Here's my take on the situation. I'm in the US but I am a UK citizen. It appears that such things are relevant to this problem somehow.
At 304k miles, the engine is reaching the limits of it's serviceable life. So in my mind, the question is whether it is worth doing anything more than just a head job on it. If you can confirm via a leakdown test that the valve is the culprit, you face a simpler decision. Is the car and engine worth the cost of a head job? The cost of a complete engine rebuild is far higher and involves much more work. If the valves are seating well and the leakdown test points to a ring problem, it might be better to simply continue driving the car while looking for a low mileage replacement engine which would be much cheaper than rebuilding the existing one.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

+1. Cost of a head gasket and reworked head is about the same as a serviceable used engine. If you yank the head a find a problem in the bores, you're taking the bus while you find a replacement.

It starts, it pulls, good enough till you find a good one in a deerslayer.

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CC: NSA

All things are burning, know this and be released.

82 Benz 240 D, Kuan Yin
12 Ford Escape 4wd

You're four times

It's hard to

more likely to

concentrate on

have an accident

two things

when you're on

at the same time.

a cell phone.

www.kiva.org It's not like there's anything wrong with feeling good, is there?

bzzzzt

Devil you know with a fairly minor problem that can be easily repaired, vs Devil you don't know, and A VAST AMOUNT MORE LABOUR.

Seriously, an engine swap being billed as being easier and faster and cheaper than a little head work on a known good motor???

Can I have some of what you people are smoking.

Market's different in LA vs NY (born NY'er here, while we're on the subject of origins..). NY was full of people who change the oil and never wash the car. LA people wash the car weekly and never change the oil. Lots of good chassis out here with bad motors. My engine is actually a NY engine, swapped into a low-rust chassis. This mill has 351k on it right now (I should update my sig..), 200k by me.

In all this testing, what was at question was the bottom end, rings & pistons. Either I can determine with confidence they're bad, or I reach some set of possible faults.

1. Conclusion: bottom end failure. My action: drive it till it quits, enjoy the rest of my time with it.

2. Conclusion: tests inconclusive, possible bottom end, possible head. My action: drive it until I have time to pull the head, enjoy another 10 years with it.

I'm with #2. We'll see what the head removal brings.. give me about a month or so.. I'm not that great at getting time for stuff.

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'82 300SD 351k

Worst thing you can possibly do to your engine is drive it like that.... at 100 psi low you're running at about 14.5:1 compression, enough for a tuned petrol engine, not enough for a diesel, so low in fact you are probably not even getting ignition, which means diesel fuel running into the bore, acting like a cutting compound on the piston / rings / bore, and eventually going into the sump causing sump dilution and possible eventual runaway diesel...

Despite what you state above, the tests you have done are anything but inconclusive and quite sufficient (assuming you checked injector / heater blowby and tight valves) to say with a great deal of confidence that what you have at the moment is LARGELY a single valve problem, almost certainly the exhaust valve.

I was thinking about the possibility that a worn cam lobe might not be making the #5 intake valve open fully.

At cranking speed almost any inlet valve lift is sufficient to full charge the cylinder. Plus of course inlet valves are always larger so the same amount of lift = greater opening WRT an exhaust valve.

With just short manifolds you can easily hear blowing valves on tickover.

Actually its way easier and cheaper, certainly for this vehicle. A complete engine swap can be accomplished in a few hours by one guy. Lets say half a day to a complete day at most to do the lions share of the labor if its done at a shop.

Additionally, it can be accomplished by a far less technically competent mechanic, someone who knows nothing about the internals, allowing the vehicles owner to find just the right place at the right price, or do it themselves in a driveway over a few weekends, and also requires no special tools of any kind, which is an investment needed to turn the engine into a short block. Engine for a few hundred bucks, labor at a few hundred bucks, you could have a good yard engine in the car in one day for a good price.

Of course, you still have to do some preliminary tests, like a compression test on the donor engine, but heavens! what a waste of time!

It does not sound like the OP wants to do this, and will be working on this specific motor and weighing his options, but its definitely a viable option, and since people A- need their cars, and B- don't usually have money to burn, its a great option to discuss.

Engines can be had around here for 500 or less. I don't pretend to know what engine prices are in your area, so lets try and be a little more polite to other people Mr. "this guy on the internet", while forgetting you are also "this guy on the internet" to someone else.
You sound like you have valuable data to give to the OP, so less obnoxious grandstanding, and more civility please.

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This post brought to you by Carl's Jr.

not a problem - I found a shop in local to me (Metric Diesel) that charges $550 to rebuilt a 617 head. If I can find a crane or a friend with big guns, I'll have it off this weekend.


Oh how I hope you're right, but I'll believe it when I see it.

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'82 300SD 351k

Actually this is not necessarily true. If the lobe is worn in a way that changes the duration of it's open position the cylinder will not fill properly and hence will give a low compression. This would show in a leak down test as a cylinder with sound rings and sound valves.

Your advice is good to a point but not necessarily for a do it yourselfer.

And a repalcement cam is a lot less work than pulling a head and a good used cam can be had for probably less than a head gasket set.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

In this scenario, low compression would only be possible if the valve restricts airflow to such a degree that there is a slight vacuum in the cylinder prior to the compression stroke.

I cannot fathom any scenario where this would occur at cranking speed unless the cam lobe is basically non-existent.

Well said.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

X3

The diesel benz crowd seems to have more dedication to detail and general enthusiasm than your average group of motorheads. I appreciate everyone's comments and suggestions, there's lots of experiences out there to hear about.

To answer some questions raised:

Cam looked fine. All lobes smooth, bright, & shiny.

Glow plugs have been serviced several times in that motor's history, including #5.

Motor swap is out.. the local market for motors is poor, I'd be looking at least $2000 before I got a motor in significantly better shape than mine. I watch craigslist for other 300SD's, but if they're good, they're priced as gold, and if they're crap, they're still priced as if they're good. Besides, I think I'm more attached to the motor than the car.

I'm driving this car because I have a high-mileage commute through the pit of zombie road pirates known as the San Fernando Valley. I want something that doesn't depreciate with miles and is tough enough to take a hit from an Escalade with no loss of life. I will keep it alive because it keeps me alive, and because I've developed an irrational emotional attachment to which I'm sure most of you can relate.

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'82 300SD 351k

How about we all take a deep breath & let this guy have some time to digest all the suggestions that have been made. Its his car & at the end of the day he will make his own mind up!! If he wishes to do more diagnostics he will. If he wishes to pull the head or motor, he will.
I am very interested to follow this problem to the end. No one on here is too old to learn something new!!
Any encouragement that I can give you is on offer mcneil !!
Good luck with your motor!!!

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving