Startup wrapping (knocking)

8825 Views 10 Replies 4 Participants Last post by NickD, Mar 11, 2016

Chevycruzeclark

Discussion Starter · Mar 9, 2016

I've had this issue for a very long time. I own a 2011 Chevy Cruze Lt In the mornings or when the vehicle has sat for a period of time the engine knocks for a short period of time. I brought it to the dealer and they told me it's normal. Well what's gotten my attention was this morning it knocked so badly the engine stalled. Almost sounded like it seized up. But I waited a couple of minutes and it started right up quiet. I don't know if this is something I should be worried about

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NickD

· #2 · Mar 9, 2016

A knock or a click? Inside the engine, knocks are reserved for connecting rod bearings, they don't go away. A click is like a collapsed hydraulic valve lifter, putting your ear against the camshaft cover, would be the loudest. Trained ear picks this up quickly. As the engine warms up, this click will go away for a lifter that is not stuck that bad.

Adding 4 ounces of Seafoam to your engine oil may clear this up, they don't get better, but get worse. Usually not a problem if you are using a dexos approved oil, if you get your oil changed professionally, use this word with a grin on my face, don't know what they are using.

Is this normal? No, sign of a dirty engine. New valve is only around five bucks, but the labor will kill you.

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jblackburn

· #3 · Mar 9, 2016

Piston slap (a light metallic tapping) is normal for an engine with some mileage on it.

If it stalled on a cold start, something else is going on and it may have been idling way too low before it switched to closed loop mode - maybe a vacuum leak.

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NickD

· #4 · Mar 10, 2016

Ha, a piston slap is normal? Apparently, we went to different schools.

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jblackburn

· #5 · Mar 10, 2016 (Edited)

Yes. It's normal.

Pistons are made from different metals than they were in 1930, and they have extremely short skirts. This car uses hypereutectic pistons that expand as the engine that warms up. From the factory, they had a coating to quiet them down that now is worn off.

You see the same thing with the GM 5.3, Toyota 3.5 (forged - they make a heck of a racket when cold), and various other engines on the market today.

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NickD

· #6 · Mar 10, 2016

Not a coating for a piston, but an alloy where silicon is added to that aluminum, copper, magnesium as part of the alloy essentially to limit expansion not to increase it.

Correct term is a eutectic piston, hypereutectic means over eutectic that is no good as it makes the piston too brittle and would crack like a wine glass if a bit too much pressure is applied. Typically only about 10% of silicon is considered safe.

By controlling expansion, the piston will last a lot longer, is an American invention, but the stockholders and marketing wouldn't let us use it, back in the 70's would add a whopping 15 cents to the cost of each piston.

And engines that lasted longer, owners would keep vehicles longer reducing future sales. No BS here, did you work in automotive the most of your life? Were you in these meetings?

In the 70's, the Japanese vehicles were the laughing stock in the automotive world and quickly learned people wanted quality, they did not invent the eutectic piston, we did, but they were the first to use it for the so-called 200K mile engines. Really cut into the domestic market so forced domestics to use eutectic pistons as well, and this is the only reason.

But their quality really went down when they devalued the buck, the Chinese sure learned from this. But still getting by with terrible quality.

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jblackburn

· #7 · Mar 10, 2016 (Edited)

NickD said:
Not a coating for a piston, but an alloy where silicon is added to that aluminum, copper, magnesium as part of the alloy essentially to limit expansion not to increase it.

Correct term is a eutectic piston, hypereutectic means over eutectic that is no good as it makes the piston too brittle and would crack like a wine glass if a bit too much pressure is applied. Typically only about 10% of silicon is considered safe.

By controlling expansion, the piston will last a lot longer, is an American invention, but the stockholders and marketing wouldn't let us use it, back in the 70's would add a whopping 15 cents to the cost of each piston.

And engines that lasted longer, owners would keep vehicles longer reducing future sales. No BS here, did you work in automotive the most of your life? Were you in these meetings?

In the 70's, the Japanese vehicles were the laughing stock in the automotive world and quickly learned people wanted quality, they did not invent the eutectic piston, we did, but they were the first to use it for the so-called 200K mile engines. Really cut into the domestic market so forced domestics to use eutectic pistons as well, and this is the only reason.

