Anyone knows how to replace a broken Valve Spring in an OS FS 70 four stroke!! (there is a little spring retainer)

I am not sure what kind of tool I can use to open the retainer for spring valve!..

http://www3.towerhobbies.com/cgi-bin...?&I=LXCW87&P=Z

Also, is it possible to use any spring of similar size or it has to be an original Valve Spring from OS ?


Thanks in advance!

You had best get the original spring. Get both springs while you are replacing springs.

The main problem in working on the spring is holding the valve up (or closed) while you are getting the retainer off and on.

To do it with the engine assembled, you will need to have a glow plug adapter to fill the combustion chamber with air pressure or else stuff enough string into the glow plug hole to hold the valves up.

The other way is to remove the head from the engine and set it over a little wood block or something to hold the valves closed

When you have set up some device to hold the valves close, you can push down on the spring retainer and slide out the valve retainer keys.

Then the retainer and spring should lift off. If the retainer will not come off with both keys removed, there will be a lip on the edge of the valve stem that has been peened by the keys or the rocker arm. This lip will have to be removed with a fine honing stone before you can get the retainer off the valve.

Another problem with this job is that those little keys will go flying through the air and you will loose them. You can do all this inside a plastic bag so if the key goes flying - It will stay in the bag and you can find it.

Either way, the rocker arms will have to be removed and you will have the reset the valve lash when you get the engine reassembled. The valve lash setting is .002" - .004"

Thanks a lot for your help!

The reason I want to use any other spring because I was planning to fly tomorrow and I can not wait to order a new one. And here in kuwait our RC shops do not carry such parts! Would I be able to find a similar spring at ACE hardware or any hardware store?

As I am typing this message, I am still struggling to open the spring


Thanks again!

In your case, it would be worth a look but unlikely that you will find one.

When the springs break, they collapse down within themselves.

Thanks again!

Can I use the prop to find the valve sweet spot (ie, turn the prop until and valve is in the right position then hold the prop at that point)?

That will not do you any good to hold the valve closed. When the piston is at top dead cent the valve will still open too far to get the clip off or on the valve stem.

I hate to say this but I could not get the spring off

If it is this hard to get it off, then how I would be able to put a new one in ?


I think I am missing something here!

I am sorry I put the wrong engine model number.

It is an OS FL-70 four stroke not FS-70 if this makes a difference in the valve spring settings

Thanks

There is a disk and a little C-clip that hold the spring in place. You must push the disk down and slide the C-clip off the valve. The the valve spring retainer disk should liftoff. Then you should be able to lift the spring pieces off.

It would probably be advantageous to remove the head. I place the valve over a socket so when I push down on the spring the valve stays in place. Also, do both springs. Don't use just whatever you have laying around. The correct springs are tempered and can take the heat. If you use just a plain steel spring, it will deform and or snap when it gets hot. If you are having trouble finding them, the rocker arms, valve cover, push rods and springs are the same ones used in the FS and Surpass models.
The OS part # for the springs is 45960210, and the last ones I bought were like $7 for the set.

Thanks W8ye! Thanks broke_n_bummin! Success!

Finally I was able to take off the broken spring and replace it with a new one which I was lucky to find at a local hobby shop here in kuwait that sells os engines. It was easy after I opened the engine head (or the cylinder head).


You guys are real great!


Merry christmas and Happy new year to you in advance!

That's nice you were able to fix it. Everyone here was glad to help.

I made a little fixture and it worked for me. The fixture is a piece of 1/8 inch plywood, drilled some holes to match the head bolts. Glue a piece on the top of the fixture roughly the shape of the combustion chamber in the head. Bolted on the fixture. This allows one to put down pressure on the valve springs with the valves not moving down. The keepers are easily removed at that point. They are tiny but work the same way as big old gasoline engine.

Once the spring keepers are removed, the springs can be swapped out. It is a tedious process to get the spring keepers reinstalled but a wife watching over you helps. Prevents certain curse words and adds a set of eyes to spot an errant keeper flying off somewhere or other. Take your time.

Cheers,

Chip

Considering the better dexterity of your wife's fingers, she would most likely be better with the small keeper than you?

I have learned that the curse are absolutely necessary for successful completion of the job.
bhady