Engine basics > Four strokes only

OS FS-20 Valve Springs

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Stuart Bell:
There was a post or two on another forum about the FS 30 valve springs breaking but I am new to running fourstrokes so missed most of what was happening with the FS 20s and 30s back in the 80s and 90s when they were most popular. I think breaking valve springs most likely isn't a problem for the majority of flyers who are running these engines and looking after them well.
For a bit of context the FS 20 I have looks like it was well used until the model it was in secumbed to the overwelming effects of gravity and the engine was then thrown in a cupboard many decades ago. It did take a bit of work and a few new parts to get it back running again but bringing these engines back to life is half the fun. 
The down side of it not being oiled up properly before being stored for so long is that many of the expose surfaces of the steel components inside the engine were covered in a thin layer of surface rust. It was easy enough to clean this off with a chemical rust remover but I'm taking a guess that what might have caused the problem with the valve spring in my engine is that the corrosion had been more severe in patchs on the surface of the wire and created some weak spots and that is where it failed. There might be another reason but thats my thinking for now.
Hopefully a with couple of new valve springs the engine I have will run like new for a good number of years again.

Motorman:
If push comes to shove, .7mm is close to .025" music wire. Some experimentaion as to the drill bit diameter to wind it around would need to be discovered as it would spring open when released. I don't think spring pressure would be all that critical as long as you don't get valve float. The thing to watch when retro fitting springs would be coil bottoming out under compression (coil bind). Lots of springs at Ace Hardware maybe take look there?

MM

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