earlier it was said the pop pressure can change the timing as well for an individual cylinder.

__________________
Adam Lumsden
(83) 300D
Vice-President of the MBCA International Stars Section

I actually wondered about that when he showed us stuff on his laptop.....I thought "wow, he has a lot on his laptop, I wonder if he backs that all up...."

Guess not.......


I have all of the data that I use stored on two servers that mirror each other....needless to say, I'll never loose a file unless this plot of land is swallowed by the earth.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Back on this subject, our '83 still idles exceedingly rough, even with the bosio nozzles, would this be a timing issue? We know that the engine has about 2-3 degs of stretch on the timing chain, and its last valve adjustment was probably 12-13k ago. Vibration at idle has recently (within the last few k) gotten a lot worse. Anyone have any suggesstions as to what this might be? Oh, and when in drive or reverse (especially drive) it feels like the engine is stumbling, kindof a "bump....bump....bump...." feeling in the already massive amount of vibration. As sooon as you press the pedal it goes away, and when I was messing with the idle, I set it around 900-950 and put it in drive, and the vibration and bumping feeling went away as far as I could tell, but I could also tell it was idling waaay high, a lot higher than my '82 does, and that one is silky smooth at idle. This stuff has all started happening very recently, so I don't get it. New nozzles, balanced/pop tested, the works, and it also has essentially 0 blowby at all, we started this beast at 12 deg's F with TWO working glowplugs before (50 seconds of cranking) and it started. With all 5 plugs it will start at 0 degrees in about 4-5 cranks. Thats whats so odd, it starts so well in the cold, but idles soooo rough. Why?!

I know you have said yours shakes/idles rough too, maybe its a similar cause? His can't shake though, it seems as if the engine is bolted to the frame of the car, but its on the normal motor mounts. Rev'ing it, it won't "lean" like mine does, and turning it off it barely moves by itself, it just shakes the entire car. Seems like its in there too tight, if thats possible.I know if I grab my engine's valve cover I can rock it back and forth an inch or so, his engine does not move, at all, it moves the car. Seems very strange....

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

I apologize for inadvertently hijacking this thread, but would like to respond to some of the other posts. That was the most severely damaged piston along with one other that was similar but not quite as badly melted. The other two were somewhat damaged but far more minorly. The two injectors for the two damaged sylinders did pop at somewhat lower pressures and spray patterns were slightly worse, but not dramatically. Yes the probe was immediately after the turbocharger and so add 250°F for a pre-turbine measurement of 1150°F.
With regard to EGT's of advanced timing being cooler here is my understanding. If the injection interval is advanced primary combustion will occur more on the upstroke developing intense heat as the burning gasses are compressed. Simultaneously more heat is passed to the cooling system as the head and upper cylinders are hotter. Then as the piston is pushed downward the gasses cool rapidly due to the expansion of the chamber and the more complete combustion of the fuel. If fuel is still being burned in the exhaust then the EGT's will be significantly higher than if the fuel is more completely burned. Therefore, advanced injection timing results in both elevated peak combustion chamber temps and lowered EGT's. A very frightening combo. Go ahead, give it a try and report back your results. How about 30° BTDC? Or if you don't have as much belief in your argument that advanced timing does not lower EGT's while raising peak combustion temps, then retard your timing to 15° BTDC and check out the EGT gauge. I am quite sure you'll see it elevated.

Andrew

The position of the probe now begins to make some sense. The temperatures at the ports could have been well on there way to 1200°F. The damage to more than one piston also answers some additional questions.

I fully agree that retarded timing will cause increased EGT's, but the concept of reduced EGT's due to advanced timing remains difficult to grasp. If the combustion temperatures are higher.......for all the reasons mentioned.......the exhaust temperatures at the exhaust ports should also be higher. I simply can't envision a the scenario where an elevated combustion temperature can dispose of all that excess heat into the cooling system in a very short period of time and result in a lower exhaust temperature.

However, I've never tested it.......so........I reserve the right to be wrong.

