Tester
But tester failed to explain the mechanism by which a stretched timing chain causes high NOx formation. If I have a stretched timing chain and loose steering, it does not follow that the loose steering is caused by the stretched timing chain. Of course, valve timing is much more closely related to proper engine operation than to steering, but it does not follow that a stretched timing chain causes high NOx formation. HI can see high HC readings being caused by a stretched timing chain, but I cannot see how a stretched timing chain causes combustion chamber temps of 2500 degrees. If anything I would imagine that combustion temps would be lower with a stretched timing chain.
Thank you tester. Now can you explain how a stretched timing chain causes combustion chamber temps of 2500 degrees and higher?
Engine Timing Problems
For maximum running efficiency, the motion of the pistons inside an engineās cylinders are precisely timed to capture the most energy from the expanding gas. Older vehicles often have adjustable timing, which allows it to be set improperly. This will lead to improperly burned fuel that creates higher NOx emissions.
Tester
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But in his experience, that causes high NOX and HC.
Iāll give it a goā¦ the retarded valve timing that results from a stretched timing chain would cause a late intake charge and a late exhaust exit. It tends to improve high rpm a bit at the expense of low end torque. That would imply a loss in cylinder pressure at low rpm.
The late intake charge and the 3 degrees retarded ignition timing seems like it would prevent a complete charge burn and a loss in cylinder pressure since both are late. That would account for the high HC - incomplete combustion. The late exhaust valve opening would increase the heat in the combustion chamber since it holds the combustion process longer thus increasing NOX levels.
So there you have my analysis of the situation but the proof is in changing the timing chain.
Long before computer controlled engines, late timing, either valve or ignition could cause engine overheating.
Seeing that you have a vacuum gauge, Iād run a few tests on the engine with it
https://www.gregsengine.com/using-a-vacuum-gauge.html
The timing that this article refers to is ignition timing. This is not the same as valve timing, which is what a stretched timing belt affects. Are you the expert here?
What turns the distributor?
Tester
2 Likes
That may true, but I have gauges and they tell me that this engine is not overheating. Now, they may be lying to me, I wouldnāt put it past them. But as there is no other evidence of overheating, I will believe themā¦ for now.
If you are trying to make a point, please make it.
Tester
2 Likes
The case which I described is āslow to open, early to closeā, so indeed it can cause gas circulation deviation from the original design.
The engine holds a steady vacuum at idle between 19 and 20 pounds. All tests at the link you provided indication a healthy engine. I am beginning to think the water jacket needs flushing to improve heat transfer from combustion chambers to coolant. Coolant temp gauge reads normal, but combustion chambers may not be getting cooled enough. This would definitely contribute to high NOx readings.
There are other, more likely causes of high combustion chamber temps, one of which is rust and other deposits in the water jacket, creating a layer of insulation, preventing proper cooling. So now I am looking for suggestions for the best cooling system flush to deal with that specific situation, improving transfer of heat from a 30-plus year old water jacket.
wow!
so you ignore the obvious problem to fix, yet invent some another project to entertainā¦
I bet this thread will get into 3-digits fastā¦
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Tester is very knowledgeable around here, and his advice is valid.
Engine timing needs to be in sync all the way through: you need ignition timing to be in line with valve timing- so that the vales are open and closed at the appropriate times to let in air and exhaust out correctly during the firing cycle. If they arenāt in sync, it wonāt function properly. period. If the heated exhaust gasses arenāt being allowed to escape at the proper times, you would have increased combustion chamber temps.
By Testers test, you have verified a stretched timing chain and been told repeatedly that this can cause your very issue. Why are you so against this advice and trying to find other causes?
The obvious problem being what? The stretched timing chain? If anyone here can explain precisely how a stretched timing chain causes higher than normal combustion chamber temps, I will āentertainā it as a possible cause. So far, no one has. A water jacket coated with insulating rust DOES cause higher than normal combustion chamber temps. That is a given, so yes, eliminating that to highest degree reasonably possible is my first step.
āTester said soā is not a precise explanation.
How about āTester, in his many years of experience, has found that stretched timing chains lead to failed emissions tests.ā
If true, I wouldnāt have to know the physical cause. Would I be curious? Sure, but you need a solution to your problem, not an automotive thermodynamics lesson.
So youāre thinking a cooling system flush of a great-working cooling system will solve your emissions test problem? Good luck with that!
For you to get the appreciable temperature rise through this cause you would be burning your oil like crazy. Yes, it contributes, but not to raising the temp by hundreds of degrees.
I did explain to you how the bouncing chain can shift gas distribution phases.
Do you think your stretched chain goes smoothly one direction?
Let me bring you the news - it does not!
If chain is not tight, as camshaft lobe slides of the lifter, it gets the slack in the chain and closes the valve fast and abrupt, reducing the open valve time.
I bet once you get to disassemble the top, you will see the marks of that on the back sides of the lobes, same as I did.