W123 Turbo Issue - PeachParts Mercedes-Benz Forum

chief_noseeum · #1 10-13-2004, 07:21 PM

Hi All,

I first posted on Sept 24 about my 1982 300 TD problem. To recap, one of the oil hoses ruptured while I was driving at 65 mph on the Interstate. I pulled over when the engine started to lose power and stopped the car. After repairing the hose and adding six quarts of oil, I tried to restart, but it would not.
I had the car towed home and here it sits. It easlily started cold, but it ran roughly and smoked a lot. I suspected engine damage from the lack of oil, so today I removed the valve cover and inspected the cam, liflters and adjusting nuts, they all looked fine, but the valve cleareances were off - too tight. I adjusted them per specifications, and reasseambled the valve cover. It started right up and ran smoothly without any smoke.
I took it for a test run around the block. As the engine warmed up, it lost power, and I noticed a whine from under the hood. I suspect that the turbo is responsible for the power loss. I had previously checked it by spinning the suction wheel when the engine was both cold and hot. It spun freely, but that is as far as I got with it.
I'm now assuming that the cylinders were not damaged by the short time the car was very low on oil. The problem seems to be the turbo.
Any thoughts or recommendations?

Regards,
The Chief

#2 10-13-2004, 07:28 PM

Quote:

Originally Posted by chief_noseeum

I suspect that the turbo is responsible for the power loss. I had previously checked it by spinning the suction wheel when the engine was both cold and hot. It spun freely, but that is as far as I got with it.

Grab the turbo spindle and move it in/out and up/down. There should be very little to no movement in those directions. If it does, it's time for a turbo rebuild or replacment.

If you do go the replacment route, I strongly suggest the 3K turbo over the garrett.

psfred · #3 10-13-2004, 07:32 PM

Sadly, it's quite possible you have bearing trouble, scrapes on the cylinder walls, etc, but if you have proper oil pressure (at least 1 bar at idle) and aren't making smoke, it may just be the turbo.

check the boost signal line for clogs at the intake manifold, and verify that it holds pressure all the way to the ALDA.

Check the turbine wheel for axial play. I'm willing to bet that the turbo was more likely damaged by low oil than the engine.

I suspect you will find a bit of axial play and more side play than you should have, and it won't spin up properly hot. If you rotate it, you will find it doesn't spin freely, but has some vaguely defined tight spots in rotation.

If the oil pressure is low hot, it's rebuild time.

Peter

chief_noseeum · #4 10-13-2004, 09:20 PM

Thanks guys,

I will check the turbine for axial and radial play and also check the signal line for blockages.

Any idea how much a turbo rebuild costs? Is there someone with a website that specializes in this type of work?

Regards,
The Chief

chief_noseeum · #5 10-17-2004, 01:11 PM

Since my last post, I checked the 617 turbo for boost pressure and play in the compressor wheel. I hooked up a T fitting with a pressure/vaccum gauge to the banjo intake manifold fitting near the firewall. I could not get a positive pressure by racing the engine in park. In fact, there is a slight vacuum as rpms increase. I also did a load test consisting of driving the car and observing the pressure gauge. Again, no positive intake manifold pressure.

I also observed the turbo was spinning when the engine was running. There was very little axial play in the compressor wheel with the engine stopped.

Conclusion: The turbo spins in an apparently normal way, but does not pressurize the intake manifold. I looked at the drawings of the turbo in the 617 engine manual and came up with the following three possible causes of loss of pressure.

1. The pressure regulator valve is stuck open causing all pressure to vent to exhaust

2. There are leaks in the shaft seals that allow the pressure to vent

3. The loss of oil flow to the bearings caused the wheel to rub resulting in larger cleareances between the wheel and the volute body

Does anyone know if there are rebuild kits available for the bearings and shaft seals or do you just by used turbo?

Regards,
The Chief

psfred · #6 10-17-2004, 01:26 PM

Most likely the waste gate is stuck open, venting all the exhaust around the turbo so it won't produce much boost. Slight vac would indicate some function, but not much.

However, slight binding when moved manually means no decent turbo speed, so if the wheel shows ANY roughness or stiffness when you turn it by hand, it will not produce boost, period.

There are several options -- any decent diesel injection service will be able to fix it, most likely it needs a cartridge (really a whole turbo minus the inlet and outlet housings). You can do this yourself if you want, you can even grind the bolts off if necessary since you won't be doing anything but swapping the bearing housing, shaft, wheels, and bearings out whole.

You can also get the bearings replaced by the shop if you want, this may or may not be cheaper. I woudn't do this my self, as you really need to balance it afterwards.

Check to make sure the linkage between the wastegate actuator and the servo is still intact -- on some of the turbos used by Benz, this linkage can come off and you will (obviously) get little or no boost with the wastegate hanging wide open...

Peter

dieseldiehard · #7 10-17-2004, 02:25 PM

You cannot get pressure in an unloaded condition, the car has to be running down the road (or on a dyno) to see pressure. Hook a hose with your gauge at the end to the rear of the manifold with an added tee or to the alda, run it to the inside of the car either thru the firewall or under the hood and around into an open window temporarily. You should see pressure as you accelerate.
I've had turbos rebuilt by Majestic turbos in Waco TX. I believe its http://www.majesticturbo.com

Brian Carlton · #8 10-17-2004, 04:09 PM

Quote:

Originally Posted by psfred

You can also get the bearings replaced by the shop if you want, this may or may not be cheaper. I woudn't do this my self, as you really need to balance it afterwards.

