Rebuilt Engine Break-in

This does not seem right. Are you sure your PCV valve is closing? I may have the name wrong. The valve I am referring to recycles part of your exhaust through the turbo so the nitrogen is more completely burned. It is a pollution control feature, and if it is not closing your engine will have no power at low RPMs and will be hard to start. The recycling is only supposed to kick in when the engine is warm and over a certain RPM.

Who rebuilt this engine?

I had the 617 in my 1982 300 TDT remanufactured by Metric Motors in Cayugah Park, California and it never lacked power the way you describe once I got that valve closed, but it did when that was not functioning. It's mounted on the right side of the engine (passenger side) on the exhaust manifold and has vacuum lines going to it from the switching box on top of the valve cover.

Something is wrong beyond breaking in if your engine lacks power to the degree you mention.

My engine has about 25,000 miles on it now and it runs great. I would say that it reached peak performance at about 15,000 miles. But even when it was brand new it had more power than it did before the rebuild.

This sounds like the rings did not seat properly. Did you have them resleeve the block and put in standard pistons, or was the block bored out and oversized pistons used?

My engine has new sleeves and standard pistons, so it really is just like new.

Did you use a shop that specializes in Mercedes diesels? Metric Motors is such a place. My remanufacture included a new turbo and injection pump and cost about $6000.

Actually, the turbo was not new, but a rebuild from an L.A. shop that specializes in rebuilding turbos.

You mean the EGR valve:

This sounds very much like a probability in this case. I will have that EGR valved checked today. The engine has very low power upon accelerating away from a stop, and very weak all through the gears. I would have expected it to be improving by now.

Thanks for the advice.

The engine was rebuilt by a reputable M-B shop, by a Stuttgart-trained Mercedes technician. The cylinders were bored and oversized pistons installed.

It is of course possible that the rings did not seat properly; however, I did everything necessary to ensure that they did, in terms of the initial run-in. Although there are varying opinions as to how to properly break in a diesel engine, I followed a deliberate and valid break-in schedule thus far, in order to ensure proper ring seating. Still, it is something of a crapshoot on any rebuild, I suppose...

I did check the EGR valve and it functions OK, so this is caused by another problem.

It is of course possible that the rings did not seat properly; however, I did everything necessary to ensure that they did, in terms of the initial run-in. Although there are varying opinions as to how to properly break in a diesel engine, I followed a deliberate and valid break-in schedule thus far, in order to ensure proper ring seating. Still, it is something of a crapshoot on any rebuild, I suppose...

It's not a crap shoot. If the engine is done properly the rings will be seated by the time the engine is up to operating temperature. However, I think your problem is injection pump timing, and/or cam timing.

snipped-for-privacy@mac.com ha scritto:

I presume you're concerned by the quality of the job done to your engine. I'd suggest to check compression. Or ask to the shop to run a compression check while you're there.... It's hard to say from Italy what's wrong in your engine, based on your description. It's only easy to say that something is wrong...

That does seem like a possibility. And I would say, something to hope for, as opposed to a bad overhaul.

Thanks for the reminder - Yeah it's the EGR valve.

Certainly the shop must have some sort of guarantee on its work. If the rings didn't seat, they have to do it over. If it's not the EGR valve, and the compression is good, I agree that the timing is the next thing to check.

I don't mean to hijack the thread but this is a related question for both Randall and Paul (or anyone who knows): What is that made you decide to rebuild? Excessive smoke - if so when hot or cold or both? Low compression? Low power?

In my case, the engine failed prematurely as the result of wrongly set valves. This lead to valve burning, no compression and engine failure. The engine only had 215K on it and would not have failed at that point without some external factor. My initial impulse was to replace the engine with a factory new one, but found out that that is no longer the option it once was. COnsequently, rebuild was the next best solution.

Yes, the engine is under warranty. I am having the engine checked for compression on Monday, and if that's OK, they will retime the injector, which more and more, I am thinking makes sense as the reason for the low power. There is very little likelihood that the rings have not seated properly.

My engine had 394,000 miles on it. I didn't understand the EGR valve and it had stuck open, making the engine extremely difficult to start. I didn't know it at the time, but the head was cracked in 6 places, reducing compression. The lower end of the engine was probably fine. The oil consumption was about a quart every 2000 miles, and the new engine consumes oil at approximately the same rate.

I think I got cheated a little bit on the rebuild because I was supposed to get a new camshaft, but I think the same camshaft was reused because some pitting that was present on the edge of the lobe for the #1 cylinder exhaust valve appears to still be there.

But the engine runs great and has significantly more power than it did before. A new head would probably had the same effect and saved me $5000, but I am still glad I went with the remanufacture, especially getting a new timing chain, injection pump and rebuilt turbo.

Long thread...

There is definitely something wrong. There are several possibilities...

1. Vacuum pump dead. Easily checked with gauge.

1. Valve adjustment off... unlikely but possible.

2. Turbo not kicking in is real possibility.

1. Poor compression... very unlikely.

Bring the car back to them and have them recheck everything... it is just not right to have so weak of an engine.

_____ I agree completely.

After any engine overhaul the mechanic is obliged to make an extensive test run. Only after it passes objective performance metrics shall the repairs be considered "completed". Then the customer can be invited to collect the car.

I once had a used engine installed in my 1981 300 SD. When i retrieved the car the gear box was shifting very harshly. The mechanic did not test the car thoroughly enough. In an ideal world this small error would have been caught. I knew that the tranny relied on throttle position dependent vacuum. Sure enough, the mechanic had mixed up some of the nylon vacuum connections. After i corrected the error, the gears shifted smoothly again.

In the case of poor power after rebuild i believe the most probable cause is incorrect injection pump timing. Cam timing could be off a bit, but this is unlikely.

/ JCH

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Well, it goes back into the shop tomorrow morning to have all these items checked. This is a non-turbo, but everything else will be checked. I have a suspicion that this may be due to a badly-timed injector pump, but time will tell. The engine is very flat from a standing start, and is flat on the top end, but seems to have more-or- less normal power in between.