OS 61 FS leaking - RCCanada - Canada Radio Controlled Hobby Forum
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Old 12-10-2009, 08:25 AM   #1
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OS 61 FS leaking

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I have an older OS 61 fs it leaks fuel/oil between the head and the main case and only in one spot. Have tried two of the alum seals, no seals, one seal, over tighting the head screws.( so much that the heads stripped when I tryed to remove them, so I had to drill the heads off)
still leaks. the head doesn't seem to warped. I can not see any cracks with a glass
Don't know what else to try, looking for help
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Old 12-10-2009, 09:38 AM   #2
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Re: OS 61 FS leaking

Hi, I had a problelm with an OS 40, what I did was to use a little valve lapping compound, and rotated the head on the cylinder, back and forth, remember to pick the head up and move to a different spot, and start again, then remove the head and check to see if there is any spots that are uneven.....this should show you where the high and low spots are, keep this up till the area is all the same color.

Happy wife, happy life
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Old 12-10-2009, 09:43 AM   #3
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Re: OS 61 FS leaking

Distortion of the head itself is probably causing the leak and improper tightening of the head screws is usually the cause. The head can be fixed but the easiest way by far is buy a new head. Take a straight edge and hold it across one of the bolt holes one at a time, or even two at a time. If you can see a gap anywhere the head is distorted. I can be fixed but it is very labour intensive. Get a piece of ordinary flat glass, some 320 wet or dry sandpaper and some oil. Put the paper on the glass ( rough side up) squirt some oil on it, put the cylinder upside down, mating surface down on the oiled sandpaper. Hold the paper firmly and with light pressure move the cylinder around in circles on the sandpaper. Every few strokes turn the cylinder 20 deg. or so. Make sure that the cylinder does not tip and the paper does nor crease. After ten or fifteen circles a clear pattern will emerge on the top of the cylinder. Wipe the top clean and repeat until the new pattern covers all of the top of the cylinder. If you grab the cylinder really close to the paper it will have less tendency to tip. This will straighten the top of the cylinder. When you install the head put your thumb in the middle of the head and press down firmly. Tighten the screws lightly. Maintain the pressure with the thumb. Tighten one screw snugly, tighten the opposite screw an equal amount. Go to the screw that is furthest away from the one you just tightened, Probably next to #1 and tighten the same amount still maintaining the thumb pressure. Now go to the opposite screw and tighten, maintaining the thumb pressure. Now go to the last screw that is on the opposite side of the head and tighten it maintaining the thumb pressure. Then go to the last screw that should be opposite and tighten it. Remember this is a light tighten. Now you can remove the thumb pressure. Now go around the screws in the same order and tighten some more. After a couple of times around the screws will cease to turn and you will risk stripping the head or the allen key. A machinist could fix the head for you and you could lap the head to the cylinder using valve grinding compound. Thats the labour intensive part.

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Old 12-11-2009, 04:38 AM   #4
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Re: OS 61 FS leaking

Thanks guys, will check it out with some grinding compound. it doesn't sound good, to bad, it is a nice running engine (other than the leaking) anyone have a parts engine or just the head/with the screws??
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Old 12-11-2009, 07:48 AM   #5
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Re: OS 61 FS leaking

Would some of that famous "red sealant" (high temp) work?


Going along with the grinding compound idea, there's a way I use to ensure a tight fit with a computer CPU and the associated heat sink

Can provide more details if needed but basically you use wet/dry sandpaper and dish washing liquid and sand the surface.

Paper I use for computer parts:

o 400 Grit Super Fine Wet/Dry
o 600 Grit Ultra Fine Wet/Dry
o 800 Grit Ultra Fine Wet/Dry
o 1000 Grit Ultra Fine Wet/Dry
o 1500 Grit Mirror Fine Wet/Dry
o 2000 Grit Mirror Fine Wet/Dry

and the liquid and a smooth (like a sheet of glass/mirror would do) surface.
Now for this, you wouldn't have to go to the finest grit.

If this sounds more to your liking, post and I'll continue. It's a bit more detailed than what I've posted.

Last edited by voyager_663rd; 12-11-2009 at 07:53 AM.
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