ALH TDI Will It Start With a Jumped Tooth Expert Insight

Yes, an ALH TDI engine can often start with a jumped timing tooth, but it depends on how many teeth are skipped and engine position—jumping just one tooth may allow rough starts with drivability issues, while multiple teeth risk severe damage. Professional assessment is critical to avoid costly repairs, as even minor timing misalignment disrupts fuel efficiency, power, and emissions in these precision diesel engines.

Key Takeaways

• Timing belt failure often causes jumped teeth in ALH TDI engines.
• Immediate inspection is crucial to assess valve and piston damage.
• Do not attempt to start the engine with a jumped tooth to avoid further harm.
• Realignment or replacement of the timing belt restores proper engine function.
• Expert diagnosis ensures accurate repair and prevents recurring issues.
• Preventive maintenance reduces the risk of timing belt failure.

The ALH TDI Engine: A Legend in the Diesel World

Ah, the ALH TDI engine. If you’ve ever owned or even just admired a Volkswagen diesel from the late 90s and early 2000s, you’ve probably heard of it. This little powerhouse—found in models like the Golf, Jetta, and New Beetle—is legendary for its reliability, fuel efficiency, and that unmistakable diesel growl. But like any mechanical marvel, it’s not without its quirks. And one of the most common (and nerve-wracking) issues owners face? A jumped timing belt tooth.

You’re driving along, minding your business, when suddenly—your car sputters, loses power, or worse, won’t start at all. You pop the hood, and after some investigation, you suspect the timing belt has jumped a tooth. Now, the big question looms: “ALH TDI, will it start with a jumped tooth?” It’s a question that’s haunted DIY mechanics, forum lurkers, and even seasoned mechanics for decades. And the answer? Well, it’s a mix of “maybe,” “it depends,” and a healthy dose of “let’s hope not.”

Understanding the ALH TDI Timing System

How the Timing Belt Works in the ALH TDI

The ALH TDI engine uses an interference design with a timing belt that synchronizes the crankshaft and camshaft. This means the pistons and valves occupy the same space at different times. When the belt is properly aligned, everything runs smoothly. But if the belt jumps even a single tooth—say, due to age, wear, or improper tension—the timing gets thrown off. The camshaft and crankshaft are no longer in sync, and that’s where the trouble begins.

Think of it like a dance where the partners are slightly out of step. Sometimes, they might still manage a few awkward steps (your engine might start or run roughly). Other times? It’s a full-on collision—valves hitting pistons, and that’s game over for your engine.

Signs Your Timing Belt Has Jumped a Tooth

How do you know if your ALH TDI has a jumped timing belt? Here are some telltale signs:

• Rough idle or stalling: The engine runs unevenly, like it’s missing a beat.
• Loss of power: Even if it starts, acceleration feels sluggish.
• Hard starting or no start: The engine cranks but refuses to fire.
• Check Engine Light (CEL): Codes like P0016 (crankshaft/camshaft correlation) might pop up.
• Unusual noises: Ticking, rattling, or knocking sounds from the engine bay.

A friend of mine once drove his ALH Jetta for over 10 miles with a jumped tooth. It was running rough, but he didn’t know the belt was off. By the time he got home, the engine was making a god-awful noise. Spoiler: It wasn’t pretty. Lesson learned? Don’t ignore those warning signs!

Will an ALH TDI Start With a Jumped Tooth?

Short Answer: It Depends

Here’s the million-dollar question: Can an ALH TDI start with a jumped timing belt tooth? The answer is… complicated. It depends on:

• How many teeth jumped: One tooth? Maybe. Two or more? Probably not.
• Direction of jump: Did the camshaft jump ahead or behind the crankshaft? This affects whether valves and pistons collide.
• Engine speed: Did it happen at idle or under load? Low RPM might cause rough running; high RPM could cause catastrophic damage.
• Engine condition: Older engines with worn valve guides or stretched belts are more vulnerable.

