The peak in NOX would correlate with the peak in EGT.
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| Very lean and running rough/missing https://slantsix.org/forum/viewtopic.php?t=55750 |
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| Author: | Chief915 [ Fri Jul 11, 2014 2:09 pm ] |
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I should have it the rest of the way apart tonight to see what we're working with! |
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| Author: | Chief915 [ Fri Jul 11, 2014 7:03 pm ] |
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Quote: Sounds like a burnt #6 exhaust valve...
We have a winner! #6 is burnt. I pulled the valve out and the seat looks fine. I think a quick valve job is going to be all that it needs. Of course I will put new valve seals in it too while it's apart.....and probably a timing chain.Let us know what you find once you pull the head. DD <a href="http://s1285.photobucket.com/user/chief915/media/20140711_204703_resized_zps86c030f6.jpg.html" target="_blank"><img src="http://i1285.photobucket.com/albums/a599/chief915/20140711_204703_resized_zps86c030f6.jpg" border="0" alt=" photo 20140711_204703_resized_zps86c030f6.jpg"/></a><a href="http://s1285.photobucket.com/user/chief915/media/20140711_204658_resized_zpsc63f9f6a.jpg.html" target="_blank"><img src="http://i1285.photobucket.com/albums/a599/chief915/20140711_204658_resized_zpsc63f9f6a.jpg" border="0" alt=" photo 20140711_204658_resized_zpsc63f9f6a.jpg"/></a> |
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| Author: | Sam Powell [ Sun Jul 13, 2014 5:39 am ] |
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High exhaust temps would be part of the cause, but good valves should take it. Aviation engines run at 50 degrees off max EGT all day long, and on both sides of max EGT. Sam |
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| Author: | wjajr [ Sun Jul 13, 2014 7:42 am ] |
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yup, that puppy is toast. |
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| Author: | Reed [ Sun Jul 13, 2014 8:33 am ] |
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Interesting. This makes me wondr if perhaps the air injection system also functioned to cool the back face of the exhaust valve. Or maybe Chrysler just used cheap valves in the 80s. |
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| Author: | emsvitil [ Sun Jul 13, 2014 4:50 pm ] |
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Do you have power brakes? I'm thinking the power brake booster was connected to the #6 runner and had a slight leak causing a lean running condition...... |
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| Author: | Chief915 [ Sun Jul 13, 2014 6:37 pm ] |
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Quote: Do you have power brakes?
You're correct....it does have power brakes and did have a slight vacuum leak at the rubber cap on the booster check valve when I got the truck.
I'm thinking the power brake booster was connected to the #6 runner and had a slight leak causing a lean running condition...... |
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| Author: | Sam Powell [ Sun Jul 13, 2014 7:29 pm ] |
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Very good Ed. Quite a sleuthing job there. I still say though that good valves will not burn if run lean. One of my good friends Wayne takes care of the planes for a rich dude here in Maryland, and he says the temp maxes out as you make it leaner, and then it hits a point where it is so lean it gets cooler again. You can run an aviation engine 50 degrees off of that max EGT for best fuel economy. That is what pilots do all the time. They dial out the fuel until the EGT maxes and then go either 50 degrees cooler on the lean side or on the richer side. He says richer sounds and feels better, but leaner actually gets a little better mileage. So Ed, good for deducing the leak in the power brakes. But, I think the valves were not of he highest quality for sure. I would say that if you have stock valves, which most do, it is advisable to make sure there are no vacuum leaks or this might happen. Sam |
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| Author: | wjajr [ Mon Jul 14, 2014 6:25 am ] |
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I suspect aircraft valve metallurgy is of a higher quality than run of the mill auto engines. After all its not like one can pull the old Piper Cub off to the side of the road during a valve failure, and air craft also operate at varying oxygen levels seeing lean conditions at constant high rpm that an auto never encounters unless fuel injected or turbine powered. I agree, #6 has been sucking a lot of air for while. If it were a vacuum leak shared by all six cylinders damage would have been seen on additional valves. |
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| Author: | Sam Powell [ Mon Jul 14, 2014 6:53 pm ] |
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I took a closer look at the head I pulled last night off the '83 truck engine. The exhaust valve on #1 looks identical to the exhaust valve on number six of these photos. It is seriously burned! There is no brake booster port near that intake runner for number 1, but it is possibly the hottest part of the engine, and number one and number six do run lean on carbureted slants. Sam |
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| Author: | Reed [ Mon Jul 14, 2014 7:31 pm ] |
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The two mid 80s heads that I have encountered that had burned xhaust valves had them on cylinders 3 and 4. This could be poor valve quality, it could be vacuum leaks, it could be the lean burn system going too lean. I guess the moral of the story is be prepared to pull the head on an unknown condition hydraulic slant. |
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| Author: | emsvitil [ Mon Jul 14, 2014 7:38 pm ] |
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Quote: The two mid 80s heads that I have encountered that had burned xhaust valves had them on cylinders 3 and 4. This could be poor valve quality, it could be vacuum leaks, it could be the lean burn system going too lean. I guess the moral of the story is be prepared to pull the head on an unknown condition hydraulic slant.
Doubt they were too lean on a lean-burn system.I would think 3 & 4 would be the richest (lean burn or not) and on a lean burn system they hit the sweat spot for being the hottest 2 cylinders.... |
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| Author: | emsvitil [ Mon Jul 14, 2014 7:48 pm ] |
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The peak in NOX would correlate with the peak in EGT. |
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| Author: | Sam Powell [ Tue Jul 15, 2014 3:39 pm ] |
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Interesting. Ed, you always communicate a great deal with minimal words. That is interesting that the co2 emissions curve is opposite that of NOx. At least with that system, choices are a compromise at best. Sam |
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| Author: | Chief915 [ Mon Jul 21, 2014 5:25 am ] |
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The truck is back together and running beautifully. The machine shop ground all of the valves and seats, knurled the guides and replaced the valve seals. They had to replace 2 exhaust valves, the one that was burnt obviously and another that had a spot on the face that looked like it was starting to burn through. I've put about 260 miles on it since I got it back on the road and it's doing just fine. |
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