Sleved cylinder Knocks

[RickB]

Island Cessna wrote:If that's the cause of the knock there is nothing you can do about it. Injection timing is one setting for the whole motor. Time it right for the other 7, and live with the knock for this one.

Back to my question that was not answered by you or Craig, how does timing correct the "knock" in that cylinder?

Assume that each cylinder could be timed independently, which way would the timimg be altered, advance or retard?

Why would the increase in cylinder volume create the knock?

What would timing do to eliminate the knock?


-- Edited by RickB on Sunday 11th of March 2012 06:50:31 AM

 

[Forkliftt]

I'm thinking that less volume in the one cylinder would encourage a "knock". We presumably have more volume. Excessive clearance on a wrist pin or the rod bearing could be the source. I have seen wrist pins " knock" for years and have never actually seen one come apart. "Piston slap" is possible. If the piston had enough wear between the skirt and cylinder wall- upon firing- it would pop the skirt against the wall making a knock. For peace of mind, why not pull a couple of SOS (Cat's oil samples) bottles through the summer to trend out any wear pattern. I would do this without changing the oil. I could send you some with the gun (you send me $) and hose. You pull a clean sample, fill out the form and drop the provided shipping container in the mail. Cat knows what each bearing, bushing and piston is made of and would know the acceptable PPM for each. IMO, a failing rod bearing would be the only problem that would justify shutting the engine down.

 

[RickB]

The knock could be from any number of issues. I am just curious how the increase in cylinder volume can cause a knock and how changing the timing in some unspecified direction would eliminate it. Besides, the last word was that the sleeve was flush, not inset, so there is no volume increase anyway.

3208s are known for grenading due to failed wrist pins. A quick Google search will turn up lots of examples.

But diagnosing an engine from thousands of miles away is beyond my skills. I just want to know about the timing and lower compression knock thing.

 

[Forkliftt]

RickB wrote:
The knock could be from any number of issues. I am just curious how the increase in cylinder volume can cause a knock and how changing the timing in some unspecified direction would eliminate it. Besides, the last word was that the sleeve was flush, not inset, so there is no volume increase anyway.

3208s are known for grenading due to failed wrist pins. A quick Google search will turn up lots of examples.

But diagnosing an engine from thousands of miles away is beyond my skills. I just want to know about the timing and lower compression knock thing.

When then I suggest you Google THAT to get an answer. Instead of putting so much effort into making me wrong. I was a mechanic/ then sales for our Cat dealer for 7 years in my previous life. And I don't recall a 3208 "wrist pin issue". I suspect if you did a Google search on "bicycle chain failures" you could turn up lots of examples of that to. Why don't you participate on the things you are familiar/ experienced with. Have you ever pulled a head off of a 3208? I know SkipperDude has......

 

[RickB]

Forkliftt wrote:

When then I suggest you Google THAT to get an answer. Instead of putting so much effort into making me wrong.

I don't know why you are getting your knickers in a twist, I wasn't even commenting on anything you posted.And you flatter yourself if you think I put any effort whatsoever into making you right or wrong. Find another argument to make with someone else, please.

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.

It really is that simple and you and your insecurities are not part of this* topic so keep out or take it to OTDE.

 

[Forkliftt]

He he he.

 

[BruceK]

Now now boys, play nicely.
Googled "wrist pin/Cat" (aka gudgeon pin), a number of hits for Cat engines, especially failed retainers either end of the pin, with post disaster fragments found in the oil pan(sump),plus horror stories of pistons exiting the side of the block.
Returning to the actual issue, the "balance of probabilities" suggests a nexus between the noise and the sleeve,why not just keep running it until something really goes wrong or you repower, especially as it seems to be a very minor noise. Alternatively for abundant precaution, re-sleeve the cylinder. BruceK

 

[RickB]

What will re-sleeving do besides the obvious?

Obvious = it will require removing the boat from around the engine. At which point a complete rebuild should eliminate all the issues.

I'd still love to know more about the compression/timing thing but it looks like that will remain as mysterious as the noise.

 

[FF]

Not much choice in timing a 3208 , its done by pushing a pin into a hole and locking the injection pump when it fits in.

Might try a higher open pressure on one injector to delay the fuel squirt.

IF you want to have a non throw away 3208 , you need to find its daddy , the CAT 1160.

There were too expensive to make as all the cylinders have factory replaceable sleives , and the skool buss folks got new buses from the highway trust fund money dump, for 10% or less of cost.

So rebuilding was never an option chosen.

IF you want a 150,000 mile 1160 (50 miles to an hour for conversion, so 3000 hour engine ) for a grand , contact me .

Engine is in Arcadia FL. Use your old manifolds and marine tranny.

 

[skipperdude]

Thanks for all the ideas and thoughts on this subject.

No real definitive answers. the general consensus is to run it and fix it when it really breaks. So that is going to be the approach*I take on this.

It is more of a loud tap than it is a knock. I think I can live with it.

Everything else on the boat is first class and top notch.

I don't think I could buy a new boat that is in better shape.

I'm Good.

Thanks.

SD

*

*

 

[Island Cessna]

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

 

[RickB]

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

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.

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.

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

That is correct, the other poster also stated that changing the timing might eliminate the knock.

Your first post contained the following explanation:

"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."

Your last post contains the following:

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

"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.
*

 

[skipperdude]

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