If you have ever heard the phrase “check the gear on the shafts” from car mechanics or on forums, but did not understand what they were talking about, this article is for you. Term shesnar (or camshaft gear) is not so often found in official documentation, but is widely used among engine repairmen. This is a small but critical detail on which the synchronization of the valves and pistons depends.
In this article we will look at:
- 🔧 what is a gear and where is it located in the engine;
- ⚙️ how it interacts with other mechanisms (timing belt/chain, crankshaft);
- ⚠️ what signs indicate its wear or breakdown;
- 🔍 how to check the condition of the gear yourself without disassembling the engine;
- 💰 cost of replacement and is it possible to save on repairs.
We will pay special attention a common mistake: many people confuse the gear with a crankshaft damper or flywheel, which leads to incorrect diagnosis and costly consequences. If you notice a knock in the timing belt area or an ignition failure, read on.
What is a shaft gear and why is it needed?
Term shesnar is a slang name camshaft gears (sometimes crankshaft). It is a gear that:
- 🔗 ensures synchronization of the rotation of the camshaft and crankshaft through a timing belt or chain;
- 📏 determines the gas distribution phases (moments of opening/closing valves);
- 🔄 transmits torque from the crankshaft to the camshaft (or vice versa, depending on the design).
In most modern engines, the gear is made of hardened steel or cast iron and has helical teeth for smooth engagement. On some motors (for example, VAZ 2108-2115 or Renault K7M) the camshaft gear can be plastic - this is a budget solution, but less durable.
The main function of the gear is to maintain precise synchronization of the shafts. If the gear wears or shifts, the valve timing is disrupted, resulting in:
- ⚡ misfires;
- 🔥 detonation;
- 🚗 loss of power;
- 💨 increased fuel consumption.
Where is the gear located and how does it work?
The camshaft gear is located at the end of the shaft on the timing drive side. The exact location depends on the engine design:
- 🔧 B 8 valve engines (for example, VAZ 2111 or K4M Renault) there is only one gear, located at the end of the camshaft under the timing cover.
- 🔧 B 16 valve engines (for example, VAZ 21124 or Ford Zetec) there are two of them - one for each camshaft (intake/exhaust).
- 🔧 B diesel engines (for example, 1.9 TDI) there may be an additional gear to drive the injection pump.
Structurally, the gear consists of:
- Hubs - the central part that sits on the shaft.
- Ring gear - external part with teeth for engagement with the belt/chain.
- Fixing element - key, bolt or retaining ring.
On some motors (for example, BMW M50/M52) the camshaft gear can be composite: steel hub + plastic ring gear. This reduces noise but requires more frequent inspection.
How to distinguish a gear from a crankshaft damper?
The crankshaft damper is a massive wheel with a rubber ring located at the opposite end of the crankshaft (flywheel side). The gear is much smaller, located on the camshaft and has small teeth for the timing belt/chain.
Signs of gear malfunction: when to sound the alarm
Wear or damage to the camshaft gear does not appear immediately, but the symptoms cannot be ignored. Here are the key signs:
| Symptom | Possible reason | Consequences |
|---|---|---|
| Knocking or rustling noise from under the timing cover | Worn gear teeth or stretched chain/belt | Belt failure, valve bending |
| Floating idle speed | Valve timing shift | Increased fuel consumption, loss of power |
| Difficulty starting the engine | Timing timing marks mismatch due to gear slippage | Detonation, piston damage |
| Check Engine (P0340, P0341) | Camshaft position sensor error (CPS) | Switching to emergency mode, limiting speed |
The most dangerous symptom is metallic knock, which increases with increasing speed. This may mean that the gear teeth are “licked” or the gear has turned on the shaft. In this case, the operation of the car prohibited - the risk of timing belt breakage and valve bending is 80%.
⚠️ Attention: If after replacing the timing belt/chain the engine begins to run worse, check the marks on the gear. A common mistake is installing a gear with a shift of 1 tooth, which leads to a phase imbalance.
How to check the gear yourself: step-by-step instructions
Diagnostics can be carried out without removing the timing cover, but dismantling will be required for an accurate result. Here's what you can do yourself:
Remove the upper timing belt cover (if there is access)|Turn the crankshaft with a wrench at the pulley bolt|Inspect the gear teeth for wear and chips|Check the alignment of the marks on the gear and cylinder block-->
Step 1. Visual inspection
Remove the timing cover (on most cars it is plastic, secured with 3-5 bolts). Inspect the gear:
- 🔍 The teeth should be smooth, without hangnails and ′′ licked ′′ edges.
- 🔍 There is no play between the gear and the shaft (try shaking it with your hand).
- 🔍 There are no cracks or chips on the hub.
Step 2: Checking the labels
Turn the crankshaft so that the mark on the gear coincides with the mark on the cylinder block (or rear timing cover). For example, on VAZ 2110 The mark on the gear should face up, and on the block it should coincide with the protrusion. If the marks do not match, the gear has turned.
