Hey any actual Chevy employed mechanics read here?

I've got a 2003 LL8 that's developed a knock. Sounds like one piston. Knocks for 1 second when cold. Not at all until warmed up to operating temperature. Never run on low oil pressure but the owner states he did run it a few quarts low on oil. These hold 7 quarts by the way. Owner added 3 quarts but maintains a diligent viewer of gauges and at no time ran lower than 45 PSI at idle. Owner drives the vehicle like a granny because of poor gas mileage. Knock developed at around 80,070 miles and has not gotten worse. The engine idles smoothly performance is not effected. No smoke out the tailpipe.

My backyard mechanic interpretation is a wrist pin bearing or rod bearing around the journal is out of tolerance. If you accelerate there is minimal noise until you back off the throttle slightly and minimize torque then the knock increases until drivetrain drag puts torque back on the crank and the knock then diminishes.

My proposed repair is to replace all 6 pistons sets from the crank up including rings.

Question is; is their a decent publication that will show me nut and bolt torque specification? I have the tools and the experience in pushrod type

4 cyl motors to do this work but am a bit concerned of the DOHC and VVT. Plus all aluminum construction. Also if the rings are new will I have to score the cylinders so the new rings seat properly? I do intend to mic the crank journals to see if they are in-spec.

Any advice will be appreciated.

Reply to
A. Baum
Loading thread data ...

If it's only a slight knock in one hole I would drop the pan and see if it's just a bearing. If so you could just replace the mains/rods and be done in a LOT less time.

If you intend to replace the pistons I would suggest going the rest of the way and boring to the first oversize and do an overhaul on the rest. check all the valves,stem wear and seals. Basically do a full rebuild if you're going to tear it down anyway. Better in the long run.

As for torque specs those are easy. Lot's of places to get them.

Oh and FYI just because the gauge "never dropped below 45 psi" doesn't mean that the low oil didn't cause the problem. I would bet that the low oil allowed the crank to be starved for oil flow and caused the bearing damage.

Reply to
Steve W.

Thanks for the reply. I had the same question in my mind too. Where does the oil pressure sensor read from? If it's top end then hell yes it's possible for the bottom to starve for oil. Here again is the scenario shortened for brevity. In the morning, after the motor first starts (usually within 5 revolutions, there are 5 knocks then quiet. During the period before motor reaches say 4/5ths operating temp, no knock at all at at normal acceleration through the gear rang - up to about 3 grand on the tach. Once the motor reaches op temp then the knock develops. less with acceleration torque but tip back the throttle and the knock increases.

I wouldn't expect a temporary starve for oil in the bottom to send a rod bearing out of tolerance. But I suppose it can happen. And it's hard to tell if it's a rod bearing or wrist pin. But you are right. If I'm going to rebuild, I might as well take my chances first and replace the rod bearings at least. That won't take much time. If that's it problem solved. I doubt if it is a main bearing. The LL8 had at least 4 or 5 mains but I haven't researched it enough yet to know exactly the count. The motor has a good history of oil changes too so that's one thing. I drove it today and the knock was much less than when it was originally presented to me. I dumped a quart of STP in it a week ago to help keep the oil viscosity up when it warmed and it did quiet down the motor by maybe 50%.

Anyway, the owner doesn't drive it more than 5 miles a day and never on the interstate. I've got a Jeep 4cyl I'm doing an overhaul on now so garage space is limited.

Reply to
A. Baum

Sensor pulls oil from the top of the filter housing so it reads the oil pressure right out of the pump. That doesn't mean that the same oil pressure is through the engine. Only takes a small chunk of crap to block an oil passage long enough to cause problems.

That description sounds like a rod bearing. Wrist pin would be a double tap sound as the piston changes direction, Rod bearing would be a single knock as the engine fires. You could localize it by pulling off plug wires. The one for the bad cylinder will usually stop the knock when pulled.

With the way bearings are made today it doesn't take a lot through them out enough to make noise.

Reply to
Steve W.

I have a friend who swears by Castrol. Before I drop the pan I'm going to change the oil anf filter. It seems that something is on the verge of being out of tolerance and as i increase the oil viscosity the knock diminishes. It's non-existent when cold maybe for the first 5 minutes of driving. But this is an all aluminum IL6 so it heats up really quick. I can go a couple miles with no knock at any rpm from a cold start. Except the first few revolutions when it's fist started before the oil pressure comes up. Funny though, when it's warm at operating temp, If I start it there is no knock. The LL8 IL6 is easy enough to work on from the bottom. Don't care to pull the head with the DOHC and VVT. But I'll do what needs to be done. The vehicle is in primo condition otherwise for 81k miles on it and 8 years old. It's soil change record was kept up well. Valvoline synthetic blend ever 4k miles. Never hauled a trailer, not been off road, been driven to Florida and back once, 2300 miles. I think now if it has a mechanical problem it's a rod bearing. I've rebuilt a 750 Honda CB7-F with an in-line DOHC 4cyl. Split the case, bored, new top/bottom end. Took me awhile but I can't imagine much difference in an LL8 except 2 more cyl holes.

Reply to
A. Baum

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.