If any of you fellows get to this point and need the unit balanced, prior to putting it back into the housing, let me know. I have the resources to balance the impeller/turbine wheel assembly down to the required tolerance.
With the proper equipment, it is a two hour job at most.

chief_noseeum · #9 10-17-2004, 05:20 PM

Peter,

Thanks for the info. I checked the rotation of the turbo by spinning it. Although there is no wobble and no sticky point as the wheel rotates, I suspect that there is too much friction in the bearings. This is a very subjective test as I don't have another tubo to compare it to.

Dieseldiehard,

I did a road test as you described by connecting a T to the ALDA line at the intake manifold and running the line our throught the fender well. I taped the pressure gauge to the windshield and drove the car around the neighborhood. There was no positive pressure in the intake manifold.

Since the loss of power coincided with a loss of oil from a ruptured oil hose, I am betting that the turbo bearings were damaged, but not destroyed. My theory is that they bearings are generting too much friction for the turbo to reach proper speeds.

Now the question is whether to have this unit rebuilt or simply buy a used one to replace it.

Regards,
The Chief

#10 10-17-2004, 07:12 PM

Maybe you cracked the overboost sensor
line while adjusting the valves.

It happend to me when I replaced
my valve cover gasket.
Result: reduced power since there was no signal
to the ALDA.

Also check the lines and banjo bolts for gunk build up.

Louis.

psfred · #11 10-17-2004, 07:18 PM

Normally the turbo will turn with very light pressure. The one on my sister's 740 gas turbo would spin freely, but the ones on the diesels wont' spin much if you flip the wheel.

My Volvo didn't spin at all when the turbo finally died -- you could turn it fairly easily, but it didn't spin if you flipped the wheel with a finger tip, and it definitely had a couple binding spots in rotation. No boost at all, and VERY low power...

worth having it check out, for sure.

Peter

dieseldiehard · #12 10-17-2004, 09:03 PM

The Chief said: "Now the question is whether to have this unit rebuilt or simply buy a used one to replace it."
There is nothing wrong with a used turbo as they last a very long time. But watchout for any turbos that don't come with a guarantee, hopefully off a known running car. The labor to R&R is too great to take a chance on say an eBay turbo.
I had a supposedly newly rebuilt turbo that even had too much play end to end, the 300D ran awful.
That is how I learned that the turbodiesel is designed to live off its turbo. No turbo or a bad turbo and the car simply won't run right at all. I agree the loss of oil must have damaged the bearings and now its got friction is probably the best explanation of what happened..

chief_noseeum · #13 10-17-2004, 09:26 PM

Thanks for the advice. I will update this thread as I make progress. I was ready to scrap the car, but I am encouraged by everyone's help so I will pursue a repair.

I looked up the procedure to remove the turbo in the MB manual. It doesn't look too difficult, maybe two hours if exhaust flange bolts don't resist too much. My plan is to pursure both repaining the existing unit and locating a used turbo.

I found a lot of 617 turbo's on car_parts.com. Prices vary greatly ($75-500) so I'll start working up from the low end and ask about the history of the car it came from as well as any guarantees.

chief_noseeum · #14 10-26-2004, 08:24 AM

Since I last posted I have obtained a used turbo through car-parts.com. I recommend the web site. It is very easy to use and I quickly found a plethora of used W123 turbos. I contacted one used parts house in MA and two days later, the part was on my doorstep.

On Saturday, I started to remove the old turbo and was quickly stymied by the 1/n rule. By this I mean there is always one bolt or nut out of n total that resists turning. In my case I could access three of the four nuts that hold the turbo to the exhuase manifold from the top of the engine. The fourth was only accessible from under the car. Even then I needed to go to sears and get a long box end 17 mm wrench before I fould loosen the nut. One I got past this, the rest was very easy. I was surprised that the exhaust flange nuts came off as easy as they did after U sprayed them with rust penetrating oil.

I have not installed the replacement turbo yet. I wanted to maximize the chance that it would work correctly before instaling it. After cleaning up the outside with engine degreaser, I started to flush the bearings with carb cleaner to remove any old oil residues. I noticed that the friction in the bearings decreased after this step. I then continued by spraying penetrating oil into the bearing case and manually spinning the turbo. This further reduced friction so I let it sit overnight. Meanwhile, I removed the cover plate on the pressure control valve to make sure it was closed and tight. The valve was closed and looked fine.

I will start reassembly later this week. I need a new O ring for the oil return tube and it will take a few days to get one. I will post againg after I re-install the turbo.

Regards,
The Chief

psfred · #15 10-26-2004, 08:10 PM

Re-oil the turbo before installing or running, or the bearings won't survive. Fill the oil inlet with motor oil and spin turbo -- I'm betting the "stiffness" will return (full floating frictionless bearings -- they don't spin freely unless full of warm oil).

Peter