Hi!

Today when warming up the OS .91 FS Surpass engine just before test-flying my new aerobat the engine suddenly lost revs and quit. It completely lost the compression. The compression was felt through the breather nipple, so the idea was there is something wrong with the valves.

It turned out, that the spring on the exhaust valve collapsed. Valve remained opened all time with gap approx 2 mm wide. I will try to order the spring tomorrow in nearby Graupner shop which sells OS engines and accessories - but the question is how do I replace the spring? Or more specified - how do I dissasemble the valve spring retainer and split cotters?

Engine is Surpass I series (with unpainted metal valve cover) with very low running time - it has burnt around 10l of hi-quality glow fuel (Aerosynth II Competiton). I never had any problems with it.

The luck was that this didn't happened on first take-off or short after.

Sašo

Saso,

To replace the valve spring, you'll have to remove the cylinder head. Place it on a small piece of wood so that the wood rests on the valves. You can grab the outside of the valve spring retainer with a small pair of needle-nose pliers. Press down, and the retainer will release the small clips.

Remove the old spring. Put in the new spring. Put the round retainer on the spring and press it down to compress the spring. Insert the smal wedges to lock it all togeter.

You have to have the valves supported so that they won't move when you press the retainer down the valve.

Hi!

Thanks for the fast reply. I have the engine head dissasembled, but I am having difficulties to get the valve springs. I can order complete valve assembly, but I can't order just a valve spring.

Do you have any idea where could I get only the valve springs for my OS .91 FS Surpass?

Sašo

I am at work actualy, but tonight I am going to check in my engine spare parts, I think i have a valve spring for your OS.
I'll mail it free for you if i can find it

Valve springs for all O.S. Max four-stroke engines should be availble through your O.S. Max distributor. They ARE available as separate parts. Here are the O.S. Max part numbers:

45960200 VALVE SPRING FS91SUR

This is for both the O.S. Max FS-91 Surpass and the FS-91 Surpass II.

Hi!

Thank you again for a nice reply. But unfortunatelly I must correct you - valves are not avaialble as a separate part from delaer (Graupner) in Europe. You can buy whole valve assembly, which cost around US$ 50 per valve. I carefully read the papers with the engine and with the OS .91 FS Surpass II engine in the shop - you have part numbers in original OS engine booklet with the exploded view of the engine, but with the german translation (and in catalogue is the same) the parts list contains less parts and no exploded picture of the engine. The answer is that the rest of the parts can be only installed with the OS serviceman in Graupner - and unfortunatelly cannot be bought.

Leroifort kindly offered me help - I hope this will work. Otherwise I will order the valve springs at Justengines in UK, which offer really great service to its costumers.

Thank you very much again

Sašo

but I think here is what you need, it's free because literaly all the others parts of that .91 have been destroyed in a crash
just give me your adress in PM

here