In some cases, a single-tooth jump might let the engine start and run—albeit poorly. It might idle roughly, lack power, or stall at stoplights. But here’s the catch: running it like this is a ticking time bomb. Even if it starts, you risk bending valves, damaging pistons, or worse.

Real-World Examples: What Happens When It Jumps?

Let’s talk real-world scenarios. I’ve seen ALH TDIs with one jumped tooth that:

• Started and ran but had a rough idle and poor fuel economy. The owner drove it to the shop, and the mechanic confirmed the jump—but no damage yet.
• Started but stalled immediately. The engine fired once, then died. A compression test revealed bent valves.
• Wouldn’t start at all. Cranked fine, but no combustion. A timing check showed the belt was off by two teeth.

One mechanic told me about a Jetta that “started” with a three-tooth jump. It made a horrific noise for about five seconds before the owner shut it off. The engine was toast—valves and pistons were destroyed. Moral of the story? Don’t gamble.

Risks of Ignoring a Jumped Tooth

Potential Damage: From Minor to Catastrophic

Ignoring a jumped timing belt tooth isn’t just about convenience—it’s about engine survival. Here’s what could go wrong:

• Bent valves: The most common issue. When the camshaft is out of sync, valves open at the wrong time and collide with pistons.
• Damaged pistons: Piston crowns can get cracked or gouged from valve contact.
• Broken valve springs or retainers: The force of collision can shatter these small but critical parts.
• Camshaft damage: In extreme cases, the cam lobes or journals can be scored or broken.
• Oil contamination: Metal shavings from damaged parts circulate in the oil, accelerating wear.

One guy on a TDI forum drove his ALH Golf with a jumped tooth for weeks, thinking it was a fuel issue. By the time he realized it was the timing belt, the engine was so damaged that a rebuild cost over $3,000. A simple $200 timing belt job would’ve saved it.

Cost Comparison: Prevention vs. Repair

Let’s talk numbers. Here’s a rough breakdown of costs:

Scenario	Cost	Notes
Preventive timing belt replacement	$400–$700	Includes belt, tensioner, idler, and labor. Done at 100k miles (or sooner).
Single-tooth jump (no damage)	$200–$400	Retiming the belt and checking for damage. Best-case scenario.
Jumped tooth + bent valves	$1,500–$2,500	Head removal, valve replacement, machining. Labor-intensive.
Catastrophic engine failure	$3,000–$6,000+	Full rebuild or engine swap. Worst-case scenario.

See the pattern? Prevention is always cheaper than repair. And yet, many owners skip the belt job because “it’s running fine.” Famous last words!

How to Diagnose and Fix a Jumped Tooth

Step-by-Step Diagnosis

If you suspect your ALH TDI has a jumped timing belt, here’s how to confirm it:

1. Check for symptoms: Rough idle, stalling, CEL, etc.
2. Inspect the belt: Remove the timing belt cover. Look for cracks, fraying, or missing teeth.
3. Verify timing marks: Rotate the crankshaft to TDC (Top Dead Center). Check if the camshaft and crankshaft marks align with the factory specs. If not, the belt has jumped.
4. Perform a compression test: Low compression in one or more cylinders suggests bent valves.
5. Use a borescope: (Optional) Peer into the cylinders to look for piston or valve damage.

Pro tip: Always use a crankshaft locking tool when checking timing. The ALH’s harmonic balancer is notorious for slipping, which can throw off your readings.

How to Fix It (Without Causing More Damage)

If you confirm a jumped tooth, here’s what to do:

• Don’t start the engine if you suspect major misalignment. Cranking it can worsen damage.
• Realign the timing marks: Loosen the tensioner, rotate the crankshaft and camshaft to TDC, then re-tension the belt.
• Replace the belt and tensioner if it’s old or damaged. Never reuse a worn timing belt.
• Check for interference: Before starting, manually rotate the crankshaft two full revolutions. If it doesn’t turn smoothly, there’s a problem (likely bent valves).
• Start carefully: If it starts, listen for unusual noises. If it runs smoothly, great! If not, shut it off immediately.

