Compression Experts Please Help!! - PeachParts Mercedes-Benz Forum

GRIESL · #1 12-12-2006, 11:44 AM

I really respect the expert opinions on this forum. I've been searching for specifics on my case and haven't found exactly what I'm looking for, so decided to solicit advice directly. Thanks in advance for any help.

Car: 85 300d turbo diesel, 260k, no signs of any major engine work (I've had it the last 6k miles), but I have replaced injectors, valve seals, timing chain, adjusted valves.

Sympton: Blowing blue smoke mostly only at idle, tea kettle test dances the filler cap, but doesn't totally blow it off--so could be worse; using about 1 qt rotella 15/40 per 900 miles. At initial takeoff, I observe a pretty impressive puff of blue smoke in the rearview, but then it dissipates underway. So tested when parked--I give it the fuel, puffs blue initially, then I hold rpm's at 2k or so and smoke dissipates.

Car performance: Really quite good--15 sec. 0-60 times consistently. Idles well when warm and burning either bio or Cetane 45 diesel. I've fooled with ALDA and have it to where I get a small puff of black under heavy load and then it dissipates. Doesn't use coolant to signify head gasket.

Here's the kicker: Ordered up my Harbor Freight compression tester off of Ebay ($35 including shipping) to really see what I'm up against. Did the dry/wet (squirted 1 tsp. oil in cylinder) in a semi warm engine (got up to operating temp., then sat maybe 40 min.s in 50F weather (yeah, beautiful day yesterday!). Numbers as follows:

#1 - 360, 420
#2 - 260, 300
#3 - 220, 220
#4 - 100, 120
#5 - 260, 320

Did I mention that when doing timing chain (should have just done a rebuilt head then, but just wanted to get GRIESL bake on the road), noticed a few valve guides giving a little play, but I didn't write down which ones, wish I had, but I suspect #3 and #4.

Obviously a few issues going on here. Number one way up there, etc, but.... I actually view #3 and #4 as good news that they didn't respond to the oil squirt. The car runs so well now that I was shocked I had a hole at 100!

Question: Is it head or rings? Or heaven forbid a holed piston.

How do I interpret these numbers. Are the wet numbers on 1, 2 and 5 so bad that I should resign to doing rings? Or are the dry numbers on 3 and 4 encouraging enough to remove the head and have it reworked by, say, Metric? Would the squirt of oil reveal broken or stuck rings? Combined with the info about smoke dissipating at high rpm, is that a sign that would point more in the direction of valve guides?

I really like the car--body is great with no rust, handle's well, shifts well, and I have about 3k in it right now. I'm not opposed to doing the head (I would probably do the labor myself), but an engine rebuild would take too much of my time and the cost to pay someone to do it may make me pause. I'm currently mining ebay and other sources for a good used engine, but that seems risky if my engine only needs a head.

Again, thanks in advance for help.

rrgrassi · #2 12-12-2006, 11:57 AM

Could be valves out of adjustment, timing chain stretch, or even worse, blown head gasket, bad rings, burned valves, holes in piston, cracked sleeve/block.

Worn valve guides can cause the valve to not seat fully or incorrectly, resulting in improper wear.

vstech · #3 12-12-2006, 12:27 PM

http://www.peachparts.com/shopforum/showthread.php?t=172886&highlight=compression+test
The HF test kit is finicky.
make sure the numbers are correct.
John

GRIESL · #4 12-12-2006, 01:08 PM

I listened for seeping air from the instrument--all seemed well.

I'll redo today to be sure (ran out of time yesterday, so injectors are still out).

Where are those guys who recommend the oil squirt. It seems like a meaningful test, I just need to know how to intrepret the variations. And would the oil squirt reveal broken or stuck rings. For example, would the squirt of oil be able to seal a broken ring and boost the reading in the 100lb. hole?

btw, timing chain is new (boy was it way off - made huge improvement on running) and valves are freshly adjusted.

Like I said, I love the car, so if I can get it to where the smoke is at a minimum (I actually don't care about putting oil in, and 1qt/900 miles doesn't even sound that bad from what I hear), then I'd keep the car and do the head.

If I do the head, would problems with rings, cylinder walls, pistons be evident by looking down into the holes?

vstech · #5 12-12-2006, 01:25 PM

Quote:

Originally Posted by GRIESL

I listened for seeping air from the instrument--all seemed well.

I'll redo today to be sure (ran out of time yesterday, so injectors are still out).

btw, timing chain is new (boy was it way off - made huge improvement on running) and valves are freshly adjusted.

If I do the head, would problems with rings, cylinder walls, pistons be evident by looking down into the holes?

Hmm. I would think nothing would be visible through either hole, possibly a mini camera could be placed in the gp hole to inspect the piston top and the valves.
how far off was the timing chain? enough to damage a valve? I can't belive the car is running smooth with 100psi on one cylinder... unless the valves are totally gone and no pressure is building in that cyl at all. then it would be running like a 4 cyl... hmm. when you did the valves, did you notice if the cam lobe was bad on that cyl? a badly worn lobe would not allow much air into the cyl. just a thought. check it out.
John

GRIESL · #6 12-12-2006, 01:54 PM

Thanks for the speedy-quick posts. I wish I had taken more note of the camshaft condition. There was nothing obviously wrong with it, but I didn't spend a whole lot of time inspecting it.

I had not thought that the chain stretch could actually cause damage to a valve. It was way off--can't remember exactly how much, but I remember thinking that it was so off that it was getting close to being off by a whole tooth, which I think is 18 deg. It may have been off by like 15--it was a lot. Are you thinking that timing could have been off so much that a valve could come in contact with a piston?

