Compression results: 320 - 220 psi, is it terminal?
 

Hi all, can you give me an assessment of these compression numbers?

1 - 300
2 - 290
3 - 310
4 - 320
5 - 220 :eek:

Check done on a 1983 300SD with 350k, cold (70F) engine, US General tester via injector. Valve clearances all checked & adjusted before. Fully charged battery with assist from charger.

I ran the check twice after I saw #5. First time I went 1->5, then charged the battery for another 3 hrs, and ran it again 5->1.

I added oil to #5, but couldn't get it to read above 220 no matter what. Pulled the valve cover and re-checked clearances, no dice. Couldn't spot any leaks, either.

Car runs well, but mileage has dropped since the last valve adjustment (~10-15k ago). Smoke has gotten worse.

All injectors tested good (Metro Diesel in Santa Fe using Diesel Kiki tester), so I think the smoke is coming from #5's low compression.

So here's the question.. is it likely repairable, and if not, think it would run another 50k miles?

#5 is a worry.
Is there much blow by?
It could be stuck rings.
Has the car been run on WVO?
What was the reading on #5 before the oil was added?
Is the car idling roughly?
The test should have been done on a warm motor.
Does it use much oil?

The change in mileage since adjusting the valves points to a mistake in the #5 valves. I would recheck that first.

X2

Unfortunately, if the exhaust valve was set to intake specs, it's likely to have hung open at certain operating points and has burned.

Oil consumption is low.

Adding oil to #5 made almost no difference (200 psi vs 220 psi).

Car has never seen WVO.

Blowby could be better, but I've seen much worse.

I should restate myself - The mileage decrease wasn't immediately after the valve adjustment (May - 10k ago). It ran fine then started smoking more in the last 2-3 months. I'm pretty sure I adjusted the valves right.. I've done it about a dozen times over the last 10 yrs. One thing I noticed is that #5 always needed adjustment.
I was thinking burned valve seat, since #5 had about .2mm clearance on the exhaust valve when I adjusted it before the compression check.

Yep.

I'm thinking about buying a rebuilt head.
What are the chances of me pulling the head and finding the bottom end is toast or something else terminal? Does the information so far point pretty solidly at the valve seat?

Hi
Seems to me a leak down test might be in order.
Joseph

Why?

Once you have excluded the obvious three like leaking injector seal, leaking glowplug seal, and too tight tappets....

NO MATTER WHAT THE PROBLEM IS, the head has to come off to do any kind of remedial work.

Once the head is off, even if you discover the problem is stuck / cracked rings and the head is perfect, you have lost PRECISELY NOTHING. In either time or money.

What is it with this forum that people keep suggesting successive tests, all looking for a specific result that gives a cheap / fast / easy cure?

The guy already did a cold dry and cold wet (add oil) test, it made bugger all difference so as much as it is possible to know, he doesn't have a ring problem.

Take the bloody head off and let the dog see the rabbit.

Have you ever pulled a head on a mercedes diesel motor?

Hi
Well, to each his own I guess. A leak down test is easy, fast & cheap. A broken piston/ring or even a scored cylinder wall might well mean the engine isn't worth repairing. On the other hand, leaking valves or failed head gasket might mean the expense wont be that great.

Being on the lazy side myself, I wouldn't pull a diesel head just for the fun of a look see.

Cheers,
Joseph

x2 leak down test first

And that, folks, is everything that is wrong with this world.

The addition of oil down nos. 5 pot did not much increase the reading.

This points to Valve/s leaking....

Pull the head, re-guide and re-valve, re-cut seats and lap in new valves, fit new valve seals.
Check closely valve-springs and compare to FSM spec, or replace.

Replace the Lock-Nuts on valve-stems, as the high milage will probably mean that these have worn down below min thickness.....

Nice easy weekend job....:)

Lacking a real leakdown tester, I rigged up a 20 psi regulated source to the compression test fitting (See picture, sorry about the quality)

http://lh5.ggpht.com/_o_3o6xcLap8/TM...0/100_3273.JPG

It's pressurizing the crankcase.. If I hold my hand over the crank breather, I can feel the pressure. If I hold it over the compressor inlet, nothing. Sounds like it's blowing into the crank, can't hear anything in the exhaust.

Hole in the piston?