5.0 engine knock on start up only

[Schurkey]

Not all oil filters have an anti-drainback valve. The ones that do, can cook the silicone rubber so that it leaks--which is effectively not having an anti-drainback valve.

I would not expect piston slap to be "done" with three knocks. Fifteen or thirty seconds...maybe.

Similarly, a lifter bleeding-down overnight might "knock" or "tap" upon startup...but probably longer than three knocks and then silence.

Same deal for a cracked flexplate. Don't know why that would knock three times on startup, then never until the engine cools off again.

Off-chance that this is ignition-timing related due to a failure somewhere in the electronic timing circuitry, during the change in timing authority between the ignition module and the computer...but it'll be tough to track down.

If this thing is knocking three times on the ceiling, maybe it wants you.

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[Scooterwrench]

Sounds like cold start rod knock. How many miles on engine,how much oil pressure?

 

[someotherguy]

Same deal for a cracked flexplate. Don't know why that would knock three times on startup, then never until the engine cools off again.

My experience with this situation had me 100% sure it was a rod knock. It would knock 2-3 times on cold start, I'd drive to work, it would sit in the parking lot all day, then on cold start to go home it would knock again. If I went anywhere in between like lunch or a quick errand, it wouldn't knock.

I didn't have room at the time to do any serious work, only a steeply sloped crumbling asphalt driveway, so I took it to someone I trusted. He determined it was the flexplate. Took it out and it was broken all the way around the crank flange, came off in two pieces. Replaced it, no more noise.

Why it would stop knocking as it came up to speed, don't know. My best guess on why it wouldn't knock on warm re-starts is heat grew the pieces just enough to close up gap on the crack.

The evidence was hard to ignore when he showed me the two pieces and returned my truck to me no longer knocking, for the cost of a flexplate and some labor. I drove that truck several more years/countless tens of thousands of miles beyond, before blowing the engine up with an unmistakable rod knock accompanied with glitter oil. It was past 200K at that point. (This was my '92 ECLB 1500 I did the Caddy clip on.. after replacing the engine with a low mile used one out of a burnt RV)

Richard

 

[Pinger]

Why it would stop knocking as it came up to speed, don't know.

Only partially filled with ATF at initial start-up and therefore out of balance?

 

[someotherguy]

Only partially filled with ATF at initial start-up and therefore out of balance?

Flexplate was broken, not the torque converter or anything that would have atf in it. My best guess is centrifugal force pressed the broken pieces together as it spun up so it only knocked when it was cold and below idle speed.

I don't have a picture of it (this was back in.. 2000? 1999?) but there are plenty of examples of this damage across the 'net. I snagged this pic at random just searching for one years ago, but it pretty much mimics what mine looked like - the kind of damage that amazes you the thing still cranked over and ran without coming completely apart

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While on the other hand, I experienced flexplate failure in a 2008 F550 with the Powerstroke 6.4, and it left me dead in the road as the truck quit moving. Had to get towed in. With the break being a near perfect circle, it's understandable how this one quit moving while the SBC's break didn't. The 6.4's failure was sudden with no warning. Was rolling right along the freeway and then bam, speed dropping off quickly, I barely managed to coast to the exit ramp.

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Richard

 

[PlayingWithTBI]

Looks like a broken flex plate to me

 

[_rgk]

My Nissan did this. It turned out to be inadequate oiling at the timing chain. It would only do it when cold, not when at all warm or driven that day. The inadequate oiling was due to worn bearings, which also caused a rod knock. But this knock surfaced only at 3-4k rpm.