Question
My Spitfire at the Riv
Sound like loose marbles in the base of my distributor at idle. If you advance the timing or increase the RPMs the noise goes away. I've heard these distributors get worn and cause problems. I just did a 500 mile rally with no noise until now. Did I just finally just wear it out? 1980 Spitfire 1500
AnswerI don't think so. The wearing out of the distributor will first cause the timing to jump, as radial play of the distributor shaft causing the timing to change randomly. You can check for this by putting the timing light on the engine while running, and how "steady" is the timing light on the front pulley, without reving the engine. If the mark doesn't move, and is "steady" the distributor isn't worn enough to cause a problem
There are no bearings in a distributor to make it sound like marbles, which is what a bad bearing noise can sound like. It sounds more like you too much end float in the relationship between to the dog gear and the distributor, or the mounting is loose in some way.
The distributor is just a large bushing, or bronze sleeve, that is a close tolerance fit to the distributor shaft. Between it and the camshaft is what's called a "dog gear" which sits in a bushing the block. The dog gear takes the horizontal spinning of the engine and converts it into vertical spinning, to drive the oil pump and distributor.
The marble noise may be related to the components not having enough end float, or too much, and the dog gear is jumping or moving vertically more than it should
Some things to check:
-distributor itself is firm in the steel housing that connects it to the block with 2 studs, and the clamp that holds the position of the distributor housing. CHeck the clamp and housing is not loose where it mounts to the housing and block, respectively
-the distributor radial movement should be minimal; take the rotor off, and attempt to move the shaft to the front of the engine (left) or to the right (rear of the block) or towards the engine (away from you) or towards the left front wheel (towards you). This "radial play" should be almost zero, and the distributor itself should be attempting to move, and the not the shaft in relation to the distributor housing.
-pull up & down on the shaft that holds the rotor. There should only be slight movement here. This is the end float of the distributor shaft, and can't be too loose or too tight.
If you have a bently workshop manual and feeler gauges, there are ways and procedures to measure the end float and make sure the "play" in the distributor is within tolerance. Checking the distributor/dog gear end float is a slightly more involved process, if the above 3 don't check out.
