MECHANICAL CHECK The mechanical checks and adjustments described below are performed with the engine off Except where noted the car may be at either room temperature or operating temperature 1 REMOVE SPARK PLUGS AND TEST COMPRESSION a Remove spark plug wires b Remove any foreign matter from around spark plugs by blowing out with compressed air then loosen all plugs one turn NOTE To remove or loosen center park plugs it will be necessary to disconnect or remove carburetor throttle rod and use a universal drive on spark plug socket c Start engine and accelerate to 1000 rpm to blow out loosened carbon NOTE Clearing out carbon in this manner is important in preventing false compression readings due to chips of carbon being lodged under the valves d Stop engine and remove spark plugs s LD PLASTIC TUBING M6 WOODEN DOWEL STAPLED TO DOWEL THREE PLACES Fig 7 1 Spark Plug Holding Tool NOTE It may be desirable to use a special spark plug socket that is equipped with an internal O ring seal to grip the spark plug or the serviceman can fabricate a tool as shown in Figure 7 t to grip plug after loosening with socket to avoid the possibility of dropping plug into origin shroud assembly e Remove sir cleaner and block throttle and choke in wide open position f Hook up starter remote control cable and insert compression gauge firmly in spark plug port fig 7 2 NOTE Unless special adapters are available it will be necessary to remove both carburetors to perform the compression test g Crank engine through at least four compression strokes to obtain highest possible reading S AND ADJUSTMENTS y mr rV x Fig 7 2 Checking Compression h Check and record compression of each cylinder Compression should read as indicated below and variation between highest and lowest reading cylinders should be less than 20 pounds The minimum pressure should be 130 pounds i To determine whether rings valves or head gasket are at fault if one or more cylinders are low or uneven oil would ordinarily be injected into each cylinder and compression rechecked Due to the design of this engine horizontalopposed the oil would lay in the bottom along the cylinder wall of each cylinder thus preventing an accurate check A careful diagnosis with a vacuum gauge oscilloscope etc should be used with this compression test to determine what if anything is at fault The compression check is important because an engine with low or uneven compression cannot be tuned successfully to give peak performance Therefore it is essential that improper compression be corrected before proceeding with an engine tune up If a weak cylinder cannot be located with the compression check see Cylinder Balance Test under Additional Checks and Adjustments in this section 2 CLEAN SERVICE AND INSTALL SPARK PLUGS Inspect each plug individually for badly worn electrodes glazed broken or blistered porcelains and replace plugs where necessary Refer to spark plug diagnosis information presented in Ignition System Section 8 for an analysis of plug conditions Use new spark plug washers when reinstalling cleaned plugs anvvmo auna u nnum