Question about old engine

Jun 26, 2005 9 Replies
J

So...I've got this old OS 35 engine. Hasn't been run in at least 3 years. It was last on my old Eagle 2 and worked great...up until I crashed the plane all to hell!


So...I've since taken the engine off, and cleaned it up. I want to try to get it started again but I have no idea if it will actually go or not. I figured the first thing was to clean it so it won't be all gummed it. I lightly oiled the parts and put it all back together.



Now...test time will be tommorrow. But I'm just wondering about compression. I remember when I first got into the hobby that I bought an engine from a guy and it never would start because it didn't have good enough compression. I had to throw it out and buy this one. And now I'm worried that maybe this one wont have enough compression either because it seemed pretty weak when I turned it over by hand today.



So...my questions are: Why do engines loose their compression over time? What causes this? And is there any possible way to salvage it and get some compression back?



I guess another one...does anybody know of any good tricks to get this thing running after its been sitting for so long? I remember that we use to put a few drops of fuel right into the carb when engines were having difficulty starting.



Thanks for the tips, Jeremy


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A

Refer to ABC, ABN, Ringed & Lapped - differences

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and Model Engine Tech Questions
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many other articles under "Engines,Plugs,Tuning, Petrol, Turbines, Mufflers, Cleaning, etc" at Alan's Hobby, Model & RC Web Links
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Many engines if left sitting for a period, especially those used with mostly castor based oils such as 2 str methanol powered "toy" engines "gum up" whilst sitting. The castor oil residue hydrogalising or other contaminants causing the parts to be stiff and not giving that familiar "pop" when flipped over the top end.

A few squirts of methanol and repeated flips will move the gum in crankcase, shaft etc and the familiar feel will return. This especially if engine has been heated with a hair dryer or similar first to soften that sticky goo which soon dissipated expect in the needle valve area.= manual clean with a thin nylon cord - blowing will do nothing except let the jelly flatten to one side.

regards Alan T. Alan's Hobby, Model & RC Web Links

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P

Engines usually lose compression as they wear out. With ringed engines you can usually just install a new ring and break it in again. With ABX engines, you need to replace the piston and sleeve.

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E

Squirt some 3-in-1 oil in the exhaust port and flip it over a few times. I'll bet the compression comes right back.

Lapped piston engines (pistons without piston rings) do not lose compression over time. Neither do most ringed engines, but they are slightly more prone to do it than lapped piston engines (I'm including ABC, AAC, etc., in this category).

However, the oil that is needed to complete the seal so that compression is evident evaporates over time, leaving gooey stuff behind. Give it a shot or two of oil and all will be okay.

Ed Cregger

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J

Completely different. WD-40 isn't a proper lubricant, although it may have some temporary lubricating properties. It's a solvent and water displacer, which is where the WD name came from. I've got something linked in my memory that says it contains a significant amount of Stoddard solvent.

3-in-1, on the other hand, is a lubricant (although these days there are a number of better ones). "Vintage" 3-in-1 (50s amd 60s) was bad about eventually gumming up, because of it had a vegetable oil base. Anyone know if it does, still?
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C
3-in-1 is a brand name for a light machine oil. There are many suitable alternatives Air tool oil Automatic transmission fluid Gun oil Sewing machine oil After run oil I'm sure there are many more; these just popped into my head

Carrell

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J

So anyways....I did manage to get my engine put back together and believe it or not, the compression got back and I actually got it running. Wasn't that difficult. Took a few minutes but then she fired up. My problem now though is that I don't know how to set it all up properly. As soon as I pulled the glow clip off the engine tended to die. I need to learn how to properly adjust the needle valve and what-not to make the right mixture. I'm not to sure how to do this....any tips?

Jeremy

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A

"As soon as I pulled the glow clip off the engine tended to die" first sign of a failed plug. Buy a new plug to suit your engine and for tuning, refer to articles and pictures at =

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section = "Engines,Plugs,Tuning, Petrol, Turbines, Mufflers, Cleaning, etc"

Alan's Hobby, Model & RC Web Links

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F

Settings on your engine's carb. should start out at about 1 1/2 turns out on the low side needle valve, and probably 2 turns out on the high side needle valve. These settings should get you close enough to get you started, then tune in as required. Note when screwing the needle valve down, do not over tighten them, just snug them all the way in, then back them out to the mentioned settings. Prime, battery to the glow, and go. It would be a good idea to run a Rich fuel mixture for awhile till everything gets loosened up again.

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