560 Knock on Start-up
I'll put this in a new thread in case it can help someone with the same problem and eliminate all that frustration I experienced.
My baby (black 87 560sl) with 158K on it was givinge off what sounded like three or four knocks when started. It didn't sound like a timing chain rattle or lifter noise. Timing chain, guides and tensioner were replaced about 40,000 mi. ago and the car runs well.
After almost giving up I heard that my problem might be the timing chain tensioner. The chain, guides and tensioner were replaced about 40,000 miles ago so I thought they should be fine.
To be on the safe side, I removed the valve cover and checked for a sloppy timing chain after the car had sat for 24 hours. The chain seemed tight when I poked at it with a big screwdriver.
To make a long story short, I replaced the tensioner and all is well. The noise is gone and the car seems to have more power.
These tensioners operate with both hydraulic and spring pressure and I understand that if an 'O' ring in the tensioner is leaking it will be giving insuffient pressure on the chain and cause it to rattle.
This still amazes me since even without hydraulic pressure, the spring located in the tensioner seems to exert pleanty of pressure upon the chain.
Has anyone any ideas as to what happened here?
Like I say, all is well but know I'm wondering exactly what happened.