Engine basics > Four strokes only

OS FS-20 Valve Springs

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Stuart Bell:
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

Robert Zambelli:
Try this site:  https://www.theworldmodels.com/store/?action=product&sub_id=216&subsub_id=269&filter_index=valve+springs

Also, you can find quite e few parts on eBay.

spare_parts:
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.

Stuart Bell:
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.

 

Robert Zambelli:
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.
 

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