Help troubleshooting

[cali_surfer]

I posted this on Chevy Talk, but was wondering if you guys could help me out here. I seem to have a problem. Just recently my motor has developed what sounds to be a knocking noise at idle. My friend and I built the motor a few years ago, but I don't drive the truck that much (maybe has 10,000-20,000 miles on it). It was balanced, 10:1 pistons, Edelbrock aluminum 70cc heads, 234/234 cam, and I run 91 oct. gas all the time. This seemed to happen a few months ago after I installed aftermarket air conditioning on my truck, I don't know why. What I didn't like about the install was the bracket that holds the Sanden AC pump touches the tall valve covers I have, although it doesn't sound like that's making the noise at idle. The A/C pump also needs to be dealt with. I haven't touched the distributor other than setting initial timing. Its a cheapo HEI from one of the big autopart chain stores. Will too much advance at idle create a knocking sound? After idle the motor runs nice and smooth, but at idle it sounds like its rattling from the drivers side of the motor. Oil pressure is good, 30-35psi at idle, 40ish in normal driving range. I'm also going to replace the motor mounts, as they are what I suspect to be the originals (don't know why I didn't replace them when i built the motor). I'm just a little nervous hearing it rattling when i'm stopped at a traffic light or stop sign. Any suggestions or welcome

[1970 CST Short Wide]

Is it an Automatic? A cracked or broken flex plate will give a knock sounding almost like a rod

[cali_surfer]

Yep, it has a TH350 behind it

[cdowns]

also check that the balancer hasn't loosened uo and is wobbeling

[PanelDeland]

Forged pistons will sometimes give you a slight knock at idle.Some of the newer LS6(I think) do this and GM dealers say it's normal because of the forged pistons.

[cali_surfer]

Will check the balancer. I wish I had an LS6 in it!!! just a small block with hypereutectics in it

[Huck]

Get a piece of garden hose and stick one end at your ear (not in it!) and use the other end as a probe to try and isolate the sound to a location. That will help in indentifying what is make the noise. If you timing is kaka, you will get all sorts of noises. You might want to disconnect the belt to your A/C and back off the pump away from the valve cover to eliminate that --easy and quick. You can also loosen you dist and change you timing a bit to see if that helps---. Good luck---Huck

[68C15]

it is entirelly possible the noise is from inside the ac comp.. disconnect the 2 wires going to the comp. & if the noise goes away you will need a new one along with reciever-drier/accumulator (has desicant in it which absorbes humidity & does'nt let go no matter how much you suck it down). hope this helps, just seems odd it started after ac install.

[MACKL]

If you are still running a manual fuel pump, it can make a noise. Don't forget to listen to it with Stethoscope. (Works much better than a garden hose, but not as inventive.)

[cali_surfer]

Well, I just crawled underneath the truck to have a look. The bolts that hold the converter to the flexplate looked good, except for one. It feels like its going to strip, you know that feeling when its bottomed out but the resistance isn't what its supposed to be. That kinda sucks. Replacing the motor mounts, what the easiest way to do it with the motor still in the truck? Loosen the tranny mount almost all the way, unbolt the mount, jack it up, and then put on a new one? I would like to replace the mounts.

[Hooter]

You dont need to unbolt the tranny mount, just jack up the motor to take the weight off the motor mount and repair it, ya it is easy to strip the convertor bolts, they dont need that much torque, not sure what I would suggest with that other then maybe you have the wrong bolt in there, like a metric threads instead of standard, try another bolt

[cali_surfer]

I have ARP bolts in there rightnow. It just seemed loose, so I proceeded to tighten it more, but it isn't getting tight, so I stopped. Who knows, I hate stupid problems like this.