1. Valve Issues:
* Burnt Valves: This is a common cause of low or no compression. Burnt valves are damaged and don't seal properly. Repair: Requires removing the cylinder head, inspecting the valves, and replacing any damaged ones. This may also necessitate valve guide replacement, grinding, or even a head rebuild.
* Bent Valves: A bent valve prevents proper sealing. This often results from valve train issues (e.g., dropped valve) or foreign objects in the combustion chamber. Repair: Requires replacing bent valves, and potentially other components.
* Incorrect Valve Adjustment (if applicable): Some engines have adjustable valve lash. Incorrect adjustment can prevent proper valve closure. Repair: Adjust the valves according to the manufacturer's specifications.
2. Piston/Ring Problems:
* Broken Piston Ring(s): A broken ring won't seal the combustion chamber, leading to no compression. Repair: Requires removing the piston and replacing the damaged ring(s). Check the piston for damage as well.
* Worn Piston Rings: Worn rings lose their sealing ability over time. Repair: Requires removing the piston and replacing the piston rings. Honing the cylinder walls might also be necessary.
* Scored Cylinder Wall: A scored cylinder wall prevents proper piston ring sealing. Repair: May require honing or sleeving the cylinder, depending on the severity of the damage. Severe damage might necessitate an engine rebuild.
* Hole in Piston: A hole in the piston will obviously result in no compression. Repair: Requires replacing the piston.
3. Head Gasket Failure:
* Blown Head Gasket: A blown head gasket between the cylinder head and engine block can cause compression loss. Repair: Requires replacing the head gasket. This often involves removing the cylinder head.
4. Other Possibilities:
* Cracked Cylinder Head or Block: A crack in the cylinder head or block will allow compression to escape. Repair: Requires welding or replacing the damaged component – a major repair.
* Incorrectly Installed Spark Plug: While less likely to result in *zero* compression, an incorrectly seated spark plug can significantly reduce it. Repair: Ensure the spark plug is properly installed.
Troubleshooting Steps:
1. Compression Test: A compression test is the first step. Low or zero compression in only one cylinder isolates the problem.
2. Leak-Down Test: A leak-down test helps pinpoint the source of the compression loss (valves, piston rings, head gasket).
3. Visual Inspection: Inspect the spark plug for damage or fouling.
4. Cylinder Head Removal (Likely Necessary): Most of the issues listed above require removing the cylinder head for proper inspection and repair.
Important Considerations:
* Professional Help: Unless you have significant engine repair experience, it's strongly recommended to take your vehicle to a qualified mechanic. Engine repair can be complex, and improper repair can lead to further damage.
* Safety: Engine repair involves working with potentially dangerous fluids and components. Take appropriate safety precautions.
In short, fixing a cylinder with no compression requires a thorough diagnosis to determine the root cause. Don't jump to conclusions; a proper diagnosis is crucial before undertaking any repairs.
