Piston Slap??? '97 Vortec GMC 5.7L

[OBE]

I didn't notice this for the first few months I drove it. But when Winter came it sounded like a rod knock. High pitched and hollow sounding just like so many rods bearings I've heard over the years.
On cold mornings I start it and it is quiet. In approx. 10 seconds I hear a knock developing. It gets louder and more pronounced and stays for about a minute or two. It then begins to lessen, until after about another minute or two, it's gone. Once it's warmed up it doesn't knock under any driving conditions and it doesn't knock when I start it up throughout the day. It only does it on the first startup of the day. Winter is over now, but the thing still does it on the first start of the day.

It's not like any knocking engine I've ever heard. It does not make a sound on the coldest morning until it runs for a little while, maybe 10 or 15 or 20 seconds. When it warms up, it's completely gone.

 

[OBE]

You can see photos of the truck in my Profile Album. It is low milage, well maintained, clean oil, I'm stumped.

 

[OBE]

I've been researching all over the web. I found a common problem (piston slap) in these motors discussed but none that talked about the "delayed" knock. I've read about an oil filter solution and I heard of a cracked flex plate.
I never heard it for the first three months I owned the truck and here's what I did: (could this have something to do with it?) Wanting to continue the excellent maintenance it had, I took it to have the oil changed. I don't know if it had a special oil filter which they would have discarded. To my surprise, the transmission went on it. I took it to a very reliable place and the guy knew exactly what had broken and rebuilt it. So, the trans has been out; could it be that there's something wrong with the flex plate?

 

[THEFERMANATOR]

5.7L VORTEC did not have piston slap problems, the LS VORTEC engines starting in 99(the 4.8L, 5.3L, 6.0L, and 8.1L) did have the piston slap problem. What teh 5.7L VORTEC engines did have was problems with luifters bleeding down and making an awful racket. I have had this happen with sealed power lifters, but never with MELLINGS. Not sure what lifters GM was using in 97, but it could have been sealed power. I know in 98 they went to MELLINGS from the factory. Running to thick of an oil will also cause this as the VORTEC engines are designed to work with thin oils as the oil passages in the block are pretty small IMO. 10W30 is as thick as you want to run in them, but 5W30 is reccomended. If it has many miles I would run the 10W30 oil.

 

[OBE]

5.7L VORTEC did not have piston slap problems, the LS VORTEC engines starting in 99(the 4.8L, 5.3L, 6.0L, and 8.1L) did have the piston slap problem. What teh 5.7L VORTEC engines did have was problems with luifters bleeding down and making an awful racket. I have had this happen with sealed power lifters, but never with MELLINGS. Not sure what lifters GM was using in 97, but it could have been sealed power. I know in 98 they went to MELLINGS from the factory. Running to thick of an oil will also cause this as the VORTEC engines are designed to work with thin oils as the oil passages in the block are pretty small IMO. 10W30 is as thick as you want to run in them, but 5W30 is reccomended. If it has many miles I would run the 10W30 oil.

Thanx for the reply Thefermanator: I watched and listened to some YouTube video and my truck sounds like a Rolls Royce compared to some of them junkers. I bought this truck because I could tell it was super clean and well-maintained. After owning it for awhile I have found that it is better than I had expected. It has no rust on the frame and the frame paint looks new. The thing that baffles me it that it makes no noise at all for a little while after starting on zero degree mornings. Very gradually a knocking sound develops to an easy to detect degree and after about a minute begins to quiet back down. The motor runs like a champ and I never "push" my trucks.

I never heard it until after I had the oil changed. The dip stick shows that the oil is the color of olive oil (the motor has been maintained that well) I have owned dozens of cars in my 69 years and I never blew a tranny on any of them (that's how gentle I am with vehicles) but this truck's tranny went on me. I will make sure I get an AC oil filter and "light" oil next time to see if that's the problem.

PS: I need some help with me 2000 K3500 Diesel truck too. I have a fuel tank problem I haven't been able to solve.

 

[WarWagon]

AC oil filters are nearly Fram "Orange cans of death" nowdays. They have the plastic inner frame and fiber endcaps. YUCK! Spend ~$10.00 and get a good oil filter that has a silicone anti drain back valve in it. Say a Mobile 1 filter. This can reduce startup clatter in some cases like anything with non-vertical oil filters. If you are 4x4 it should help as 2wd is vertical.

Do an oil sample. Cut the old filter open and see what is in it. And here is why:

A transmission failure can let the engine overspeed. Engine overspeed can stretch rod bolts and eat bearings fast. Look at aircraft piston engine procedures that vary by number of seconds the overspeed condition lasted including tear down, oil screen debris inspection, etc. In gear "loaded" RPM governors are different than Park/Neutral and grade braking no throttle RPM's. So a slipping transmission can freewheel the engine at throttle and no load. This results in a overspeed. My 1993 V6 gas engine ate the main bearings during a transmission failure (slipping till it burned up with lots of smoke) due to engine overspeed. It only had 86K on the clock. Fresh trans and the engine acts up... Didn't need an oil sample due to all the visible metal part numbers in the oil when the pan was dropped... No tach so I did not see the RPM on the freeway. The shop doing the engine told me the engine did not have an in gear RPM governor. True or not the theory is sound.

