cuz i've got one in my garage with a sporadic knock that comes and goes..
04 Cavalier, 164,000 miles. had a knock coming from the front of the engine, along with the sound of the timing chains flopping around and smacking the block.. i took the front cover off the engine, and there were pieces of plastic tensioner all busted up and both chains were loose, and the balance shafts had jumped a few teeth. the cams were still lined up and it ran smooth, so i don't think any valves kissed pistons... i replaced both chains and all tensioners, started it up, and it was quiet- for about 30 seconds.. then the knock came back as loud as before, but without the chain slapping sounds.
so, what else can go wrong in there to make what sounds like a rod knock or wrist pin that comes and goes and isn't affected by engine rpm or load? is there any shadetree way to shut off spark to each cylinder to see if it goes away?
No real way to shut off just one plug at a time. Did you reclock those balance shafts when you replaced the chains?
Keep in mind, I know nothing of this motor, but there is a very similar problem on BMW M42/M44 engines.
There is an oil pressure relief valve, that at low RPMs, helps keep oil pressure up, to keep the chain tensioner working. Once that valve goes bad, at low RPM the tensioner isn't fully engaged because there isn't enough pressure, so you get the knock/tick/slap of the chain.
If I were you, I'd find out if there is a similar setup on your engine and start there.
everything was properly lined up when i put it together. when i took it apart the second time, the balance shafts had each skipped a couple of teeth and the chain was loose. the cam timing chain was nice and tight and everything lined up..
lined everything back up on the balance shaft chain, put it back together, and it knocked again. took it apart again today, and everything is lined up and no slack in either chain.
this is why engines should have one cam with one short chain and none of that balance shaft silliness- it at least makes it easier to narrow things down and determine what isn't wrong...
the weird thing is that the ecm isn't registering any knock- at least according to the cheap scan tool that a guy from work brought over today. i've seen engines alter the way they run just by tapping on the side of the block with a hammer, but this thing just sits there and idles with a random knock going on..
i took it back apart- again- the balance shaft chain had jumped again.. i'm starting to think it's something with the oiling system not getting enough pressure to that tensioner. it's got oil coming out of the passage when i remove it, but i have no way of knowing how much pressure it is seeing in operation... the bypass spring is externally accessible via a plug on the front cover, so i'm gonna pop that out and see if it's sticky or anything like that.. but no one sells a bypass spring for it, so if it's weak i don't know what to do.. maybe shim it with a washer or something..
also might try buying an actual good oil filter for it- it's my brother's car, and not being a gearhead he always just buys the cheapest filter in the orange box.. i know some engines don't like those filters, so i'll spend the $7 for a NAPA Gold (made by Wix) and see if that helps at all.. i can definitely tell he buys the cheap oil based on what the inside of the engine looks like..
ok.. i officially give up and want to kill this thing with fire, then then crush and grind it up just to make sure it's dead enough..
took care of the chain problem- the oil pump bypass on the front cover was stuck in the "open" position so the balance shaft tensioner wasn't getting enough pressure.. put it back together, no noise.. sweet.. then after about a minute a steady and faint "thunk thunk thunk" noise starts out, then gets progressively louder.. shiny stuff in the oil.. i'm thinking rod bearing.
That sucks... Thankfully, if he's got the time and coin, the EcoTec is getting a bigger presence in the yards. Might find a good one, or drop a crank and bearing in if you feel up to it.
Sorry about the bad luck.
the cheapest junkyard motor i've found was $700.. it's a Cavalier not a Cadillac..
If it has alum bearings, just put a new bearing in with a quickie polish to the journal. I do this is rod knocking 3.3/3.8's in caravans all the time, especially if it hasn't had a lot of miles since the noise started.
Altho, since it is a Crapalier, I'd just put another lump in it. After all, it is just another disposable appliance.
