Page 15 - Summer 2017 GMC Vintage RVing

For additional technical session presentations and papers, go to gmcmi.com/technical-presentations-papers/when you turn it on or it may jump out of your hand. If the bearings are noisy, it may be feasible to lubricate them and save the motor for a while; replacements are readily available and reasonably priced.C. Photo 3 shows another place to check:That is a big mud dauber nest at the very top of the duct. Hard to see, but very detrimental to blower operation.7. Photo4showsanotherproblemarea.Thegreyitem is the blower motor resistor assembly. The blower control switch selects one, or none, of the three resistors in that assembly to limit the current flowto the blower motor, and thus its speed. Even inthe lowest switch position, one of the resistors, the largest, is conducting current if the ignition switchis ON. That generates heat. When the motor is heavily loaded, as shown in Photo 2, its current draw increases dramatically – and so does the heat in the selected resistor. Guess what can happen when the shown “tinder” contacts that perhaps-red-hot resistor? It is essential that all the debris in that compartment be removed. All HVAC air flows through there to get to the evaporator, not to mention the fire hazard.There are two ways to clean the duct behind the evaporator without removing it: A vacuum hose small enough to go into the resistor hole can be used to clean the area. Or, with both the motor and the resistors removed, a water hose can be fed into the blower outlet duct to wash debris out the resistor port. Have someone inside the coach watching for water leakage if you use this method.With all those inspections, corrections, repairs, and modifications completed, it is time to handle anything you feel compelled to paint. Then reverse the actions in steps four to one to get everything back together.I promise you will be glad you spent the hour or two at this exercise.PHOTO 4: Blower Motor ResistorsSome Quick Tech TopicsJim Kanomata | 1978 Royale | 510-742-1101| Applied GMC | appliedgmc.comSpark Plug Wire Cross-FiringThe Automotive Engine Rebuilding Association (AERA) Technical Committee offers the following information regarding spark plug wire cross-firing on an internal combustion engine. If an engine continues to operate that way, engine damage on only one piston or only one piston rod bearing may result. This can occur shortly after rebuilding an engine, or anytime the spark plug wires are rerouted.Induction cross-firing results from the magnetic field produced when an electrical current passes through a spark plug wire, causing two cylinders to fire at the same time. If cross-firing is allowed to occur, one cylinder has the spark plug firing ADVANCED 90 Degrees from the proper time. With that amount of ignition advance, it is only a matter of time until a component will fail.During disassembly of an affected engine, finding broken cast piston ring land(s) or damaged connecting rod bearings on the cylinder which was firing too early, should be no surprise. In these instances, the components have been operating beyond their intended designed parameters. A hypereutectic or forged piston will last longer, only because they are stronger. However, those engines will eventually fail, as well.Common cylinders to cross-fire are listed below in bold and underlined: General Motors 1-8-4-3-6-5-7-2 Oldsmobile 260-455Note: To avoid the risk of induction cross firing, do not run spark plug cables with consecutive firing order parallel to one another. For Olds engines, two cylinders, 5 and 7, that fire consecutively are in the same cylinder bank. Cylinders 1-3-5-7 are on the driver side and cylinders 2-4-6-8 are on the passenger side. The cables, then, for cylinders 5 and 7 should be separated in the cable loom. Show this to the person installing the spark plug wires, prior to installation, to safeguard against any future unnecessary cross-fire engine failures. The person who routes the spark plug wires is ultimately responsible for initially eliminating the possibility of engine cross-firing.Engine Temperature Gauge• Generally runs at l/4 mark• Should it go to 1/3, engine is heating up• Do not think it will go to half; by that time, you will need a new engine. Also:• Radiator Cap – pressure not to exceed 10 psi• Fan Clutch is always a suspect. If you do not hear the fan lock up, replace it.Rear Parking Brake• Must re-set by backing up and firmly applying the brake when backing up• When you are using brakes frequently and severely, take time to re-set the rear brakes.GeneratorJim Miller referred us to a very great product for our generator.It is a catalytic converter to eliminate the smell from the generator exhaust. I hopeto install a few on the coaches before making it available. As you know, the smell of unburnt exhaust has been an issue. Eventually, the State of California will be requiring these on new units.On a hot day, best to turn on air conditioning early before it gets hot in the coach, as it will take longer to cool.SUMMER 2017 GMC MOTORHOMES INTERNATIONAL 15