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Old Style Oil Pump

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Here is the Parts List diagram of the old style oil pump fitted to many CZ singles and the JAWA 634 – do not confuse it with the modern pumps which are very effective and reliable. This article is prompted by the supply of a gasket (not shown) between the pump body and the crankcase. The member says he has an oil leak from the pump. A gasket is unlikely to resolve that as there should be little or no oil coming out of the pump provided the oil seal – item 16 is working.

These pumps are either very long lasting or are total rubbish. Usually the latter leaving you with oil dripping onto the floor and a shortage to the running engine. I have known members fit a tap into the oil supply line – not a good idea as you may forget to turn it o open when riding off. Many owners either remove them completely or simply leave oil in them and link the output to the input using a piece of piping. Then mix in the fuel tank. However you do it, it is best to then use a single cable from the throttle direct to the carburettor. That gives you a much lighter throttle action compared to the two cable system. You might try to rebuild the pump as some parts are still available BUT and it’s a big BUT there is no way to calibrate the pump afterwards. In the 1970’s even local JAWA CZ Dealers could not do this. The only calibration equipment was at Kings Lynn with the importers. Club Spares has some new (40 year old) pumps that can be supplied but carry no guarantee so very cheap. If you want one I need to know the serial numbers on your existing pump so I can check to stock. Despite looking the same the pumps are set up differently for the 125, 175 and 350 engines. We also have a few repair parts so always ask before going on to eBay. Again said member was considering buying a complete gasket set but could not tell if an oil pump gasket was included. Unlikely in my view. The gasket part number is 591-15-011 and is the same for all these pumps. It is a simple paper gasket so you can use a gasket sealant instead - provided it is oil resistant. If in doubt add 2T oil to the petrol in the tank.

By Pete Edwards

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