My 1986 420SEL was real quiet running this morning, Then I started it up this evening and now there is a "marbles in a tin can" noise coming from the front of the engine and it's louder with the oil filler cap off. Is this the timing chain slapping? If so, how big a job is it to fix? Is there any step by step instructions on how to replace the tensioner, guide rails, etc.? Or should I just bring it to a shop and get hit with a big bucks repair job? Could it just start this noise all of a sudden? Wouldn't I hear this noise lightly at first then getting louder over time????

I would say the timing chain is a real possibility or a real bad camshaft problem. I would have the car towed to the dealer. The chain on my 300Sd isn't too bad, but it's my understanding the the V8 engine can be a real swine

In any case, I wouldn't chance driving it again until the dealer or a trusted indy looked at it! A rebuilt engine can be upwards of $12,000!

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Old age and treachery will allways overcome youth and skill!

1993 S500
1984 380SL

Yeah the last thing you want to do is run that engine. Don't even start it have it cranked up onto a flat bed and towed to your house/shop/dealer. I would bet it is the timing chain. Pull the valve covers and check them out.

When was it last done? M116's should be done every 10 years / 100k miles.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Yeah, but can it just start immediately?? I mean the motor was quiet a a mouse this morning. I stopped at a store for about an hour. When I came back outside and started 'er up, klackiety, klackiety. So I cannot fix anything here and have to bring it to a mechanic?

I wouldn't chance it...the risk (and expense!) is too great!

__________________
Old age and treachery will allways overcome youth and skill!

1993 S500
1984 380SL

If you have AAA it won't cost you a thing. If not $100 for a flat bed is money well spent.

If it is the timing chain you risk doing thousands in damage. It could jump timing and bend the valves, then you would be looking at a valve job.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

To put it in perspective, the timing chain on my 380SL broke at 100,000(right on cue as it were). The bill from the dealer (AND I was out of town no less so I had to fly home and have it fixed 800 miles away!) was over $6900 And that was JUST for the repairs to the upper half of the engine! Take my advice...don't risk it!

__________________
Old age and treachery will allways overcome youth and skill!

1993 S500
1984 380SL