Hey folks!

I just bought a 1983 300D with a turbo 617 engine. It's my first Mercedes and my first diesel, and I love the thing already. However, a previous owner seems to have been quite a fan of homebrew modificatons, and I, well, am not. So I need some advice from people more familiar with this engine than I am about restoring it to a more original state, if someone could be so kind.

The ALDA system switchover valve has been removed. Evidently a number of people have done this without negative consequences, but it's my understanding the valve is there to keep Very Bad Things from happening, and I'd like it back. Searching the parts catalogue finds nothing called a "switchover" valve, is it the same thing as the "vacuum to diesel shutoff valve"? Or does it have another name?

Also, the ALDA screw has been opened and adjusted. I've read that many people break these screws while attempting to adjust them, how can I tell if mine is all right? Can you tell visually?

Lastly: I've also read about some people putting a ball bearing or BB pellet in their EGR system to deactivate it. Where is this done and how can I check to see if it has been done to mine?

I appreciate in advance any advice I might get. As I have no experience with these cars, I'm ill-equipped to pick up on their nuances. Thank you!

Welcome to the forum! This forum is one of the best places to help you enjoy your "new" car.

For the switchover valve, try this thread: Another Switchover Valve ?
The switchover valve is located on the firewall, driver's side, near the brake booster on your car.

To help you find info, try the "search this forum" on the blue header bar. Look for threads with the attachment "paperclip" and they will have photos. Another place to look is the DIY links. Whunter has segregated a multitude of threads that pertain to specific systems and usually the ones with the best photo content.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Welcome to the forum.

I was doing some searching and found this thread, a couple good videos on Alda and the EGR.

1983 300CDT (W123/OM617) Vacuum Hoses - Benzworld.org - Mercedes-Benz Discussion Forum


Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

CJ,

Welcome to the forum. I'm about 6 months into my first diesel MB as well.

FWIW, the ALDA removal/modification was/is a common practice. I guess you could lump it under DIY or home brew, but it might be wise to understand why it was removed and what function it serves.

Just my .02

My EGR valve was leaking badly, essentially blowing some of the exhaust into the intake. Blocking the control to would not have made much difference. My car is very clean but the inside of intake was covered in tar. Probably the intakes and combustion chambers likewise.

I doubt if you will have any substantial benefit by having the ALDA system put back on. I suppose if your style of driving is to push the pedal to the metal off the line then it might be wise to have it back on.

My advise would be to put your maintenance effort into making sure that the basic systems are working efficiently. Having the fluids and filters changed. The valves and timing adjusted. The glow plugs and turbo working. The suspension tight. Brakes bled.

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85 Merc 300D - Unwinding 31 years of wear
86 VW TD
Mahindra Diesel
Iseki Diesel

In 2007 I didn't own a diesel.

MB egr fun - YouTube

The above may help, as well as the attachment.

If the valve does not get any vacuum, it will remain closed, so all you need to do is put a BB in the line, or remove 'em.

Attached Thumbnails

 

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83 SD

84 CD

Hi Jack,

I'll echo the welcome.

The switch you mention is really a matter of personal preference. Put it this way, I have been on Mercedes discussion lists since 1996 and have never heard anyone indicate they had a problem, stemming from the switch being bypassed or removed.

My understanding is that it would only come into play in extreme circumstances. Given that the vast majority of these cars are actually set up well under top of factory spec for boost, you aren't likely to need that protection. I drove two of my previous cars for years without one. If you prefer to have things as the factory intended, by all means reinstall it.

The vacuum to diesel switchoff valve that you mention is not involved with boost. It's the round vacuum-operated valve that operates a push-pull lever that runs inside the pump to cut off fuel to shut down the motor. It is located on the back of the pump, facing the firewall and should have a brown vacuum line running into it. It's hard to see without leaning over and gently pulling back some of the vacuum plumbing that sits in the area.

ALDA screw: Some do break when adjusted, probably 1 in 20 based on my memory of what a shop owner posted on another list, on the subject. There is no external way to tell. You would have to try turning it counterclockwise and see if you feel any difference in increased performance.

