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Old 03-13-2012, 01:46 AM   #41
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RE: Sleved cylinder Knocks

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RickB wrote:Forkliftt wrote:

When then I suggest you Google THAT to get an answer. Instead of putting so much effort into making me wrong.
I I would just like an explanation from the two guys who said increasing the volume would create a knock and altering the timing will cure it.

I can't believe I am hanging in when this has gone past well meaning sharing of ideas or suggestions, but here goes.

First, I think we have different people talking about 2 different sources of knocks.

1. Mechanical wear or malfunction caused knocks such as worn wrist pins.*I*do not*consider these to be*related to injection timing.

2. That delightful Diesel knock or rattle that Cummins pickup engineers adore, Mercedes Benz engineers abhor, and trawler folk ignore. I follow the suggestion above, and quote from the font of all truth, Wikipedia (via Google):

"Knocking is more or less unavoidable in diesel engines, where fuel is injected into highly compressed air towards the end of the compression stroke. There is a short lag between the fuel being injected and combustion starting. By this time there is already a quantity of fuel in the combustion chamber which will ignite first in areas of greater oxygen density prior to the combustion of the complete charge. This sudden increase in pressure and temperature causes the distinctive diesel 'knock' or 'clatter', some of which must be allowed for in the engine design."

My comment on timing was related to the fact that compression creates the ignition temperature, and that a lower compression ratio delays the point where this temperature is reached. Using the above Wikipedia description this would mean comparatively more fuel is already injected in the low compression cylinder when ignition starts, increasing the knock in that cylinder.

In a 3208 you can't change the timing of one cylinder alone, but to answer the question, if you could, I would try retarding the start of injection in the cylinder with the larger clearance volume.

As for troubleshooting from 1000 miles away, I have screwed up many diagnosis sitting on top of the engine. I*certainly hope that the remote response to questions without looking, hearing, or touching the engine is interpreted as ideas for the guy sitting on top to think about, not diagnosis to act on!

While Diesel engines are constructed to withstand the pressures caused by the injection of fuel into heated environments, internet forums often are not. I hope I do not cause flames or damage by injecting these comments into the heated discussion after skipperdude has graciously thanked us and moved on!

Bill
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Old 03-13-2012, 05:06 AM   #42
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RE: Sleved cylinder Knocks

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"I can't believe I am hanging in when this has gone past well meaning sharing of ideas or suggestions, ..."
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It isn't like I didn't ask for clarification until yesterday. I have been asking for you to explain your hypothesis since you posted it. Delaying the response doesn't make the question irrelevant and explaining to those who are curious about such things is what sharing ideas and suggestions is all about.
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If you state that a certain condition causes a certain result then you should be prepared to explain to less enlightened readers why that is the case. There is nothing sinister in asking for that* kind of explanation.
Quote:
"First, I think we have different people talking about 2 different sources of knocks."
Quote:
That is correct, the other poster also stated that changing the timing might eliminate the knock.
Quote:
Your first post contained the following explanation:
Quote:
"My guess is that the 1/32 clearance between the sleeve and deck of the block adds enough additional clearance volume to change the compression ratio of that cylinder. The different compression ratio creates the knock, as the optimum injection timing of that cylinder is different."
Quote:
Your last post contains the following:
Quote:
"1. Mechanical wear or malfunction caused knocks such as worn wrist pins.*I*do not*consider these to be*related to injection timing."
Quote:
"My comment on timing was related to the fact that compression creates the ignition temperature, and that a lower compression ratio delays the point where this temperature is reached. Using the above Wikipedia description this would mean comparatively more fuel is already injected in the low compression cylinder when ignition starts, increasing the knock in that cylinder."
Now for the facts:
Depending on the version of 3208 under discussion, the compression ratio is either 15.5 or 16.5. That means the temperature of air in the cylinder at the start of ignition is somewhere around 1000*F.
The autoignition temperature of diesel fuel is variable between 400 to 500*F depending on source and quality.
If the suggested loss of compression lowered the compression ratio all the way down to 12:1, the temperature in the cylinder would still be around 900*F at the time of injection. Even if the elusive 32nd of an inch does exist (one post says it does, another says it doesn't so who knows?) and the CR of that engine is 16.5:1, the increase in volume would drop the static CR to just over 15:1 and the temperature would be about 1000*F. Certainly high enough to ignite the fuel.
The other component of this condition is that the injector spray pattern is better at lower cylinder pressures and the greater penetration and atomization reduces ignition delay. As soon as the fuel begins to burn, the cylinder temperature and pressure rises rapidly making compression temperature of no further concern.
Timing is related to fuel properties with ignition delay at the top of the list. Injection starts early enough that the fuel has time to heat up and ignite. If you delay that to compensate for a percieved lack of heat in the cylinder you will only make things worse since the ignition delay now occurs as the cylinder contents are expanding and cooling.
*
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Old 03-13-2012, 08:45 AM   #43
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RE: Sleved cylinder Knocks

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RickB wrote:*Even if the elusive 32nd of an inch does exist (one post says it does, another says it doesn't so who knows?)
*

Sorry for the confusion I got kind of mixed up on what I was trying to say.

The idea of re-gasketing the block and using a different gasket ( one for a sleeved engine ) got the conversation confused.*

*When an engine is sleeved the gasket has a wider opening*around the cylinders than a non sleeved engine. I installed a gasket for a non sleeved engine.*

What I was trying to say was that a sleeve is supposed to be level with the surface and my #8 sleeved cylinder is not

The # 8 cylinder is the sleeved cylinder. The sleeve is recessed about 1/32 of an inch below the surface of the block.

I hope this clears all of this up.

SD
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