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Old Feb 18, 2010, 01:05 AM
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compatibility of parts between the OS FS20, FS26, and FS30

Gentlemen,

I was trying to extract a valve cover bolt on my FS20 and managed to chip off the threaded portion of the head where the rear valve cover bolt enters the head. I realize I could just JB weld it back on but the thought of know i broke it would bug me to no end. Will a 26 head bolt up? My 30 looks like it's identical to it from first glance. Anyone have any experience with this? Just for the 26 parts I'm looking at what I paid for the entire engine, so maybe I should just throw it away and be done with it. It never really had that good of compression, the original owner claimed it ran well but I don't see how with as poor compression as it has. It's the reason I tried to open the valve cover up to adjust the valves to see if they needed it, to see if that would tighten the compression up any. Well, now I've got a broken head, AND after adjusting the valves it still doesn't have any better compression. So, I'm thinking ring and sleeve as well, but there really aren't any parts for the 20 on tower's website. Just 30 parts and some 26 parts. I know these all share a similar case, but did the displacement increases come as a result of larger bores, strokes, or both?
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Old Feb 18, 2010, 09:09 AM
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I have experience with all of these engines. I have a stroked FS-20. This was done according to an article in MAN soon after the FS-26 was released, by using a FS-26 crank which has a larger stroke. It displaces ~.25ci. All you needed was the crank, a spacer to raise the cylinder liner (for appropriate compression ratio), and new music wire pushrods. I got it off thebay as an FS-20 but quickly realized what it was.

FS-26 has a slightly larger bore and larger stroke than FS-20. FS-30 has a larger bore than FS-26.

Externally the components are very similar. The height of the crankcases varies as does the bore for the liner. The heads have different combustion chamber volumes and sealing face diameters to accommodate the liners.

You could probably use a 26 or 30 head, but the carb mount bolt in the back might not line up and you will have a different CR if you don't account for CC volume.

Unless the liner is scored I would use it. Check to see if the valves are leaking. A ring could be purchased from Frank Bowman.

If you end up dumping the FS-20 I may be interested.

You could always go this route.



Greg
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Old Feb 18, 2010, 09:51 AM
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I like your idea of the exposed pushrods. Visually cute and certainly better for lubrication.
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Old Feb 18, 2010, 01:07 PM
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Even the Saito FA-30S and FA-40a share at least ONE part with these OS "mills"...!

Dear Fellow Small 4-Stroke Fans:

The PIPE here...and where I've already got a Saito FA-30S "later model" four stroke (with the fully enclosed valvetrain), and hope to be able to get back to work to help get a Saito FA-40a engine for a CAD-drawn RC Scale model construction plan project I've been working on lately, I was glad to find out quite some time ago, through the help of my LHS, that the exhaust port threads on the Saito FA-30S and FA-40a are the EXACT SAME (M9 x 0.75mm pitch) threading as the "fluid-nut" style exhaust header retention nut that's used on ALL THREE of the small OS four strokes mentioned earlier in this forum thread, as my Saito FA-30S engine easily accepted the OS FS-30's exhaust gear, and "back again" between the two engines.

That could mean that one might want to use a Saito FA-30S or FA-40a exhaust setup on their OS engine, and "vice versa" for the Saito "mills", as I expect to need to do for my CAD plans project, to help make a custom exhaust setup for use with either the FA-30S or FA-40a.

The "involved fluid-nut-like part" that fits ALL five four-stroke engines' exhaust ports that I've brought up here is still available from Tower, at http://www3.towerhobbies.com/cgi-bin...5776&search=Go ... I may get three OR four of these before too much longer, as I WOULD have uses for all of them.

It's amazing how these sorts of things work out, sometimes...even BETWEEN engines from two competing firms, which both make very nice four stroke powerplants !

Yours Sincerely,

The PIPE!
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Old Feb 18, 2010, 01:19 PM
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Yes, I discovered that a while back when somebody asked me to make a custom exhaust for the FS-30. I happen to have the Saito FA-40 and OS FS-30 on the bench. One of the Saito elbows with the stock FS-30 manifold worked for him. I think two of the Saito elbows would allow virtually any exhaust angle one could imagine. And they are cheap.

http://www.horizonhobby.com/Products...rodID=SAI40A75

It really is too bad the engine manufacturers don't agree on things like that. It would make for plenty of aftermarket muffler product availability.

Greg
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Old Feb 18, 2010, 07:35 PM
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So, does anybody happen to have a spare 20 head lying about?
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Old Feb 19, 2010, 03:20 PM
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You MIGHT want to try contacting BJ's Model Engine Repair...

Dear b7gwap:

The PIPE here again...one thought on repairing/replacing that damaged FS-20 cylinder head might be to contact BJ's Model Engine Repair up here in New England about your needs...I believe I've seen that place recommended in the AMA magazine before, and it couldn't hurt to at least TRY contacting them to get something done for your FS-20, with the damaged cylinder head.

Their Web address is at http://www.bj-model-engines.com/home.html , and I'm hoping that they might be willing to help you out.

Hope this might be able to help...

Yours Sincerely,

The PIPE!
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