1 · The work order
Read the work order. The simulation stays locked for now. First you need to understand what has to be done.
Work order no. 2417
Your task
Find the most likely cause, explain the technical relationship and plan how to check the valve clearance at the workbench. At the end, you explain to Ms Lehmann in three sentences what happened.
2 · Your prediction
Commit to an answer before you use the simulation. Wrong predictions are explicitly allowed. They are exactly what you learn the most from.
3 · Explore
Work in pairs: one person operates the simulation, the other records the observations. The tasks tick themselves off as soon as you reach the required state in the simulation.
- F1 · Normal state. Set a cold clearance within spec (0.25–0.30 mm), start the engine and warm it up to at least 85 °C. Watch the clearance.
- F2 · Find the limit. What is the smallest cold clearance at which the valve just about still closes at 90 °C?mm
- F3 · Reproduce the damage. With the engine warm (≥ 85 °C), recreate the state of the customer's car: compression below 3 bar, valve head overheated. What happens if you keep it running?
- F4 · Counter-check. Set a clearly excessive clearance and warm up the engine. What do you hear and see?
4 · Formulate the rule
First compare your prediction with what the simulation showed. Then formulate the rule yourself. You will only see the model answer afterwards.
| Question | Your prediction | The simulation shows |
|---|
Model rule
Clearance too small: At operating temperature the valve stem expands more and uses up the clearance. If it becomes negative, the valve head no longer sits on the seat ring. The results are loss of compression and hot combustion gases blowing past the seat.
Why it burns: The exhaust valve dissipates most of its heat through the valve seat into the cooled cylinder head. If it does not seat, this cooling is missing while hot gas flows past the head at the same time. The head overheats and burns. This damage is permanent. Re-adjusting alone will no longer help.
Clearance too large: The valve opens later, closes earlier and opens less far. The results are poorer cylinder filling, less power, ticking noise and more wear on cam and tappet.
Therefore: Valve clearance is adjusted cold, according to the manufacturer's specification. The cold clearance is the reserve for thermal expansion.
Where does your rule differ? Add to it above before you continue.
5 · To the workbench
Now the real component counts. The simulation is locked, because it does not replace a single minute at the workbench: not the feel of the feeler gauge, not the craft.
a) Work plan: put the steps in the correct order
b) Measure on a real cylinder head or training engine
Measure the clearance of the exhaust valves with the feeler gauge and enter the values. No engine available? Then the teacher provides measured values.
| Cylinder | Exhaust, measured cold (mm) |
|---|
6 · Feedback loop
Your real measurements go back into the simulation. Would this engine be OK at operating temperature?
| Cyl. | cold | warm 90 °C | Assessment |
|---|
“Check” loads the value into the simulation and brings the engine to 90 °C.
Solution: work order no. 2417
The exhaust valve of cylinder 3 was set with too little clearance. When cold it still closes, so the engine runs almost normally when cold. When warm, the clearance is used up, the valve stays slightly open and compression collapses.
Actions: Remove the cylinder head. Check valve and valve seat for thermal damage. If the valve is burnt, replace it and rework the seat. Then adjust the valve clearance cold to the manufacturer's specification and re-check compression when warm.
Customer explanation (example): “During the last adjustment, too little clearance was left on the third cylinder. When the engine warms up, the valve expands, no longer closes and has overheated as a result. We will check and replace the damaged valve and set everything back to the manufacturer's specification.”
Learning record
Your entries are not saved. Download or print the record before you close the page.
Simulation: exhaust valve train, cylinder 3
Simplified teaching model · training engine with fictitious values · gaps shown greatly exaggerated