Rack damper bolt questionable for the bad idle? Since you have two cars a temporary swap would eliminate it as a possibility at no cost. Check the archives to see if symptomatically a marginal one can create this much disturbance or vibration at idle. As for the gentleman with the overheating or higher operation temperatures since change of nozzles. Again the only difinative answer might be substitution with a known pretty good set of other used injectors. That is of course if nothing is learnt from your new ones that are out being pop tested. But you are fundementally right. You seem to have created a lot more heat to get rid of somehow with the new nozzles. Hopefully the pop pressure test will indicate what it is. Another thought is perhaps the fellow pop testing your injectors might loan out a known good set if the problem remains with your present ones recalibrated. You may have to make positive that they are the absolute cause shortly.

now for pawosd, it seems possible to me that your car might have one cylinder that the timing is too advanced on. there is a long thread about this from about a year ago. i believe it may have been larry bible who experienced it.

at the outlet of the ip the threaded nozzles that the pipes bolt to are actually individually adjustable. and if one is mal adjusted it will fire too soon (or late) and cause very rough running. dont monkey areound with them though until you completely understand what you are doing as it is very easy to cause problems and not easy to straighten them out.

tom w

__________________
[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.

Roughness in idle. One approach is to just read the mili volt output of your glow plugs and if say one plug is signifigantly lower investigate that cylinder in a systematic way. First swap glow plugs with one that appeared to be normal to make sure it is really reading low on that cylinder. Then swap the injector in that cylinder and see if milli volts come up. If not check valve settings again. If they are good then time for compression check of that cylinder. If that is ok then it may indicate pump problem but most times you will locate and fix the individual cylinder problem before that or the cause is indicated if not practical to repair. Now if milli volt readings of plugs are all close during my initial reading of the plugs I would check the primary pump to engine timing and cam for correction. That is because the milli volt test is indicating simular strength power strokes are occuring in each cylinder. That of course being the source of a smooth idle if the principal timing etc is accurate. Bypassing all the other steps and going back only if the pump/cam setting does not clear it. You cannot loose by doing a fundemental tuneup anyways as it maximises performance and milage, cold start the whole thing so to speak. If all the above does not lead you to where you want to be there are further tests. Generally if I do not really know what is wrong with any engine many times it is revealed by just doing the basic tune up or at least many times the real fault will be indicated during the process. Guessing is terribly non productive and time wasting without a lot of daily experience.

Brian says: "I simply can't envision a the scenario where an elevated combustion temperature can dispose of all that excess heat into the cooling system in a very short period of time and result in a lower exhaust temperature."

That certainly seems to be the question as to how much of that heat can go into coolant or be radiated by the block in the time frames we're looking at. Looking at heat as work and too advanced injection using more of that heat to resist the piston on the compression stroke, it might be true. I'd sure like to know the answer to that.

