven't even examined it, I think it's safe to assume they're either stupid or dishonest...or both.

-mickey
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Old November 27th, 2001, 04:33   #4
Lug_Nut
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Default Re: How much can a timing belt slip before damaging engine?

It depends on which gear slipped.
If the fuel pump jumped, no mechanical engine damage occurs. Injection timing is off.
If the cam jumped only one tooth, maybe two, not likely to cause damage. The valves are nearly closed at piston TDC rather than completely closed as they should be. Contact not likely.
If the crank jumped two teeth, equivalent to the cam jumping four, there is a higher chance of piston / valve contact and some damage. Note: a higher chance, not a certainty.
Check relative positions of all three toothed pulleys to try to figure out which one slipped.
I'd suspect that the crank jumped due to greater load (driving, not driven) and fewer teeth engaged.
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Old November 27th, 2001, 11:55   #5
macguyver
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Default Re: How much can a timing belt slip before damaging engine?

I stripped at least 10 belt teeth on my 96 Passat where I was able to spin the crankshaft in trying to start the engine with the cam stationary and I too thought that the engine was toast. I opened the valve cover and when I didn't see the camshaft in three or more pieces, instead all looked intact, I went out and bought a timing belt installed it and have since put 20,000 km on the car with the engine not missing a beat.
Oh yeah, I had the pump and camshaft locking tools (left over from my 5000 Audi TD) which fit exactly.
Don't take anyones word what it may or may not be.
Spend $38 for a new belt and try it. Good luck.
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Old November 27th, 2001, 18:19   #6
Lug_Nut
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Default Re: How much can a timing belt slip before damaging engine?

Macguyver, How close to horizontal was the cam groove for the lock tool when you began repairs? You might be luckier than you might realize. If the groove was horizontal then all the valves were closed or nearly so.
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Old November 28th, 2001, 01:16   #7
Mike Jeremy
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Default Re: How much can a timing belt slip before damaging engine?

The garage will inspect the engine for damage this week and will give me the findings next Monday; I'll pass on what I learn. I'm optimistic. Many thanks for all your feedback. The knowledge base on this BB is impressive. Rgds Mike.
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Old November 28th, 2001, 13:02   #8
macguyver
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Default Re: How much can a timing belt slip before damaging engine?

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Jonathan Bartlett:
Macguyver, How close to horizontal was the cam groove for the lock tool when you began repairs? You might be luckier than you might realize.<hr></blockquote>
I did not take note of the cam position, but you're absolutely right that it must have locked-up in that position. And, believe me, I do realize how lucky I was!
My other experience was on an 85 Audi 5000 TD. The belt got contaninated by an oil leak from the power steering pump and soon after it broke in two. The cam was in four pieces but no damage to the rods, pistons or the head. I got a cam from the wreckers, new belt and threw in new piston rings for a total cost of C$450. The engine afterwards run better than before and I was able to get 40 mpg with an automatic trany that shifted into neutral everytime you let off the gas pedal. Great car, but unfortunately my daughter wrapped it around a pole after skidding on ice.
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Old December 2nd, 2001, 04:51   #9
redtdi96
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Default Re: How much can a timing belt slip before damaging engine?

Come on guys on a diesel you can slip """0"""" teeth. If you slip 1, the valves will hit piston at RPMs.
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Old December 2nd, 2001, 08:50   #10
Lug_Nut
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Default Re: How much can a timing belt slip before damaging engine?

Please put in a smiley or other emoticon to let us know when you are joking. You are joking, aren't you?
The cam and fuel pump pulleys have 42 teeth. Jumping one tooth will result in 8.57 degrees of rotation of the cam or fuel pulley. The crank pulley has 21 teeth. One tooth change at the cam or pump will result in 17.14 degrees or rotation.
The pistons could hit the open valves but only near to TDC and nowhere ense in the rotation stroke.
Q: How much vertical motion of the piston results from rotating the crank 17.14 degrees BTDC to TDC? What are the valve's positions in this crank position range?
A: not much and so nearly closed that no contact will result.
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