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OS 91 Valve Spring question?

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Old 02-27-2012, 06:43 PM
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nrad2000
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Default OS 91 Valve Spring question?

I have an OS FS91S spring # 45960200 - the spring broke before flight. I tried ordering a new part but they discontinued it. I ordered the OS FS70 - FS91 spring # 45960210. It came in today. I looked at the spring and the new one is slightly wider. I tried slipping it into place but it was a real snug fit. doesn't just drop in like the old one. You guys think it is safe to use?
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Old 02-27-2012, 07:31 PM
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Default RE: OS 91 Valve Spring question?

While I'm not familiar with your engine, i would saw "No" don't use that spring. It will bind up in the spring pocket.

I would suggest looking at the OS parts manuals for different engines. See if any of them use the same part number as your 91 does. There are many things that much be matched in a valve spring; length/height, outside diameter, wire diameter which translates onto the amount of pressure the spring puts on the valve and a few others.

Good luck on your quest.

Ken
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Old 02-28-2012, 06:23 AM
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Default RE: OS 91 Valve Spring question?

Also look at other brands. Some are copies of OS designs. Thunder Tiger is one.
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Old 02-28-2012, 08:07 AM
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Default RE: OS 91 Valve Spring question?

If you can, measure the inner and outer diameter, and length, of the original spring.

Maybe someone who has another brand of engine will see the thread and give you some alternatives.
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Old 02-28-2012, 07:30 PM
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Default RE: OS 91 Valve Spring question?

Aren't Magnums a OS knock off? You could try that.
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Old 02-29-2012, 07:14 AM
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Default RE: OS 91 Valve Spring question?

I'm still researching
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Old 02-29-2012, 08:51 AM
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Default RE: OS 91 Valve Spring question?


ORIGINAL: tacx

Aren't Magnums a OS knock off? You could try that.
As the OP knows, OS changed springs between the original Surpass and Surpass 2 so I wouldn't assume a Magnum (or any other brand) spring would fit just because the overall design of the engine "looks" like the original Surpass.
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Old 02-29-2012, 02:05 PM
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Default RE: OS 91 Valve Spring question?

Go into the glow engine forum then to the OS support and ask Bill Baxter for a straight answer. Then come back here and post up what Bill has to say. I have a coupld of the IIs and the original FS and would like to know myself just in case. I would have thought the Mgnum springs would work but I would think the tension would/could be different?? Always ask Bax first, I do.
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Old 10-11-2018, 06:59 PM
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will say that I the spring does fit in the pocket and the pocket is only deep enough to retain the spring's location, it should be safe to use. however...you might want to get another spring for the other valve so that the working spring pressures are the same from valve to valve,..... widely uneven valve spring pressures make engines vibrate more than necessary.
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Old 10-14-2018, 05:45 AM
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Not that I think it's urgent to answer a 6 year old question immediately, but in the interest of keeping good info on our forum I'm going to have to disagree with you about that. Improper valve spring tension won't make an engine vibrate. What it will do is cause valve float if it's too weak, leading to catastrophic destruction of the engine pretty quickly. A too strong spring will cost you torque, which our little glow engines are pretty sensitive to anyway. This is an area to not try to jerry rig something.
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Old 10-14-2018, 02:57 PM
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you're not "jerry rigging" anything by making valve spring pressures as close to the same as you can from valve to valve. and you think widely different valve spring tensions don't make a 4 cycle engine vibrate, go talk to some NASCAR engine builders. I built racing engines for anything from a 7 time Midwest Region SCCA champion E-Production racer to Alcohol fuel rail to Briggs WKA gokart engines. and in every case,.....valve spring pressures watched closely for valve float (the obvious reason you state) and uniformity of compression because the engines vibrate less when the springs are within a few lbs of each other... widely differing pressures are what set up destructive harmonics in a valve train. and "float" is not what destroys valves, float is sometimes used to prolong open valve timing and is sometimes deliberately built into a valve train where the rules limit valve timing and lift. it is the valve slamming shut and bouncing, that causes more problems, and that comes from something other than spring pressures.
I could go on,...but it seems like you know it all already.
as for answering a 6 year old question,.....I guess the problems people had with valvesprings 6 years ago, don't happen now anymore,...right ?.
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Old 02-17-2019, 05:34 AM
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Perhaps an update for additional information might be in order?

I can attest that folks still DO have valve spring issues. =)

When the spring in my .91 gave up the ghost, I purchased this spring. https://www.towerhobbies.com/cgi-bin/wti0001p?&I=LXWY25

Also worked in my Thunder Tiger .91, and yes, I bought two and did intake and exhaust at the same time. Main reason being, if one spring is compromised, how long until the other spring shows the same issue? I will say that the O.S. .91 runs like a sewing machine!

Here is a thread I did highlighting the spring swap.
https://www.rcgroups.com/forums/show...iners%21%21%21

Hope it helps!
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Old 02-26-2019, 07:09 PM
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Isn`t valve float when the tip of the valve is actually flung off of the cam due to an overspeed condition?
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