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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Timing cover off my 305. What’s the tube on the timing indexer for?
Fyi- this cover came in the 305, but it also had a bolt on indexer which I used to time the engine. The bolt on was far right of this welded on version and timed us correctly. This weld on seems way to far out of place? Curious. Enlighten me.
I believe that is for a magnetic probe. Way back when I was in otto skool, my prof told us that some cars have a magnet in the damper. You'd slip a magnetic probe into that section of pipe and read timing from that with some kind of magnetic-prob'n tool. I'd guess something like an old, SUN Engine Analyzer. In my 30 years of being a mechanic and being the boss of mechanics, I've never used that feature or tool, or seen them used.
That's the stock 305 TC. The tube is at approx 0° when used with the stock 305 crank damper; that is, the mark on the stock 305 damper passes under it at TDC.
The aftermarket "bolt on indexer" is in the wrong place for a stock 305 damper. Using its indication in that combination (stock 305 damper & aftermarket tab) will set your timing about 25° retarded from where it should be as a result. Those aftermarket bolt-on tabs are in more or less the correct location for a stock 60s accessory setup, where the stock 80s PS pump location doesn't get in the way of seeing it. Some of those in fact, the stock 80s PS pump won't even install on top of, because the pump hits them. They can be very difficult to see in any case, depending on where the pump happens to end up after tightening its belts.
Not sure how you know "timed correctly" with certainty. However, when using an aftermarket 60s spec damper (which nearly all aftermarket ones are made to that spec), those bolt-on tabs may be at least close to correct.
Not sure if I said "stock" and "aftermarket" enough times. I'd be happy to clarify as necessary.
I've never seen or heard of any magnetic thing in relation to that. No stock dampers ever had anything magnetic about them in that way, that's for sure however. Butt I'm FAR FROM being able or willing to claim that I've seen or heard of everything, or that just because I haven't seen or heard of it, it doesn't exist. Maybe there was some factory tool or something that you put on the damper and put a pickup or something in the tube; I wouldn't know about that. I'm no expert on all the THOUSANDS of Kent-Moore J-xxxx-xx tools that were ever made and sold to GM stores for their techs to use.
I believe that is for a magnetic probe. Way back when I was in otto skool, my prof told us that some cars have a magnet in the damper. You'd slip a magnetic probe into that section of pipe and read timing from that with some kind of magnetic-prob'n tool. I'd guess something like an old, SUN Engine Analyzer. In my 30 years of being a mechanic and being the boss of mechanics, I've never used that feature or tool, or seen them used.
This is essentially correct. Back when EVERY shop that did a quality tune-up work had a machine like this...
....and if that machine was "modern" enough to have that pickup among the many cables to be connected to the vehicle, one of the ends would be a bendable "wand" with the magnetic pickup on the end. That end went into that round tube.
This listing even brags about "magnetic timing", which I believe is a reference to this system.
Interesting... I guess we can all learn something old every day
Not everyone is willing to learn something every day....but there is certainly something to learn, every day!
DynoDave, Yep that was the tool that I was referring to. We used one in school, for measuring spark dwell, even at that time, that tool was old. It's actually a pretty awesome tool though, if you know how to use it and what you can do with it.
This is essentially correct. Back when EVERY shop that did a quality tune-up work had a machine like this...
....and if that machine was "modern" enough to have that pickup among the many cables to be connected to the vehicle, one of the ends would be a bendable "wand" with the magnetic pickup on the end. That end went into that round tube.
Well, THAT brings back memories. I worked with a 920 (miniaturized version of the 1120) for several years. It had an inductive timing light with variable advance, along with some other useful features, but not a magnetic pickup.
I always thought that tube was a good place to stash a 22 LR blank, but you'd only get one signal so paying attention would be critical.
