Please take a look at the attached picture. Note the dried up rubber bushing on the vertical part of the stem. Was this bushing originally on all 66 401/425 standard distributors? This is from a 425. Thanks
That bushing is on MANY of the vacuum advances to limit the amount of advance. Many are missing because they have dried out, cracked & fell off inside the distributor. There is also one on, again, many distributors to limit the mechanical advance. I use my own mod that will never dry or fall out. Tom T.
Thanks Tom! - Very Interesting. Wonder how many cars are running around with too much advance because of these things falling off unbeknownst to the owners. Quite surprising that GM would choose this method over adjusting the slot lengths in the steel. When I call you tomorrow about the rocker shafts I'll inquire about the possibility of getting your replacement bushings. This is for a 2x4 66 MZ code engine. The bushing is gone from the mechanical advance pin. I don't know if this tells you anything but currently (no bushing) I put a dial indicator on the mechanical advance pin under the slot and there is .223 of travel from one extreme to the other.
This is one of the big reasons so many people have pinging/detonation problems, and think they have to run super havy octane gas to keep it from happening.
Get a aftermarket curve kit, it has a brass bushing along with the spings and wieghts to improve perfomance, thanks Bill.
The old points-style distributors also have a limiting bushing for the centrifugal advance. Often M-I-A. Replacement bushings and the installation tool are (or at least "WERE") available at NAPA or other "real" parts stores.
I had this same problem with my '69 LeSabre. It was causing a part throttle ping. I replaced it with by dissecting a #40 roller chain link. The inner sleeve fits great on the rod. In the end that dried out bushing was adding 12 degrees advance to my 350.
x2 The other possibility for a replacement bushing would be a 1/4" piece of overflow hose on a motorcycle/ATV battery. However, this too will wearout over time.
