617 flywheel - Page 4 - PeachParts Mercedes-Benz Forum

Stretch · #46 01-22-2012, 12:09 PM

Quote:

Originally Posted by t walgamuth

If you disagree that reduced vibration is a benefit of the heavier flywheel why do you suppose MB equipped the 300 motors with it?

And what is your explanation of why my 300 with the 38# FW idles so much more smoothly than an automatic equipped 300?

I think the heavier flywheel was chosen to fit the 5 cylinder 3 litre engine because they wanted a bigger store of kinetic energy than for the 4 cylinder 2.4 litre engine. The flywheel helps the engine along...

I don't quite understand what you mean by the "idles so much more smoothly" comment. Are you comparing two separate cars?

t walgamuth · #47 01-22-2012, 12:13 PM

Quote:

Originally Posted by Army

I think the heavier flywheel was chosen to fit the 5 cylinder 3 litre engine because they wanted a bigger store of kinetic energy than for the 4 cylinder 2.4 litre engine. The flywheel helps the engine along...

I don't quite understand what you mean by the "idles so much more smoothly" comment. Are you comparing two separate cars?

1. In what way does the heavier flywheel help the five cylinder along?

2. Yes. My observation is that automatic equipped 300d engines hop around like a jack rabbit in breeding season. My 300 na with the 38# flywheel just sits there and idles as smoothly as an inline six.

3. The 300 na manual equipped car also came with a small flywheel attached with the front flex plate on the driveshaft, IIRC.

Stretch · #48 01-22-2012, 12:28 PM

Quote:

Originally Posted by t walgamuth

1. In what way does the heavier flywheel help the five cylinder along?

Sorry I'm not being 100% clear about this.

A flywheel is meant to help any engine along where the source of power isn't continuous. (See Flywheel - Wikipedia, the free encyclopedia for example)

For some reason or other MB decided to fit a heavier flywheel to the OM617 than the OM616 - this could be like you say to "help the engine along" (sorry my term!) at idle - to make it seem more refined. But I don't think a heavier flywheel would help reduce vibrations at higher speeds.

Quote:

Originally Posted by t walgamuth

...
2. Yes. My observation is that automatic equipped 300d engines hop around like a jack rabbit in breeding season. My 300 na with the 38# flywheel just sits there and idles as smoothly as an inline six.

...

Good to know - I've not seen enough OM617s to know about that. Perhaps that has something to do with oil sloshing about in a torque converter?

Quote:

Originally Posted by t walgamuth

...

3. The 300 na manual equipped car also came with a small flywheel attached with the front flex plate on the driveshaft, IIRC.

My '81 W123 non turbo doesn't have that. Was it on a W115 or later on?

t walgamuth · #49 01-22-2012, 03:27 PM

It was an 83 euro non turbo 300.

I doubt the fluid in the torque converter sloshes much since it has no air in it. I think it is due to less weight to dampen the vibrations.

panZZer · #50 01-22-2012, 04:26 PM

Quote:

Originally Posted by winmutt

Thats balancing.

All the 85 and up tachs (84 190's) pick up their tach off the FW starter gearing using a hall effect sensor.

In todays world it is often referred to as a crank position sensor as well.

Well --The "car Wheel" I have has a series of lightening holes machined in to different depths on the edge of the ring--on two opposite sides. the truck 617 wheels do not have such machined holes--and the ring is about 1/2 thick instead of 3/4 thick truck 33lbs -- car 37lbs.

junqueyardjim · #51 01-22-2012, 05:02 PM

I have the light weight flywheel on my 617 Turbo. Idle was very good with the automatic, and idle is perfect now with the light flywheel. I did put in new motor mounts when I made the switch over to the 617. My compression is very good on all five cylinders also, I would think that helps a lot.

Stretch · #52 01-23-2012, 03:36 AM

Quote:

Originally Posted by t walgamuth

It was an 83 euro non turbo 300.

