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Old 02-09-2009, 07:26 PM   #1
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OS 1.60 question

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I picked up a lightly used OS 1.60 from a fellow RcCanada'er and it looks almost new. Question is, after installing it on my plane I noticed that when I flip the prop it's much easier than my other 2 engines (Saito 100, and OS .46AX). Both my other engines are very hard to flip, you can really feel the resistant in the cylinder which I take as a very good sign of compression. The OS 1.60 does have it's compression points where is resists, just no where near as much as the others. I put a new Type 8 plug in it just in case, seems about the same as the old one. Any reason for concern?? Thoughts???
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Old 02-09-2009, 07:52 PM   #2
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Re: OS 1.60 question

Think it has something to do with ABC which if I remember is something to do with the metal and the shape of the cylinder. When you hand flip your 46 it gets to a point which feels like a great resistance then pop over it goes(tapered cylinder no Ring I believe). If your 160 had that kind of resistance I would think it would be almost impossible to turn over. It should also have rings on the pistons. I hope that this info helps a little and I haven't screwed it up in trying to describe why. The one thing you could do is google the 46 engine and read the company info on it and then do the same for the 160. It might help you understand what I was trying to say better
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Old 02-10-2009, 08:00 PM   #3
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Re: OS 1.60 question

Your first reply more or less is on the mark.

Your OS 46AX is of an ABC type construction - not actually ABC, but that's something else. The deal there is that the cylinder sleeve is indeed tapered to a narrower diameter at the top. When the engine runs at operating temperature, the fit between sleeve and piston is correct and in fact a bit looser than what it appears to be to you when you are turning it over by hand.

The OS 1.60 engine has a ring on the piston. If you turn this engine over slowly by hand, especially when it is very new, you will feel very little compression. The ring is not seated so the seal with the cylinder sleeve is poor. Compression improves as the engine runs more and the ring gets seated. You will also find that if you flip the engine over briskly, the compression will appear to be much better than when you just crank it over slowly. The internal pressure helps to push out the ring giving a better seal. And this happens quickly enough that there is lots of air still in the cylinder, which otherwise escapes by the not yet seated ring when you crank it slowly.

That leakage by the way is what's called blowby - the air/fuel misture in the cylinder which leaks by the piston & ring. And that's what lubricates the lower end of your 4 stroke Saito.

If your Saito is well run in, it would be expected that it shows greater compression than the OS 1.60 which is not run in.
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Old 02-10-2009, 09:10 PM   #4
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Re: OS 1.60 question

How to check out the piston and valves seal. Put a few drops of after run oil, 3 in 1 oil, sewing machine oil ( pick one) in the intake, it works best if you turn the engine upside down. Flip it over a few times. Open the carb wide open. Turn the engine over reasonably slow. Listen to the intake then the exhaust then crankcase vent. If the valves are leaking you will hear it out the appropriate port and if the piston ring is leaking you will hear it out of the crankcase vent. If it leaks out the valves, check the clearance. Remove the rocker covers and wiggle the rocker arms up and down, rotate the engine to take the pressure off the spring. You are looking for .004" (four thousands), a couple layers of printer paper.

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Old 02-11-2009, 04:00 PM   #5
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Re: OS 1.60 question

Thanks for all the good info guys. Seeing how it was soo mild I put my Goldberg Edge 540 (the big one 77" ws) in the garage and fired up the OS 1.60. The Pitts style muffler sounded awesome, almost like a 4 stroke. Seemed to have tons of pulling power. My Hobbico 180 starter flipped the prop no problem. I put the power to the spinner and it took after about 5 seconds. Got somewhat smoked out with the smell of after run oil in the garage...and didn't impress the wife cause I didn't entirely close the door from the garage to the house when I was trying to manouver the plane from the house into the garage. When she came home and walked it was somewhat smokey in the house. I had no idea...thanks again for the info.

Last edited by vgjunky; 02-11-2009 at 05:34 PM.
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