|
A 208 is way too small to run a sander. It sounds like your valves are shot. Some Quincys use the exhaust valves as a check valve. The intake valves have unloaders on them, which activate when the compressor shuts off. A small copper line runs from the tank, through a small hydraulic unloader valve on the side of the crankcase, then up to the two unloader towers on top of the head. When the compressor stops, the oil pressure drops, allowing the hydraulic valve to open, which lets air from the tank into the unloader towers, which then prop open the intake valves and releases any trapped air pressure inside the cylinders, allowing for a loadless start. This is a good setup for several reasons, not the least of which is that if you are low on oil, the hydraulic valve will not see enough oil pressure to close and the compressor won't pump, thereby giving you some time too see what is wrong before you seize the pump. Also, since the compressor unloads the cylinders only, the system from the exhaust valves down can remain pressurized, thereby negating the need for a check valve in the system (although this is not ideal from a mechanic's standpoint when trying to troubleshoot the system). Anyway, as you might well guess, if there is any problem with leaking exhaust valves, tank pressure can now come back through the valves, into the cylinder, and straight out the propped open intake valves. This can be a difficult problem to diagnose, since the root cause is a valve guide which has worn out-of-round and is now allowing the small metal disc valve to sit to one side of the valve port, instead of covering it completely as it is supposed to do. If this wear is subtle, it can be hard to see. Also, on some occasions, the valve disc WILL sit properly, and function normally. This had me pulling my hair for about 3 hours one day. I'd take it apart, everything looked lovely, put it back together, and it began popping and farting and leaking back throught the intake on shut down. The only cure is a new set of valves. I'd replace all four, since if one is gone, the others are not far behind it.
|
