Got a minor noise issue coming from the distributor area. The noise isn't "audible" if I have my ear near either valve cover, but if I listen directly over the distributor cap (with the shield cover off) I hear a slight knocking noise. I shimmed out some excessive gear/housing clearance a few thousand miles ago when I put the current engine in, so I "shouldn't" be having noise from the shaft bouncing up and down (I'm still open to being wrong, though.). Two other things pop into my head as candidates: Tach cross shaft slop noise (although the Tach display itself is smooth, and not jumpy or erratic). The second item that I'm curious about is the oil pump drive shaft between the distributor and the oil pump. I'm curious if the shaft could be "rattling" up and down a touch, or if some harmonics in the oil pump could cause the driveshaft to "rotationally wiggle" (for lack of the correct term) and transmit noise up the distributor shaft.

Just looking for some input here in case another member has run into this same noise situation, or has knowledge of what might be causing it. It's such a PITA taking the distributor out of this engine due to the usual tach cable and shielding issues, but I've also got my electronic ignition wiring and stuff hidden in the shielding, so I'm holding off pulling things apart until I've mulled over some of the cause possibilities.

Thanks for any constructive input.

 

Mike -
Do 2 things:

1. First, disconnect the vacuum hose from your vacuum advance unit. If you have a vacuum advance control unit that is only partially "retracted" at idle, engine vacuum can make the control unit "flutter." If the connection hole in the breaker plate to the vacuum advance rod is not really tight, this will make the distributor "rattle" when running under some engine/vacuum conditions. If yanking the hose cures the problem, you need a vacuum advance with a lower pull-in point (meeting the "2-inch rule" as outlined in my vacuum advance papers).

2. If that's not the issue, grab the top of the distributor cap with the engine running and push it around from side to side. I've seen caps that have the contact points non-concentric in the cap, and the rotor can touch some of the contact points. By pushing on the cap, you can move it just enough to make the condition better or worse. If things change when you push the cap around, get another cap.

Lars

 

I'll give those a try. I appreciate the suggestions.

 

Piece of heater hose. Good stethoscope. Gets loudest when pointing at the source.

 

You can buy a brand new distributor fairly cheap to swap out and locate the noise source. You don't need a fancy tach drive distributor for this but just a cheap one that works with the ignition system you have. What I'm implying is a tool box distributor just for troubleshooting if you haven't thought of this youreself.

Hope this can help.

 

i had a distributor problem this spring when the bushng that has the retaining clip sheared and the rotor slowly ate the contact out of the top of the cap. A stethoscope with the metal rod dticking out of it is a great suggestion. You can get them at most autoparts stores or harbor freight

 

Well, update so far. Slow going, as life keeps finding things I should be doing instead of working on a toy.

a) I can't find any mechanical damage evidence that the rotor is hitting the cap (everything looks unscratched). I wrestled with the cap, but no obvious change of sound.
b) The noise didn't change with the vacuum advance disconnected. (I did find that the engine will die damn quickly without that advance, until I turned up the throttle a bit.)
c) Broke out my trusty heater hose stethoscope, and when I directed the end down by the points door and opened it up, I darn near got hearing damage. I decided to pull the distributor at that point.
d) Looked at the distributor after removing it (weightwise, it's 5#, compared to 2.7# with the aluminum body), and the magnetic pickup (converted the distributor to electronic a hundred years ago) air gap is near zero, and the bottom of the reluctor wheel may be hitting the pickup mounting tab/bracket. These two items need immediate attention.
e) Looking down the distributor hole I see some shiny metal that would be just below the bottom of the distributor gear. The shiny metal is hopefully a machined surface (aluminum) and not wear from the gear, but I'll do a depth measurement of the hole, and inspect the bottom of the distributor gear tomorrow (I had it all wrapped up before seeing the shiny hole).
f) While I've got the distributor out to fix some obvious too-close clearances at the sensor, this is probably a good time to tweak/shorten the advance curve. I've been distracted with weight reduction projects on the car that was a higher priority than an additional curve tweak, but now is the time to do the curve update.
g) I've got a drawer full of distributors that I can throw in the engine for a quick test, but most are points or bigger HEI units, while the current distributor is a magnetic reluctance conversion (as I mentioned above). I do have a points distributor that I converted to a Chrysler sensor and reluctor wheel, which is essentially identical to the parts in my current distributor (a conversion kit sold by Hays a hundred years ago). It worked fine on the distributor machine, but I've never had the opportunity to try it in an actual engine.
h) If it weren't for that damn tach drive crap, I'd sure like to drop a lighter aluminum distributor in the engine instead. But right now I'm not willing to invest the money or time on an aftermarket distributor or a new tach.

