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... the valve train is all normal in its operation? the throw of rocker arms etc
y'know, funny you should mention that. I've only rebuilt two cars, neither of them had any trouble to start with. Done my fair share of troubleshooting but it's been 20 years since I've opened up an engine. So I was just thinking that I really could have done a better job of troubleshooting before opening things up.
No, didn't think to spin it when I had the covers off. TBH, I had to go get a remote starter to get the trans disconnected. I did think to look at the valves first but all I did was to wiggle the rods, bump the starter a couple times to cycle it through the stages, so I know that at least the valves seem to be adjusted correctly at both intake and exhaust throughout the cycle. There is quite a bit of wear on the rod guides, to the point that the metal is a little knurled on a few.
TBH I don't know what I could possibly find when I take off the manifold. I mean, what could make that noise that I would see it then? My hope is that I'll find something literally loose, flopping around. I will put the pistons through their cycles and hit them with a rubber hammer just past TDC (to see if there's slop in the bearings); but even then, wouldn't that be a consistent knock? I'm also hoping that maybe it's something like oil pump, but then I've never opened up a Chevy engine so don't know what I'm going to find. Is the fuel pump electronic or mechanical?
Anyways, I'll get back to it Monday and I'll look at the valves as you suggested. Will let you know.
There should not be wear like you describe on push rod guide plates. That coupled with intermittent noise would make me want to look for a bent push rod and possibly a loose push rod guide plate/rocker. Is this a roller cam/lifter engine? Stock rocker arms? Maybe I missed that detail. I still think your noise is top end related. Any galling on the pushrods that run through the worn guide plates?
Another real long shot, some cars have experienced their Harmonic Balancer separating from hub. Normally they just loose timing alignment. Could you be the Extreme and it's now banging around knocking against timing cover.
Finally got the intake manifold off! Rods are straight and tight, lifters seem tight as well, valves seem ok. Anyone see something I don't? At this point I don't think it's a top-end problem.
I'm a bit reluctant to remove the heads (sure is tight in this C4 engine bay). Or am I overthinking it?
I could go back to looking at the bottom end. When I removed the oil pan, I didn't remove the oil pickup; I just turned the engine a few times and visually inspected (no metal flakes, no scoring on cylinders, rods seemed tight side-to-side, no weird noises). I'm wondering if I should go back to that and try tapping on the rod caps with a hammer when they pass BDC (to see if they shift at all.)
I'm just wondering if there's anything else I can do without pulling the engine. If I pull the engine then that takes me down the path of what mods I can/should perform in addition to fixing whatever is broken (i.e. better top end, cam) but I'm not ready for that. If I go that route then I'll start a new thread, don't want to divert this one.
But the question is, what's my next step to discover what this noise could be, without removing the engine?
P.S. apologies to anyone if you've suggested something and I didn't respond; please thump me upside the head and remind me if that's the case..
Keep everything in order.... pull all the pushrods and lifters. Roll all the pushrods on a really flat/smooth surface to make sure they aren't bent and inspect all the lifters.
Get a cheap borescope that works with your phone/tablet and inspect the cam lobes through the lifter bore and the cylinders/piston tops through the spark plug holes.
The chirping is indicative of a main or rod bearings or possibly a failed lifter roller.
It is hard to tell from the video but a common diagnosis technique with the sound is..... Does it sound like a screwdriver tapping the block or do some of the knocks sound like you are striking the block with a hammer?
Taps and ticks with a screwdriver = top end noise. Hammer strikes are generally going to be a rod or main bearing.
Also, have you cut open the oil filter or dumped it out to see if there is any metal in it?
@Krusty84 thanks very much, I wouldn’t have thought to do any of that. The sound is definitely not ticks; more the sound of solid metal on metal. I need to get a scope. Will follow your recommendations.
Removed and checked the rods and lifters. Nothing seems wrong; all are straight, no scoring, everything's tight and smooth. To be fair to the guy that sold it, the gunk could be from parts of the engine that were not cleaned when it was "rebuilt", so it may just be that whoever "rebuilt" it did the minimum necessary and didn't properly clean the block. Regardless, there's some small amount of buildup on the sides of the lifters but nothing that concerns me.
I get my scope tomorrow (ordered this scope) so this afternoon I'm removing plugs. Got #1 remove and there's dielectric grease on it and color looks good; dry, no carbon buildup, burning, or oil. On to the other 7... https://a.co/d/676ALdv
A couple concern me.
#7 looked like it had a chip but on closer look I don't think so.
#5 is really built up with carbon. Might also be oily but not sure how to tell.
#8 has oil on the outside of the plug; assuming an oil cover leak. But the inside looks ok.
Just read the whole thread. Did you check the catalytic converter on that side? I saw someone else mentioned that as well. My 96 has a cat on each side and one down on the bottom. The left one came apart one day while driving down the road. Sounded like rod bolts in the oil pan! I was horrified! I had just rebuilt the motor myself a few months prior. The reason I think it could be that is because the sound is intermittent. That sqeaking could be an exhaust pipe rubbing on something or cracked but a crack would be a ticking noise. My 2016 Silverado has a bad exhaust hanger and when you idle while in drive there is faint squeak. Metal on metal rubbing and it's very annoying and it only happens from time to time.
I would also advise cutting open the oil filter. If you find sludge in there or metal shavings between your fingers when you test the oil it would be time for a rebuild anyway. I mean who doesn't like rebuilding engines?
Just read the whole thread. Did you check the catalytic converter on that side?…?
@Furias15x How would I check a cat? Also, the oild looks good (I didn’t keep the filter, hadn’t thought to tear it open). Oil felt and smelled old, but not burned nor did it have any sparkles.
The Converters sometimes break up inside the pipes if they are killed to the point of rattling/knocking can be tested with a rubber mallet, you can give them a smack but I think you're problem is deeper
Appears to me that the engine needs a rebuild. It is just a SBC a rebuild should not really cost that much, since it appears to me you are capable to putting it together. I bet you could do the whole thing for less then $2000 and it would work great,
@bjankuski I believe you’re right. I used my new scope to look at the cylinders and they all have no scoring and no nicks on the pistons. I suppose I could pull the pan and continue inspecting under the car, but I think that considering the little shortcuts the previous guy took, my smartest move is to rebuild it myself. At least then I’ll know it was done right.
09-25-2022, 08:29 AM
