420SEL @ 245K, What to do?
 

Morning Guys,

So I'm facing some decisions when it comes to my 420SEL and I'm looking for some input/thoughts/comments/what would you do/etc.

It's got about 245,000 miles on the odometer. Hits about 17.3 MPG average with my driving.

The Bad:

1) Needs a valve job.

-Burns about a quart every 180 miles or so.
-Fouls out #8 plug (mitigated with spark plug non-fouler)
-Other plugs seem OK
-Perhaps this hints more towards a valve seal issue?
-Quoted 3500-4500 for job

2) A/C Leak

-Leak appears to be somewhere in the TXV or EVAP.
-New condenser (Parallel Flow)
-New dryer
-Compressor is young
-New seals everywhere up until TXV/EVAP

The Good:

-Complete suspension rebuild
-Steering gearbox rebuild
-Repainted, not car show grade but looks nice.
-Brakes are new
-Front/Rear windows replaced and resealed.
-Catalytic converter replaced (single cat unit now)
-New rims and tires.
-Timing chain, upper guides, tensioner, was replaced 36K ago.
-Interior is in pretty decent shape. No glaring issues or notable cuts/deformations/etc.
-New motor mounts.

The Unknown:

-Underbody rust. Last I checked it was fairly clean under there. There may have been surface rust on a few areas. By far the cleaner of all my 126's. I caught the rear window leak before rust could set in.

I've attached my maintenance/repair summary data if anyone was curious.

Just looking for some thoughts.

This is your turning point. How do you feel about the car? If its been good and you enjoy driving it ....drop a reman motor into it and drive it for another decade. It only takes a quick visit to the dealership to view a new S class and you will understand its financially a good decision. Also there are quite a bit of update items for 123, 126, and 140 to let you obtain some creature comforts.

Why a reman motor? Best I can tell prices range from $7-9K for a long block. That's double the valve job. I was under the impression that the M116 bottom end was fairly robust and should last quite some time. Top end on the other hand does need work periodically.

That's doable as well. I tend to go all in and get it done - but that's just me. The 116.965 can probably be had for $5K (ish). The 126 style is timeless and worthy of refurb. Once you get through the mechanicals everything else is fairly inexpensive.

Now $5K ish isnt bad. I was going by prices found online from Metric Motors. Do you know of another reputable vendor?

IMHO rust is the deciding factor. Get under the car with a screwdriver and start poking. Pull off the body cladding. Pull up the carpet. Fell up on the truck roof, where the rear window gasket is. If it's really rust free keep it going. If it's rotten find a better car :)

I'd think oil fouling the plug is more of a valve guide or piston ring issue. A compression test would be a good place to start.

Can the valve guides be replaced with the head installed? I'd think the valve stem seals could be at least.

-J

I would not do a valve job on a 250,000 mile engine. Its going to need bearings and rings soon enough. I would look for a complete engine on car-part and see if you can find a "euro specialist" in your area to swap it in for a reasonable price. A quick search shows there are plenty of 4.2 m116 engines out there for $1500 and less. That would also be a good time to do seals on the transmission if its been in there for a while.

I say this because this is not an AMG or otherwise special engine. I don't even bother with head gaskets on anything over 200,000 miles unless its a rare engine that needs to be rebuilt.

Another option is to see if you can just find a lower mile clean car with a price delta less than what you're looking at for repairs. Then let someone who is a more DIY get your car and keep it going.

How soon is soon you think?

Does your 200,000 limit apply to diesels too? I've got 321K on my 602, I think it may need a head gasket here soon. Just a hunch really.

If I owned the diesel I'd do a head gasket because they do go for quite a bit and run for a long time. However I don't know how much a shop would charge and I would have to do the math on that one.

I disagree on those mileage numbers. These Mercedes gas engines wear almost as well as the diesels. I've seen several gas Mercedes in the yards with more than 300K, I've even seen one with 450K, most of them were in accidents or rusted to hell. I bought a beat to crap 190E 2.6 once as a parts car, it had 209K miles, and left it at my mechanic's shop for a few days trying to get stuff moved around at my house. He was bored on a slow day and decided to get it running and did a compression test. It tested at factory specs on all 6 cylinders. I'd do a leak down test instead of a compression test, or you could do both. There will certainly be wear on the engine at 245K but I don't think it's probably anything you have to worry too much about. If you can find a good low miles engine for cheaper, that may be more cost effective but your engine might be salvageable.

Obviously you know nothing about the bottom ends of the M116/7s of this generation. You are the one that should be doing a search for information.



I vote for the top end. This style V8 beats the hell out of the top end every 100k, bottom ends do not go bad on them. Ask any tech. Only issue is the initial up front labor due to the block usually needing Helicoils. Once the block has the steel threads, top ends are easy.

Remember, I did a top end on my 300SEL around 270k, car has 320k on it now. Cylinder walls were beautiful and I have 160-170psi on all six...and the M103 did not have the Alusil linings these V8s have installed.

One of the shop owners on here had a customer's 420 that had around 700k before a rod bearing failed from what I recall. Steve Brotherton I believe.

Just one example - http://www.peachparts.com/shopforum/1789665-post8.html

TXV seals are not super hard. 134A is just going to leak due to molecular size. Run R12 since the rest of the system is new or R152A for R12 head pressures and $4/can.



Think of it this way Kris, if you spend say $4k for the top end... what can you buy that is worth a damn for $4k that does not need $5k put into it?

How do they get 4-5K for a valve job, esp. In NE Ohio where machine shops are as common as convenience stores?

If I din't want to pull the heads, I'd probably do the valve seals. They have to be fried to a crackly crunch at this age.

I own 2 M117 cars currently, both need engines, and have worked on a wide variety of cars. I can tell you that if OP has a car that is burning oil valves and valve seals are not the only thing that are on their way out. Are there nice high mileage engines out there? Definitely. The thing is those engines typically don't consume oil. I would not risk the cost of having a shop do a top end on a high mileage engine that may have possible bottom end issues. Not when you can buy a complete engine for about a grand.

For every engine that makes it to 500,000 miles be it an older Mercedes, a Cummins, or Honda there are 20 that gave up the ghost at 200,000 miles.

I think the number I have written down is $3500-4500. I would have to double check and see just what all that included exactly.

This is another idea too, buy a low mileage good running M116 and drop it in...

Or I suppose a M117 could too but I think there would have to be electronics change overs. EZL/ECU for sure.

I think my shop charged me somewhere around 600-800 to swap in a different M103 in my 190E. I figured $2,500 all said and done to buy a motor, address whatever seals/external things that you should do while its out and drop it in.

Or buy a rebuilt motor.

Adsit lists on at $5600 but they provide no details (suppose I could call) but I have not heard many good things about them. Idk.

Metric Motors is $8900.