I was shocked as well that the car could run with 100 in one of the pots. I do recall when I did the seals that at least two valves I could move a little side-to-side in the guide. Not a whole lot, but probably enough to prevent some pressure in the cylinder.

What about the smoke dissipating underway or at high rpm? When rings are bad, does the blue smoke dissipate at high rpm? Or is that more indicative of valves?

rrgrassi · #7 12-12-2006, 01:58 PM

Yep, the oil "fills the gaps" of the rings. That is why you will get an increase in PSI readings. Also since it is cold, the oil is not thinning due to heat from combustion. If you get readings that are way higher with the oil. then rings are suspect. Your readings looked pretty normal between no oil added and oil added. The really low PSI readings are a concern, and point to something else other than rings IMHO.

GRIESL · #8 12-12-2006, 02:03 PM

Quote:

Originally Posted by rrgrassi

If you get readings that are way higher with the oil. then rings are suspect. Your readings looked pretty normal between no oil added and oil added. The really low PSI readings are a concern, and point to something else other than rings IMHO.

That sounds like a relief to me. With new chain, valves adjusted and no coolant loss or coolant in oil, would you say that the most likely culprits are valves and valve guides?

vstech · #9 12-12-2006, 02:07 PM

IIWM I would pull the VC back off and pull the springs off those valves and very gently turn them feeling how they feel against the piston top. if you have a burned valve, you should be able to feel the valve "grind" against the piston in some positions... only if you have a really bad valve though. a lightly burned valve will damage the seat and the valve seat area of the valve... leaving the valve itself still round... but worth a try anyway. the guide wear shouldn't affect compression. just cause oil to leak into the chambers, although, really bad guides could cause the valve to bounce around and damage the seat. pretty far fetched though.

vstech · #10 12-12-2006, 02:10 PM

totally unrelated to the compression problem, but turbo seals are known to cause blue smoke under acceleration and such... ya might wanna get them checked, cause a runaway turbo fed motor is not a fun thing to put up with...
John
do a search for runaway diesel and prepare for some horrifying stories!
John

Biodiesel300TD · #11 12-12-2006, 02:12 PM

Blue smoke at idle and take off can be worn valve stem seal too. Might look into that.

thorsen · #12 12-12-2006, 02:30 PM

If it was me, I'd pull the head and have a look. You're not going to be able to stick a camera in the glow plug hole and see the piston or valves, all you can see is the combustion chamber.

Best case sceanrio is new valves/guides/seals, and the head needs to come off for that. Worse case is burned piston/broken pistons, and the head has to come off for that, too.

GRIESL · #13 12-12-2006, 03:54 PM

Quote:

Originally Posted by thorsen

If it was me, I'd pull the head and have a look. You're not going to be able to stick a camera in the glow plug hole and see the piston or valves, all you can see is the combustion chamber.

Best case sceanrio is new valves/guides/seals, and the head needs to come off for that. Worse case is burned piston/broken pistons, and the head has to come off for that, too.

What's the best "how-to" type manual for pulling a head? Are there any articles on here or another friendly website that gives instructions on how to do it. I've done engines before, but not been that far into a Benz Diesel. There's a DVD on Ebay that says they give a step-by-step instrution, but it's $80 or something high like that.

davidh · #14 12-12-2006, 06:19 PM

Quote:

Originally Posted by GRIESL

Thanks for the speedy-quick posts. I wish I had taken more note of the camshaft condition. There was nothing obviously wrong with it, but I didn't spend a whole lot of time inspecting it.

I had not thought that the chain stretch could actually cause damage to a valve. It was way off--can't remember exactly how much, but I remember thinking that it was so off that it was getting close to being off by a whole tooth, which I think is 18 deg. It may have been off by like 15--it was a lot. Are you thinking that timing could have been off so much that a valve could come in contact with a piston?

I was shocked as well that the car could run with 100 in one of the pots. I do recall when I did the seals that at least two valves I could move a little side-to-side in the guide. Not a whole lot, but probably enough to prevent some pressure in the cylinder.

What about the smoke dissipating underway or at high rpm? When rings are bad, does the blue smoke dissipate at high rpm? Or is that more indicative of valves?

we use to use the downhill test to check for bad rings. de-acceleration for an entended down hill trip and at the bottome of the hill if the rings were bad, you would have blue smoke on take-off. lots of it. it would accumulate the unburned oil as you traveled down using the engin compresion as a brake, kinda. does this make sense to you ? hard to explain. we have a main street hill thats a bit over a mile long and did this when we wanted to check for bad rings. . .

GRIESL · #15 12-12-2006, 08:56 PM

Quote:

Originally Posted by davidh

we use to use the downhill test to check for bad rings. de-acceleration for an entended down hill trip and at the bottome of the hill if the rings were bad, you would have blue smoke on take-off. lots of it. it would accumulate the unburned oil as you traveled down using the engin compresion as a brake, kinda. does this make sense to you ? hard to explain. we have a main street hill thats a bit over a mile long and did this when we wanted to check for bad rings. . .

Makes sense, thanks. I live up a pretty big hill and I shift into S sometimes to give the brakes a rest, but also when the engine is cold to warm her up. I've noticed any more smoke than usual in that case.

Also, someone mentioned turbo seals. I thought bad turbo seals would not cause excessive smoke at idle (which is what I have) but that the oil would accumulate in the turbo and wait for the next wallop of air when you hit the accelarator.