Unusually loud Knocking - Help

[veggie]

Hi All,

I have been experimenting with various speeds to run my listeroid for two reasons.
1] Sound control in a residential neighborhood
2] I only need a maximum of 800 to 1000 watts to charge a battery bank for 2-3 hrs. each day.
    ( 55 amps X 12 volts = 660 watts + 20% for losses = 792 watts )

I have been swapping pulleys and belt combinations to get 1000 watts of power when fully loaded and at a reasonably low speed.
The magic speed for the engine/generator seems to be 465 rpm.
The system has gone very quiet EXCEPT FOR THE DIESEL KNOCK !   Angry    It stayed.
Wow ! the ignition sounds like a guy hammering on an anvil with a sledge hammer.

I don't think I'm anywhere close to the point where the engine is in a hammer/detonation mode.
Many other members have run at speeds lower than this.

My question to everyone is in regards to injector timing and injector spring setting.

A] When I first got the engine 2 years ago, the Lovson factory suggested I loosen the injector spring screw by 1/2 turn if I wish to run the engine slower. Does this make sense ?

B] And what about injector timing. Has anyone been able to control knock by retarding the timing ?

cheers,
veggie

PS: Also posted on the microcogen forum

[38ac]

DI engines and heavy knock go hand in hand. My (brief) experiance with bio fuels is they also cause the knock to be louder. Easiest and most redustion in ignition knock would come from going IDI. Easy on a CS but not sure on a GM90?

[xyzer]

B] And what about injector timing. Has anyone been able to control knock by retarding the timing ?

Not sure of the effect on DI as compared to IDI but in playing with timing on my offset idler quest it defiantly has an affect on a IDI 6/1. It is easy to try for sure and I suspect a constant speed engine like we have we are dealt a different set of cards when we change RPM.

[ronmar]

Are you absolutely certain your flywheels are tight, with particular respect to the width of the key compared to the keyway?  I have had a key come loose, and it initially manifested itself as a louder than normal knock at reduced RPM...  This knock was the flywheel rocking back and forth on the crank, or perhaps more correctly put, the crankshaft turning and slamming into the keyway slop inside the flywheel hub, during the deceleration/acceleration of compression/ignition.  The torque pulses are larger/more severe at reduced RPM, so if you have a weakness in the key, it will find it... 

If this is a 6/1, I do not really think you are going to get all that much actual noise reduction in just 200 RPM.  Most of what you do get will probably be in pumping noise.  You could probably match the noise reduction at rated RPM with a set-in-place enclosure over the engine, and larger mufflers on intake and exhaust...

I personally don't see reducing RPM below rated being all that advantageous especially when you consider the possible effects of reduced oiling caused by the lower crank/dipper velocity.  It is not like you can just run down to the corner roid store and get another when this one fails...

[rleonard]

Ronmar, I instantly thought the same thing.  Flywheels will loosen and sound really bad.

Bob

[BruceM]

I would think 465 rpm would be safe for splash oiling. Turn the dipper sideways, perhaps?

I think Loveson's advice to reduce the injector pop pressure is dubious, but perhaps worth the try if the slower flame front from poor fuel atomization did do the job.  Hard to know if it's just someone trying to sound knowledgeable (BS) which seems equally likely.

The loose flywheel and injection timing change (retard) advice both seem on the mark to me.

[xyzer]

B] And what about injector timing. Has anyone been able to control knock by retarding the timing ?

Not sure of the effect on DI as compared to IDI but in playing with timing on my offset idler quest it defiantly has an affect on a IDI 6/1. It is easy to try for sure and I suspect a constant speed engine like we have we are dealt a different set of cards when we change RPM.

Are you absolutely certain your flywheels are tight, with particular respect to the width of the key compared to the keyway?

Oh yea!.....had that happen also! Definatly should be checked before anything else!

[veggie]

Flywheels are good.
I will start with the IP timing and report back.

Ronmar, I did experience a considerable reduction in mechanical noise and exhaust noise by dropping to 465 rpm.
This GM90 engine is a 900 rpm, 8hp version.

cheers,
veggie

[LowGear]

Here comes another one of those easy to answer questions.  How come 465 RPM?

I ask only because 666 could be blamed onto the Devil and 444 would be easier to remember.

Casey

[veggie]

Here comes another one of those easy to answer questions.  How come 465 RPM?

I ask only because 666 could be blamed onto the Devil and 444 would be easier to remember.

Casey

The goal is 1kw of power at the slowest speed possible.
On this engine, that equates to 465 rpm.

Veggie

[Thob]

It seems to me that the desired result of ignition timing is to complete the burn at a certain point.  Since the burn rate is more or less constant (doesn't vary with RPM), it seems that the slower the RPM the less advance you would want.  Is it proportional?  If the original timing was 20* at 800 RPM, I'd try 465/800*20 or about 12 degrees.  I'm not sure how much you can vary the timing as my understanding is that the timing mechanism is to shorten or length the plunger between the pump and the cam lobe; if you shorten too much it won't pump at all.  Try it, see what happens, let us know!

[Sfene]

I agree, timing too far advanced for slower RPM, another thought: injector leak. That may have the effect of advancing timing even further. Just a guess.....

[veggie]

Here comes another one of those easy to answer questions.  How come 465 RPM?

I ask only because 666 could be blamed onto the Devil and 444 would be easier to remember.

Casey

Casey.....

Come to think of it.... as I approach that "ever so sinister speed", the words "Abey Road....Abey Road...." arrise within the engine noise !    

veggie

[LowGear]

How about when you're walking backwards around engine.  What do you hear then?

I was really wondering if that was some super sweet spot for this engine?

Casey

[38ac]

Hard for my bad ears to tell from a video but fellas I'm sticking with typical DI knock. I have both styles in a standard CS type 6/1 and there is a large differance between the IDI CS and my Metro DI engine both spill timed to same spec.

 Although again hard to tell from a video and I had no load on it when this was taken you can hear the heavy ignition knock on my DI 6/1 Metro. It is lots louder than my CS IDI types.  Put about half a load and it sounds just just Veggies.
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