Engine Tapping Sound

[Brice Road]

Hello everyone. I am new to this site. I have seen a lot of knowledgeable folks here so I thought I'd sign up. I appreciate any help I can get and I am by no means an expert on these cars but I have been tinkering with them for many years so I will certainly help others in any way I can.

I have a '70 Barracuda Gran Coupe. The car originally had a 318 auto but was replaced with a 440 4 speed before I got it. It's no show car but it's a lot of fun. I rebuilt the engine when I got the car. I've had this engine in the car for approximately 7-8 years. I haven't done anything new to the car recently. Somehow something happened and now it is making this tapping sound. I got some bad gas and I originally thought that I blew out one of the exhaust gaskets but I just finished changing all four gaskets and no change in the noise. The strange thing is there is no noise at idle. As I go up in RPM the noise starts and then gets louder. Another weird thing is there doesn't seem to be a noticable loss in power. I was thinking is it possible that a pushrod bent enough to cause the noise but still opens the valve almost all the way so that there isn't a very noticable miss? I plan to take the pushrods out tonight to measure them against a straight edge.

Any help would be appreciated as I want to take the car to Carlisle this weekend. Thanks in advance.

[dfrazz]

I was going to say sounds like the valves, but it looks like you already checked.  How long ago/many tank fills did you get bad gas () and was it just low octane or something worse?

[bandt]

I have a 340 and mine does exactly the same thing at the same point.  Can't hear it at idle but starts with some rpm. Gets worse the hotter the engine gets. Sounds worse at decel from highway speeds. Hate it. Checked my valve train all seems well. Pulled my push rods they look ok. Was thinking it could be a bad or dirty lifter not fully pumping up. 

Will be following this post.

Brian

[dfrazz]

Are your lifters tapping?

[bandt]

Still in the process of trying to find exactly where the noise is from.

[Brice Road]

Thanks for the replys. I don't get home from work until late. I talked to a guy here at work about the problem and he said to him it sounds like what Brian mentioned above. That it is a lifter that cannot fully pump up. He said at idle it is OK because oil pressure is low but when the RPMs go up along with the oil pressure the lifter cannot maintain the pressure and is basically letting the oil right back out. I don't know if I am explaining that correctly it was a couple of hours ago when I talked to him. Looks like I will ride with my friend to Carlisle. The bigger problem is if he is correct and it is a lifter how will I figure out which one it is?

I had a feeling the gas was bad. It came out of my other car. It was only about 3 gallons. I should have found a way to dispose of it but I figured if I immediately added fresh fuel to it then drove the car around to burn it all off it would be OK. I didn't think I would do any damage to the engine. I guess I should have just disposed of the bad fuel. Well, that was a real bonehead move. Lesson well learned.

[PlumCrazyRTSE]

I would suggest that you take out the oil filter, cut off the top and make sure there isn't any sign of metal shavings just to be sure that it isn't a more serious problem like a bad bearing.  Better to be safe than sorry.

[jimynick]

I don't think the gas had anything to do with this. How could it? It'll either burn or not and the or not part goes out the exhaust. Also, you only used 3 gallons and diluted it with fresh. As for the tapping, if you're convinced it's a bad lifter you could take the valve covers off one at a time and with the engine running faster than an idle, I'd take a .010" feeler gauge and see if it'll slide under any of the rockers. If there's a loose one, it'll immediately quieten down and you've found the culprit. This may be a bit messy and an old pair of valve covers cut down so that only the bottom inch or so remains would help to control oil flow. A stethoscope can also be your friend here if applied to the trunnion part of the rocker to listen for what'll sound like a big a$$ knock. Good luck 

[Brice Road]

Thanks for the help guys. I really appreciate it. I don't think it is a bearing. It just doesn't have the type of sound that a bearing makes. If it came down to it being a lifter I was going to try the stethoscope idea but I don't have one. I was going to use a screw driver to my ear but I figured I already had the valve cover off I might as well check the push rods. I found a level surface to check the push rods with and started with the RH side cylinder head. I did one at a time. When I got to #1 cylinder I found that the intake push rod was severely bent. I don't know how the engine was not missing with this push rod bent in this manner. I tired pushing on the lifter and it doesn't seem any different than the one next to it. I think I may have dodged a bullet here. I will get a new push rod and see if the problem clears up.

I had been doing a lot of internet searching about this problem and I was even starting to think that maybe the cam could have failed. I use a product called Cam-Shield so that the engine has enough ZDDP. The guy who designed the stuff was at Carlisle about 3 years ago and he sold me on the stuff. I'm not saying it is the best way to go just the way I do it. I'm glad to know that most likely my cam is OK. I have no idea if the Cam-Shield stuff helped or not. Ever since a guy in my car club (he has a '67 GTX 440 4spd) gave a speech about how one of the lobes on his cam got wiped out due to lack of Zinc I've been a little paranoid about it.

Jimmy, I was thinking the same thing about that gas. Even though it was mixed with Super the engine didn't like it. I ran the car until it ran out of gas just to make sure I got all of that gas out of the system. I don't know exactly when the tapping started but it was just after I put in the bad gas. Perhaps because the engine didn't like that fuel it jerked itself around or something and bent the push rod?

Thanks again for all the help.

By the way, my name is Phil. Maybe I will see some of you at Carlisle. I will catch a ride with my friend if my car can't make the trip.

[PlumCrazyRTSE]

Nice troubleshooting work, sounds like you've found your problem.

The reason I had suggested looking at the oil filter was because I had a very similar tapping sound in one of my cars recently.  At first, I thought it was an exhaust leak but could find any.  Then I thought maybe a collapsed lifter so I tried to track down which one.  I removed the valve covers and checked the rockers with the engine running and there didn't seem to be any issues there.  Then a friend suggested that I drain and strain the oil.  The oil looked fine but when I removed the oil filter and checked it, sure enough there were lots of metal shavings.  I'm just glad I found the problem before it became catastrophic.  Needless to say but I parked the car for the time being.  Going to temporarily swap out that numbers matching engine for a spare built 440 that I have.  When I get around to doing a complete restoration on the car in a few years, I plan to rebuild the original engine and put it back into the car but until then I can continue to drive it with my spare 440 installed. 

By the way, the Challenger Service Manual provides the following information on how to check for a lifter problem.

Tappet Noise Diagnosis
(1) To determine source of tappet noise, operate engine at idle with cylinder head covers removed.
(2) Feel each valve spring or rocker arm to detect noisy tappet. The noisy tappet will cause the affected spring and/or rocker arm to vibrate or feel rough in operation.