Step 3. Checking the play
If the gear sits on the shaft with play, this is a sign of wear on the seat or the shaft itself. Backlash of more than 0.5 mm is critical. It can be checked this way: take the gear by the teeth and try to swing it perpendicular to the shaft.
If traces of “waves” (uneven wear) are visible on the gear teeth, this is a sign of a stretched timing chain. In this case, change both the gear and the chain with tensioners.
What to do if the gear is worn out: repair or replacement
The camshaft gear is non-repairable part. If worn or damaged, it can only be replaced. The cost of work depends on the engine design:
| Engine type | Gear cost (RUB) | Cost of work (rub.) | Difficulty |
|---|---|---|---|
| 8-valve (VAZ, Renault) | 800–1 500 | 2 000–3 500 | Average |
| 16-valve (VAZ, Ford) | 1,200–2,500 (per piece) | 4 000–6 000 | High |
| Diesel (1.9 TDI, 2.0 HDI) | 3 000–5 000 | 8 000–12 000 | Very high |
On some cars (for example, Toyota 3S-FE or Mitsubishi 4G63) the camshaft gear is sold only assembled with the shaft. In this case, repairs are more expensive - up to 20,000–30,000 rubles.
Is it possible to save money?
- 💰 Buy gears only from trusted suppliers - soft metal fakes wear out within 10,000 km.
- 💰 If you change the gear, be sure to check the condition of the timing chain/belt and tensioners. Their wear is the main cause of gear failure.
- 💰 On 8-valve engines, you can replace it yourself (you need a set of keys and a shaft lock).
⚠️ Attention: On diesel engines (for example, 1.9 TDI) the camshaft gear is connected to the injection pump drive. If it is installed incorrectly, the pump will fail within 500 km.
Common mistakes when replacing gears and how to avoid them
Even experienced craftsmen sometimes make mistakes when working with the camshaft gear. Here are the most common:
- Failure to fix the shafts when replacing. If you do not fix the crankshaft and camshaft in the TDC position, the marks will become confused and the valve timing will be disrupted. Use special fasteners (for example, for VAZ - device
67.7811-9516). - Tightening the gear bolt. On many engines (for example, Renault K4M) the pinion fastening bolt is tightened with a force of 50–60 Nm. If you overtighten, you can break the threads in the shaft.
- Using an old chain/belt. A new gear with a worn chain will not last long. Always change the set: gears + chain/belt + tensioners.
- Lack of lubrication. When installing the gear on the shaft, apply a thin layer of lubricant (for example, LIQUI MOLY MoS2) to the seat. This will prevent corrosion and make future removal easier.
Another typical problem is buying the wrong size gear. For example, on VAZ 2112 The intake and exhaust camshaft gears differ in the number of teeth (20 vs 21). It is easy to confuse them, but this will lead to unstable engine operation.
When replacing the gear, always check the condition of the camshaft oil seal. If it leaks, oil will get onto the timing belt, which will cause it to slip and break.
Prevention: how to extend the life of gear
The camshaft gear lasts 150,000–200,000 km, but this period can be shortened or extended depending on operation. Prevention Tips:
- 🔧 Monitor the condition of the timing belt/chain. A stretched chain or worn belt will accelerate wear on the gear teeth. Check tension every 30,000 km.
- 🛢️ Use quality oil. Cheap oils with low detergency lead to deposits on the shafts, which makes it difficult for the gear to rotate.
- 🚗 Avoid sudden loads. Sharp acceleration on a cold engine increases the load on the timing belt.
- 🔊 Listen to the engine. Extraneous sounds from under the timing cover are the first sign of problems.
On diesel engines (for example, 1.5 dCi Renault) the camshaft gear is additionally loaded by the injection pump drive. In this case it is recommended:
- 🔧 Check the condition of the gear every 100,000 km.
- 🛠️ Use only original spare parts (e.g. for Renault - art.
7701470064).
If you often drive off-road or tow a trailer, check the gear more often - vibrations and loads accelerate its wear.
FAQ: Frequently asked questions about gears on shafts
Is it possible to drive if the gear is knocking?
No. A knock indicates critical tooth wear or gear play. The risk of timing belt breakage and valve bending is up to 80%. Operation prohibited.
How to distinguish gear wear from timing chain wear?
A worn chain produces a “rustling” sound at idle, and a damaged gear produces a metallic knocking noise that intensifies with increasing rpm. An accurate diagnosis can only be made after removing the timing cover.
Is it possible to replace the gear without removing the cylinder head?
Yes, on most engines (eg VAZ 2111 or K4M) the gear can be replaced without removing the cylinder head. You will need to remove the valve cover, timing belt and camshaft retainer.
What happens if you install the gear with a shift of 1 tooth?
The engine will run unstably: misfires, loss of power, phase sensor errors (P0340). On some motors (for example, VAZ 2112) this may cause the pistons to collide with the valves.
What oil should I use to lubricate the gear during installation?
It is better to use a special timing lubricant (for example, LIQUI MOLY Montage-Paste) or motor oil with molybdenum. Do not use graphite lubricant - it can clog the oil passages.