Started a HUGE project 420 SEL to 617 Diesel
 

Well ive finally started it. I have a MINT 86 420 SEL with a bad motor. I bought an 82 300 SD in the junkyard with 183 K on the enigine. I'm going to strip the car in the yard and bring everything home and convert the 420 into a diesel. I know it wont be easy but i am set on doing it. I want a 126 long wheel base with the 617 diesel engine. Wish me luck!

Sounds excellent!! The 1986 420SEL had one of the crappiest engines in MB history, now nearly extinct as ALL of em blew their heads.

Good luck with the conversion. If it was me I'd be mostly worried about complicated vacuum lines for heat, doors, etc on the POS 420SEL. Everything else along with 300D ignition switch oughta be piece of cake.

I think you may have a screw loose. That seems like an awful bunch of work. Why don't you just sell what you have and buy an SDL?

Cool! Good luck. Post pictures along the way.

no SDL
 

I would if they ever put the 5cylinder in the SDL i dont want the 6 cylinder

Same here, I don't think I'd want the SDL just because of the 603. I am a 617 man. :D

This is the first I've heard of the M117 4.2L V8 being a bad engine. Have any proof?

They sure aren't extinct in California. You couldn't throw a glowplug in a parking lot without hitting one here... ;)

Strange, I see more 420SELs around than 560SELs or 300SE/Ls...



You guys that like the 617 need to drive, then you'll want to own a 603 powered car. I love my L. :D

There's no problem particular w/ the 420SELs. They do not have the M117s, but rather the small block M116 engines. The 380SELs they replaced had engine problems because they received single row timing chains for a couple of years. Otherwise, the M116 are a long lived as any other Mercedes gasser engine of the time. All the V-8s stretch their chains after a while, and if ignored can lead to broken rails, etc.

engines
 

I have nothing against the 603 really... Im sure they drive nice and have lots of power but im so in love with the 617. I know it, know were i can get parts for it. The only thing i long for is self-adjusting valves.

Notorious head benders, thats what they are. MB retooled the head and made it too thin for the 420SEL alone. Common knowledge they rarely see 200k miles without blowing a gasket and bending the heads.

But if somebody is looking for a decent MB body shell with blown engine (uncommon to find) then 420SEL's are the way to go.

I'll hold out for my grandmother's 420SEL then. It has ~280k miles now and will still light up the tires. Good thing her car doesn't know that it is on borrowed time :)

Good luck with the project. Be sure to post pics.

-Tad

I also see a lot of 420's driving around just fine....I doubt its a "bad" engine....I never see 500's/300's or 380's though. 90% of the time its 420's or 560's around here....

rear end?
 

Any one know if the rear end in the 86 420 and 82 300 SD are the same? I suspect they are different and need to be changed

I'd keep the 420SEL one, it's a 2.47:1 versus the 3.08:1 in the '82 SD. Meaning perfect for in town in 3rd gear and lower freeway RPM at 65-75mph (where most speed limits are currently). :)

If I were doing that I would bring the bone yard car home and have it as close to the "operating room" as possible. I've done a couple simple 240D swaps and I was always running back and forth, I cant imagine all the things your gona deal with.

excellent advise
 

if you can swing it.

tom w

to many cars
 

Ive got too many cars sitting around as it is. Im goign to strip the car complety label everything and bring everything home before i start with the 420. I also have an operating 300 SD to use as a model. it is my everyday car.

Dude no offense but you dont know what you are talking about. First search autotrader and educate yourself on how many gas W126's are out their, they outnumber our diesels like almost 10 to 1. Then look at how many have 200, 300, 400 thousand miles on them.

The M116 is a fine V8, lots of power and good milege. They do not have head issues other then the valve stem seals going bad. As with any MB gas engine of the era they require timing chain changes at 100k. The M116's are much more sensitive to this then the larger M117's. The also usually need valve work in the 150k-200k, and the cams tend to wear a bit. But the bottom ends hold up forever, actually I think Gilly works on a few that have over 500k on them.