Timing chain stretch? - PeachParts Mercedes-Benz Forum

#1 05-17-2002, 09:30 AM

Hello everyone,

I've got an '82 240D with about 180,000 miles and unknown quality of maintenance for the prior 165,000 miles or so.

After several months of blissful driving, the following symptoms have appeared. Car bogs down on hills (more than the usual 240D bog) At first, thought it was fuel related and replaced primary, secondary, and tank strainer to no avail. Hard starting when it got cool followed by not starting period. Glow plugs working fine as well as new glow plugs installed. During crank attempts, small puffs spitting back up through the intake. Removed valve cover to adjust valves and all clearances close to normal, nothing tight. Performed the dreaded compression check to find all cylinders evenly about 165-180 lbs. Oil pressure always fine but oil consumption was always on the high side. I immediately assumed the worst for my engine and have made plans accordingly until I checked one last thing...

I know that checking timing chain stretch without the dial indicator seems to be a topic for much discussion but this is what I've found. With the cam marks perfectly lined up on the cam tower, the crank timing indicator is about 11 degrees ATDC. Conversely, when the crank is on TDC, the cam tower timing marks are off. Is this normal if there has been an offset key installed and/or could a stretched chain be causing all of my problems including the low compression and spit-up through the intake?

I would hate to be the first one on this board to have to change out an engine at such an early age.

Thanks for any input, this board is great!

engatwork · #2 05-17-2002, 10:21 AM

I would suggest replacing the chain and tensioner before tearing into the engine.
The compression sounds awful low.

#3 05-17-2002, 10:23 AM

Your chain is most definitely stretched. I expect that the previous owner was not dilligent with oil changes. If not changed frequently the oil builds up microscopic particulate that will wear away the pins and rollers in the chain.

Although the chain should be replaced, I will be surprised if it is the source of your other ills. Since it needs it needs replacing anyway, you should probably roll in a new one and see what it does for the performance of the engine.

You might want to look closely at the tensioner while you're at it. The chain can be changed by removing the valve cover, grinding away a side plate, temporarily connecting the new chain and turning the engine to roll it into place. Then put the new link in place, back it up with a body dolly or large hammer and peen the pins in place with the ball side of a ball peen hammer.

Good luck,

#4 05-17-2002, 10:36 AM

300 pounds would be incredibly good for an engine with this many miles that has evidently not seen frequent oil changes. The engine should run okay with this much compression since it is consistent across all cylinders. The other bad symptom is the fact that the engine is using oil.

I believe, however, that there is no reason that this engine could not be made to run well, although you will need to carry some oil in the trunk.

Have a great day,

#5 05-17-2002, 11:32 AM

One of the convenient things about a diesel engine is that once it gets tired, as long as it starts AND as long as you can carry enough oil with you to get where you're going, you can keep driving it. With a gas engine this is not true because when it gets this tired it fouls spark plugs and otherwise won't run right.

A trailer with an oil tank and a hose to the top of the valve cover would be helpful.

BTW: when a diesel is burning oil, it is indeed burning the oil and sending you down the road with that energy. That oil you pour in is basically expensive fuel. In a gas engine, the oil does not get burned.

Have a great day,

gnolo · #6 05-17-2002, 12:03 PM

A pressure in lbs is the same thing than a pressure in psi ?

Sorry to bother you with that but I'm not very used to yours units.

#7 05-17-2002, 12:13 PM

"lbs" is an abbreviation for pounds. The proper term is "psi" which stands for "pounds per square inch". PSI is what pressure is measured in here in the US.

JimSmith · #8 05-17-2002, 12:23 PM

gnolo,

To answer your question simply, I would say "yes" that the intended units called pounds are pounds per square inch. And they are typically pounds per square inch over atmospheric pressure.

I hate to get nasty discussion on compression going, but the reported values are approaching those of a high performance gas car, not a Diesel, and in my neck of the woods I think if I could get the car started it would be by pulling it down the road at thirty miles an hour in third gear for a few miles.

With a compression reading like that I would invest in a wet compression check to see if the leakage is going past the piston rings and cylinder walls, or if it is due to valves and possibly valve timing problems. With that in hand, I might do a leak down test to find out where the leakage was going as well. Then I might invest in a chain, if the test results supported that the chain was going to help. Otherwise you might as well face it, you're a victim of prior owner abuse. If the car is really nice, I might invest in a rebuilt engine from a place like Metric Motors, or rebuild it locally if you have a source of good independent mechanics familiar with these cars. Running the car trailing a cloud of nasty oil smoke just because you can does not sound like much of a choice to me. I like my cars and I would have a hard time liking a machine that was borderline EPA disaster material, and might abruptly decide not to run once I got somewhere and shut it off.

