1981 Volkswagen Rabbit L from North America - Comments

20th Aug 2005, 02:53

You want to have your car timed. The beauty of the diesel motor, is once you set the timing, it's set, and there's nothing to wear out. Then you just change the oil and filters, and that's all the maintenance.

To set the timing, you first have to set the valves, then you set the injector pump, and then you adjust it. The basis of timing is it's all based around the engine's number 1 cylinder being at top dead center. You go over to the flywheel housing on the transaxle, and there is a access port with a plug you remove. Once it's removed, you'll find it has an arrow, and there's an arrow on the flywheel, and when they're lined up, the number 1 cylinder, which is the cylinder on the far left, is completely at top dead center. Then you remove the cam cover and the timing belt cover.

At the far right end of the cam, there is a flat cut in the cam. You put a tool in this called a cam lock. This locks the cam at top dead center. You have to make sure the two came lobes on number one are symmetrically pointed up. If not, you need to turn the motor over one more revolution. The cam lock needs to fit in perfectly when the flywheel TDC mark is perfectly lined up. You cannot be one tooth of on the belt. If the timing is off, the valve will still be out when the cylinder comes up, and they will hit, the valve will be bent, and the cylinder head will be destroyed. If you're half a tooth off, undo the bolt on the cam timing cog, and tap it with a plastic hammer, that's how you fine tune it.

On older motors, you might consider having the valve seats ground. A lot of the efficiency in the motor has to do with how well sealed the chamber is, how well the valves seal, and how well the cylinder rings are sealed. You can find out by having a compression test.

To set the injection pump, you need a dial indicator. You insert the dial indicator into the injection pump. The indicator has a feeler needle that goes up against the plunger in the pump. The plunger goes back and forth, and turns around pumping and distributing the fuel to the proper injectors. As you turn the motor, the plunger will push out until it stops. You then center the dial indicator, and you turn the engine back to top dead center and the number one. The dial indicator is the number you time the motor by. The closer to top dead center you inject the fuel, the higher the pressure in the combustion chamber, the longer the time the fuel has to burn, the cleaner the motor runs, but when the crank is directly up, the connecting rod doesn't have much leverage over it, so as you delay the timing, you start burning the fuel in a area where the connecting rod has more torque over the crankshaft. The power will be longer and more mature.

If the timing is too late, the engine will start to smoke a lot, because the fuel will not have the time or temperature to completely combust. Anyway, just stick with the factory spec on timing, it's very precise stuff.

Timing is everything. It all has to come together precisely at the right time, and when it does, it's almost magical, the way the motor fires on the first rev, and how smooth and precisely it makes every explosion like clockwork.

Once you got the timing right, you set the idle speed and the top speed on the motor. You don't want to put too much fuel in the motor, or it will not have enough oxygen to fully combust, and it will produce lots of black soot. Diesel have no throttles, because they need to suck up as much air as possible, so they have as high a pressure in the cylinder at all times, because they use compression to ignite the fuel. The air is always the same, and the way you adjust the power in a diesel is by the quantity of fuel injected in the motor, and therefore by adjusting the air fuel ratio.

Diesels have a very high air fuel ratio; 40:1 up to 120:1 at idle. Basically the less fuel you put in the chamber, the more air there is to combust that fuel, and the more efficiently the motor burns the fuel. For this reason, diesels have very high part and low throttle efficiency. This is a way in which the diesel is superior to a petroleum motor. Very little fuel goes a long way in a diesel. So if your timing is correct and you see lots of soot coming out the exhaust pipe of your diesel under full throttle situations, it means you need to back off the full throttle stop a bit.

Also have all your wheels aligned so your car rolls down the road easily. I don't know how to do that.

6th Oct 2012, 08:57

We have an 1981 VW pickup that will start for a few seconds, but if you give it gas, it will backfire and die. We replaced the fuel pump, fuel filter and fuel regulator line. Still the same problems; we figure it has to be out of timing, but we cannot find the timing marks. This is a gasoline engine, not diesel. Any help would be extremely helpful, as we are at our wits end and this is our only transportation. We need it running desperately, as we have a disabled daughter with many doctors appointments. Thanks in advance.

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