Engine noise ...what would you guess is the cause ?

[71violetcuda]

I have what I'll call a rattle, which is loudest under very light--barely on the throttle--cruising down the road kind of scenario. Give it just a little gas and the noise will go--at least to my ears--away. I bought the car back in 2004 with a 68' 440 that has stampings on the engine pad at the LF corner showing it was bored .030 and the rods and mains .010 over. My guess is piston slap, but I was never really shown/taught what different noises sound like under real world conditions, other than the obvious ones (e.g., valve tap, etc.).

I have good oil pressure 80psi at 1500 and it drops to around 40psi at idle with a warmed up engine. Engine runs good, doesn't miss, plenty of power. I would just love to know if something really bad is gonna happen soon, or can I let it go for awhile until I can tear the engine apart.  Wish I could put the actual sound it makes on here:)

Thanks for any input!    71 Cuda 440 4spd 70K (??) miles
 

[jimynick]

My dad taught me that under very light throttle and when you rev it just a bit and as it's floating off and down, that it may be a wrist pin noise. As you mention, it doesn't do it under load up or down. Just my    worth. I don't think it'd be particularly dangerous under reasonable driving.   

[Racer57]

Have you tried listening with the hood up and working the throttle by hand to locate ? Could it be a bearing in the alternator, bushing in water pump, etc ?

[71violetcuda]

Thanks guys...2 good ideas you had there. Wrist pin would be a definite possibility by how this noise acts.
I have tried making the noise while under the hood and it won't rattle. It seems to need just a little load to make the noise...that's why my guess was piston the area. Thanks again !

[Brads70]

Any chance it's a detonation issue, like maybe adjust the vacuum advance just a wee bit?

[71violetcuda]

Nah don't think so,never had an engine knock under this type of very light load just almost coasting down the highway.Good thought tho...might mess with the timing now that u mention it,just for ***** and giggles

[B5fourspeed]

Could you pull off 1 plug wire at a time rev it up and see if it doesn't make the noise on a certain cylinder.

[MoparLeo]

Doing the plug wire check is a good way to isolate a cylinder if that ius the problem.
 You need to be under the hood as recommended bdfore to see where the noise comes from. Top, bottom, front, back. That will narrow it down a lot. Cracked or loose flexplate as well.

[dodj]

Any chance it's a detonation issue, like maybe adjust the vacuum advance just a wee bit?

Just to be sure I'd back off the timing a bit and see if it changes.

[B5fourspeed]

Did you ever find the source of the engine noise?

[71violetcuda]

Did you ever find the source of the engine noise?

Not yet..busy with other stuff. I will let u know what I find

[torredcuda]

Backing off timing is easy and will eliminate detonation as a cause, also pull a couple plugs and check for color and any metal particle residue which could also be a sign of detonation.