Good luck, Jim

gnolo · #9 05-17-2002, 12:46 PM

What are the compression when the engine is new or almost new, 450 lbs ?
On my 81 240D, I have 430 lbs on 3 cylinders and 350 lbs at the 4th. But the worst is that this engine run very bad (impossible to do more than 3 miles) !!!

But when can we consider that a diesel engine is used ? I read somewhere than when the compression are below 220 lbs, a rebuilt of the engine is require.

NO1ZE, I don't figure out how you can started your engine with such compression. On my 300D the average compression is about
270 lbs and it's tough to start it when the temperature is below 32F.

tcane · #10 05-17-2002, 12:47 PM

NO1ZE:

The compression is too low for 1) enough air to be drawn into the cylinders and 2) the incoming air to be heated to high enough temperatures to completely ignite the injected diesel - evidenced by the hard starting. M-B spec calls for normal compression of 22-24 bar/319-348 psi, minimum compression 15 bar/218 psi, and I've seen 380-420 psi on engines with a lot more miles than your 180,000 mi. (the 240/300 cast iron engines can easily go 500,000 mi. before an overhaul is needed - with a bit of proper maintenance - your 180,000 mi. engine is only a bit over 1/3 of the way).

Your compression of 165-180 psi is 17-24% lower than M-B's minimum compression spec. I've seen trouble with starting and decent running with 200-220 psi.

Your high oil consumption is also evidence of low compression causing problems as oil slips by the rings (called blow-by) and then out the exhaust valves. What do you see when you open the oil filler cap when the engine is idling - engine has run a 2-3 minutes after start-up? I'll bet a lot of oil vapor puffing out the oil filler cap. As you wrote there is a lot of oil in the intake further indicating oil blow-by past the rings.

Sounds like the timimg chain has stretched a lot (but, did someone put an offset woodruff key in before, the max offset is like 10-12 degrees of camshaft timing as I recall). More likely the chain is stretched because the oil/filter was not changed as needed.

The more probable cause for the bad compression and timing chain stretch is poor/no maintenance, esp. timely oil/filter changes that have caused the engine parts to wear-out prematurely. The poor maintenance is not your problem because you just got the car, the blame is on the PO.

An observation about maintenance and the attitude some M-B owners have. I was at the parts/service counter at the M-B dealer here in San Antone. At the other end of the counter was a woman dressed to the teeth (fur, diamonds, gold, expensive dress, etc.) who had just had her M-B serviced. This woman was raising hell because of the repair bill and the level of her voice was at the level of a jet plane taking off. She went on and on about how much *&$%#& money she spent buying the #@&*$%# M-B and for that much money the $%*&@# car should never need any more work done to it and/or any work done should be done for free. You should have seen the counter folks scatter!! Soon, a person from management showed up to try and calm this woman down - without much success as he led her to a private office where the volume level diminished a bit after the door was closed, but every word she yelled was clearly audible as I paid for my parts, left the building, made my way to my M-B, and closed my door ending my ability to hear the woman yell. I have heard other owners who have similar attitudes toward maintenance - little to none - by M-B owners and owners of other makes. I would venture to guess that the PO had an attitude similar to this woman and that regular/preventive maintenance was very far down on the list of things to do, if it was on the list at all.

You can try putting a new timing chain in, but I'll bet any improvement will be minimal at best. Worn parts are worn parts, and when the cylinders are worn changing/renewing other parts won't help much. But, you can try to forestall tearing the engine down, inspectiing it, finding the problem(s), and repairing it. In the meantime, if you really like this car (as it sounds you do) you can look for a car with a bad body (salt damaged northern car, wreck, etc.) with a good drive train to buy and swap engines. Or, save your $ to rebuild your engine or find a used engine with a warranty. Or, look on eBay or other places for someone selling a rebuilt engine cheap - they do show up from time to time.

Good Luck!
Tom

#11 05-17-2002, 02:06 PM

I must chime in after seeing reference to a wet compression test. This is a gas engine step, it SHOULD NOT BE DONE ON A DIESEL!!

The oil CAN cause the engine to start which will blow your compression guage to Kingdom Come. If you're in the way of it, it'll put something on you that the doctor can't take off!

To safely determine whether the problem is rings or valves, do a leak down test and listen for where the air is leaking. If you hear it through the oil cap, it's rings, through the air filter, it's an intake valve, and through the exhaust is an exhaust valve. If you hear the air escaping everywhere it's a seriously worn out engine.

Be safe,

franklyspeaking · #12 05-17-2002, 04:20 PM

Timing chain replacement might be worthwhile, if stretch is so great that valves are not shut at Top Dead Center. Could be where your losing compression. The leak down test above should verify the source of your leakage. If it's through the valves, I'd try the chain replacement.

Good luck!

JimSmith · #13 05-17-2002, 04:30 PM

Hey, I guess I won't do that again - not really interested in giving the doctor a challenge. Thanks for the heads up while it is still connected, Larry. Jim