I doubt the fluid in the torque converter sloshes much since it has no air in it. I think it is due to less weight to dampen the vibrations.

Weight has no damping effect - you can however, change the "position" of a resonance by altering the system's weight or stiffness. The amplitude of a resonance is dependant upon damping.

Vibration - Wikipedia, the free encyclopedia

When comparing two similar engines with a light flywheel and a heavy flywheel a resonance for the situation with the heavier flywheel would be at a lower frequency than that of the system with the lighter flywheel.

As for the torque converter - that's an interesting situation.

I think there is likely to be some air in it as the system isn't bled (like brakes) - but I don't know how much. If you measure the height of the oil in the transmission on the dip stick with the oil settled in the sump and the engine turned off you get a high reading. Start the engine and the oil level drops down the dip stick as oil gets sucked(?) / transfered from the gearbox through the hollow shaft (on the 722.1 and 722.3 transmissions at least!) and into the torque converter:- because "space gets made" in the torque converter as the existing oil inside gets spun out to the internal circumference of the torque converter and gets forced through the impellers.

Torque converter - Wikipedia, the free encyclopedia

If there is say 2 litres of oil forced to the circumference of the torque converter then there's roughly an extra 2 kg (plus a bit of weight of the torque converter) added to the effective mass of the flywheel. At the moment I can't tell if these numbers are even in the right ball park - I'm just trying to imagine what is going on in there!

t walgamuth · #53 01-23-2012, 06:07 AM

Quote:

Originally Posted by Army

Weight has no damping effect - you can however, change the "position" of a resonance by altering the system's weight or stiffness. The amplitude of a resonance is dependant upon damping.

Vibration - Wikipedia, the free encyclopedia

When comparing two similar engines with a light flywheel and a heavy flywheel a resonance for the situation with the heavier flywheel would be at a lower frequency than that of the system with the lighter flywheel.

As for the torque converter - that's an interesting situation.

I think there is likely to be some air in it as the system isn't bled (like brakes) - but I don't know how much. If you measure the height of the oil in the transmission on the dip stick with the oil settled in the sump and the engine turned off you get a high reading. Start the engine and the oil level drops down the dip stick as oil gets sucked(?) / transfered from the gearbox through the hollow shaft (on the 722.1 and 722.3 transmissions at least!) and into the torque converter:- because "space gets made" in the torque converter as the existing oil inside gets spun out to the internal circumference of the torque converter and gets forced through the impellers.

Torque converter - Wikipedia, the free encyclopedia

If there is say 2 litres of oil forced to the circumference of the torque converter then there's roughly an extra 2 kg (plus a bit of weight of the torque converter) added to the effective mass of the flywheel. At the moment I can't tell if these numbers are even in the right ball park - I'm just trying to imagine what is going on in there!

Your assertion that weight has no damping effect for vibration is surprising to me. Perhaps it is a semantics issue.

In my experience weight is used to control vibration in any case where vibration is a potential problem. My elevator motor for example in my old office building sits on a nice thick concrete pad. In factorys where large machinery is housed, typically they will sit on huge pads to reduce the effect of vibration. You say it is not damping? Perhaps there is another more scientific term to describe it but the weight reduces the effect of vibrating machinery.

Cars which are raced typically will have little or no flywheels because instantanious acceleration and decellaration is desired. In these applications a little extra vibration is an acceptable trade off.

Where smoothness is the priority a heavy flywheel is used. My stick flywheel for my 51 caddy must weigh 50#.....smoothness is the priority there.

I am not an expert on automatic trannys but I do know that when changing the fluid in a tranny you must drain the torque converter.

Whether it is full up with no space or not I don't know either but my understanding of it is that it would need to be full to work properly.

Stretch · #54 01-23-2012, 07:58 AM

Quote:

Originally Posted by t walgamuth

Your assertion that weight has no damping effect for vibration is surprising to me. Perhaps it is a semantics issue.

