why don't you go get an oil anly'sys, and at least know if you have a engine making METAL....then, you will know for sure wth is going on....don't quess...find out, and it only costs pennies...jolly
[EMAIL PROTECTED] wrote: > There is a need for much more information in order to diagnose problems such > as these. Was the oil pressure in flight ok during the winter and spring but > now it is too low? What sort of oil temperature do you see? What is the oil > temp at idle? What is the oil temp at startup? How long does it take for the > idle oil temp to stabilize at 35 after the first startup? (This no longer > counts since the mechanic has changed the relief valve.) When did you last > change the oil and with what grade? (Straight 50 weight such as Shell 100 > would be correct for this engine.) > > Think of your oil system in this way: The oil pump delivers oil in a volume > that is proportional to engine speed. The oil in the oil galleries flows > past the bearings in proportion to the pressure and inversely proportional to > viscosity. The oil pressure relief valve is a coarse regulator which begins > to limit pressure at 35 lbs ( higher in yours). It is common practice to > shim the relief valve spring on the assumption that it has weakened over time > and is the cause of your low oil pressure. This is seldom the case and your > relief valve should be returned to its' original configuration at some > convenient time. The function of the valve is to prevent damage to the > engine when the oil is too thick. I had a car engine which would rupture the > oil filter on each startup because the valve was frozen. > > When you feel like running your engine we need to know how the pressure > behaves during flight. What is the pressure when you take off? The oil will > be thick and the pump will be able to achieve the pressure set by the relief > valve until the oil warms up unless something else is wrong. When you > level at cruise does the oil pressure follow rpm? Do you have higher > pressure at 2500 than at 2200 rpm? If so then you have a loose engine or > thin oil. If not then you have a faulty gauge or relief valve. What is the > oil pressure at idle on landing? If the engine is loose I expect to find > something like 5 to 10 psi. higher than that suggests that the engine is ok > internally. > > Should you find that the engine is really loose then you are very close to > splitting the case and spending a lot of money. The last thing that you may > choose to do is remove the cylinders and measure the clearance of the rod > bearings. The measurement is performed with plastigauge which your mechanic > is well familiar with. If you find that the rod bearings are loose then you > may suspect that the mains are also loose but there is no way to measure them > without splitting the case. Before removing the cylinders your mechanic > should check the torque of the crankcase through bolts. If they are loose > then the case may be loose enough to allow a main bearing to spin in the case > which would not be visible until the case is split but would be a big > problem. > > You don't want to think about it but if you should end up rebuilding your > engine and need a crankshaft, there is an STC allowing the use of an O-200 > crankshaft in the C-85. You get to change the pistons and rods too but you > get a 6% larger engine and the O-200 shaft is $1000 cheaper than the C-85 > shaft. > > My last overhaul is like yours kind of vague. It was done some time ago in a > log book now lost so I knew when I bought the plane that the engine might > need overhaul at any time. It turned out that three of the cylinders were > pretty junky at 400 hours but the lower end of my engine has shown no > troubles. > > Good luck > Bob Condon
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