I've just purchased a 91' 420 SEL with 101,000 miles on it.

After reading the archives regarding guide failures, etc, I've acquired a very nervous feeling about the risk of driving it any further without getting it into a mechanic to check it out(which I plan to do in a few weeks).

However, I have a vacation planned tomorrow in which I really wanted to take the car out, forgoing cramming the family into the truck. I'd be putting on about 600-700 miles.

Would it be taking too much risk to drive it another week?

Is it unusual for the failures to occur at 100k or less, relatively speaking? Any thoughts on, at what mileage, failure typically occurs?

The car idles fine and no unusual noises at startup. Maintenance records thru 80k indicate very frequent oil changes, etc.

P.S. - And this is a great forum, thanks in advance for any opinions/thoughts.

I would take the 420SEL
 

on the vacation and enjoy the ride then get it taken care of when I returned. If the oil has been changed often up to 80k miles then it should be fine. It is my opinion that the care given to a car the first 100k miles determines really how long the car will go. I had a 1986.5 Nissan 4 cyl pickup truck that I changed the oil at every 3k miles and sold at around 65k. I saw it the other day and it is now showing over 280k miles and I know they have never touched the timing chain.

How handy are you? You could take off the valve covers and check the condition/color of the guides (white-light = good. amber-dark=bad) I sugjest you replace the valve cover gaskets if you do this.

I personally would not risk it without at least checking the guides, too much downside risk. I got mine done in the nick of time. If you live in SoCal I know a great mechanic.

i need a mechanic
 

fred segal, i'm in so. cal. Which mechanic can you refer me to and where is he located? I need to get the timing chain done also. Thanks in advance.

If you are handy with a wrench you may want to check this out yourself. Remove the valve cover that is handiest and rotate the engine with a socket on the dampner bolt head. Follow the normal direction of the engine rotation (look at the cooling fan blades). Carefully rotate steadily with constant pressure until the cam mark lines up with the cam tower mark. Note the indication of timing on the dampner wheel (you may need to do this several rotations until the cam mark lines up and the dampner marks are visible, remove spark plugs to unload compression and engine will turn easier). After you have determined a timing mark on the dampner, reverse the direction very slowly until the cam start movement in the opposite direction, note the position of the dampner timing mark. What is the difference. There is no set amount of allowable play that is published but I would not like to operate an engine with over a 5 (I have read 10) degrees difference.

You might want to have it checked out for peace of mine!
I've seen those chains break at less miles than a 100k
The left upper rail is the big target point for breakage.
As far guides go unless the plugs have some oil deposits
on them i would'nt worry to much about them.Those were
good motors if well maintained!

P.A RONDEAU

20 YR M&B TECH (ASE.)
MERCEDES BENZ OF
BLOOMFIELD,HILLS MI.

Paul, I am confused. What plugs affect a guide?

Nevermind, I thought you were talking about the chain guide rails, not the valve guides. :)

rsamson830,

The shop is called Mr.MB Motors and it's in Tarzana. I was just there on Friday,because my shifter was making a metalic sound. Enrique put it up on the lift and changed both bushings, no charge (he said I should buy my daughter a present) I'm not saying he will do free work on your car but I promise you will feel this is the best money you ever spent. Enrique will repair your car and give you the pease of mind you wish the dealership could deliver.


http://www.peachparts.com/shopforum/california-southwest-us-az-nv/144503-mr-mb-motors-tarzana-ca-post93523.html#post93523

420 SEL Timing chain/guides - failure risk
 

The timing chain rail breakage on the 420s would be described by anyone as a catastrophic failure and, as such, you can't really put a time limit/mileage range around it.

Some have said that frequent oil changes mean that you shouldn't worry; others have said look at the color of the guides. No disrespect meant here whatsoever, but a catastrophic failure is a catastrophic faiure. Another example that has been discussed recently on this list is the single row timing chain in the 3.8 engines. One could change oil every 500 (five hundred) miles in this engine and yet, you are still "rolling the dice" on continued driving with the single-row chain. Same with the problematic guide; a less-than-$5 part in this case . . .

I would venture a guess that the major explanatory factors for guide failures are the number of hot/cool cycles and the amount of in-town driving, because we're talking about a plastic guide here. The only reliable visual in my mind would be hairline stress cracks; I know that several have seen this evidence on guides. Color to me would provide minimal information unless it is near black.

Consequently, back to the original poster's question: "Is the car safe to drive on vacation?" As someone has already pointed out, guide failure is unlikely to occur in this 6-700 mile interval. However, life is a series of risk assessments. You have a known catastrophic failure for your specific engine. How much risk are you willing to assume for this known problem?

Richard Easley
Waco, Texas