Inconsistent tapping from 400 sbc

[Broton2]

Put new cam in my 76 K20 with a 400 and it was properly broken in, all steps followed and lash set. Now every once in a while it taps and kind of sounds like lifter noise. Super inconsistent and it doesn’t really change with rpm and smoothes out around 700-800 rpm. I let the truck sit for 4 days and it ran perfectly, but I hopped in today and it came back. Any advice helps

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(Here’s the link to the video)

 

[PrairieDrifter]

Check the fuel pump. Should be resistance on the arm even on the base of the lobe.

 

[Sad Sack]

Were new lifters installed? Almost mandatory on new cam installations especially where warranty is in play.

 

[fast 99]

Have seen lifters make irregular noise. Lifter quality today isn't great unless a name brand part is installed.

 

[Frankenchevy]

The video won’t play for me, but also consider an exhaust leak.

 

[Broton2]

New cam and lifters were installed yeah it’s a edelbrock performer plus 2102 with the matching lifters, I know I have an exhaust leak somewhere but seeing as the engine shakes when the tapping happens I don’t think it’s that

 

[Chevy 88]

I don't think its this, but we gotta brainstorm all avenues - right?

If the engine shakes when the tapping/ticking sound is there, could this be a loud spark plug wire short? Sometimes if the spark is good and hot, and jumping in the right spot - it can make some pretty snappy sounds. Plus it would account for the engine shaking while the noise is present.

I would see if you can repeat the issue at night, and then look around the engine in the dark.

 

[YakkoWarner]

I don't think its this, but we gotta brainstorm all avenues - right?

If the engine shakes when the tapping/ticking sound is there, could this be a loud spark plug wire short? Sometimes if the spark is good and hot, and jumping in the right spot - it can make some pretty snappy sounds. Plus it would account for the engine shaking while the noise is present.

I would see if you can repeat the issue at night, and then look around the engine in the dark.

I had this exact thing happen with my 454 - I was convinced I had a lifter or rocker loose but also inconsistant. When I happened to be poking around in the engine compartment (for something else) I saw an errant flicker down low on the drivers side - #7 plug wire was completely off and laying on the frame, cheerfully arcing away. Popped it back on (after turning off the key) and noise was gone. Not sure how plug wires just fall off, but there it was.

 

[cadillac_al]

I don't want to be a jerk, but maybe I am. I don't trust anybody's valve adjustment. I can only do it with the intake manifold off or the dreaded engine running valve adjustment. When people tell me their valve adjustment procedure with the intake manifold on, I just roll my eyes and say oookay. We are all assuming that the break in went well with no defective parts failing. There are so many horror stories of new parts failing for no reason. Next time I change a cam I will use only made in USA lifters and put the lifters that came with the cam on a shelf. Good luck.

 

[Bennyt]

There are probably only 2-3 companies worldwide making an 817(SBC hydraulic) lifter these days. In the 90's, and I might be wrong, there were only 5 companies making 817's and popularity has drastically dwindled down since then. They are all probably manufactured/ machined in Mexico and distributed to the various other "manufacturers" who might disassemble, machine an extra groove for vacuum or magic, etc. I'm sure there is some boutique manufacture out there machining their own but that would probably cost $50 a lifter.

If I recall, most of the domestic lifters have a .0003 tolerance in them so doesn't take much to take them out.

When I worked at PAW as a teen, I used to have to Rockwell test and subsequently destroy "soft" cams/lifters that were returned. Probably did 2-3 a week for 2 years. Not once did I ever find a metal hardness out of spec. And the blank manufactures said it was in theory impossible as the casting process eliminated that probability. If for some reason a batch of blanks did have an issue, it wouldn't even be machinable. I literally disassembled hundreds of lifters only to always find debris.

 

[Broton2]

eliminated spark plug wires as an issue, going to probably take it in to a local shop in the next coming days

 

[77Dmax]

Run it without the belts on. That will eliminate tons of white noise. Check all your pulleys while your at it.

 

[Broken85]

Get a short broom handle. Put one end up to your ear and poke around the engine with the other end. That will narrow it down for you.

 

[72velle]

I had a similar sound in my 350, drove me nuts. I bought an engine stethoscope to isolate the noise. It turned out it was my ac compressor. Topped it off and the sound went away. I hope it's that simple.