Intro and Valve Adjustment Help

[rotor_kin]

Hello all,

I've been poking around the forum for a couple of months now, learning a ton about my new (to me) 71 c20 pickup with a 402 and TH400. As a quick backstory (jump to the last paragraph if you wanna skip the story and get to the goods)

Bought the truck in Christmas eve for a great price. Drove the truck same day back to fort worth and changed the oil, checked fluids, and got some new tires. The next week I drove it the 200 miles down to Austin and the truck ran like a top and didn't skip a beat, I was so proud of it! Since then I've been fixing small things here and there like carrier bearing, heater fan, etc...

As of late I have been digging into one issue thats been lingering which is a pretty rough idle. The idle mix screws seem to make little difference, and turning the idle speed below about 900rpm ends up stalling out every once in a while at a traffic light. The truck runs well outside of this, however I am also not quite sure the secondaries are opening on the quadrajet.

Long story short, now is a perfect time for me to learn more about this truck and get it going strong as I have another car I can use if any fixes cause major downtime. I called cliff of cliffshighperformance to get a rebuild kit and some advice, and he told me the carb on my truck after giving him the carb stamp, was from a 78 chevy and seemed like a californian emissions carb (the carb number really had him stumped, said he hadn't heard that number before?). So I am working with him on getting the carb setup to run well with the 402. While I am at it i figured I would double check the valve lash as I am not sure what the PO had done mechanically. This is where I run into my current conundrum:

Looking at the lifters it appears as though they are hydraulic. They have the small wire type clip, and none of the valves had any gap between the roller and the valve stem. However none of the valves also were very tight, all of the push rods would rotate pretty freely. So it seems like the valves were adjusted to be snug and left there. The one thing that seems weird is when I go to adjust the #1 intake valve (as if it were hydraulic) I see no movement in the pushrod after snugging the rocker bolt, and clearly see the valve spring compress after about a 1/2 turn past snug. I wanted to get the advice of the forum before I went adjusting the valve lash one way or the other to make sure I'm not crazy. I've attached a pic of the lifter looking through a fancy bore scope my buddies got me for xmas.

Any advice would help. I am new to american cars, but have worked on a few older japanese and european cars, and a boat load of 60's and 70's motorcycles so I have a decent mechanical compass. I know that once hydraulic lifters are set they rarely need adjustment, but mostly I am interested in learning how to do it and learning more about my new toy. Thanks

[chevytruckluver]

Welcome to the forum from Ft Worth.
You will most likely hear from several members that have experience in all aspects of these trucks and your big block.
As I read your post and you asking about valve adjustments, I hope you have not made adjustments to the rockers before you understand the correct procedure. (You really have no need to view the lifter with your bore camera) If you over tighten the rocker arm nut you may cause damage to your valve train or possibly your engine.
I do see that someone has installed aftermarket roller tip rocker arms and would have made adjustments at that time. That would cause me to ask a few questions.
Why do you think you need to make adjustments? are the rockers making noise?
Do you know anything else about the engine?
have any other parts been replaced? cam and lifters maybe?
Give us more information and we can give you a better perspective on what direction you might want to go next

[rotor_kin]

The rockers on the driver side were making a bit of noise, but mostly I was curious to learn the procedure and also ensure that the valves were set properly by the PO. I noticed the roller rockers, along with some other promising aspects of the truck to make me believe the PO knew what he was doing (fresh grease on all the suspension components). The truck is running well outside of the rough idle, so if all signs point toward not messing with the valves then that is fair I was following the EOIC procedure for valve adjustment, and only played with cylinder 1 intake valve.

Unfortunately I don't know much more about the engine. Engine stamp is to326clb, which nasty z28 says is a 71-72 402 originally for a chevelle or monte carlo. I've been trying to figure out how to identify the cam without pulling it out, if you have any tips there that would be great. Thanks for the reply!

[Lattimer]

Only way to really ID the cam is either pull it or it the PO had info on it. Engine definitely could have other goodies in it, so if you get your carb issues fixed it might be a nice runner.

Are you sure the noise was from the valves? A small exhaust leak can sound similar.

You definitely have hydraulic lifters, so they should be set at zero lash plus 1/2 turn (or whatever it is for big blocks--I'm a small block guy) following the procedure to make sure you are on the cam base circle when you do the adjustment.

Stalling issue could be the carb itself, could be a vacuum leak, etc. Have you checked your timing? Lots of issues caused by improper ignition timing.

[geezer#99]

Here's a wiki on adjusting your valves.
http://www.crankshaftcoalition.com/w...raulic_lifters

Your mix screws not reacting on your carb means you have the throttle set too far open at idle and you're idling on the power circuit. The cure is in your initial timing. You need to set it at 12 to 14 degrees and hook your vac advance to a manifold port. Your idle will increase because of the higher initial. Turn the idle on your carb down and the mix screws should start working. Set your idle at 650 rpm. If you idle at 850 or higher then you're likely kicking in the mechanical timing in the dizzy.
When I set my lifters I bring them all to zero lash by wiggling the rods and then shut the motor down and turn them 1/4 more. That way the plunger in the lifter will compress and the spring/valve won't move.

[rotor_kin]

Geezer#99 that link is extremely reassuring. I was very nervous about seeing the valve open when I turned past zero lash, but the video in the link states this is normal and the valve should return to the closed position momentarily. I'll set the valve lash tomorrow and throw everything back together to start playing with the carb. Thanks for all the help so far, this forum is truly invaluable.

I set the timing to 12* advanced pretty soon after I got the truck down to Austin. I'm not positive that my vacuum advance is connected to manifold vacuum, so I will try this and reset timing. I am definitely idling close to 900 rpm right now, so I'll drop that down and see if I can then make the proper mixture adjustment. One hopefully not dumb question:

When I go from park to reverse/drive my idle typically drops about 200rpm, so do you guys set idle speed and adjust mixture while in gear? I might have to make a neighbor friend to jam on the brakes while I turn some screws under the hood, I don't trust my dog enough.

[geezer#99]

Get the timing up first and the vac advance to manifold port, adjust your mix screws and get the idle down around 700 to 750 in park.
You can't always trust a neighbour or the mother in law not to panic while holding the truck in gear. I used a power pole once or twice. Hooked a chain to the rear bumper. Sometimes you gotta 'Mcgyver it'!!