That's it. Just been slow going trying to get anything done lately.

 

Hey Lars, just curious if you've noticed what wear pattern is "normal" for the distributor gear. Mine seems very biased to the bottom half of the gear. I'm just trying to get my head wrapped around the different minor/secondary things that might bias the wear downward.

Thanks.

 

WAG
Maybe the mainshaft and / or upper-lower bushing(s) have enough side play to allow the rotating bits to bump into stationary bits ?

 

I don't have a good feel for how fast a distributor will wear out, but I certainly won't discount any possible issue that might need some closer look. This is the original distributor (with only 70k miles, although a lot of them were at upper RPMs). I've got it apart at the moment, and everything looks pretty nice, but I'll take a close look.

 

Things are starting to balloon a bit. While I've got the distributor out and checking things, I wanted to shorten the centrifugal curve a touch. Was kicking around some options and seeing what parts I have on the shelf, when it dawned on me that it might save some time if I just do some mixing and matching of parts from different distributors, The points distributor I converted to electronic a few years ago (as a project) has a shorter advance curve, and the reluctor wheel is the same as the one in the '69 distributor. I can easily swap the reluctor assembly in, but I need to do some distributor machine testing to see where the reluctor wheel and pickup sensor phasing differences are between the two distributors (and then probably move the pickup sensor to get the ignition/timing points to play well with the rotor/cap position). I've seen guys drill/cut holes in a distributor cap to be able to see where the rotor is relative to the cap tower during ignition firings, and I'll just copy that for the testing. Other than a bit of time to set it up, it ought to be pretty simple. I've got a selection of springs and weights in some boxes, so that ought to give me some options when setting up the final curve.

It all sounds good sitting here. Hopefully the distributor will cooperate a bit in the deal.

 

A quick question. Gotta couple spare vacuum advance canisters in the parts box. They're labeled B1 and B25. Anyone know what the specs are for those two pieces?

Thanks for any help.

 

I had a dist in a truck that the bushing wore out and allowed the rotor part of the shaft to contact the pick up coil. Maybe something to check, might not apply to your setup.

 

Just another request for specs on those two VA canisters. Thanks.

 

B1 starts at 8-11Hg. max advance 8deg. @ 16-18Hg

B25 starts at 5-7Hg. max advance 8 deg. @ 13-15Hg

 

Thank you, friend.

 

Just a suggestion for checking rotor phasing is Mr. Gasket still sells a variety of clear distributor caps for chevy.

 

That might be a pretty good idea to pick one up one of these times. I'm going to be running this distributor on my Sun machine to get the advance curve dialed in, and am presently just using a spare cap that I drilled some holes in to be able to see the rotor tip.

(OTOH, a clear cap might look too professional for my garage. )

 

I need to mention the clear cap I have was pretty brittle and cracked easily. It sat a long time in a box before using it so it wasn't exposed to UV/sunlight. Be careful handling one.

Good luck

 

Look for reluctor paddle contact with foot of pickup. Might need to press reluctor up a bit. It will move without drama.

Look from the side for rotor screw contact with top of pickup shoulder. I cut the length of my screws down to suit.

This is a concern because you shimmed the gear, changing the height of the pole assembly. It does not push up as far anymore. Those 2 clearances are pretty tight.