Timing Belt keeps jumping one tooth

[powerram250]

My car which I just got on the road has jumped one tooth on the crankshaft pulley. I bought the car that way and this is now the 3rd time it has done that. With the high miles do you think the pulley is worn enough to allow the belt to slip? When it jumps it just goes one tooth. Luckily no damage has been done, yet. I can re-time it and tension the belt and the car will start and run perfect. That is the only thing I can think of that might be causing it to do that. -Kevin

 

[rackaracka]

Are you sure you are properly tensioning the belt? Is your tensioner tang in its seat?

 

[Dimitri16V]

I would like to know how you have determined that the timing belt "jumped"

the only timing issue caused by crankshaft sprockets is when they are not tightened down correctly and they wear out the woodruff key developing some slack which will make the static timing to change

 

[TheDieselIdea]

I bought the car that way and this is now the 3rd time it has done that.

I assume that we are assuming that somewhere between buying the car and the 3rd time a new TB kit was installed?lol Just wondering!

 

[steelmb]

You know what they say about the word A$$ U ME. I am assuming that you have assumed wrong since the OP has not stated that it has been changed. Stupidity knows no bounds some times and I will guarantee when you figure that you have seen it all, you have not.

 

[TheDieselIdea]

Exactly, I read it 3 times to see if I was missing something.

 

[powerram250]

Yep, new timing belt and tensioner. The belt tension was still tight (according to tensioner lines) when I checked and confirmed the crank timing was off one tooth again. The tensioner is locked into the notch on the back side. I can't figure out why it wants to do this unless my crankshaft pulley is worn a little and causing it to slip one tooth.

 

[steelmb]

Did you put in a complete kit or just the belt and tensioner? Did you tension it in the right direction? Have you inspected the keyway on the crank? You are playing with fire by running it and not knowing the cause.

 

[powerram250]

Did you put in a complete kit or just the belt and tensioner? Did you tension it in the right direction? Have you inspected the keyway on the crank? You are playing with fire by running it and not knowing the cause.

Yeah I know, I'm living on the edge with the problem. It is really bugging me on what's causing it. Just the belt and tensioner is what I've replaced. The direction is counter clockwise for the tensioner, correct? Now can I just go and take the 18mm bolt/nut off the crank and pull the small pulley off, then there should be a key for it to line up with when putting back on?

 

[steelmb]

I haven't done one so I am not sure of the direction but I had clockwise in mind. I know there has been talk that one of the "how to's" on here has it wrong though.

 

[TDICADDGUY]

On the ALH it is clockwise for the tensioner, and I'm 99% sure it is the same way for the AHU.

 

[manual_tranny]

What he said.

 

[Growler]

Guys this is an AHU with close to 300k on it. my thoughts are a bad harmonic balancer and a beat up crank snout that allow the crank timing to wander.

he is risking his engine every time he starts it. the belt is not actually jumping teeth, the crank pulley is actually rotating a few degrees and it is noticable on the flywheel end. it only gets worse. Happened to Matt98AHU. and another of my customers.

it gets worse & worse the more you drive it until it either wont start, or something interferes. and thats not good.

fix is find a good low mile used crankshaft and have the engine rebuilt afaik. there are others like Franko6 and Jasontdi who would know more about this that should be asked as well.

 

[Lug_Nut]

Which is jumping time?
The crank (pump and cam still align to each other, but not at flywheel TDC),
The cam (pump and flywheel still align to each other but the cam lock plate can't go in),
Or the pump (flywheel and cam align to each other but the pump pin doesn't go in)?
Almost never are two items slipping / jumping. Determine which one.

I suspect that you'll find that the crank sprocket (and there's no Woodruff key on the TDI crank snout) has been removed previously and not properly installed with a new bolt and 66 lb*ft torque plus 90 degrees additional. Improper installation allows the crank belt sprocket to move relative to the crankshaft and causes wandering. (and the sprocket doesn't have to be removed for belt change anyway.)
Fortunately the crank is harder than the sprocket, so the sprocket wears first. A new sprocket will fit securely in almost all cases.

