What is the method for replacing valve stem seals without removing the cylinder head?

[LaLandon]

You can use a thin rope to suspend the valve. If necessary, remove the spark plug of that cylinder and introduce high-pressure air through the spark plug hole to hold the valve in place for valve stem seal removal and installation. Normally, the engine cylinder head needs to be removed, and after holding the valve in place, the valve stem seals can be replaced and other operations performed.

[VonManuel]

I've seen mechanics perform this cylinder-head-on operation several times, mainly by pressurizing the cylinder through the spark plug hole to secure the valves. Specifically, they first remove the camshaft, then use a specialized valve spring compression tool to compress the spring, removing the keepers and old valve seals. The key is maintaining stable air pressure in the cylinder to prevent valves from dropping into the cylinder – I've seen novices accidentally drop valves, which creates major complications. The entire process requires extremely meticulous operation, with each spring keeper needing proper storage (I recommend using a magnetic tray for these small parts). After installing new valve seals, always remember to check valve clearances – never rush through this critical step.

[OAngela]

I've tried doing this with a makeshift method myself, and the principle isn't actually hard to understand. First, remove the ignition coil and spark plug, then use an air compressor to inject air into the cylinder through the spark plug hole to secure the piston position. Next, use a valve spring compressor to press down the spring, carefully remove the valve lock and retainer, and then you can replace the old hardened and deformed valve seal. The most challenging part is the spring disassembly and reassembly—applying the wrong amount of force can easily cause small parts to fly off. I recommend adding a few drops of engine oil to lubricate each valve seal during replacement. After installation, be sure to rotate the crankshaft to test the valve movement. It's best to have a borescope ready to inspect the valve stem condition.

[WilliamDella]

To save money on major engine repairs, consider this method. The key is to use air pressure to hold the valves in place and prevent them from dropping. Professional repair shops will have specialized tool kits. After removing the camshaft, use socket adapters of different sizes to compress the springs and remove the lock pieces to replace the oil seals. The biggest advantage is that the timing system does not need adjustment during the entire process, but the working space is very limited. Be careful not to install the oil seals in the wrong direction, and soak the new oil seals in engine oil beforehand. After completion, it is recommended to drive a few hundred kilometers and observe whether the oil consumption is normal.