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  #1  
Old 07-08-2003, 11:11 PM
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Question 1987 420sel longevity ????

I have a friend who is interested in a 1987 420sel. Seems to run extremley well & has recieved good care (according to the svc records). The only conern is the 188k on the odometer. How many more miles can the 4.2L v8 go with good service? Thanx 4 your input.
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  #2  
Old 07-09-2003, 04:54 AM
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The M116 is as hardy as they come. Probably due for a timing chain and rails if it hasn't had the job done recently. 1987 might have been an iffy year for valve seals. Coming to the end of the typical original transmission life as well. A well cared for car might have had all these items addressed recently in which case it should be good for another 200K miles. Definitely worth the investment in these major service items if they're due.

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  #3  
Old 07-09-2003, 07:59 AM
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Well, my '87 560SEL has 339k miles on it. 420 is really the same car withslightly smaller displacement motor. Life on them seems to be related to frequency of fluid changes. Mine had regular changes on just about every liquid or semi-liquid in it. I'm only the third owner. Chain w/guides and valve seals seem to be the only thing beyond regular tune-up stuff. I have heard that the head gaskets can develop slight oil leaks. General practice is just to live with the leak as it is very small. Transmissions aren't cheap, but not unreasonable either. Once again, fluid changes seem to have a hugh effect on long life. Nitrogen cells on the rear suspension will go bad and give bad ride. Just replace them when they die. Look for rust in the usual places. Don't pay too much. The prices are coming down on these cars. Bad for sellers, but great for buyers as you can drive a really fine car for not much money if you are willing to do a bit of maintenance.
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Old 07-09-2003, 11:29 AM
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I agree with the previous posters...188k is really nothing to these engines and as long as you keep em up they'll pretty much keep on rolling. My 560 has 238k and nothing major has ever happened to the engine since I got it 3 years ago. I pretty much do all of the maint on her and its a DIY friendly automobile.Just be sure you get the timing chain switched to a double row chain (if it doesn't have one already- not sure about yours)when you do replace the rails,etc so you'll have double protection. Hell I wish my baby DID have 188k on her. That engine's just getting broken in. Good Luck!

Alan
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  #5  
Old 07-09-2003, 12:18 PM
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Chain and rails

Those seem to be the major maintenance items - a loose chain smacks the rails on start up, they break, chain jumps a tooth or two and you need a new top end.

Replace the upper chain and rails and put in a new tensioner while you are in there. BTW, I believe this is an M117 motor (420, 560), not M116 (380, 500).

I did these on our 380 (M116 - rails and chain) and 560 (M117 - only did the rails as the chain was OK) and illustrate both on my site.

The tranny, as has been wisely pointed out, is the other major area of concern - you are looking at $1500 for a rebuild/overhaul. Not cheap, but may be worth it if the car is priced right and has excellent paint and upholstery - these are very expensive to fix - and is rust free.

Steve Brotherton once mentioned that he has a customer whose 420SEL has over 500k on it, and the customer has finally learned to have the chain and rails changed every 100k after two top end jobs.... Steve has also stated many times that the bottom ends on these engines are pretty much bullet proof. No reason why you shouldn't get this car up to 500k with proper maintenance. Mr. Brotherton has seen more of these engines than most of us have seen hot dinners.

BTW, no nitrogen cells on the 420SEL rear - it uses regular Bilstein shocks. The 560SEL has the cells. Also, I suspect many of the valve cover leaks are caused by overtigtening the bolts (these need very little torque), reusing old gaskets and not using new crush washers every time. Check your valve cover on a really flat surface (glass) and see if its warped.

All M117 engines have the double row chain - pre-1985 M116 380 engines have the dreaded single row. The 500 always had double row.

Last edited by Thomaspin; 07-09-2003 at 12:23 PM.
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  #6  
Old 07-09-2003, 01:40 PM
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To clarify:

M116 = 3.5, 3.8, 4.2
M117 = 4.5, 5.0, 5.6

The M116 and M117 were available side-by-side in just about all model years, though not always in the US.

Only some 3.8l M116s have a single row chain and possibly only US/NorAm models. All 3.5l and 4.2l M116s have double row chains.

Sixto
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  #7  
Old 07-09-2003, 04:20 PM
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I think Sixto is right - my error.
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