So I’ve gone for a few drives recently after removing the AIR pump and swapping the valve seals (and consequently readjusting valve lash). Ever since then, I’m getting a raspy, grindy vibration, especially at low RPM (like starting from a stop). It’s hard to describe, you feel it more than hear it, and it’s a vibration in the pedals (I feel it in the brake and accelerator). It’s relatively minor, certainly doesn’t feel like somethings falling apart. It very well may be nothing at all, but it’s new and I’d like to know what it is if possible. Here’s a few of my thoughts:

Exhaust leak. I didn’t cap anything when I removed stuff and I’m relying on the check valves which likely leak a bit. I’ll eventually cap them off but I need to work on it.

Misadjusted valves. I think I did them right, I adjusted them hot, tightened them until they stop clicking them 1/2 turn past that. I’m including this for completeness.

vacuum leak. I removed stuff and moved vacuum lines. I doubt this is it.

the eliminator pulley. This changes the geometry of the engine a bit, as well as the belt having a slightly different tension on it. Nothing is particularly out of line here but it’s a big change so worth mentioning. The bracket is very rigid.

spark plugs? i had to take them out to change the valves.

something else? I mean I removed stuff from the engine so maybe something else changed?

Like I said, it is very likely nothing major. It just bothers me that something changed and I can’t figure out what it is. If anything the car has more power not less.

thanks for reading.

 

What year Vette?

Using a screwdriver or rubber hose, move around the engine while idling to see if you can isolate the noise source.

Since you can feel vibration in both pedals it's not something to be ignored, IMO.

 

can you explain a little more what you’re suggesting? You mean like using a screwdriver as a stethoscope?

EDIT: also it’s 1985. Also, I definitely noticed little things so it’s entirely possible it’s nothing.

 

Hello again Bfenty!

Is it clearly an engine generated sound or could it be something else like coming from the Chassis?

Could it be something that is a result of removing the AIR pump and the new eliminator parts?

Might the vibration be something that was there before you removed the AIR system and now notice it since the sounds changed?

Have you replaced any of the Motor mounts or transmission mounts? Did you put it in reverse and watch the engine to see if you have a bad motor mount? If the engine rises up and wants to contact the hood while reversing you will know pretty quickly. Watch the eliminator brackets for any vibration while revving the engine.

Things that rattle and cause vibrations can and might be mistaken by your ECM as "detonation" and cause your ECM to retard the ignition. That would cause a "Loss of Power" so it is probably unlikely to be the culprit.

I would check your mounts and then go to the new hardware looking for the vibration, while watching the engine while running you might be able to hone in on the source.
With the torquing from the engine those mounts are able to get loose in their older age. I once had a motor mount fail and that did shake everything more after it broke free. Very common on higher mileage cars. Remember that the rubber only last so long.

Be Well and Stay Well!

 

Can you clarify a bit what it seems like? The plate (at least on my air pump) had some rubber bushings on it that could attenuate some vibration I suppose. If the tensioner is close to maxed out (either tight or loose) I think it could do that too. My ac also made this feeling as well.

 

I’m sorry I’m not able to describe it well. If I had to guess, I’d say it feels like a pulley or something is grinding a little bit and that is transferring through the block. I can free spin the new pulley. I’ll check the tension but it seems ok. It feels like a vibration that’s in a component, not in the engine. Because there is not any give out damping in the new pulley it might be transferring vibration? Because that’s really what it feels like. It doesn’t feel like a full engine vibration. the other thing it could feel like is exhaust rattling or something.

I hope this helps. Thanks guys for the help.

EDIT to say-it does feel like an AC compressor grinding or something. Except all the time.

 

I would lean toward it probably isn't anything major. Does the belt track straight over the pully? If the routing is a little off it may be binding that way.

 

I’ll check that. I could try recording it but like I said it’s so minor I doubt it shows up on phone video.

 

Yes, exactly.

 

Poked around a lot today. I found a few things-

One of the spark wires was a little loose on the plug, wasn’t clicked on. I read that can cause a miss at partial throttle and, in fact, it made the engine run smoother.

the cat heat shield has come loose and was rattling. I used some metal zip ties to secure it in place. That wasn’t the sound I was hearing but it helps get rid of extra noise.

i also found a Vacuum leak on this tube. Is on The drivers side underneath the plenum. I think it’s EGR related? I put some RTV on to seal it up.



I can describe the sound better now. It’s a high-frequency buzz, like a buzzer. It’s very minor, but I can feel it coming through the pedals. I’m leaning towards it being related to the new bracket for the pulley. The belt appears to line up, at least close enough not to matter. I can feel the buzz in the bracket for the pulley and hear it with a screwdriver stethoscope as well. I’m thinking I’m just being paranoid. I listened all over that engine and that’s the only place anything buzz-like was noticeable.

 

The bearings inside the pulley's might be going south. That is fairly common on older cars. Frequently it starts with the tensioner pulley going bad. If the bearings rust up internally they will make some horrible sounds while grind away.

I have seen Turn signal relay make a "buzzing" sound before but it is not loud enough to hear over the engine. The noise would be coming from the center console above and behind the radio on my 1988. If you can feel it through the pedals then this is highly unlikely to be the cause. Since you feel it in the pedals it must be one of the pulleys on the front of your engine like you have mentioned checking earlier.

While your engine is running some time take a metal tool and tap on the side of your crankcase to make a metallic sound to trigger your Knock Sensor. When a Knock is heard the timing should retard about 10 degrees and the idle sound will change a bit. If nothing happens check the knock sensor. Overactive knock sensors can kill the power your engine can make.

 

Have you run engine without belt? Is noise gone?

 

... is that a good idea? I have not done that, no

 

its perfectly safe when the engine isn't completely hot or you only run it for a minute or so.

I try to keep it under 30 seconds at a time if possible.

 

I’ll try it.

I’m about 99% sure it’s the smog eliminator pulley. You can feel it buzzing when you touch the bracket for it. For now I’m not terribly worried about that-I’ll try running without the belt to confirm this.