FYI: '83 OM617a flexplate - not neutral balanced - Page 2 - PeachParts Mercedes-Benz Forum

Govert · #16 04-15-2013, 05:20 AM

Quote:

Originally Posted by barry12345

I wonder if one of us should contact the classic centre to see what was the situation during production of the 123 diesels. A few grams might be within the manufacturing tollerances of the flexplate. There are about 28 grams in an ounce. I knew or believe during the earlier gas era the balancing was done including the flywheel.

The balancing is mentioned in the FSM:

The crankshaft of 200D/220D/240D was balanced together with the front balancer and flywheel.

The 300D N/A and turbo engine is balanced as a whole.

t walgamuth · #17 04-15-2013, 06:37 AM

Quote:

Originally Posted by Govert

The balancing is mentioned in the FSM:

The crankshaft of 200D/220D/240D was balanced together with the front balancer and flywheel.

The 300D N/A and turbo engine is balanced as a whole.

I don't understand your intended difference in meaning between your second and third statements. Would you add more information please?

Govert · #18 04-15-2013, 07:43 AM

Quote:

Originally Posted by t walgamuth

I don't understand your intended difference in meaning between your second and third statements. Would you add more information please?

My understanding is:

The crankshaft of the four-cylinder engines is balanced together with balancer and flywheel and then it is put into the engine.

The five-cylinder engine is put together, and then the crankshaft is balanced, so with pistons attached.

See below for the FSM:

97 SL320 · #19 04-15-2013, 09:08 PM

The 617 balance can be done piece meal in a shop, spinning everything up at the factory is likely more cost effective when you are building thousands of engines. The pistons, rings, rods and bearings are weighed then bob weights clamped to crankshaft rod journals to simulate these parts. This assembly is then spun up on a balancer. Some engine builders purposely under / overbalance to counteract internal forces, tune to RPM ranges making balancing somewhat of a black art.

For internal balance cranks, no other parts are needed. For external, the vibration damper and flywheel need to be installed.

Stretch · #20 04-16-2013, 02:36 AM

Quote:

Originally Posted by Govert

My understanding is:

The crankshaft of the four-cylinder engines is balanced together with balancer and flywheel and then it is put into the engine.

The five-cylinder engine is put together, and then the crankshaft is balanced, so with pistons attached.

See below for the FSM:

I think that the statement "the whole engine is balanced on a balancing machine" is ambiguous. I don't understand what that means or what it is meant to mean.

I can't see how you could efficiently balance rotating parts of an engine with an engine fully assembled - sure you might be able to mount sensors on certain parts of a machine and make measurements: But then to make adjustments you'd have to dismantle and then reassemble and retest - I can't see that happening in any mass manufacturing environment. They might do something like this for huge gas turbine power generating sets because the spinning parts are so big; but for an automotive engine... ???

I think the FSM is all messed up on this subject.

My understanding of what is done is described by 97 SL320 above.

snowbrd84 · #21 04-16-2013, 09:01 AM

I just got done putting an OM617.951 out of a 85 300sd into my Jeep. The one thing I did not do was match balance my neutral balanced flex plate from the Jeep that I used in the swap. I have no vibrations or anything over 1000 rpms, at wot, it runs smooooooth. Would i know it if there was a balance problem?

Govert · #22 04-16-2013, 03:04 PM

Quote:

Originally Posted by Stretch

I think that the statement "the whole engine is balanced on a balancing machine" is ambiguous. I don't understand what that means or what it is meant to mean.

I can't see how you could efficiently balance rotating parts of an engine with an engine fully assembled - sure you might be able to mount sensors on certain parts of a machine and make measurements: But then to make adjustments you'd have to dismantle and then reassemble and retest - I can't see that happening in any mass manufacturing environment. They might do something like this for huge gas turbine power generating sets because the spinning parts are so big; but for an automotive engine... ???

I think the FSM is all messed up on this subject.

My understanding of what is done is described by 97 SL320 above.

For the purpose of balance, only the short block needs to be assembled and balanced.

I understand that MB spent some time when they designed the OM617 to get it running smooth: it is difficult to design diesel engines which don't vibrate, five-cylinder diesel engines are even more difficult, so it is not strange that more attention was payed to the balance of the OM617 engine. The 300D was sold to the upper part of the market, you cannot sell them a expensive massage machine.

KAdams4458 · #23 04-16-2013, 04:19 PM

Funny... Wrapped up the manual swap on my 300D yesterday, and the first thing I notice when I fired it up was an almost complete lack of vibration and a surreal quietness in the cabin. It took me a second to realise the motor was running. A few test runs later, and I can confirm this seems to be the new demeanor of the beast. It's quiet like a modern car, now. No weird throbbing in the floor pan, no shaking side to side at stop lights. I didn't touch the motor during the swap, and all the mounts are still the same...

The automatic transmission seems to have been solely responsible for all of the rumbling and vibration that the car used to have. How? No idea here. I may disassemble and diagnose the old tranny at some point just for the heck of it. For the time being, I am too happy that my 5-cylinder diesel runs as smooth as a new Honda 4-cylinder to care what was wrong with it before.

Now, I know that none of this has anything to do with balancing, but I had to set the stage for my findings that may be relevant to a properly match balanced flywheel. Time and again folks that have swapped to manual transmissions have noted that there can be vibrations at certain RPM ranges regardless of the gear they are in. Frequently this has been attributed to using the lighter 240D flywheel. I have found no such vibration in my swap using the same flywheel, so there is a possibility that the absence of vibration at certain crank speeds in my swap is due to a properly balanced flywheel.

To help you understand where I am coming from, think of a road wheel that is not balanced; at certain road speeds they frequently develop a vibration, but speeds above or below that point cause the vibration to fall off and become less noticeable. I propose that an imbalanced flywheel can exhibit the same kind of RPM-dependant vibration, but I'm not qualified to state this as fact without a better understanding of the physics involved.

t walgamuth · #24 04-16-2013, 04:35 PM

Quote:

Originally Posted by snowbrd84

I just got done putting an OM617.951 out of a 85 300sd into my Jeep. The one thing I did not do was match balance my neutral balanced flex plate from the Jeep that I used in the swap. I have no vibrations or anything over 1000 rpms, at wot, it runs smooooooth. Would i know it if there was a balance problem?

It would be very obvious. It would shake your teeth out.

t walgamuth · #25 04-16-2013, 04:37 PM

Using a stick flywheel instead of an automatic creates additional mass which smooths out the idle compared to the automatic. It definately reduces dramatically the hop at idle. With the 38# 617 flywheel it is even better. Of course you have the weight of the clutch and pressure plate too.

KAdams4458 · #26 04-16-2013, 04:53 PM

I don't know if it could be smoother than this, but the added mass of any flywheel should help. Still, the autotragic transmission was clearly contributing to vibration somehow. at idle it would rattle fillings out of your teeth, and the entire cabin resonated under acceleration like a big subwoofer. Felt like driving a school bus. LOL.