M104 3.2 Burning Oil after Head Rebuild -- Thoughts and Guidance, please. - Page 8 - Mercedes-Benz Forum
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post #71 of 98 (permalink) Old 02-18-2017, 01:02 PM Thread Starter
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Originally Posted by Bryce Mack View Post
As the previous owner of a auto repair shop I have seen too many times that you rebild the head and it pulls oil UP past the rings and causes oil burning. Its a simple matter of vacuum. I guarantee that this is the issue, the leakdown test works because its positive pressure you are dealing with NEGATIVE pressure.
Is this something that will, then, remedy over time as the top end wears?
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post #72 of 98 (permalink) Old 02-18-2017, 02:30 PM
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No the rings wear in an arch to the bottom so therefore the top of the ring is at a larger dynamiter than the bottom, its an angle so the only answer is to do the bottom end or at least the rings to solve the problem.... not a happy alternative....
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post #73 of 98 (permalink) Old 02-18-2017, 02:54 PM Thread Starter
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No the rings wear in an arch to the bottom so therefore the top of the ring is at a larger dynamiter than the bottom, its an angle so the only answer is to do the bottom end or at least the rings to solve the problem.... not a happy alternative....
In your opinion, is this a problem that can be foreseen prior to starting a job like this? If not, is it something that is customarily brought up as a potential risk?

After the engine was disassembled and the bottom end exposed, could anything have been done to assess the cylinders with the block in situ and alert the mechanic to a potential problem before the engine was reassembled?
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post #74 of 98 (permalink) Old 02-18-2017, 06:43 PM
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Very interesting that this does not show up in the leak-down test. I was pretty sure that your valve guides are not warn but this assertion at least fits the original assessment of the shop. Top and bottom ends not matching...Hmmm. Compression of >200PSI sounds high to me but that must be normal for a brand new valve job. I also have a couple of questions to you both:

(1) Is there a way to definitely prove this is the case?
(2) Stardivari, what type and viscocity oil are you using? I suspect synthetics would be worse for this but certainly a viscocity of 20W50 may help in your case. That is what I use in my M103, 20W50 conventional.
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post #75 of 98 (permalink) Old 02-18-2017, 07:07 PM Thread Starter
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Very interesting that this does not show up in the leak-down test. I was pretty sure that your valve guides are not warn but this assertion at least fits the original assessment of the shop. Top and bottom ends not matching...Hmmm. Compression of >200PSI sounds high to me but that must be normal for a brand new valve job. I also have a couple of questions to you both:

(1) Is there a way to definitely prove this is the case?
(2) Stardivari, what type and viscocity oil are you using? I suspect synthetics would be worse for this but certainly a viscocity of 20W50 may help in your case. That is what I use in my M103, 20W50 conventional.
The shop that did the work reported compression of ~180psi across all cylinders. The data obtained yesterday were from a third party shop, now approximately 300 miles since the plugs were changed. He said that when he pulled the plugs there was no sign of fouling but did note the white smoke from the tailpipe. He didn't rule out that the bottom end could be contributing to the matter but at the same time felt that the oil consumption was excessive given the test results.

The car was put on 5/30 synthetic when the rebuild was done. I tried switching to 20/50 conventional around 5000 miles and it doesn't seem to make much, if any, difference.

One observation I've noticed is that the rate of consumption doesn't seem to be consistent through the 500 mile period. It will surely burn a quart every 500 miles, but sometimes no consumption is seen for the first 2 or 300 miles (and every time I see that I think, "ooh, maybe it's stopped") and then the consumption progresses rapidly over the next couple of hundred miles.
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post #76 of 98 (permalink) Old 02-19-2017, 04:57 AM
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Brycemack thank you , for that bit of information about the bore .I never knew about the ark . Would this be due to the way the piston travels, in line with the crank or would the ark be the same all around the bottom of the cylinder.?
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post #77 of 98 (permalink) Old 02-19-2017, 05:09 AM
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Further to oil burning

Quote:
Originally Posted by stradivari1689 View Post
In your opinion, is this a problem that can be foreseen prior to starting a job like this? If not, is it something that is customarily brought up as a potential risk?

After the engine was disassembled and the bottom end exposed, could anything have been done to assess the cylinders with the block in situ and alert the mechanic to a potential problem before the engine was reassembled?
Lets face it the reason the top end needed work was WEAR whether it be valves or guides. Unless it was an issue with a head gasket look at the mileage on the assembly.

Whenever we did top end work on a higher mileage vehicle we ALWAYS told the customer of the potential of lower end issues coming to light with the rebuilt top end.

Sounds like your oil burning issue is just a little smoke and a quart of oil too regularily but bottom line is drive your nice car and remember your not making huge monthly payments on a new plastic car.

LOL
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post #78 of 98 (permalink) Old 02-19-2017, 05:25 AM
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Quote:
Originally Posted by Trevor Hadlington View Post
Brycemack thank you , for that bit of information about the bore .I never knew about the ark . Would this be due to the way the piston travels, in line with the crank or would the ark be the same all around the bottom of the cylinder.?
It's more a matter of FORCES on the rings when the engine is under compression and fireing stroke the force is downward. This causes a really tight seal of the ring to the cylinder wall. However in all other stroke the ring is not under pressure and the ring kind of floats and contorts in the bore. therefore the top of the ring remains larger and the bottom and sides wear more (yes marginally) but at 2000+ rpm for thousands of miles it makes a difference!

Bryce
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post #79 of 98 (permalink) Old 02-19-2017, 09:05 AM
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Quote:
Originally Posted by Bryce Mack View Post
As the previous owner of a auto repair shop I have seen too many times that you rebild the head and it pulls oil UP past the rings and causes oil burning. Its a simple matter of vacuum. I guarantee that this is the issue, the leakdown test works because its positive pressure you are dealing with NEGATIVE pressure.
This might be more applicable with a"lesser" marque but low mile (under 150k) M103 bottom ends are tight. I did heads on two of my M103s (one at 230k and the other at around 175k)and both resulted in oil consumption of less than a quart between changes (3000 miles). My experience is not unusual with these motors. A quart every 500 miles is excessive and unusual.

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post #80 of 98 (permalink) Old 02-19-2017, 09:48 AM
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Originally Posted by tuttebenne View Post
This might be more applicable with a"lesser" marque but low mile (under 150k) M103 bottom ends are tight. I did heads on two of my M103s (one at 230k and the other at around 175k)and both resulted in oil consumption of less than a quart between changes (3000 miles). My experience is not unusual with these motors. A quart every 500 miles is excessive and unusual.
Hi Tuttebenne, this is a higher performance M104 Engine. I'm just an observer of this forum with the M103 Engine and a previous owner of the M104 engine.

I'm just surprised that no one else with a M104 Engine who has done the exact same thing is chiming in here. So why is this case a one off in this forum? It should be more common among same Engine class. Maybe a M104 valve only job is not that common? It is very common with M103 but M104 could be a very different matter all together. Basically, Mercedes has squeezed 25% more compared to a 2 valve old style engine in a 4 valve M104, even if with same material used, perhaps the wear patterns are different.
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