Under $100 for sprocket and bolt, but you'll need to do the cam belt labor all over again to get to the sprocket.


If the cam is the one, the taper fit might be compromised. This requires only 33 lb*ft. Overtightening can split the taper and make for a loose fit despite the bolt tension.

If the pump is the one, check the Woodruff key. It might be sheared.

 

[oilhammer]

Guys this is an AHU with close to 300k on it. my thoughts are a bad harmonic balancer and a beat up crank snout that allow the crank timing to wander.

he is risking his engine every time he starts it. the belt is not actually jumping teeth, the crank pulley is actually rotating a few degrees and it is noticable on the flywheel end. it only gets worse. Happened to Matt98AHU. and another of my customers.

it gets worse & worse the more you drive it until it either wont start, or something interferes. and thats not good.

fix is find a good low mile used crankshaft and have the engine rebuilt afaik. there are others like Franko6 and Jasontdi who would know more about this that should be asked as well.

Ding-ding-ding! We have a winner!

Oh, and there is no "woodruff key" on the front of the crankshafts.

Bah, Lug Nut beat me to the post! That is what I get for stopping to take a pee....

 

[powerram250]

Which is jumping time?
The crank (pump and cam still align to each other, but not at flywheel TDC),
The cam (pump and flywheel still align to each other but the cam lock plate can't go in),
Or the pump (flywheel and cam align to each other but the pump pin doesn't go in)?
Almost never are two items slipping / jumping. Determine which one.

Under $100 for sprocket and bolt, but you'll need to do the cam belt labor all over again to get to the sprocket.

The pump and camshaft pulleys alway have lined up, it's been the crankshaft pulley that is off one tooth everytime. I'll pull the crank pulley off tonight and check the backside of it. Also where can I find a new crankshaft timing pulley for this car? Thank You guys for the help. -Kevin

 

[KLXD]

He said he tensioned it CCW. Wrong! I'd fix that before chasing after the sprocket.

The sprocket moving on the shaft isn't going to appear to keep jumping a tooth. It might seem to do it once but once it was retimed it would be stable unless it jumped back. If it keeps jumping the valves are going to hit.

This assumes it was always jumping in the same direction of course but since the OP didn't state the contrary...

 

[CoolAirVw]

Once I thought my 85 Jetta had jumped a tooth, after locking the cam then looking at the flywheel mark. It looked off, but simply leaving the cam locked, belt still on and turning the crank a bit made the marks line up.

 

[KLXD]

I guess he should clear up: one tooth off on the belt or one tooth off on the flywheel?

He still needs to tension it in the right direction.

 

[Lug_Nut]

Also where can I find a new crankshaft timing pulley for this car?

shameless plug:
http://www.idparts.com/catalog/product_info.php?products_id=1649
Don't forget the new bolt.
Re-using the old, stretched bolt will put you right back where you are now.

 

[powerram250]

Well, here we go. I got the crankshaft bolt out and easily pulled the crank pulley/gear off. I see the flat spot on the crankshaft but inside the pulley there is no flat spot or keyway. The way it is now allows the pulley to free spin on the crank 360*. Total surprise to me. I have ordered a new pulley and torque to yield bolt. There is noticeable belt wear on the toothed part of the pulley too. Also, so the tensioner should be turned clockwise to tension? I've got some pictures, but don't know where to go to post. -Kevin

 

[steelmb]

If there is still some play when you put the new pulley on, due to wear on the crank I would give that loctite 660 a try.

 

[powerram250]

If there is still some play when you put the new pulley on, due to wear on the crank I would give that loctite 660 a try.

Yep, probably apply it to the bolt and smear a little on the backside of the pulley where it contacts the crankshaft. Hopefully there's not too much play with the new one.

