New to listers, is a knock normal?

[thinder]

HI all,

 Ive inherited a listeroid of the powersolutions variety. It had a cracked cylinder block from freezing temp and other small issues.  All have been remedied with the help of Utterpower.  But now that its all back together and running.  It does seem to shake more than I expected with a noticeable hollow sounding knock.  I'm thinking its just the injector pulse and combustion but I want to see what you guys think. 

It seems to be more clearly heard at a distance, say 50ft.  It seems to go away when you kill the injector or decompress via the exhaust tappet.  The rhythm seems to be in time with the exhaust pulse but not co-incident. 

Here is a pic of the setup just for reference.

[starfire]

Its diesel knock, and normal.
The sound does vary, sometimes will worsen as a "stalagtite" of carbon builds up on the piston crown under the injector if you burn oil for long periods without water injection.
The knock i think is  mainly the piston thrust faces swapping sides as the rod angle changes under combustion pressure. Cast iron pistons seem  worser, and they act like a bell.
Air cooled diesels are VERY noisy, the cooling fins amplify the sound, cooling water jackets insulate, but the big crankcase acts like a sounding chamber in both.
Just turn the music up and ignore......

[MachineNLectricMan]

Could also be a rod bearing. Better check your bearing clearances.

If it is piston slap, that does have a distinctive sound, and as noted is far worse on air cooled engines.

Injection timing could also be too far advanced.

[starfire]

Rod bearings knock at engine speed, not just on the expansion stroke. Advanced timing causes hard starting and rough low speed running, this symptom has not been mentioned. Any youtube Lister video, including my own substandard attempts will demonstrate  this noise.  Chances are very good thats it is completely normal, especially as the engine has been recently reassembled and checked.

[thinder]

Thanks for the input guys!   I don't want it to be a rod bearing, so I'm leaning towards normal knock.

It seems to be most noticeable at operating speed,  and I would think the rod would be noticeable all the time.   When I had the cylinder off I didn't notice any obvious play in the rod. Not that I necessarily would have felt excessive clearance.  Low speed operation is fine and starting hasn't been an issue.  I timed the pump a while back, so it couldn't be that!!

[starfire]

Listers are indirect injection, ie, they inject into a small ante chamber in the cylinder head, as opposed to say my Petter AV1 that has a depression in the piston crown, and a flat cylinder head, this one squirts directly into the cylinder.
As the injector initially squirts into the chamber, it fires and immediately uses up the small amount of air. This small heat pocket rapidly expands out into the main piston/cylinder proper, carrying the following unburned atomised fuel at great velocity and extreme turbulence where it hits the main volume of air  and thereafter burns normally.
This is the secret I think to why Listers burn cleanly, but also causes that very rapid initial expansion contributing to that knocking noise.
The Petter on the other hand is quieter at similar revs and load, but is much dirtier in the exhaust despite being plumbed  into the same fuel supply.
The COV actually varies the size of the antechamber, and I believe lowers the overall compression ratio from 17:1 to 14:1. Mine knocks less with the larger chamber, COV out, indicating more of a "cushion" to the initial firing event.....
I could be wrong, but thats what I think.

[MachineNLectricMan]

In my previous post, the idea was to be on the safe side and make sure the knock wasn't from something bad first.

I have far more diesel engines than SI engines. When tinkering with these engines the first thing is to check the injectors to make sure they spray a completely atomized mist with all ports.  I also check the valve train and the compression. If all is well in those area's, the next thing I like to check is the type of smoke the engine makes under a higher load. It should be black without any hints of white smoke. If there is some white smoke, advance the injection timing a little at a time until it just turns all black. I always notice an increase in the "diesel knock" when this is done. Too far advanced is not good either as the engine not only knocks louder, but also generates more internal heat without any gain in power or fuel economy. This shortens engine life. Timing by the book doesn't always give the best performance either. You do have to be sure the engine is in good shape to time by the smoke as a bad injector, low compression, bad valve timing, or poor valve lash setting will also cause white smoke. Some smaller generator engines require you to make custom injector pump timing disks to change the timing. I've done that too, and with very pleasing results.

Now the indirect injection Lister's use a pre-combustion chamber system. There is also another type of system called an "energy cell" which is quite different from the Lister design. While the energy cell system is known to be a little finicky about over fueling, I am suspicious that it would do very well with WVO, better than a normal pre-combustion chamber design. A good experimental project to look into some day.

[dieselgman]

What is being called rod-knock here might confuse the issues a bit... Rod knock is NOT normal nor tolerable in an engine. Ignition knock on the other hand is common in many diesels - especially when ignition timing is advanced beyond optimum.

Rod knock is to be avoided, proper lubrication and proper bearing clearances are essential. Engine damage and likely failure will be the result of any sustained problem in this area.

Ignition knock is often the result of injection timing being too far advanced. Something around 20 degrees BTDC is called for. While these engines will tolerate 25 BTDC as far as I have seen, much more than that will start the noise symptom and cause a degradation of performance and engine life.

Set your timing correctly! After that, inspect and measure your big-end bearing and rod journal.

A reasonable amount of diesel knock is just normal for these engines. If possible, go listen to some good runners in operation to judge what is "normal" and to be expected.

dieselgman

[thinder]

I agree with you,  I'm going to pull the crankcase cover and just give it another once over.  could I use a dial indicator on the rod end and move th crank back and for to see if I have excessive clearance?  just to avoid taking the cap off.

[ronmar]

Since rod knock is the result of slop in the bearings being taken up when the rod changes directions, it can usually still be heard when you interrupt fuel or decompress. The fact that you said the sound goes away when you remove fuel/decompress leads me to believe it is IDI diesel knock.  Now if your timing was off it could be more pronounced, but as mentioned would run poorly at low speed and be difficult to start...

Starfire, that was a great description of IDI:)

[thinder]

I took a video of it, I'm not sure I f youll be able to tell or not.  but here it is.

https://youtu.be/7Sodulxo0-c

[thinder]

I pulled the cover and with the dial indicator I could only get about .001"  play side to side.  I couldn't figure out a way to get vertical play.  So I'm thinking its not a rod bearing. 

[Tom]

To measure bearing clearance, PlastiGauge is used. It is a soft plastic rod that goes between the bearing and journal while being torqued to spec. The bearing cap is then removed and there is a gauge on the side of the package that will give a reading on clearance based on how much the short piece of rod was flattened.

[thinder]

To measure bearing clearance, PlastiGauge is used. It is a soft plastic rod that goes between the bearing and journal while being torqued to spec. The bearing cap is then removed and there is a gauge on the side of the package that will give a reading on clearance based on how much the short piece of rod was flattened.

I'm familiar with plastigauge.   I was asking if I could use a dial indicator to avoid the mess of pulling the rod cap off. 

[Tom]

Not that I've ever heard of. It would probably talk longer to setup the dial indicator than removing the rod cap. The rod bearing on my 6/1 was checked with plastigauge after about 2k hours and it only took a few min. The bearing was well in spec too.