My OS FS70 Surpass Mk1 stopped suddenly and cost me a Wot4. It had a broken inlet valve spring. Here, for any-one interested, is how I fixed it.
Inlet valve is nearest to us. See the gap??
It’s not a difficult task but the parts are very small, like the split colletts that hold the spring on…
Undo the cap head screw and remove the valve gear…
Unscrew the five cap head bolts holding the head and remove…
Remove the carb, inlet manifold and exhaust pipe.
Lift out the valve pushrods, they are identical so just put them safe…
Use whatever method you can to hold the valve in place while removing the split colletts and spring retainer..
Broken inlet spring and the OK exhaust spring. Also the colletts and spring retainer with a screwdriver tip to give it scale.
Gave it a de-coke while it was apart.
No damage to the piston, and it’s nice and clean.
Re-fit the head taking care to seat the push rod tubes correctly. They have a rubber O-ring at each end.
Replace and tighten the five cap-head screws holding the head. Tighten diagonally, like wheel-nuts on your car. Do them bit-by-bit and do not over-tighten.
Replace the pushrods into their tubes. Turn over the crankshaft to make sure they have seated correctly.
Replace the valve gear. Check the gap when both valves are closed, when the piston is at TDC on the ignition stroke. The OS manual says the valve gap should be between 0.04 and 0.1 mm, not 0.4 mm.
At this point I normally add a few drops of after-run oil to make sure everything is slippery for the first start.
All back together ready for the first run in a test stand. Always test an engine in a stand before committing it to a model.
There, not so bad, was it. Any questions please ask.