SOHC knock or chain slap

[thomurp68]

I have 2000 ish 4.0 Sohc that sometimes has a knock at start up that goes away after it warms up. Seems to be worse when it's cold. I replaced all the timing chains about a year ago, 10,000 miles. The knock sounds like it originates in the crank case near the balance shaft but it's hard to tell. Coincidentally it didn't start until after I replaced a broken belt tensioner, about the same time the weather got cold. Anyone have an idea how diagnose this short of pulling the engine apart?

Thank You,
Tom

 

[koda2000]

I have 2 things for you to try:

1. Remove the serpentine belt and start the engine to see if the "knock" goes away. If it does you may need a slightly shorter serpentine belt. The noise might be the belt tensioner hitting its stop. Often the part number of a belt actually includes things like its number or ribs and its length.

2. You can also try putting your foot to the floor on the gas pedal and holding it there while you crank the engine (this turns off the fuel injectors). It may take up to about 7-10 seconds of cranking to see oil pressure, depending on engine and/or oil temp. Releasing the gas pedal will now allow the engine to start. If the noise is gone it's being caused by loose hydraulic chain tensioners, which tighten once you have oil pressure. Not a lot you can do about this issue, other than adding a pre-oiler, or always cranking your engine before allowing it to start. It's just that hydraulic tensioners (which rely on the oil pressure to apply full tension) are a poor design.

 

[Flash]

What Koda said plus, some of the tensioners aren't good quality and I don't know how to ensure you get a good one.

It might also be the balance shaft chain.