OS Max-S 35 Engine info

Measuring clearances is a bit more involved than most of us get. If you find an old engine and you think you may want to run it, standard procedure is to make sure it's clean and free of dirt, mount it on a plane, and see if it runs. If so, mission accomplished.

It's an oldie all right...it was made before mufflers became mandatory, so I would hazard a guess that it is at least thirty years old. Not a screamer, but you could throw away the baffle and lock the throttle barrel open and use it for C/L...and you might find a muffler to fit it, if required where you fly C/L. I think OS made one that strapped on later. Frank

I wasn't too serious about measuring clearances. I don't have the equipment to measure the kinds of clearances you see in these engines - my micrometers aren't accurate enough. And it wouldn't tell me much. I like to squirt some lightweight oil in them and turn the crank until the piston is at TDC. Then wait and see how fast the pressure bleeds past the piston. Even light machine oil is relatively heavy for these engines, so it had better hold the pressure real good. This one does, and the crank is nice and tight indicating no wear in the connecting rod to crank connection. I'm not a collector - I want to run this puppy until it dies :)

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Whether an engine holds compression for so many seconds/minutes is totally irrelevant. What is necessary is that it holds compression for the milliseconds that it is required when running. Why create standards that have no basis in reality?

Ed Cregger

"Ed Cregger" wrote

I'm glad I'm not the only one thinking that.

At 12,000 RPM, the compression is being formed and released 20 times per second.

You could have a brick going up in a piece of pipe casing, and get compression, that fast!

At any rate, it sounds as if he has the right idea. Start it up and run it. If you're having fun, it's working right.

The S35 indicates that it started production in 1963. The picture on the web site

The OS Max .35S R/C was being sold well into the late Seventies, at least. Yes, later on it came with a strap-on muffler.

There is no need to remove the throttle. Just use a short pushrod and keep it at open throttle with the pushrod fastened to somewhere on the firewall/fuselage. Then, if you decide to fly R/C at a later date, or want to sell the engine to an R/C flyer, you'll have everything in good working order.

This engine requires 25% all castor oil lubricant in order to survive running for any period of time. I've owned and flown half a dozen of these sweet engines. Never came close to wearing one out. Even without the requisite 25% all castor lube.

Ed Cregger

Ouch, gimme a break, guys :-)

What is the first thing you do when you pickup a second hand engine? You put a prop on it, squirt a few drops of fuel or oil into it, and turn it over. If it freewheels, then it might be too worn out to be usable :-P

"Robert Reynolds" wrote

That's the acid test!

If it won't keep running, with good fuel and good technique, then it might be worn out.

"Ook" > wrote

Yeah, OK!

I never did the oil test, but I realize that would help. I could tell by the resistance and the sound of the "pops" if it was any good to give it a try, I think.

If it was questionable, I would want to run it before buying it.

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Does anyone remember when the K&B .40 came out with the Dykes ring? A bunch of them were sent back to K&B and were claimed to be defective because they wouldn't pass the old compression test that Ook is referring to.

I'm not picking on you, Ook. Well, maybe a little, but it is all in fun.

Ed Cregger

It's all good :-)

I have an old OS Max .35 I am cleaning up and checking out for a buddy, that was only delivered to me today as a matter of fact, and it has a fairly contemporary looking cast aluminum muffler but of the strap-on variety. If the example Ook is referring to (Ook being a word I used frequently in my teens and early twenties I find this a mild case of deja vu..) has a similar case then there is hope for a muffler that fits somewhere out there in the ether. If not, is Bisson still in business?

Although, form first appearances the prognosis is not good for the slop in the con rod's small end, although the big end is fine. We'll see.. maybe spin up an oversize wrist pin and... then again maybe not.

MJD

There are quite a few sources of workable mufflers for this engine (OS Max .35S). Mac's makes mufflers from tubing that resemble tuned mufflers somewhat. I'm sure they would have a universal strap-on version. If not, how hard could it be to buy an old fashioned radiator hose clamp at an auto supply store and fit it to one of these mufflers? Piece of cake.

And yes, Bisson is still around. Good company and products.

Tatone even sells manifolds and such that are strap-on, so they would fit also.

Ed Cregger

I read a really nifty article in RCM a few years ago about making mufflers from aluminum bar stock and tubing. It wouldn't be too hard, if you have a few power tools.

"Robert Reynolds" wrote

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Yep, it isn't difficult at all.

I just bought one of Harbor Freight's el cheapo combination vertical mill and lathe units ($600). I plan on making a few adapters so that we can fly the old Fox Eagle .60 (baffle piston) engines again. Most Eagle .60s for sale are sans muffler. Not that the stock muffler was much to begin with.

I'll use aluminum plate to make my adapters. I'll pick a cheap to purchase muffler, like the Tower .46 muffler, and adapt it to the Fox Eagle 60. It should be plenty big enough and it may even offer a slight boost in power. We shall see. If not the .46 size, then the .60-.75 size.

Ed Cregger

We have a metal retailer here in Kansas City called Metal By The Foot, where you can buy just about anything with no minimum size. They have a very handy scrap bin full of little chunks of aluminum bars, plates, and tubes for a couple dollars or less. I always see airplane parts when I look in those bins. All I need is one of those milling machines.

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Hi, Bob.

I'll have to look around and see if we have anything similar in the Chattanooga, TN area. That would really reduce the price of producing the parts that I have in mind.

Ed Cregger