In my experience weight is used to control vibration in any case where vibration is a potential problem. My elevator motor for example in my old office building sits on a nice thick concrete pad. In factorys where large machinery is housed, typically they will sit on huge pads to reduce the effect of vibration. You say it is not damping? Perhaps there is another more scientific term to describe it but the weight reduces the effect of vibrating machinery.

...

I agree that making things heavier is often used to "solve" a vibration problem - sometimes it is a good / cheap practical solution. The other solution is to add in more bracing - make it stiffer - and that way "solve" a vibration problem.

In buildings adding weight isn't such a big deal but in aircraft design it is. So I guess the solution to your elavator problem was probably cheapest to fix by adding in weight; whereas a vibration problem in an aircraft would probably be to add in stiffness.

But in both of these cases the solution is more like moving the problem elsewhere - by adding mass or stiffness to a system you are changing the dynamics. In my experience with aircraft structures this is most certainly the case: you fix one bit only to find another bit further along breaks next...

Damping, however, is a different thing. Damping is arguably best thought of as the dissipation of energy in the form of heat. Lots of dampers utilise friction such as oil flowing through restrictions in a shock absorber or a dashpot (viscous damping). Damping predominantly acts at a resonance - adding damping to a system will have the greatest effect of reducing the response / motion / movement / amplitude of the system at a resonance where potentially there is the greatest risk of over stressing the structure or fatigue.

Stretch · #55 01-23-2012, 08:04 AM

Quote:

Originally Posted by t walgamuth

...

I am not an expert on automatic trannys but I do know that when changing the fluid in a tranny you must drain the torque converter.

Whether it is full up with no space or not I don't know either but my understanding of it is that it would need to be full to work properly.

I'm also no expert with transmissions but I'm learning. I wonder how high up the gearbox the fluid sits? Before I put my tranmsission back in my car I'm gonna have to make some measurements so I can get a better idea. There most certainly needs to be enough fluid in the torque converter for it to operate - but again how much is enough? Perhaps the German copy of my FSM can help - translation is slow going for me though...

Stretch · #56 01-23-2012, 08:34 AM

Quote:

Originally Posted by t walgamuth

...
Where smoothness is the priority a heavy flywheel is used. My stick flywheel for my 51 caddy must weigh 50#.....smoothness is the priority there.

...

I think this smoothness has most effect at idle.

In an OM617 you have 5 cylinders firing for every two rotations of the crank. So 5 bangs per 720 degrees or 1 bang per 144 degrees.

The crank has to turn 144 degrees before more energy is put into the system in the form of ignition expanding gasses etc etc etc

A flywheel will help the crank rotate by dissipating its (kinetic) energy back into the system that powered it in these periods of 144 degrees between each point of ignition.

Please note this is a very crude way of considering it - as the effect of combustion in the cylinder is not instantaneous; it is dependant upon several issues like how fast the crank is rotating / rate of combustion / fuel / pumping losses of the cylinders not firing (most relevant at idle) etc => but please go with it for the moment!

The point I'm trying to make is that at idle - say 800 rpm - these unpowered periods of crank rotation (144 degrees) equate to a time of 0.03 seconds.

{Calculated this way => 800 / 60 = 13.3 revs / s ; 1/13.3 = time for one rev ; divide that by 360 degrees to get time for one degree ; mulitply by 144 to get answer}

And at 5000 rpm - these unpowered periods of crank rotation (144 degrees) equate to a time of 0.0048 seconds.

(Very) Roughly speaking the engine has more time to slow down at an idle of 800 rpm => 30 milli-seconds, than at 5000 rpm => 4.8 milli-seconds. In this way I think the flywheel is more important for the smoothness of an engine at idle than it is at high engine speeds.

I bet if you had a gucci fine point tachometer that could make say 500 pulses per revolution and a decent time domain data acquisition system (only has to be acoustic quality) you could measure the time between each of these pulses and actually see the engine slowing down during these tiny periods of unpowered rotation - the geek in me would like to see that - however I'd probably have to fit a light flywheel!

panZZer · #57 01-23-2012, 05:06 PM

Quote:

Originally Posted by Army

I think this smoothness has most effect at idle.

