gbowler300

I replaced the tach drive gear a while back, but didn't notice the car ran poorly at first. Later, it ran like the timing was too far advanced. A non-dial strobe timing light showed the timing at 16º BTDC while idling at 700 rpm w/ vac disconnected and plugged (should be 6º BTDC according to factory shop manual). I had to rotate the distributor a tooth because the vac advance hit the coil at 10º BTDC. I figured I had reinstalled the distributor incorrectly after installing the new tach drive gear. After setting timing to 6º and verifying proper dwell angle, the car ran great! I drove it for a few days before it started running poorly again. I checked the timing again and it was back to 16º BTDC. Thinking I had imagined rotating the distributor a tooth the first time, I rotated another tooth. Setting the timing to 6º BTDC was easy and the car ran great for about 25 miles. After limping it home, checked the timing...16º BTDC AGAIN! After verifying the timing mark was at 0º when the motor was at TDC, I tried rotating the distributor another tooth, but now the car won't even start. I'm afraid something in my distributor is broken, but don't want to mail order a new distributor for $X00 without knowing I need it. Because the car is due for inspection at the end of the month, I have about three weeks to get it running again, so I'm concerned I'll run out of time. This is the original, un-rebuilt engine with ~134K miles. Any ideas?

Gregg

66jack

Just guessing here...But what about your "advance springs", could they be shot?

Gary's '66

Timing chain maybe? If you're sure it's the distributor don't buy a new one, contact Lars. He can be found here on the forum. He's located in Colorado and IMO he's "THE MAN" for distributor rebuilds/issues.

MasterDave

The pin holding the distributor gear at the cam side could be sheared (unlikely) Or the harmonic balancer is slipping and moving the timing mark.

6T5RUSH

I agree on the possibility of the harmonic balancer slipping. On a 300 horse motor that harmonic balancer is a slip fit. There's no bolt or hole in the crankshaft snout to secure it.

Jim
In God We Trust!

maxpower_454

The engine would have different symptoms if the balancer was moving. The timing would not actually change, the perceived setting where the car runs good would be changing. It is not.

Maybe your bolt for the distributor hold down is stripped and the distributor is actually moving?

63split63

There may not be a bolt but the balancer is a press fit and there is a key to prevent it from moving .
Bill

Vet65te

The key only holds the 'inner' hub of the damper. If the elastomeric band is giving up, the outer ring with the timing mark will be the one to move around.
Mike T - Prescott AZ

wjw2

are you checking the dwell each time?

leif.anderson93

Double check your shop manual...I think your initial timing should be 4 degrees (not that big a deal). You say this is an original, untouched 134k mile engine...then my bet would be the timing chain has stretched, the original nylon cam gear is worn and the chain is jumping. The fact that you're having to remove the distributor and rotate a notch every time this happens tells me it's the timing chain. Could be the dizzy gear at the camshaft but unlikely.

gbowler300

Thanks for all the suggestions! I hadn't thought about the balancer or the timing chain. It's odd that it resets to 16º each time, but if the chain is jumping, it would likely be the same amount each time (i.e. one tooth = 10º). To answer the other questions: the distributor bolt is not stripped and I have checked the dwell each time. I thought about the pin being sheared, but I wouldn't think the change would be the same each time. I had the rubber go bad on our Subaru's harmonic balancer, but I don't recall the timing being off...it just made a horrendous noise and vibrated a bunch. I'll check it and the timing chain tomorrow, then pull the distributor after that. My tach hasn't worked since I replaced the drive gear, so I need to get into it anyway. I'll try to report back tomorrow night. And I'll double-check the shop manual timing spec too! :-)

mrscott25

You have impeccable timing! (no pun intended).

I am having the EXACT same problem and I think I just figured it out about two hours ago!

I am betting it is just a worn dist clamp.

Here is how I proved it on mine. Probably will want to try this test before messing with your timing chain, balancer, etc.

I scribed a mark on the dist and the manifold. Took the car for a drive and after 20 minutes or so noticed a lack of power. Popped the hood and viola, the marks no longer lined up (the dist retarded about 8-10 degrees). That is proof that the dist is moving under engine load.
I have timed this sucker three times and the dist felt tight as could be. I am guessing the repeated torque applied to the dist under driving conditions is greater than my hand trying to move it.

I can't fix it until I get a new clamp tomorrow, but I really can't think of any other reason for the dist to be moving. I am confident I have figured out my problem, and it won't surprise me if it is also yours.

MikeM

The OP says his distributor is advancing. Second poster's distributor is retarding. If you suspect the distributor is moving with the clamp tight, make sure the distributor shaft isn't bottomed on the oil pump shaft because of no end play in the distributor.

65tripleblack

Splain.

gbowler300

I pulled the distributor because it was the quickest and easiest thing to look at first. I found that the advance springs seem to be working fine. I also found that the tach drive gear and cross shaft are shot, which explains why my tach isn't working! The distributor drive gear looks great, as does the roll pin. Bottom line: I don't believe my timing problem is distributor related. I also don't believe the harmonic balancer is slipping because the timing mark is at 0º when I hand-turn the motor until piston #1 is at the top of the cylinder. Next check: Timing chain!

MikeM

Stick the distributor back in the block and bottom it out. Then twist the rotor clockwise/counter clockwise and see if the shaft has vertical travel without trying to raise the distributor out of the hole.

If the timing chain had jumped, your ignition timing would be badly retarded (not advanced) along with your camshaft.

ghostrider20

If the timing chain has a lot of play, your timing will jump around when you blip the throttle while observing the the timing marks with a timing light, as the chain loads and unloads.

If the chain has jump on the sprockets, you would have valve timing issues, exhaust sound change, possible back and after fire as well.

I would investigate a possible binding situation with the advance springs that is not allowing them to re-park in the collapsed position.

The next time you have this problem disconnect the vacuum advance and rev the engine and note the total WOT timing number.

gbowler300

ghostrider20's description of what happens when the chain jumps is exactly what I've been experiencing. The engine doesn't want to idle, it backfires both through the carburetor and tailpipes, has a markedly different exhaust note, and I lose about 2/3 of my fuel economy. I did note that the advance weights weren't as smooth as I expected them to be, but they do return to their park position. Due to the broken tach drive gear, I'm going to have to replace the distributor shaft. I'll check for wear when I remove the weights.

gbowler300

I tried to send Lars a message last night to ask him about getting distributor parts, but his inbox is full enough that the system won't accept any more messages. Is there another way I can contact him?

62Jeff

He typically only responds to e-mails sent directly to his e-mail account. Did you send an e-mail, or did you send a PM?