clickity clack, my engine goes smack

[kjc292]

hey new to the site. I've always wanted to own an older chevy truck and a few months ago I finally made the purchase. I bought a 1978 c20 with a 292 and 3speed granny low. I almost passed on it but the 292 sold me. When i bought the truck it ran fine, no noise really, just a bad throwout bearing. well within the past two weeks a very pronounced clacking noise has came from what i believe to the upper block. when its in low idle its pretty much not there, but when accelerating and cruising(with foot on gas) the sound is there. now I've already tryed to tighten the lifters but no luck. I'm thinking a bent lifter. Not really leaning towards a bad piston or anything in the lower block just because its not a low knock. any ideas or what I should do?

[INSIDIOUS '86]

May be just a bad exhaust gasket really bad lifters clack no matter the rpm
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[kjc292]

Hey thanks for the reply. I talked to my boss when I got to work today. He said the same thing. Why he believes its an exhaust is I have a 2929 and the noise is a lot louder on the manifold side. Tomorrow I plan on lock fighting all the manifold bolts and replacing the seal from exh. manifold to pipe. I just had the manifolds machined about two months ago. Hoping I won't need to again. Also yes I had them machined while bolted together.
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[geezer#99]

Make sure the washers on the studs that hold the intake and exhaust on to the head are making square/flat contact . If you mix them up you'll get leaks.

[lilpoindexter]

I used some expensive ass Nord-Lock washers I got from McMaster Carr on the troublesome exhaust manifold on my integrated head 250...they worked, they were worth it. Your 292 doesn't have the same crappy design, but it's something to think about.

[kjc292]

Geezer99. When I had the manifolds machined I forgot to put the studs right back were they came from...yeah it was stupid. I also forgot to lock tight the studs. I'm thinking I need new hardware since the nut and lock washer were rusted in place. I'll look into those washers. I'm just curious as to why they never made an I6 with intake on the driver side and exhaust on the passenger side. It seems like everything would bolt down better and have better air flow in/out.
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[BigBlocksRule]

You're referring to a "cross flow" engine. Chevy didn't make one, but Ford did and used it to kick Chevy's inline 6's butt.

[85Bowtie]

Well, you can't "bend" a lifter. A pushrod, yes.

Do you know how much pre-load is on the lifters?

You might have weak springs inside the lifters, causing a delay in the spring back and you're getting a tapping sound.

Or, you could just have worn cam lobes creating excessive clearance in your valvetrain.

[Telecasterjoey]

Wild guess but make sure your timing isn't too advanced.
You said under load it knocks, spark knock can sound pretty bad.
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[85Bowtie]

Originally Posted by Telecasterjoey

Wild guess but make sure your timing isn't too advanced.
You said under load it knocks, spark knock can sound pretty bad.
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Didn't think about that, good advice.

[kjc292]

After reading all your suggestions it's hard to narrow it down. I need to check my spark plugs still and also need to time my truck. It seems that it isn't running smoothly. By that I mean it seems to surge in a sense when taking off in first. Almost as if air flow is being restricted then opens up then restricted then opens up... It's like a slug when starting out. I'm assuming its because its a low rpm motor. Monday I'm going to get all my manifold bolts torqued down, check the spark plugs. Then study up on how to time an engine. Thanks for all suggestions. Should make troubleshooting a little easier. The cam lobe being wore down is great possibility. Engine hasn't been rebuilt and is the original. It's hard to really open up the engine when you live in a duplex with no garage and your work space is whatever parking spot you can find
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[kjc292]

Well it my truck out back together enough to hear it run, and still making that noise. It's sounds like its only coming from the drivers side. Going to check spark plugs then read up on timing it. Checked the gasket, it was fine, replaced all hardware for exhaust manifolds(air intake too) got a new gasket for the flange... I'm thinking it might be a bad cam. But not looking forward to doing the work in a street out in front of my house.
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[geezer#99]

Maybe you've got a rocker stud pulling out. Pull the valve cover off and put a straight edge across the top of the studs. A pulled one will show up easily.

[kjc292]

pulled the valve cover, put the straight edge to them and didnt see anything wrong. checked my spark plugs, the guy who the truck must of changed them right before he sold the truck to me, the looked new. one spark plug did have an excessive amount of oil on it though out of the number two cylinder.

[geezer#99]

So now check your timing. Easiest timing check is pull the vac hose off the distributor and plug it.
Take it for a longish drive to check.
Could be detonation like Telecasterjoey said.

[kjc292]

alright, i tryed everything im capable of. thinking about taking it to local mechanic down the street. guy at work says hes cheap and does good work. if anything he might be able to tell me exactly what it is. its frustrating its keeping me from driving it. i know its not good to keep driving it. if its a cracked exhaust manifold ill probably switch over to headers... if not and i need to take the head off and get whatever fixed i have a head off a 1967 292 thats lumped ported. will probably get that tanked, machined flat and add some few HP. Also in the middle of redoing my interior. Getting black carpet, painting panels black and getting a woodgrain dash bezel.