Flexplate spins, Timing belt doesn't

Hey, I'm Scott, new to the forum. I've got an 05 Jetta TDI with the BEW motor. 240k miles or so. I've owned it for about 2 years with almost no problems. I was recently driving home from work and the car randomly died. No loud noises or anything, or at least not louder than my music. Couldn't get it to restart. I always go to the cheap fuel station so it runs a B20 biodiesel blend. Figured I needed to do the fuel filter. Changed that out and got it reprimed and still no start. I have the glow plug light come on, so not a relay 109 issue. I've got a working lift pump.
Just last night I was trying to get it to fire and it started cranking really fast but sounded like i had no compression this time. I have now pulled the timing belt cover and it looks good and feels tight. The flexplate is spining with the starter, but not the timing belt and gears. What has failed?
What should I be looking for? I've read about people shredding teeth off belts and then they get this problem. Maybe i did and i just can't see where. The belt is tight and I can't get it to spin freely.
Thanks in advance.

Often, it shreds the teeth off the belt at the crankshaft sprocket where it's tough to see with the balancer and lower cover in place.
Sounds like you have work to do.

Yep, timing belt only offers so many bonus miles, sounds like you spent them. Next step, take the head off. Just had a BEW in here that did the same thing. They got 12k bonus miles on that one. It is always that very last bonus mile that does the damage.

My timing belt stripped some teeth off even before it was at it's mileage limit. Hadn't even reached the new lower mileage limit that VW recommended a few years back.

Originally they recommended 100,000 miles. Then they changed it to 80,000 miles. Mine failed at 68700 miles.

So your next step is to remove the valve cover and have a good look at the cam followers. They should be smooth and flat (some probably won't be). If you can't see them well enough to be sure of their condition, remove the cam, which you'll likely need to do anyway.

If you're really lucky, and you want to take your chances, you could stop there and just replace the cam followers, put the cam back in, put on a new timing belt, and hope it doesn't drop a valve. The downside is if a valve stem is damaged, the head will probably break off and cause more damage sometime down the road. Then you'll need pistons and a full head rebuild, or new head

Once you've had a look at the cam followers and assessed their condition, if they look bad, and you want to take things further, pull the head off and see if the valves left imprints on the pistons. Check each piston at the top of it's stroke by pulling up and down on it to make sure there isn't any obvious play that might indicate a damaged connecting rod bearing, or wrist pin. Use a dial indicator to measure how far above the block the pistons protrude. Typically they are around 0.038" give or take a few thousands. They should be within 0.005" of each other or you may have a bent connecting rod. Take the measurements from two edges of the pistons in-line with the axis of the wrist pins. Measuring perpendicular to the wrist pins won't give useful results as the pistons can tilt slightly forward and back, which is normal if it's only a very small movement. You can take that measurement also, to check for worn pistons, but I don't know what the specifications are for that, and it's not strictly necessary for the purpose at hand.

If your pistons check out okay, then you can go back to considering what to do with the head. TDIClub member Franko6 is well known as an expert TDI head rebuilder, so you could consider contacting him if you want your head rebuilt. Then it will be a matter of re-installing it, along with a new timing belt.

If you're able to do all this work yourself, this is worth trying to fix it. If you have to pay a shop to do it all, it'll likely be a lot easier to just buy a different car. The cost would be similar.

So the starter spins but the timing belt doesn't move.
If the engine crank is moving wouldn't the piston collide with a valve(s) assembly?
Or can the valves happen to be aligned so as not to contact?
Being not a mechanic, I read this thread as a catastrophe, but is it possible you're just hearing the starter spin but the crank is not moving?

BobnOH said:

So the starter spins but the timing belt doesn't move.
If the engine crank is moving wouldn't the piston collide with a valve(s) assembly?
Or can the valves happen to be aligned so as not to contact?
Being not a mechanic, I read this thread as a catastrophe, but is it possible you're just hearing the starter spin but the crank is not moving?

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He says his flexplate spins. That's the part that connects the crank to the torque converter in the automatic transmission. Usually called a flywheel on manual transmission cars.

If that spins, but the cam sprocket doesn't, pistons will hit valves. I don't think it's even possible in these engines for the pistons not to hit the valves if the timing belt fails. The pistons protrude past the top of the block, and the bottom of the head is totally flat. The only space between the pistons and the head is created by the thickness of the head gasket.

If the belt slipped by just a tooth, and the cam kept spinning, maybe there would be only light piston to valve contact. In this case, the cam stopped turning and the engine kept turning. There will be some damage for sure.

Mike_04GolfTDI said:

.................If that spins, but the cam sprocket doesn't, pistons will hit valves. I don't think it's even possible in these engines for the pistons not to hit the valves if the timing belt fails..................

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That's what I thought. But I don't know what I don't know.

OP reports engine spinning fast like no compression, yet it would seem it would spin fast with percussion.

Here's what I found inside my engine after the timing belt slipped about a month ago. All the pistons had similar damage, with only the exhaust valves hitting the piston. It's just pure chance what will hit and what will not, when the timing goes off.

Exhaust valve left impression in piston


Good tappet on left, damaged tappet on right where valve stem tried to smash through


Close up of damaged tappet

if the flexplate spins but not the harmonic balancer/timing gear (and the timing belt is intact), you have to consider a broken crankshaft or, if you're lucky, broken bolts/flexplate.

Remember how you always wanted to be a mechanic????

Well.....today's yer LUCKY day!!!!!!

Not to be a smart ... I saw a bumper sticker a while back that said "VW making mechanics out of their owners for over 60+ years". That has been my case. Always something to fix over the weekend.

BobnOH said:

That's what I thought. But I don't know what I don't know.
OP reports engine spinning fast like no compression, yet it would seem it would spin fast with percussion.

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Bob, I bet if the lifters are collapsed from the valves being jammed up then the valves would stay up or not offer much resistance.
Can't wait to see the pictures!

So is Scott driving a new Toyota Corolla now, or is he busy taking apart the TDI?