Tapping noise behind the distributor
 

After replacing the spark plugs, I started up and at a low idle I have this tapping sound.

I had heard it before but thought it was a loose valve. Strangely it sounded on the top of the engine. Got a piece of hose and stared listening.

It seems to be coming from behind the distributor!! Now what could that be?

This is a 2.7L engine with hyd chain tensioners.

It has been popping at idle as well, but I put that out as a loose valve also.

Even though I can't hear any tapping with my hose on any valve cover is it possible for the sound of a loose valve to carry over to that area behind the distributor?

Kent Olsen
72t upgraded 2.7

i've seen a few loose crank gears lately.

Kent, John,

Of course the obvious is something fell in the cylinder. I hope not.

How about a broken valve spring on #1 cylinder?

How did the noise change with rpm?

I recommend you borrow a bore scope and investigate down the sparkplug port on #1 cylinder before starting again.

Best,
Grady

Well I found it.

Recently added a Mallory MSD and an electronic points trigger. There was some arcing in the distributor cap and that was the tapping noise.

Another interesting tidbit. I used to run this 2.7 engine with no vacuum advance. Now I've run with the vacuum advance for almost a year. Today while looking for the tapping, I put the timing light on her and couldn't get 30 degrees total advance. When I pulled the vacuum line it came back up to 30-32 degrees.

I'll try a run tomorrow with no vacuum advance and if it runs a little better leave it that way for the autox Sunday.

Kent Olsen
72t upgraded 2.7

Kent,
Likely the vacuum was retard for emissions. Haven't used mine for years.

Phew,

It could have been much worse.

Great.

Best,
Grady

Always good to hear the problem was found and it the fix was relatively easy! Great to hear.

Grady, not trying to hijack this thread so, please forgive my intrusion. But have you got my email responses?

Cheers