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Author Topic: OS FS-20 Valve Springs  (Read 19126 times)

Offline Stuart Bell

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OS FS-20 Valve Springs
« on: June 28, 2023, 01:49:36 PM »
From a retired RC flyer I have an OS FS-20 that I have recently started using on one of my control line stunt models. From being very consistant, the engine run started going a bit crazy on my last flight and it turns out that may most likely have been caused by the intake valve spring now being made up of three seperate components.
Aside from having a broken valve spring the engine is good otherwise so I as wondering if anyone knows where I might be able to find some springs that will work as replacements or a pair of the original OS 45760200 valve springs?

Stuart

Offline Robert Zambelli

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Re: OS FS-20 Valve Springs
« Reply #1 on: June 29, 2023, 03:18:33 PM »

Offline spare_parts

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Re: OS FS-20 Valve Springs
« Reply #2 on: June 30, 2023, 08:20:26 AM »
Finding FS-20/26 parts will be tough, long discontinued. Even FS-30 springs will be hard to find as they were known to break, so were in demand and are also discontinued at this point.

I'll measure both, maybe we can find a commercial source.
Greg

Offline Stuart Bell

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Re: OS FS-20 Valve Springs
« Reply #3 on: July 01, 2023, 05:40:03 PM »
Had thought it might take a bit of reverse engineering and that I might perhaps have to look at making some springs if I cant find anything that will work otherwise.
The remaining FS-20 spring I have measures up at 11mm long with a 6.2mm OD, and 4.8mm ID. It is wound from 0.7mm wire at a 2mm pitch and has roughly a 290g/mm spring rate but I do need to measure that more accurately.
The FS-30 springs are shorter but wound out of 0.8mm wire at a slightly coarser pitch. As far as I can tell the compressed lenght they operate at when they are installed is the same in both motors. I should have measured their spring rate when I had them out of the engine but hopefully after a lot of searching I have found a couple of OS FS-30 valve springs and they are on their way to me from Singapore. As long as the spring rates are not wildly different and the force they provide at their 8mm compressed lenght is similar by all accounts they look like they should be fine to use as replacements in the FS-20 as well.
Since my first post I have also found Just Engines in the UK have some FS-30 compatable valve springs listed on their website so will see if I can get some from them and see how they measure up as well.
Will keep an eye on eBay and see what comes up there in the future if things don't work out with using the FS-30 springs in a FS-20 but I am hoping given there are not alot of differences between the valve trains of both engines and the operating RPMs are similar they will be OK.

 

Offline Robert Zambelli

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Re: OS FS-20 Valve Springs
« Reply #4 on: July 02, 2023, 03:46:45 PM »
I'm quite puzzled by this topic.
For what it's worth, I have been using four cycle engines since the mid nineties, in particular OS (Surpass and non-Surpass), HP rotary valve, Webra rotary valve, Morton M-5 Radial (spark ignition), ENYA (both open and enclosed pushrods, and the cams can be set for reverse rotation) and SAITO (both open and enclosed pushrods). The SAITOs are my favorite.

Sizes (for CL use) from the OS FS 20 up to the ENYA 90 and everything in between.

I would estimate well over 3,500 flights and I still own around 25 four cycle engines.
I've made some custom venturis, but I have NEVER made any internal modifications.
In all this time, I have had only one mechanical failure - a broken crank pin on an OS Surpass 40.
I presently have only three planes flying with four cycle engines - the Little Cherokee (SAITO 30), Cardinette (SAITO 30) and my Colibri Triple (three Surpass 26s)
As to my puzzlement, I have NEVER experienced a broke valve spring.

Bob Z.
 

Offline Stuart Bell

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Re: OS FS-20 Valve Springs
« Reply #5 on: July 03, 2023, 03:32:35 PM »
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.

Offline Motorman

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Re: OS FS-20 Valve Springs
« Reply #6 on: July 06, 2023, 08:01:50 AM »
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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