Changing Valve Stem Oil Seals on TU1 engine.

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The TU1 engine can have its valve stem oil seals replaced without removing the cylinder head.

The tools and cylinder positioning methods you mentioned can all be used:
* Compressed air method: Most reliable and recommended; the valves won't fall off.
* Nylon rope method: Cheap, doesn't require an air pump, and many people have succeeded with it.

Simple conclusion: No cylinder head removal is required; it's feasible; just follow normal procedures.

Many types of valve stem oil seals are available and the prices are quite reasonable.