We tore the engine down due to a piston slap, but deeper, type of sound. It went away after warmup. It was ready to spin a bearing and lockup.

So your gut 'it sounds like this' may be correct.

The replacement engine had a rocker arm nut come loose and making a tick noise in the first 200 Miles. I wound up fixing it myself as they wanted 1000 miles on it before touching anything on it for warranty.

 

[btfarm]

Try Mobil1 10w30 synthetic for the next change. What you are describing is almost surely a lifters issue.

Sent from my SCH-I535

 

[THEFERMANATOR]

Definate;y sounds like a lifter to me as well. I've had decent luck with using some ATF in the oil(no more than a quart) to help loosen carbon deposits that can hang the baffle open and cause them to bleed down. Just make sure it is holding good oil pressure as I have also seen quite a few engines with over 200K miles have sludged up pickup tubes for the oil pump.

And i have never heard of a trans slipping causing an engine to fail. If your slipping the trans and somehow manage to push it through the rev limiter in the PCM, that is something. Not to mention your talking an engine that can rev to 6000 with no problems since a VORTEC doesn't really start to make much power until 3800 or so. They run these things in marine use at 5500 for hours on end in stock form at over 300HP, and they can frequently see over revs when the prop surfaces, yet they don't seem to have any engine problems. Sounds like you had other issues if you had engine trouble after trans trouble, or it was just worn out and coincedence. Not to mentio nthere is a HUGE difference between the OBD1 ECM in a 93 with crude engine controls to say the least, and the 256KB OBD2 black box controller a 97 has. It isn't a 512KB LS1 ECM like they went to in 01 for the old school engines, and 97 for the LS, but they do a pretty dang good job of protecting and alerting when theres an issue.

 

[OBE]

Definate;y sounds like a lifter to me as well. I've had decent luck with using some ATF in the oil(no more than a quart) to help loosen carbon deposits that can hang the baffle open and cause them to bleed down. Just make sure it is holding good oil pressure as I have also seen quite a few engines with over 200K miles have sludged up pickup tubes for the oil pump.
Thanx for the responses War Wagon & btfarm.

This motor was never over-reved. It made a funny sound as I pulled out onto the freeway and then drove 20 miles to my exit. When I pulled out of the tollbooth it made a loud crunch sound and wouldn't go. I gently continued to my mechanic and it wouldn't shift out of 2nd and no reverse. He gave me the broken piece: a geared device that looked like a small cooking pot with threads on the bottom and teeth on the top. The threads had ripped themselves out. He said it is common with this truck. And as for any deposits, this 80k mile motor is like new. Can you see the photos in my Profile?

I hate to let-on that I know as much as some of you fellas but what I am hearing is not a lifter. Lifters tap, this is a knock. I even had a hard time swallowing that it was an aluminum piston skirt slapping. I believe the key to the mystery has something to do with the fact that it doesn't knock at the start up. If an idle is 600 RPM then it's about 10 RPS (revolutions per second.) It makes at least 30 revolutions before the faintest knock can be heard. (about 3 seconds) it gets louder (to a point where it's as loud as someone gently knocking on a door with their knuckle) It continues for about a minute and then gradually diminishes to inaudible. The whole process has taken approx. 4 minutes and it's ready to go. Then it sounds like an electric motor for the rest of the day. It can sit at work for 4 to 6 hours and when it starts...quiet. It only does it when it sits overnight.

The draining down of a lifter sounds about right but why does it not make a racket at the start? I appreciate all the advice. Thank you all.

 

[THEFERMANATOR]

I've had lifters do just as you describe. Normally it is some deposits stuck on the check flap that cause it to happen. Once the engine starts it slowly bleeds down, and after a few minutes pumps back up. The hydraulic roller lifters tend to make a slightly different sound than the older flat tappet lifters did. As for deposits, I have seen the cleanest of engines hav pickup covered over inside the pan. not saying this is your problem, but it sure sounds like it. Maybe you could post a video of it. But if it was piston slap, it would do it right fro mthe moment it starts, and wouldn't stop until the pistons warmed up. And the trans part you are talking about is called a sun reaction shell. When it strips out you lose reverse, 2nd, and 4th.

 

[OBE]

I could make a little video. I've noticed when guys do it they open the hood and stand right next to the motor and the roar and wind distort the sounds with overmodulation of the cheap mic in the phone. I will do it standing about ten feet from the truck and you will hear it perfectly, I think. I can't do it now' cause it won't happen but I will do it tomorrow morning. Thank you very much for your help.

 

[OBE]

Well, I hate to violate "the scientific method" by changing more than one component at a time, but I just changed the oil and filter. I was reading-up on engine flush options but this truck is so "sweet" I can't believe it's gunked-up inside. I decided to simply change the oil. Being an "old-school" dude, I never went the synthetic oil route. I read where I must, with this motor, and I also replaced that Brand-X oil filter the lube joint used. I suspect that the horizontally mounted filter might drain-down and empty itself if it isn't equipped with a check valve system.
That might cause a half minute delay of oil pressure hitting the bearings (while the filter is filling) and cause a gentle "knock." My thinking is that the bearings have some lube on them because I use an additive. That might be why it doesn't knock until about 30 revolutions when it slowly starts a hollow tapping and increases in volume and almost immediately begins to lessen as oil gets up to it, all this taking about two minutes. When it pressure's up, it purrs like a kitten...actually, a LION! lol
Okay...the test came the next morning. No "apparent" knock! If I listened real closely, I thought I could hear something, but maybe it's my imagination. This morning came the 2nd test: no knocking this morning, either! Now, in truth, it isn't cold out, either, and maybe it would knock in freezing temps, but although it first started in the sub-freezing weather, it continued to do it in the morning even when the weather got warm.
It might be the filter draining! I used Mobil One 5W x 30 and a Mobil one Filter $38 for 5-Qts Oil and $13.39 for the filter.
I will keep you all posted regarding the fix. Thanx to all for your kind help!

 

[btfarm]

Excellent! Glad to hear you are encouraged so far.

 

[schiker]

I have to say there is something to synthetic oil. I had a Mitsubishi Mighty Max that the valve train tapped. If I mixed at least 1 quart of Rotella 5W-40 Synthetic oil to my regular oil the lifters did not tap. I tried different popular additives when ever I topped up that were suppose to help improve oil performance Marvel Mystery oil, STP, Rislone, maybe Lucas, and some others?. I tried different popular name brand oils like Valvoline, Havoline, and Castrol. Nothing worked til I added some Synthetic oil.

Synthetic just plain has a better viscosity index built into it and less dependent on additives and modifiers to keep the viscosity index linear.

I am not saying every engine should run synthetic but for some it makes all the difference.

 

[btfarm]

Old Smokey Yunick had a saying. "I don't know what they charge for synthetic oil,, but they should charge twice what they do..."

Sent from my SCH-I535

 

[OBE]

I still have this 1997 Sierra. It develops that annoying "rattle" after about a minute (on cold days) but it quiets down after about three minutes. It is fine for the rest of the day. Since talking about it, I've experienced a couple more "common" problems. I hit the brakes fairly hard, one day, and blew a hole in the brake line under me, along the frame. Research advised that I either remove the tank or remove the bed to get at it. I removed the bed. I now have a rough idle on cold starts that goes away to smooth running after the truck warms-up. I'll bet it's a sensor or something. Any suggestions?

 

[boatist]

My 98 C1500 with a 305 makes the same noise. I just figured it was wear since it has 378000 KM on it. I run 5w-40 T6 in it, also knocked with 10w-30 Amsoil. Mine gets louder when the truck gets put into gear so something in the rotating assemble is making the noise.

Brake lines are easy to change and don't require the removal of bed or fuel tank. I did all of mine last year since they were rusty and brittle in about an afternoon. plan on wheel cylinders if your bleeders haven't been out in a while.
Rough idle on cold starts? When was the last time it had spark plugs?

The knock is still a mystery to me. Sorry I couldn't give ya an answer.

 

[OBE]

My 98 C1500 with a 305 makes the same noise. I just figured it was wear since it has 378000 KM on it. I run 5w-40 T6 in it, also knocked with 10w-30 Amsoil. Mine gets louder when the truck gets put into gear so something in the rotating assemble is making the noise.

Brake lines are easy to change and don't require the removal of bed or fuel tank. I did all of mine last year since they were rusty and brittle in about an afternoon. plan on wheel cylinders if your bleeders haven't been out in a while.
Rough idle on cold starts? When was the last time it had spark plugs?

The knock is still a mystery to me. Sorry I couldn't give ya an answer.

That was actually a big help; the rotating thing, that is. When I first got this nice truck it didn't happen. Some one replied that they have a component on the flex-plate or something that can cause it. Ironically, I noticed it after I had the trans rebuilt! If it was a lifter it would be loudest immediately upon a cold start. But it starts okay and it's quiet for about 30 seconds and then the tap comes, gets louder till it fades away after about a few minutes.

 

[boatist]

LOL, My truck had a tranny put in it before I got it. You might be on to something!

 

[OBE]

These trucks are supposed to be driven around in Overdrive. I drive gingerly because I've driven soooo many junkers. I have never had to put more than one set of brakes on any car, I ever owned, because brakes (and clutches) last forever for me. But even I can feel that drive train kick back in after I've been "coasting" in OD. My mechanic said he's changed dozens of these trannys that strip off that big round gear (I don't know what it's called but he gave it to me as a souvenir) I think his helper may have done something wrong when they put the trans back in.