Possible Causes & Reparability:
* Burnt or Damaged Valves: This is a common cause of no compression. A valve might be warped, burned, or broken, preventing the cylinder from sealing properly. Reparability: Yes, but requires removing the cylinder head, valve job (grinding, replacing valves), and potentially head gasket replacement. This is a relatively major repair.
* Broken Piston Rings: Piston rings seal the combustion chamber. A broken or worn ring will allow compression to escape. Reparability: Yes, but requires removing the engine block, disassembling the piston assembly, replacing the rings, and possibly the pistons depending on their condition. This is a very significant repair, possibly nearing engine rebuild cost.
* Hole in Piston: Less common, but a hole in the piston will obviously lead to zero compression. Reparability: Yes, but requires the same significant engine work as broken rings – possibly requiring a replacement piston.
* Damaged Cylinder Wall: Scratches or scoring on the cylinder wall can prevent a good seal. Reparability: Potentially yes, but potentially no. Minor scoring might be fixable with honing, but severe damage might require a cylinder sleeve or engine rebuild/replacement.
* Head Gasket Failure (localized): While head gasket failures usually affect multiple cylinders, a localized failure *could* affect only one. Reparability: Yes, requiring head gasket replacement. However, it's less likely than the other issues above if you have confirmed fuel and spark.
* Valve Seat Problem: The valve seat itself could be damaged, preventing a good seal. Reparability: Yes, part of a valve job.
Troubleshooting Steps (Before Major Disassembly):
1. Compression Test Again: Double-check your compression test. Ensure the battery is fully charged (low voltage can skew results), and that the throttle is fully open during the test. Try a different cylinder compression gauge to rule out a faulty tool.
2. Leak-Down Test: A leak-down test is more precise than a compression test. It identifies *where* the compression is leaking from (valves, rings, head gasket, etc.). This is highly recommended before tearing anything apart.
3. Visual Inspection (if possible): If you're comfortable with some basic engine work, you might be able to visually inspect the spark plug hole for obvious signs of damage (e.g., excessive oil).
Repairability Summary:
Most of these causes *are* repairable, but the repairs range in complexity and cost. The least expensive option is likely a head gasket replacement (though less likely) or a valve job. The most expensive will be piston ring or cylinder wall damage, potentially necessitating a full engine rebuild or replacement.
Recommendation:
Before undertaking any repairs yourself, get a professional mechanic to perform a leak-down test. This will pinpoint the exact source of the problem, saving you time, money, and effort on unnecessary work. The cost of the diagnosis will be much less than the potential cost of a wrong repair.