In an OM617 you have 5 cylinders firing for every two rotations of the crank. So 5 bangs per 720 degrees or 1 bang per 144 degrees.

The crank has to turn 144 degrees before more energy is put into the system in the form of ignition expanding gasses etc etc etc

A flywheel will help the crank rotate by dissipating its (kinetic) energy back into the system that powered it in these periods of 144 degrees between each point of ignition.

Please note this is a very crude way of considering it - as the effect of combustion in the cylinder is not instantaneous; it is dependant upon several issues like how fast the crank is rotating / rate of combustion / fuel / pumping losses of the cylinders not firing (most relevant at idle) etc => but please go with it for the moment!

The point I'm trying to make is that at idle - say 800 rpm - these unpowered periods of crank rotation (144 degrees) equate to a time of 0.03 seconds.

{Calculated this way => 800 / 60 = 13.3 revs / s ; 1/13.3 = time for one rev ; divide that by 360 degrees to get time for one degree ; mulitply by 144 to get answer}

And at 5000 rpm - these unpowered periods of crank rotation (144 degrees) equate to a time of 0.0048 seconds.

(Very) Roughly speaking the engine has more time to slow down at an idle of 800 rpm => 30 milli-seconds, than at 5000 rpm => 4.8 milli-seconds. In this way I think the flywheel is more important for the smoothness of an engine at idle than it is at high engine speeds.

I bet if you had a gucci fine point tachometer that could make say 500 pulses per revolution and a decent time domain data acquisition system (only has to be acoustic quality) you could measure the time between each of these pulses and actually see the engine slowing down during these tiny periods of unpowered rotation - the geek in me would like to see that - however I'd probably have to fit a light flywheel!

yea well-I just drive the damn thing, seems reasonably smooth to me.

junqueyardjim · #58 01-23-2012, 06:18 PM

I serviced my bus engine this morning. Had to add a little oil, so I opened the engine compartment. Well, there it was, that big old bright yellow Caterpillar which is labeled C7, so I assume it is a Seven Liter engine, six cylinders and little more then twice the displacement of the 617. But in looking it over, I couldn't help but notice how much the front crank damper and pulley casting looked like the Mercedes flywheel. I could not see any rubber in it, I think it was just a machined casting of solid steel and I would estimate that it weighed at least 59 pounds. The bus runs an automatic transmission also. Idle is very smooth, but with a lot of sheet metal buzz. The buzz goes away as soon as idle speed is pasted.

bricktron · #59 01-23-2012, 11:33 PM

everyone knows (or should know) about the effect of flywheel mass on idling smoothness and acceleration. this question about unwanted vibrations at certain speeds is what troubles me. if the wheel and crank are balanced against each other, and the driveshaft is balanced as well, then wtf is doing the vibrating?

Stretch · #60 01-24-2012, 03:56 AM

Quote:

Originally Posted by bricktron

everyone knows (or should know) about the effect of flywheel mass on idling smoothness and acceleration. this question about unwanted vibrations at certain speeds is what troubles me. if the wheel and crank are balanced against each other, and the driveshaft is balanced as well, then wtf is doing the vibrating?

I don't know to what extent the crank and the flywheel were balanced at the factory. I get the impression from the self justifying custom balancing shop blurbs that there is a difference between the extent at which they will balance components and the extent to which a factory might do.

Just because something has been balanced it does not mean that you'll never get vibration - balancing is a method of reducing vibration.

As to what "is doing the vibration" - in an engine the primary source of vibration is combustion. I understand that the "cup of coffee on top of the engine test" has been made possible by advances in injection system design rather than by advances in balancing.

(Please note the cup of coffee test as I've called it is referring to some kipper journalist demonstrating the smoothness of a BMW diesel in the late 1990s if I remember correctly)