m-mman Posted October 24, 2021 Share Posted October 24, 2021 The car is a 1942 Hudson 8. I thought I should restore the ignition system. I bought some NORS parts on eBay. Points, cap, condenser are fine BUT the rotor is too long(!) I have never experienced this before. Perhaps it is the wrong (but look alike) rotor? I trusted the seller for the application. It fits exactly beyond the length of the conductor. The new rotor definitely is TOO LONG. It hits the new cap. I suppose I could cut it, BUT if I did, how would I know how much to cut? I could measure it against the old rotor BUT, is the old rotor too short? The old cap is grimy, used and burned, but the car ran OK. What should the rotor to distributor terminal gap be? I have never seen this problem before. Any thoughts? Link to comment Share on other sites More sharing options...
Old buicks 2 Posted October 24, 2021 Share Posted October 24, 2021 Wrong rotor. I would exchange the rotor you have for the correct one if you so desire. You pay shipping both ways. Let me know. Tom 402-359-5762 or tsvanmeet@gmail.com 1 Link to comment Share on other sites More sharing options...
Rusty_OToole Posted October 25, 2021 Share Posted October 25, 2021 You could turn the rotor until it lines up with one of the terminals. Using the old rotor, press a lump of modeling clay onto the end and install the cap. You should end up with an impression of the cap terminal allowing you to measure the gap. 2 Link to comment Share on other sites More sharing options...
JV Puleo Posted October 25, 2021 Share Posted October 25, 2021 I asked this question myself several years ago as I was making a distributor. Ultimately, I took a common distributor - I think it was for a Volkswagon - added a new cap and rotor and then cut the cap in half - making a "cut-away" distributor. I forget what the number was that I came up with but it was a much larger gap than I'd expected. Link to comment Share on other sites More sharing options...
trini Posted October 25, 2021 Share Posted October 25, 2021 Simple. Make a piece of stock the thickness of the old rotor brush. Make an elongated hole at one end about 3/16 size. Drill a hole through the old rotor and screw the stock on. Now that stock will be able to move one way or the other depending on which way you desire. Rotate the distributor shaft and keep adjusting the stock until you find what you want but remember the tip of the rotor must not touch the cap. There must be some gap for the spark to jump . You may paint the tip of the stock with nail polish to see if it touches the cap.If you have an old similar rotor, smash the bakelite and use the brass brush. Link to comment Share on other sites More sharing options...
joe_padavano Posted October 25, 2021 Share Posted October 25, 2021 An even easier way is to simply press some modelling clay onto the end of the old rotor, reinstall, align the rotor with one terminal in the cap, and then install the cap, leaving an impression of the terminal in the modelling clay. Yes, there is some concentricity tolerance as well as positional tolerance on each terminal, so you may want to test multiple terminal locations, or multiple caps, but this is a totally non-destructive and foolproof way to check. The alternative is to cut holes in an old cap and measure through the holes. Again, such measurement won't account for manufacturing tolerances, so any gap needs to be slightly larger for that reason. Link to comment Share on other sites More sharing options...
m-mman Posted October 25, 2021 Author Share Posted October 25, 2021 17 hours ago, Rusty_OToole said: Using the old rotor, press a lump of modeling clay onto the end and install the cap. 34 minutes ago, joe_padavano said: An even easier way is to simply press some modelling clay onto the end of the old rotor, reinstall, align the rotor with one terminal in the cap, and then install the cap, 49 minutes ago, trini said: There must be some gap for the spark to jump Fascinating. I will probably check and play with the old parts. Are there any specifications for the gap? I'm thinking that .028-.032 like the spark plug might be appropriate. Because it is not adjustable, I suspect that there is no published value. As an FYI Tom looked up the number I had been sent and it is the wrong one (seems there are several near identical but not exact rotors) He offered to swap for the correct so into the mail the wrong one will go. Thanks, Tom 2 Link to comment Share on other sites More sharing options...
joe_padavano Posted October 25, 2021 Share Posted October 25, 2021 17 hours ago, Rusty_OToole said: You could turn the rotor until it lines up with one of the terminals. Using the old rotor, press a lump of modeling clay onto the end and install the cap. You should end up with an impression of the cap terminal allowing you to measure the gap. Missed this the first time. Beat me to it. Link to comment Share on other sites More sharing options...
jan arnett (2) Posted October 25, 2021 Share Posted October 25, 2021 I use a glob of axle grease instead of modeling clay, 1 Link to comment Share on other sites More sharing options...
trini Posted October 26, 2021 Share Posted October 26, 2021 I do not know how wide the gap should be, I guess 010. If too far the tip will show heavy burn marks. Any thought on this ? Link to comment Share on other sites More sharing options...
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