Re: Rough Idle

Posted by Tim Cole On 2011/5/25 17:14:08

Dear Steve:

The typical rotor to distributor clearance is .030 inch. So if the rotor is smashing the cap the bushings are shot.
The reason there is more clearance than spark plugs is because spark plugs operate under extreme resistance caused by compression.

I had a great test case come in today. It had a fair idle quality with steady beat on one cylinder and random misfires not sufficient inhibit driveability.

Compression was 19% lower on one cylinder and I expect it would burn a valve on a long journey at high speeds but will hold up if used for short trips.

The dwell varied depending on the tester. A cheapo meter fluctuated with random misfires and the timing was not steady around the proper setting.

However, the timing chain is loose and the carburetor castings in poor condition so condemning the distributor is a mistake because when an engine misfires the dwell changes.

This car starts hot or cold and meets the owner's needs at present, but in reality every part in the motor is shot.

I am very particular to set Packard timing using a light despite that Junior Packards have totally rotten timing marks and I attribute the satisfactory operation to proper timing. Sometimes I have to spend hours tearing a car down to accurately paint the timing marks.

Thus, I will refrain from hanging parts on a car that runs and drives okay because the results would be disappointing.

Good luck and please note that I send distributors to a leading Packard supply house and am satisfied with the results.