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Username Post: Tapping Sound #7 cylinder        (Topic#353537)
Nicksd 
Poster
Posts: 32

Reg: 09-02-09
10-21-18 05:03 AM - Post#2749167    

I have a chevy 350 motor in a 1955 chevy convertible with a 700r4 transmission. I have this tapping sound coming from #7 cylinder, however when I pull the plug wire off at the distributor it stops. any suggestions. Also when I pull it off I get a bad shock????



 

Ecklers AutoMotive

Shepherd 
Frequent Contributor
Posts: 1554

Loc: Lake George, NY
Reg: 11-11-15
10-21-18 07:22 AM - Post#2749183    
    In response to Nicksd

You are the ground for that plug wire, didn't expect that? Pull the valve cover, check the rockers and valve spring. It also could be a bad exhaust manifold gasket, check that first.



Edited by Shepherd on 10-21-18 07:23 AM. Reason for edit: No reason given.

 
beagrizzly 
"10th Year" Gold Supporting Member
Posts: 1932
beagrizzly
Age: 68
Loc: south texas
Reg: 08-04-12
10-22-18 06:48 AM - Post#2749238    
    In response to Nicksd

Pull the other end of the wire. The one at the distributor cap.

When you kill the ignition, the tapping stops because the cylinder isn't firing. You have unloaded the valve train, and the rotating assembly.

You have also created a dead miss on #7 cylinder.

The only compression you have is whatever the engine puts up normally. That is between 100-150 psi. When you hook up the wire you get ignition compression. You then load up the piston, rod, and crank. Somewhere in that lineup, you have some slack(wear) that creates the tapping sound.

You will probably need a stethoscope to find out which component is tapping.

It could be a lifter, a rocker, piston slap, or rod journal.

Get under the engine, and see if the sound is coming from the bottom end. If it is, you probably have a rod bearing with a too much clearance.

Again, a stethoscope would be a big help.

Griff

if you're gonna be a bear..................

1960 Biscayne (the 6T)
2005 Yukon XL
2007 GMC Sierra Classic 8.1
2009 Silverado
2011 Escalade ESV


 

Ecklers AutoMotive

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