But their quality really went down when they devalued the buck, the Chinese sure learned from this. But still getting by with terrible quality.

The connecting rods are forged steel and the lightweight, hypereutectic pistons are designed with a thicker crown area and a unique ring pack to withstand the boost pressure and heat generated by the turbo system.

Read more: GM 1.4 Liter Turbo I4 Ecotec LUJ & LUV Engine Info, Power, Specs, Wiki | GM Authority

https://en.wikipedia.org/wiki/Hypereutectic_piston

The skirts are coated with a low friction coating from the factory that wears off over the course of 30-50K or so. It serves mostly to quiet them down on cold starts during the initial warranty period, but they also reduce friction when the piston changes directions.

Piston slap has nothing to do with the life of the engine. It will continue to tap happily away in the mornings and run quietly when warm. I think that's what you were rambling about, anyway.

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jblackburn

· #8 · Mar 10, 2016

Oh yeah, we have fancy diamond rings too.

http://media.gm.com/media/us/en/che...ges/news/us/en/2012/Jul/0710_sonic-cruze.html

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NickD

· #9 · Mar 10, 2016

I think that's what you were rambling about, anyway.

This is not a nice thing to say!

Cold piston to bore tolerance is the Cruze 1.4 L is 0.001 inches, absolute maximum is 0.002 inches, older engines had a maximum of 0.008-0.012 inches, difficult to realize piston slap, and that is what we are talking about with the super tight specifications of these very close piston to bore clearance in the 1.4L engine.

Eutectic pistons use a maximum of 12% silicon, and is used to prevent piston expansion with temperature, hypereutechic pistons are defined as anything about 12%, even less expansion. Cruze does not give this specification, typical maximum is 16%.

Really doubt if the OP is having piston slap, and more like a slight slap noise than a clunk.

Clunk with a cold engine and be caused by a misfire, 85% of the exhaust is H2O if a piston is down after the firing stroke, moisture is left that can foul the spark plug, when it does fire, can hear a clunk. Also in the belt drivetrain with limited lubricated ball bearings where the grease is already dried up and frozen that will produce a clunk like sound, eases up when the bearings heat up.

Just trying to answer the posters question, give me a minute to hear it in person, and will tell you exactly what the problem is.

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Robby

· #10 · Mar 11, 2016

Old engine designs with large piston to bore clearances used long skirted pistons that had the wrist pin bores slightly off centerline.
This slight off centering forced the piston to hold its skirt against the cylinder wall as it expanded to the bore......kept sloppy piston clearances quiet.

For the most part, in a quest for a combination of fuel mileage and reduced cold blow by, as well as the tightly controlled expansion rate of the new piston alloys, the skirts have essentially disappeared to reduce drag and the pin bores are now at actual centerline.

As a result, it is not uncommon to hear the piston "slap" what remains of its skirts as it grows to meet the bore.
As long as it settles down in the one to two minute range it is considered normal/acceptable/harmless.

You guys should hear the LS-1 in my Camaro.....4500 (yes, four thousand five hundred) miles and when cold sounds like (IMO) an older diesel........for almost three minutes......and then, it will quiet just a touch and within 15 seconds become mechanically silent.

Every cold start since it came off the truck.

Rob

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NickD

· #11 · Mar 11, 2016

88 Supra uses solid lifters where the gap is set with shims. With all 24 valves, set the gap to the maximum clearance. Wanted to make darn sure all 24 valves were closing, only talking about a +/- 0.0015 inch tolerance between minimum and maximum.

But as a consequence, hear a whole bunch of light clicks when I start it up, but quiet when it warms up.

Ha, Robby, had to bring up wrist pins, remember when these had retainer rings to hold them in? Switched to an interference fit and had to use a hydraulic press to get them out, one slip and would wreck the piston, anything to save two cents. Good question as to what the Cruze us using. Looks like an interference fit where the piston comes with the wrist pin.

As usual, an OP comes along with one post, probably would never see him again, us compulsive posters get into a debate. ha, we should get together and have counseling.

Good thing we are not talking about what kind of motor oil to use, thread would be 80 pages long.

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