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YS110FZ compression problem
Hi,
After replacing pison/ring in YS110FZ where conrod snapped and damaged the piston, I can not get any compression. I thught first that ring must set and this will help, but engine wouldn't run. Valves are sealing OK and timing is as it should be. Where could be the problem? |
RE: YS110FZ compression problem
Describe how you are checking for valve seal....Is cylinder wall surface damaged?...
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RE: YS110FZ compression problem
The cylinder surface looks perfect. Valves seal I checked first by leaving inverted cylinder full of fuel for a night.
None of the fuel escaped through the valves. Then I assembled the engine and keeping it upright I poured some synthetic oil to submerse the valves. When rotating the crankshaft I looked for air bubbles escaping thorough oil. None. After short attempts to start the engine, it did not regain compression, but I noticed black resude in crankcase. Lower side (on one side only) of piston is rubbing against cylider and it is kind of shiny polished/grinded. Although it shouldn't probably affect compression I suspect that new conrod is bend slightly. Otherwise what would explain piston wear on one side?. |
RE: YS110FZ compression problem
Pistons always wear more on one side.
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RE: YS110FZ compression problem
This wear appeared on piston side just after few attempts to run the engine with electric starter. The engine did not run by itself.
Besides it is ringed and not ABC. |
RE: YS110FZ compression problem
ORIGINAL: Edge3644 The cylinder surface looks perfect. Valves seal I checked first by leaving inverted cylinder full of fuel for a night. None of the fuel escaped through the valves. Then I assembled the engine and keeping it upright I poured some synthetic oil to submerse the valves. When rotating the crankshaft I looked for air bubbles escaping thorough oil. None. After short attempts to start the engine, it did not regain compression, but I noticed black resude in crankcase. Lower side (on one side only) of piston is rubbing against cylider and it is kind of shiny polished/grinded. Although it shouldn't probably affect compression I suspect that new conrod is bend slightly. Otherwise what would explain piston wear on one side?. |
RE: YS110FZ compression problem
Just where is the wear/grind marks showing, front of engine , rear, side, which side? at this stage sounds like you have put it back together wrong, possably con rod and disc valve assy. YS Service down under |
RE: YS110FZ compression problem
ORIGINAL: XMANS Just where is the wear/grind marks showing, front of engine , rear, side, which side? at this stage sounds like you have put it back together wrong, possably con rod and disc valve assy. YS Service down under |
RE: YS110FZ compression problem
The piston was wearing on its surface facing front of the engine. I removed the piston and turned around 180 deg,
put everything back together and tried again. Piston was wearing on the same side although this time facing back of the engine. That's why I suspected bent conrod. Took conrod out, inserted straight longish steel rods through both brass bearing of conrod (fairly tight fit) to chech if rods are parrarel. Were skewed a few degrees, so I bend conrod slightly until rods were parallel. I did not help regain compression, buy I will try to run the engine again, hopfully without piston side wear. |
RE: YS110FZ compression problem
I have bench run the engine for a couple of view minute sessions.
I am getting 7200 revs on APC 16X6 prop and 20/20/fuel. Although set very rich it was getting so hot that throttle barrel got stuck. Cooled down the engine and tried again on even reacher setting, but with same result. This another mystery. At least some succes, when cold, the compression is back and it is quite OK. |
RE: YS110FZ compression problem
I can see that YS agent did not enjoy enough schooling, or even prosaic hands on experience.
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