Here is a scenario I've been thinking about that might explain the piston burning, the larger ratio of "Combustion Temps / EGT's".
Imagine first, for reasons unknown, that we have a good spray pattern, but due to weak injectors, or the IP being too advanced. So, our nice fuel spray occurs too far advanced, so, the initial compression induced burning begins at multiple sites at the periphery of the cloud (which, I believe it does), then, as is normal, radiative heat from the initial compression burn sites ignites the rest of the fuel. So, the pressures and temps are much higher for a longer duration before the piston reaches TDC. We see in the image of the piston that the melting seems predominant at the periphery of the piston, which is a very normal thing as edges have more heat to move and it is a slower process. As background, I don't know how many compression rings this piston has, for arguments sake let's say two compression rings and one oil scraper. The compression rings revolve around the piston not in a uni-directional fashion at from 3 to 6 rpm, but at a rate of 3 to 6 rpm, but as the ring gaps begin to near each other pressure is built up by the first gasses passing the end gap of the ring, over the first land making it's way to the gap of the 2nd compression ring pushing both in the opposite direction relative to each other, back & forth across these 180 degrees. Now, this initial problem of way higher than designed pressures & temps during the compression stroke begins a partial melt of the edge of the piston, eventually some of this melt making it's way to the end gap of the 1st compression ring and filling it. Continued partial melt enters the end gap gradually pushing the first ring tighter & tighter against the cylinder wall. Now we have that increased heat from friction, plus we've blocked the nominal amount of gas that normally get's around both both compression rings. Eventually the 2nd compression ring make's it's way so that it's end gap lines up with the now non-existent gap of the first ring. Heat is greater there because the initial fit interference at the frozen gap prevents any up & down movement, so the 2nd compression ring now locks up, with the land between the two rings expanded by the heat locking it up. So, now we have both rings locked exerting greater pressure on the cylinder wall and concomitant heat build up. The initial problem of an early injection, prior to the sealing, whether partial or complete, overheats the oil scrape ring resulting in either partial lockup, but whatever, it now doesn't scrape the hot oil well, which removal helped to keep cylinder wall & piston temps down. At this point we have a troublesome environment in progress, with more and more of the piston at the initial melt spot having nubs and good piston top/skirt edge burning. Maybe some to the same fate of the initial burn spot and the rest being ejected to the exhaust port. As material is lost from piston this lowers compression by increasing the volume normally seen at TDC, perhaps resulting in the increased smoking & the lowered EGT, while maintaining the higher peak combustion temps because the hot piston is still igniting the cloud too early due to hot spots, even though overall minimum cylinder volume has increased. Also, if the early or later piston disintegration that I hypothesized above is true, the oil scraper is not removing cylinder wall oil as it should resulting in higher temperatures. So, yes, we do get some of the excess temp gone from wall to coolant jacket, but we also have the locked rings on the piston, deficient oil scraping, and I surmise that the piston itself transfers much heat from piston top and skirt, with poor heat transfer from skirt to oil that is normally making it's way back to the oil pan. In my guess here I am saying that we're seeing combustion temps way above normal, but much of the energy has been transferred too early contributing to higher pre-TDC temps & pressures than is normal. Yet, if the EGT's are correct, where has all the heat gone from the abnormally high peak combustion temperature? Perhaps our piston/cylinder interface can transfer a lot of this heat (it doe's have more time to do so). I'm guessing, and here I just can't visualize or intuit the physics, the way advanced peak pressure and temperature is losing it's energy partly in a normal fashion via the cylinder wall and what the head absorbs, but I would think the majority of the heat is lost through friction not only on the compression stroke, but also on the power and exhaust strokes due to locked up rings, whether complete or partial lockup, so the EGT's are normal or relatively okay as this is just a gas temp we're looking at & a good deal of the gas partial pressure energy dissipated through the piston and cyl wall much before it should have relative to TDC. I realize I can't have it both ways as regards an increase in exhaust smoke, though I'm not sure if we're talking about fuel or oil being the main component. By both ways I mean I can't say the compression rings are locked tighter to the cyl walls and less oil is making it's way past the oil scraper, and we're seeing increased exhaust smoke from either oil or fuel. though perhaps there is some balance of these processes that allows my argument to have it's cake and eat it too. My argument says we're seeing rather complete burning of fuel, more so than normal, unless normal means complete burning; so, I stick with the scenario of combustion heat, per se, exclusive of all the frictional heat, having the additional time to cool by heat transfer by the time we're on the exhaust stroke at that point where maximal EGT are normally noted. My previous post of a poor, streamlike spray pattern on a single spot of the piston most certainly wouldn't be at the interface of piston top and skirt. So, I guess on the relatively low EGT's, with all the variables I've thrown into this, I would have to say that early combustion from beginning to complete is what dominates & EGT's are low because combustion is complete way too early, much of the pressure, hence heat, is lost as described previously. The fuel:air mix has a defined maximum pressure/heat it can create. I've said by a larger percentage of that pressure/heat working against the piston as it travels towards TDC is why we see relatively low EGT's, while burning pistons with relatively high combustion temps. I don't know. I wish I did. This just seems such a problem that reveals much, if understood, of both normal & abnormal diesel function that I wish I knew if my guesses are even partially on track.

Yup having Tomj balance my set fixed the temp problem. It runs back at its normal steady 83C, well it gets up to 95 when traveling around 4000 rpm on the expressway in 4th gear.

The Bosio nozzles are not all that people are making the out to be. They lack the pre-ignition hole which causes noise and a little roughness. But the machine quality is better then the Indian nozzles.

__________________
Adam Lumsden
(83) 300D
Vice-President of the MBCA International Stars Section

Yes, perhaps. Yet, after the higher combustion temps finished the pistons and/or rings off, we now have lower combustion temps due to the loss in pressure during the compression and power stroke. So, after the damage we have lower EGT's. I'd refer to my long winded theory as to how we got very increased combustion temps with lower EGT's as a function of the presumed advanced IP Timing. Now, even after the piston/ring damage the damaged portions served as hot spots to effectively ignite all the fuel & we see no exhaust smoke. I think (I guess) that previously described faults that result in an early start of burn BTDC could very well have much of this heat removed from the cylinder volume resulting in EGT's lower than 900F (even if flash combustion temps are as high as 1500F. I think the concept of "flash temps" is important and we need to measure the average peak temp over a time period, say one half of one degree. In old Detroit Iron engines of the 60's, say the 426 Hemi or the earlier 413 Stage 3 Max Wedge, combustion temps peaked at around 4000F, hot enough to melt the cast iron head, but the key is that the 4000F is a flash temperature seen for around one millisecond or less, so no melting, just a lot of heat transfer to the block, out the exhaust or pushing the piston down the power stroke.

I the idle problem solved by balancing the injectors too?

__________________
1984 280SEL, 62,000 miles
Euro model in the USA
1983 300D (Totaled out 10/2004)
New Factory Mint Green paint
Palomino int
1982 240D (Steak dinner for two)