'90s Chevy truck elusive engine knock. Rod/Main bearings, or what?

I've been running T5 15w-40 for a number of years ( and Delo before that). For this repair, I threw in some Valvoline 10w30 High Mileage and Fram PH5 as they were somewhat inexpensive. Will probably change again by next weekend, and may just stay with the Valvoline HM for a few months. I'm guessing there could be a few metal flakes/fragments in there that hopefully will get flushed out. This truck is not a daily driver, just for occasional household chores now.
 
Well, this isn't sounding good. Have driven the truck about 12-14 miles with a couple short test trips, no knocking at all. Put in a new AC Delco oil pressure sensor (previous unit was a little erratic), and changed oil and filter today. After 5 miles my check engine light comes on, and truck seemed to be weak on power. So, I turned around and get home and there was burning smoke smell coming from around the engine (possibly around the valve covers). It is throwing a Code 43, which may indicate a spark timing issue? Anyway, what do you guys think? Is there any possibility this is related to the valve adjustments?
 
DuckRyder said:

GM Code 43 Electronic Spark Control Fault - FreeAutoMechanic

Trouble Code 43 indicates that there may be a malfunction in the Electronic Spark Control (ESC) circuit. ESC is used to sense spark knock (pinging) and
www.freeautomechanic.com www.freeautomechanic.com

Been a long time since i hooked up a tech I - id start by checking connections, particularly around the sensor you changed.
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Holy crap! When installing the oil sensor I may have moved the distributor. Apparently I didn't tighten the holddown/bolt enough when I set the timing. Could kick myself in the ...
 
Many years ago, I changed the hydraulic lifters in a very tired old 307 with 160,000 miles on it. I was working at a friend's house, and we followed the procedure in a big hardcover Chilton's book (Domestic Cars 1968 - 1976, or something like that).

I think we turned the crank pulley over to TDC with the rotor pointing to #1 and then tightened down the #1 rocker arm. Then we went to #8, then #4, and so on, through the entire firing order (1-8-4-3-6-5-7-2).

How tight? The Chilton's said to tighten until the lash was removed from the rocker arm. I interpreted that to mean until I could not spin the rocker arm with a thumb and forefinger.

We tried to start the engine and it sounded like it was being tortured, cranking very slowly and reluctantly.

We broke for supper, and while eating I had a bit of an epiphany. Perhaps "no lash" meant no up-and-down play between the push rod and the rocker arm, rather than so tight that I couldn't rotate the push rod.

We redid the job, and the engine started easily and ran perfectly. Phew!

I still have the worn-through lifter from that day.
 
Might be a good time to change the oil too. Even though it has very few miles on it you've probably dumped a bunch of fuel into the oil with the distributor giving you trouble. Just good cheap dino oil for now. Do another oil cheap change at 500 miles and at 1,000 miles switch to your favorite high quality oil.

I'd just want to get any and all junk, gas, moisture, etc out of the oil.

Also might not be a bad idea to readjust the valve lash after its run for awhile just to make sure the adjustment is done when the lifters are fully pumped up.
 
Just Dropped In said:
Main bearing # 1 was in rough shape, looks like a vinyl record. Rod bearings 1&2 had some excessive wear too. I assume these issues were causing the knock. Haven't remove all of the bearings yet, those in the middle area seem to be ok (will still replace). I've not found anything else that would be contributing to a knock. I'm still poking around in there, so might find something else?
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Those are farthest away from the oil pump. Sounds like it got ran low on oil
 
Chris142 said:
Those are farthest away from the oil pump. Sounds like it got ran low on oil
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I'm puzzled why that bearing had so much wear. The truck never burned any oil between OCI's, and I always kept an eye on oil level. As a work truck, it did its fair share of hauling & pulling over the years.
 
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Lawnman23 said:
Now that you have got some miles on it, how does it sound/feel mechanically? Any signs of knocking still there or silent?
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Haven't heard any knocking at all. Engine sounds a little more robust. There's a slight tick on one of the LH valves I might have to tweak in a few days.
 
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Bad news. Was a few miles into a 20 mile round trip (with my wife following), and the knock returned in about 5 miles. This was with around 35 miles of total driving since the repair. So, I'm back to square one. I've been dealing with this issue for 3 months now, and it looks like the engine is going to have to come out after all.
 
That’s disappointing, I think at this point assuming you have the resources I would put a new GM engine in it. If you don’t have to return it you can probably sell the core to a hot rodder for something.
 
Lawnman: went back to 10w-30 for this repair, was using t5 15w-40.

DuckRyder: Weighing options right now.

Just went for 20+ mile trip. It's sounding slightly normal again, possibly due to belt sizes. I have three serpentine belts, the tightest of the three is a Gates (and stock size), may be putting too much stress on the damper/pulley. The second belt (Goodyear) has less tension, and the knock goes away. That's the one I put back on. The third belt is a Continental, and is a little longer, and no knock with it (but that belt is a little too loose I think). So, I'm going to have to get the right belt size worked out, and see how things go. In any case, I'm just going to keep driving it and see how things go. I was a little concerned about the #1&#2 connecting rods wear (front-to-back).

Not sure if I want to put another engine in it, or do a rebuild. Right now I've spent the entire summer working on it, and I'm ready for a break!
 
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Just Dropped In said:
Lawnman: went back to 10w-30 for this repair, was using t5 15w-40.

DuckRyder: Weighing options right now.

Just went for 20+ mile trip. It's sounding normal again, possibly due to belt sizes. I have three serpentine belts, the tightest of the three is a Gates (and stock size), may be putting too much stress on the damper/pulley. The second belt (Goodyear) has less tension, and the knock goes away. That's the one I put back on. The third belt is a Continental, and is a little longer, and no knock with it (but that belt is a little too loose I think). So, I'm going to have to get the right belt size worked out, and see how things go. In any case, I'm just going to keep driving it and see how things go.

Not sure if I want to put another engine in it, or do a rebuild. Right now I've spent the entire summer working on it, and I'm ready for a break!
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The belt thing is interesting. As long as they are all the right PN for the application, the tensioner should keep the same amount of constant tension on them. You say the Gates is stock size, are you saying the Goodyear and Continental aren't stock lengths?
 
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