 

[paramedick]

If you've been tensioning the TB tensioner CCW, replace it, too. It's been subjected to stresses it's not designed to take.......

 

[Lug_Nut]

CW / CCW? Mine are digital...
Pull the top of the tensioner towards the front of the car.

My personal practice with replacing the crank sprocket is to NOT tighten the crank bolt, at least not just yet.
Install the sprocket and just finger tighten the bolt.
Proceed with the entire belt process: Lock the fuel pump and cam. Install the belt, the tensioner and loosely attach the cam sprocket.
Set the belt tension, tighten the cam sprocket, reconfirm the flywheel is still at TDC.
THEN tighten the crank sprocket to 66 lb*ft plus 90 degrees. Thread lock is overkill. Actually anti-sieze is recommended on the threads and under the bolt head to prevent bolt tightening torque from moving the sprocket.
You'll need an assistant for the "plus 90 degrees". Remove the pump pin and cam lock, put the car in 5th gear and have the assistant stand on the brakes. You'll understand why thread lock isn't needed about 45 degrees into the 90. There is more than enough tension to prevent rotational slip IF the "plus 90 degrees" is followed.
I really suspect that the issue of work crank sprockets is caused by earlier, and un-needed, sprocket removal during a belt change, followed by re-use of the old bolt or failure to sufficiently torque a replacement bolt.

What leaving the crank sprocket till last does is makes the pump pin alignment much less likely to shift the crank off TDC with each subsequent belt change by setting the crank at exactly the belt pitch count.
No more "pump is off by 1/2 tooth and the pin won't go in" blues.

 

[oilhammer]

No, the failure of these is caused by the early style (and often faulty) harmonic balancers, coupled with non-equipped or broken alternator clutch pulleys. At least that is the way I see it.

If your car sounds like an angry rooster at idle after a cold start, you have issues, and the balancer is the culprit generally.

Nobody out there should be driving an AHU or 1Z car with the early style harmonic balancer, IMHO.

I do not use any thread locker or anti-sieze on these, FWIW. Just a new bolt, new sprocket (and if necessary, a new crankshaft) torqued to spec.

 

[paramedick]

CW / CCW? Mine are digital...

OK Jon, I'll bite. I don't understand the reference.

My reference is the direction the tensioner is rotated when setting the tension on the TB. Facing the tensioner from the passenger side, you rotate the tensioner clockwise (CW) using a pin wrench, ensure that the marks are aligned, and then torque the nut securing the tensioner to maintain that setting.

 

[DPM]

he's being witty. Digital clocks...

 

[paramedick]

Doh!!

 

[Matt-98AHU]

My harmonic balancer was still in one piece. The rubber looked, well, it looked aged. But it hadn't separated. The bolt for the pulley on mine had actually loosened at some point during the engines 283k mile life, the pulley shifted and cocked sideways on the crank. Wore the crank down too, so after cleaning and test-fitting a new pulley, there was still some play (much better than the old pulley, though!). Got lucky with the fact that I had an AHU short block sitting around. Cylinder walls had been scored to hell, but the crank was still in good shape.

Mark (validius/gutzb4ll) had a timing belt service recently on his own AHU (swapped into a '97 GTI) and had the same sort of thing. The bolt for the pulley was not exactly very tight anymore and the pulley was worn. Fortunately for him, the new pulley fit very snugly on the crankshaft. The crank was just fine.

Never heard of one being completely rounded inside, though! That's bad!

Even though the sprocket/harmonic balancer were noticeably wobbling for some time, the timing stayed true until the last month of driving it. It became hard starting and pump timing was nowhere near where I had left it, indicative of the pulley shifting on the crank. That's when I made the decision to park it. I had plans to swap the engine into a different, less-rusty Jetta body anyway, so the engine was coming out either way.

Now I'm rebuilding it. Bored over, ASV pistons, Rosten rods... You know, just in case I want to get crazy with power mods