Were you on Volvo lists, many moons ago? If not, someone else used the same handle.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

Seems logical but the truth is not the same. Take your valve off the intake manifold and see if it is leaking. Mine was.

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85 Merc 300D - Unwinding 31 years of wear
86 VW TD
Mahindra Diesel
Iseki Diesel

In 2007 I didn't own a diesel.

Assuming the basics are ok (fluids, filters, etc.)

Basic freshen it up checklist, in the order I would do it: (Keywords in bold)
-Replace your timing chain tensioner spring (and gasket)
-Valve adjustment (make your own valve adjustment wrenches, can possibly reuse valve cover seal if it's not too hard)
-Get your injectors pop tested & balanced (people do it here) and get new nozzles if the old ones are worn.
-Check your boost pressure and wastegate
-Vacuum and bowden cable adjustments on the transmission
-Check your timing chain stretch (Can be corrected with an offset woodruff key)
-Adjust your injection pump timing (The drip method is the most common)
-Check glow plug operation on all 5
-Upgrade the primer pump on the side of the IP
-Upgrade to copper/ brass fuses in the fuse box and gently clean the contacts (The stock aluminum ones get clear corrosion)

After these items are done it will be a new car.

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$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment

Okay, if the valve is/was operating properly, it won't open without vacuum.

The over boost protection (switchover) valve on my CD was bypassed when I bought the car.

A Mercedes mechanic mentioned the turbo doesn't provide enough boost to trip it, the engine is quite robust and the waste gate does the same thing, limit an over boost condition.

No issues.

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83 SD

84 CD

The situation that protection is needed is listed in the Manual as when you are towing a Trailer up Hill. Apparently the Engine speed drops; droping the Transmission Pump Speed. But, the Boost Pressure rises givien you more Fuel.
The Switch Trips and cuts off the Boost Pressure and there by reduces the Fuel.
Apparently that situation is bad for the Transmission.

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84 300D, 82 Volvo 244Gl Diesel

Diesel911,
So that is in the manual. Interesting, I have a manual, guess I should read through it again. It is there for the transmission rather than the engine per-Se?

I wonder how come the boost will go over what the waste gate is set at, say 9-12. I have heard that the switch over valve is at 16psi.

I figure that by having a boost gauge I can control the max manually by letting off. No fuel = no boost. I am going to use my egr port for a bung for the ETG.

Forgot to say "hi" CalicoJack.

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85 Merc 300D - Unwinding 31 years of wear
86 VW TD
Mahindra Diesel
Iseki Diesel

In 2007 I didn't own a diesel.

Thanks to everybody for their responses and pointing out the other threads and resources! Gotta love getting this level of community support for a thirty-year-old car, I bet this doesn't happen with your average 1980s Buick.

Even if it is a waste of time, I'll probably end up putting the switchover valve back on. I'm paranoid that way. The way I see it, if Mercedes designed it well enough to last this long in the first place, who am I to assume I know better than the entire Mercedes-Benz design staff and start screwing with it?

I'll be sure to start looking at the other areas of maintenance that were mentioned. I already changed the fuel filters, and the primer pump leaked so badly I almost started laughing, it was like an April Fool's joke. I bought a replacement although I haven't installed it yet. I've also been looking for a metric feeler gauge set to do the valves, if anyone has any comments on the KD Tools set mentioned on this website please feel free to bring them up.

Zacharias: No, I haven't posted on any Volvo forums, although I did have a 240 wagon back in the day I was quite fond of. Found out the hard way that Volvos live up to their reputation in a crash. Really don't want to find out about Mercedes, although I'm sure they do.

Thanks again everybody!

Jack

You do not need a "metric" feeler gauge. Use the English equivalent .oo4" on intake and .014" for exhausts. Everything will be fine.

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85 Merc 300D - Unwinding 31 years of wear
86 VW TD
Mahindra Diesel
Iseki Diesel

In 2007 I didn't own a diesel.

Make sure you use the black primer pump, it's the uprated version.

It's worth checking your boost pressure if you want performance-the two 617s I've worked on were both set at 9-ish PSI from the factory, when the IP can put out "12 psi" of fuel (from what I've heard)

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$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment