Slight knock?

[Scooterwrench]

My oil pressure on startup is great, usually like 60, but it fluctuates driving I’m probably at 38-41, whenever I’m stopped or idling it’s 20. I’m running factory setup 5w-30 Mobil one high mileage with a mobile one filter

Yeah, that old motor is beyond running factory spec viscosity for a new engine. With that much oil pressure you probably don't need 20w-50 but 10-15w40 would be my choice for you. Add a zinc additive.

 

[tybcr783]

If it does it only on cold starts, doesn't do it on warm re-starts.. let's not forget the possibility of the good ol' cracked flexplate.

Richard

It’s does it a warm as well, so I hope it’s not that, doesn’t sound like a fun job to drop the trans and replace that. Is there any other signs than tapping for a cracked flex plate?

 

[Scooterwrench]

Cracked flex plates normally don't shut up after a few seconds of running.

 

[someotherguy]

It’s does it a warm as well, so I hope it’s not that, doesn’t sound like a fun job to drop the trans and replace that. Is there any other signs than tapping for a cracked flex plate?

I think you may still be misunderstanding me. At least in my experience, they will knock for a few moments on cold starts, but on warm re-starts, no noise. If you do end up replacing it, it's really not that bad - especially on a 2WD.

Cracked flex plates normally don't shut up after a few seconds of running.

Been there done that. The one on my '92 was completely broken in a circle around the crank flange. It would knock a few moments then stop. Next time you'd start it warm, no noise. Once it sat all day and cooled off, it would knock again. I was 100% convinced it was a rod knock. I was wrong.

Richard

 

[someotherguy]

I wish I could find the pic but I can't. When the flexplate came off it came off in two pieces. Just the little flange was left still bolted to the crank.

Theory is, once it begun spinning, centrifugal force held it together tight enough to silence the knock, and the heat once the engine warmed up expanded the parts enough to also keep it from knocking. Once it cooled off, it would knock again. I can't believe it held together as it was but I suppose the torque converter wouldn't let it walk back and separate.

This is a pic snagged from the webs but mine looked essentially like this:

You must be registered for see images attach

(pic credit: "Hitcher" on 67-72 trucks forum)

LOL.. I "kinda" found a pic of my old flexplate. Here it is in a roll-off dumpster at my old place in Atlanta. You can't see the break in it, but that's why it's in there..

You must be registered for see images attach

Richard

 

[Schurkey]

1. I run a mobile 1 filter, do you know how decent those are ?

Never used one. Probably manufactured by Champion Labs, they make a heap of oil filters with other company's brand names on 'em. There's no final "e" in Mobil.

Champion Labs has at least three "lines" of filters--cheap, mediocre, and good. I'd expect the Mobil 1 filter to be from the "good" line.

2. I’m not sure what you mean by bleed excessively

Hydraulic lifters "pump up" with pressurized oil. That oil is released into the pushrod to oil the rocker arm, valve tip, and to cool the valve spring. When the engine is off, valve spring pressure can force the oil back out of the lifter; some lifters have looser clearances than others--they bleed-down faster.

 

[someotherguy]

Never used one. Probably manufactured by Champion Labs, they make a heap of oil filters with other company's brand names on 'em. There's no final "e" in Mobil.

Champion Labs has at least three "lines" of filters--cheap, mediocre, and good. I'd expect the Mobil 1 filter to be from the "good" line.


Hydraulic lifters "pump up" with pressurized oil. That oil is released into the pushrod to oil the rocker arm, valve tip, and to cool the valve spring. When the engine is off, valve spring pressure can force the oil back out of the lifter; some lifters have looser clearances than others--they bleed-down faster.

I run the Mobil1 filters (and oil) on all 4 vehicles - the 300 SRT8, the two Silverado SS's, and now my '93 3500 7.4 - have been using them on my Mopar stuff since my first 300 SRT8 back in 2012. No complaints.

Richard

 

[Danimal08]

I've owned three of these. All of them had a slight bottom end knock on cold starts. First one had 349k when sold...ran the dogpoo out of it. My dad is still driving one with 250k. I'm currently replacing engine in the third after discovering poor quality rebuild after pulling apart to do head and intake gaskets. Replacing with a lower mileage used replacement. I fully expect slight knock on it too.

If you wanna feel better about that, drive a higher mileage GMT800. The piston slap in those makes that seem normal. Mine sounds like a diesel if you take off to early in it.

 

[skylark]

I'm confident to say that is piston slap. GM short skirt hypereutectic pistons have a tendency to try to rock in the cylinder until the skirts warm up just enough to cause them to expand. I've had many vortec era engines do the but never a TBI. As mentioned, LS (especially the early ones) do this. My 5.3 Suburban with over 300k sounds like a Duramax on a cold start. It has an instant 70 psi of cold start oil pressure. It runs at idle for about 30 seconds and it is quiet all day afterwards. I feel that just a little warm up would slow down the onset.

 

[Scooterwrench]

I'm confident to say that is piston slap. GM short skirt hypereutectic pistons have a tendency to try to rock in the cylinder until the skirts warm up just enough to cause them to expand. I've had many vortec era engines do the but never a TBI. As mentioned, LS (especially the early ones) do this. My 5.3 Suburban with over 300k sounds like a Duramax on a cold start. It has an instant 70 psi of cold start oil pressure. It runs at idle for about 30 seconds and it is quiet all day afterwards. I feel that just a little warm up would slow down the onset.

You should warm the engine prior to loading it to begin with. Have you ever seen anyone fire up a cold aircraft engine and immediately take off?

Hypereutectics are suppose to go in tight because they don't swell as much. Wonder if GM is still boring to forged specs? I've never looked up the piston to bore clearance for GM engines with those pistons installed in them but the clearance for Harley motors is .00075"-.0015". which doesn't work well in an air cooled engine. Skirt galling is a big problem created by thermal shock.