240D Engine Autopsy - PeachParts Mercedes-Benz Forum

Charlie20 · #1 11-21-2009, 01:51 PM

A few months ago I completed an engine overhaul for my 79 240D. I thought some of the forum members might be interested in the internal condition. The engine had about 230K miles on it, and had been well maintained over it's life. I can attest to this because it is a one family car that was bought new by my in-laws, and my father in law is a stickler for maintenance. So it was never overheated seriously, and had regular oil changes. It used about 1 qt of oil (probably a lot was leakage) every 600 miles, and belched a huge amount of smoke on startup. What I found:
-The middle ring on the #1 piston was broken (see photo). About a year earlier compression readings were 310, 350, 340, and 350, with the low one being #1. So I am guessing the ring was broken at the time of the measurements.
- The intermediate gear set was excessively worn (see photo).
- The crankshaft was in specification and needed polishing only. Replaced main bearings, but the old ones were still good.
- the camshaft and bearings were good.
- All cylinder liners were worn beyond re-use and were replaced. I attached a photo of the block after it came back from the shop.
- Pistons showed out of spec wear and were replaced.
- Oil pump was replaced, just for GP
- The major oil leak turned out to be from the head gasket, at the rear of the engine. I had misdiagnosed it as being the rear seal, but there was actually only a small amount of leakage from there.
- I had the head completely reconditioned: new valves, seals, guides, etc.

Everything is back together now, and I have about 8K miles on it. There are no leaks, it starts right up, does not smoke at startup and runs much better. It was a lot of work and $, but a good experience for an amatuer like me well worth it. I especially want to thank this forum, because without the information I got from it, things could have been much more difficult and turned out much worse.

leathermang · #2 11-21-2009, 02:01 PM

Thanks for that report.
At 8K it should be broken in... so tell us about what you are getting in mileage...and whether it is a manual or auto trans.
Number one cylinder is often an anomaly.
When you put the new head gasket on... did you check in the FSM and make sure you got the latest design for your engine ? There were some changes made in water jacket holes and such over the years...

JEBalles · #3 11-21-2009, 02:06 PM

Those compression readings seem kind of weird. That's similar to mine, but my runs fine. No smoke, starts easy with a good glowin'. I thought a broken ring would cause super low compression in one cylinder.

leathermang · #4 11-21-2009, 02:16 PM

With as many rings as they have...and as tight as the fit is supposed to be ... the condition of the piston lands in keeping the broken ring contained may make more difference in some situations.

Charlie20 · #5 11-21-2009, 02:23 PM

Quote:

Originally Posted by leathermang

Thanks for that report.
At 8K it should be broken in... so tell us about what you are getting in mileage...and whether it is a manual or auto trans.
Number one cylinder is often an anomaly.
When you put the new head gasket on... did you check in the FSM and make sure you got the latest design for your engine ? There were some changes made in water jacket holes and such over the years...

It is an automatic. I did not keep track of the mileage before the overhaul, but afterwards it has ranged from 26-28. This is mostly on my work commute, which is freeway speed (I try to keep it under 70). During the break-in period I was careful to not do any sustained freeway speeds.
As for the head gasket, it is supposed to be the right one. In any case, the hoels lined up exactly. I made sure to check that.
Also, oil consumption is much less, less than 0.5 qt. in 2500 mi.

leathermang · #6 11-21-2009, 03:33 PM

Sounds like you have an engine which will serve you for many decades...

pawoSD · #7 11-22-2009, 12:11 AM

Seems odd that it would break a ring at only 230k....all of ours have way more than that on them, and run fine.....mine has a "decent" amount of blowby but will still start without a block heater at below 0 temps with maybe 5-7 seconds of cranking and a single glow cycle.

t walgamuth · #8 11-22-2009, 07:22 AM

If it broke an oil ring the compression might be fine.

Oldwolf · #9 11-22-2009, 08:10 AM

Thanks for the great report. Did you piece out the work that you could not do yourself to separate local shops or did you take the block and head to one place for refurbishment? What parts did you have to replaced and what parts were you able to reuse?

I often wonder what I will do when I have the first major problem with mine? Probably tackle it myself like you did.

Charlie20 · #10 11-22-2009, 11:46 AM

Quote:

Originally Posted by Oldwolf

Thanks for the great report. Did you piece out the work that you could not do yourself to separate local shops or did you take the block and head to one place for refurbishment? What parts did you have to replaced and what parts were you able to reuse?

I often wonder what I will do when I have the first major problem with mine? Probably tackle it myself like you did.

I had the head reconditioned by Metric Motors (www.mercedesengines.net) and they also did all of the work on the block. I first contacted Mike at Metric Motors, and explained that I wanted to overhaul the engine, and that to me it did not make economic sense on this particular car to purchase a reconditioned engine. Plus, I just wanted to do it myself. He had me bring in the pistons, block, head, and crankshaft for evaluation. Based on this, he gave me a quote. The quote was broken down between labor and parts. I checked the parts prices and he gave me wholesale prices. The charges for labor were very reasonable, I thought. The quality of the work excellent, and he was very helpful with good advice.

Parts replaced: pistons, rings, piston liners, crankshaft bearings, rod bushings, gaskets/seals, timing chain & rails, intermediate gear set (fortunately Metric Motors had a good used spare), valves, springs, prechambers, oil pump. Also, there is an oil pump drive bushing that needed replacing.
Parts kept: crankshaft (polished the old one), camshaft & bearings, everything not mentioned above as replaced.

The ring that broke was the middle ring (scraper ring, I think), so the oil ring and compression rings were still good. The engine started reliably but only after about a 20 second glo-plug heating. It was still running like this when I tore into it, and may have kept running indefinitely, but this was the only time window I had to do the overhaul, and I knew I wanted to keep the car, so I went for it then.

Stevo · #11 11-22-2009, 12:21 PM

Quote:

Originally Posted by t walgamuth

If it broke an oil ring the compression might be fine.

Good point. I posted about a friends 240D that has great compression but goes through a qt of oil every 200 miles, its not leaking and all the usual things were checked, except tearing down the engine to look for a broken oil ring.