66 ignition trouble

[Don Keller]

During my Sunday ride this afternoon, I noticed my 66 327/350 started running rough and was not able to stay at idle. After starting it again and diving on, I also noticed that the tachometer was no longer working. I'm getting a little back fire but not much. I assume there is a problem in my distributor. Are the two related and where should I start to troubleshoot.

Thanks,
Don

[Ed Jennings]

Re: 66 ignition trouble

I think you will find your tach drive gear has broken. When it broke, it tried to lock the distributer shaft and jerked the distributer enough to disturb the timing. This happened to me once, but it jerked the distributer so far out of time that it killed the engine.

[Ed Jennings]

Re: 66 ignition trouble

I think you will find your tach drive gear has broken. When it broke, it tried to lock the distributer shaft and jerked the distributer enough to disturb the timing. This happened to me once, but it jerked the distributer so far out of time that it killed the engine.

[Ed Jennings]

A little more info

Assuming that I am correct in my diagnosis, you can take the following steps to get going on a temporary basis, sans tach:
Disconnect the tach cable.
Unscrew the brass retainer and remove the small shaft and gear.
Replace the retainer and the tach cable.
Retime the engine.
To make a permanent repair and get your tach going again, you will have to replace the small shaft and gear, and will almost certainly have to replace the distributer main shaft, as the gears on it are almost certainly damaged as well. Once in a while you may get lucky, but not very often. An alternative is to get a rebuilt tach drive distributer. I would stay away from the aftermarket tach drive distributers because most, if not all, lack a vacuum advance.

[Ed Jennings]

A little more info

Assuming that I am correct in my diagnosis, you can take the following steps to get going on a temporary basis, sans tach:
Disconnect the tach cable.
Unscrew the brass retainer and remove the small shaft and gear.
Replace the retainer and the tach cable.
Retime the engine.
To make a permanent repair and get your tach going again, you will have to replace the small shaft and gear, and will almost certainly have to replace the distributer main shaft, as the gears on it are almost certainly damaged as well. Once in a while you may get lucky, but not very often. An alternative is to get a rebuilt tach drive distributer. I would stay away from the aftermarket tach drive distributers because most, if not all, lack a vacuum advance.

[Don Keller]

Re: A little more info

Ed,
You are correct. The tach drive cross gear had a flat side on it. Thanks for getting me started. I have not pulled the distributor mainshaft yet to see if there is any damage to it. But, I bet your right again.

Thanks for your help..

Don

[Don Keller]

Re: A little more info

Ed,
You are correct. The tach drive cross gear had a flat side on it. Thanks for getting me started. I have not pulled the distributor mainshaft yet to see if there is any damage to it. But, I bet your right again.

Thanks for your help..

Don

[Ed Jennings]

Re: A little more info

Once you get your distributer out, I believe you will be able to see the gears on the shaft as you turn it. (been nearly 30 years since I've had to do this, so my memory is a little faint). If all the gears look ok, you can probably get away with replacing the small gear. I strongly suspect you will find some broken or chipped gears which will necessitate a main shaft change. Not difficult to do, but like everything else that is Corvette specific they are pricier than the corresponding Chevy part. If you have to change the shaft, there are bronze bushings in the distributer housing that may need to be changed as well. Matter of fact, if they are loose, they could be the cause of the gear failure by allowing side play in the main shaft. Be sure to check then out.

[Ed Jennings]

Re: A little more info

Once you get your distributer out, I believe you will be able to see the gears on the shaft as you turn it. (been nearly 30 years since I've had to do this, so my memory is a little faint). If all the gears look ok, you can probably get away with replacing the small gear. I strongly suspect you will find some broken or chipped gears which will necessitate a main shaft change. Not difficult to do, but like everything else that is Corvette specific they are pricier than the corresponding Chevy part. If you have to change the shaft, there are bronze bushings in the distributer housing that may need to be changed as well. Matter of fact, if they are loose, they could be the cause of the gear failure by allowing side play in the main shaft. Be sure to check then out.

[Bill Clupper]

Re: A little more info

Don't for get to check for wear on the housing where the crossgear bottoms on the back of the housing. A worn spot here will trash a lot of new parts quickly

[Bill Clupper]

Re: A little more info

Don't for get to check for wear on the housing where the crossgear bottoms on the back of the housing. A worn spot here will trash a lot of new parts quickly

[Ed Jennings]

Re: A little more info

I've never had occassion to do this, but isn't there some sort of bronze or nylon button available now to prevent wear in this area. Seems like I've seen something like that mentioned. Maybe later model distributers had something like this from the factory? Inquiring minds and all that......

[Ed Jennings]

Re: A little more info

I've never had occassion to do this, but isn't there some sort of bronze or nylon button available now to prevent wear in this area. Seems like I've seen something like that mentioned. Maybe later model distributers had something like this from the factory? Inquiring minds and all that......

[Clem Z.]

Re: A little more info

even if the main shaft teeth are intact i would take the main shaft out and clean the housing because those broken off teeth are laying in the bottom of the housing and will grind their way into the main shaft. been there done that

[Clem Z.]

Re: A little more info

even if the main shaft teeth are intact i would take the main shaft out and clean the housing because those broken off teeth are laying in the bottom of the housing and will grind their way into the main shaft. been there done that