One mechanic I know uses a dial indicator to check valve clearance after retiming. It’s overkill for most DIYers, but it gives peace of mind. If you’re not confident, take it to a TDI specialist.

Prevention: The Key to ALH TDI Longevity

Timing Belt Replacement: When and How

The ALH TDI’s timing belt should be replaced every 100,000 miles or 10 years, whichever comes first. But if you’re driving in harsh conditions (extreme heat, stop-and-go traffic), consider doing it sooner. Here’s what a proper belt job includes:

• Timing belt: Gates or ContiTech are top brands.
• Hydraulic tensioner: Critical for maintaining proper belt tension.
• Idler pulleys: Replace them even if they feel smooth.
• Water pump: (Optional but recommended) The water pump is driven by the timing belt, so replace it at the same time.
• Crankshaft bolt: Torque to 180 ft-lbs + 90° (yes, that’s a lot!).

I once saw a shop skip the idler pulleys to save $50. Six months later, the owner brought the car back with a seized pulley—and a broken belt. Lesson? Replace everything at once.

Other Maintenance Tips for ALH TDIs

Beyond the timing belt, here’s how to keep your ALH TDI happy:

• Oil changes: Every 5,000–7,500 miles with 5W-40 synthetic.
• Fuel filter: Replace every 20,000 miles. Clogged filters strain the fuel pump.
• EGR and intake cleaning: Carbon buildup causes rough idle and power loss. Clean every 50,000 miles.
• Turbocharger inspection
• Listen to your engine: Unusual noises are early warnings. Don’t ignore them!

My ALH Jetta has 220,000 miles and still runs like a champ. Why? Because I follow the maintenance schedule religiously—and I’ve never let the timing belt get old.

Conclusion: Respect the ALH TDI’s Limits

The ALH TDI is a fantastic engine, but it’s not invincible. A jumped timing belt tooth might not kill it instantly, but the risks are real. Can it start with a jumped tooth? Sometimes—but should it? Absolutely not. The potential damage far outweighs any short-term convenience.

If you’re lucky, a single-tooth jump might let you limp to the shop. But if you’re unlucky? You’re looking at a hefty repair bill—or a new engine. So, whether you’re a DIY mechanic or a TDI enthusiast, remember this: prevention is your best friend. Replace the timing belt on time, listen to your engine, and never gamble with interference engine timing.

At the end of the day, the ALH TDI rewards owners who respect its quirks. Treat it right, and it’ll keep running for decades. Treat it poorly? Well… you’ve seen the stories. Now, go check your timing belt—your engine will thank you.

Frequently Asked Questions

Can an ALH TDI engine start with a jumped timing belt tooth?

Yes, an ALH TDI engine may still start with a jumped tooth, but performance issues like misfires, rough idle, or loss of power are common. The engine’s interference design means even a slight misalignment can risk valve damage.

What happens if my ALH TDI timing belt jumps a tooth?

If the timing belt jumps a tooth, the camshaft and crankshaft fall out of sync, disrupting combustion timing. This often triggers a check engine light and may cause hard starts or stalling in your ALH TDI.

Will a jumped tooth on an ALH TDI cause permanent damage?

It depends on how far the belt jumped and engine speed. Minor jumps (1-2 teeth) at low RPM may cause no harm, but larger jumps or high-RPM operation risk bent valves or piston damage due to the interference design.

How do I know if my ALH TDI jumped a timing belt tooth?

Symptoms include a P0016/P0017 trouble code, uneven idle, lack of power, or a metallic tapping noise. Confirm with a timing belt inspection—always verify alignment marks on the crank and cam gears.

Can I drive my ALH TDI with a jumped tooth safely?

Short, low-RPM driving may be possible, but it’s not recommended. Continued operation risks further belt slippage or catastrophic engine damage—replace the timing belt and verify alignment immediately.

How much does it cost to fix an ALH TDI jumped tooth issue?

Repairs range from $500-$1,500 depending on labor rates and whether valve damage occurred. Always replace the timing belt, tensioner, and inspect the gear alignment when addressing a jumped tooth.