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OS Sirius FR5 300 5 Cylinder lost compression!

Old 10-23-2015, 07:48 PM
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outacontrol41
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Default OS Sirius FR5 300 5 Cylinder lost compression!

A couple of months ago this engine ran fine, I flew it around the field in my Hangar 9 giant scale Beaver (30cc). Landed, no problem. Couple weeks ago I went to start it and noticed it had noticeable compression loss but still started and ran okay. Today was going out to the field for a flight and was shocked to find NO compression whatsoever! It just spins over like an electric motor! Truly at a loss as to what's causing or caused this. Any thoughts?
Old 10-26-2015, 06:50 AM
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No/low compression can be caused by several things: an overheat that took the temper out of the rings, debris eroding the ring/liner fit, badly-set valves, trash in the system causing the valves to stick due to crud buildup on the valve stems, crud in the cylinders that keep the valves from closing, parts just worn out and not sealing...the list can go on and on.

If your engine was cowled, the most likely problem cause was an overheat.
Old 10-26-2015, 10:37 AM
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((((((((( trash in the system causing the valves to stick due to crud buildup on the valve stems, crud in the cylinders that keep the valves from closing, ))))))))

Upon inspection, this was the culprit. The push rods/valve stems were clogged tight preventing the valves from opening, closing. Thank you for your valuable advice and input.
Old 10-27-2015, 06:13 AM
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We're glad to help. It's really more common than one would think to find the valve stems getting a buildup of residue...especially the exhaust valves. That's because of the high oil content in the fuels we use, and the fact that the oil doesn't burn off in the combustion process, so it can get deposited on the valve stems.
Old 10-27-2015, 07:16 AM
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Thanks , Bill. Looking at my options now.

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