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  #1  
Old 08-21-2005, 08:18 PM
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Rebuilding 240D Engine - Flywheel Balancing Question

HELP!!!

I am rebuilding a 240D engine. New pistons, rings, bearings, etc. Have got to the point where I am putting the flywheel on. When reading my MB Shop Manual, it mentions LINING UP MARKS ON THE CRANK SHAFT AND THE FLYWHEEL.

I see a mark on the flywheel but cannot find even a hint of a mark on the crank shaft. One problem..is in order to rebuilt this engine I had to use some parts from another engine. This is not the original crank shaft, but from a donor engine. I am using my original flywheel. In reading my manual it talks about balancing flywheel to flywheel if you are to use a new one but obviously I don't have the flywheel to do that nor the tooling...

My main question would be....

Am I making to big of a deal out of this???

I have the engine all put together and don't want to take the crankshaft back out.......but there is good machine shop in my town, should I have them check the flywheel and neutrally balance it...

Or in anyones experience, have you just put the flywheel back on possibly with the engine at top dead center and made an educated guess on where it should be installed????

Thank you and ANY help sure would be appreciated...

David

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  #2  
Old 08-21-2005, 08:54 PM
ForcedInduction
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Quote:
Originally Posted by dave1shere
but there is good machine shop in my town, should I have them check the flywheel and neutrally balance it...
Some of these flywheels are off-balance when attached to the crank. My 240D's flywheel is 250grams off neutral. That's an entire tube of toothpaste!

You can't just throw it on. Use some brake cleaner on the crank end and look VERY close for any marks. Sometimes they are just a tiny nick, sometimes they are marked very well, and sometimes they just hit the flywheel when they were marked.
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  #3  
Old 08-22-2005, 12:21 AM
t walgamuth's Avatar
dieselarchitect
 
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i dont

agree with the concept of there being any marks on the flywheel or crank. in my experience you can mount the flywheel in any of the twelve positions available with no adverse consequences.

the flywheel weighs 38 pounds. if his is 250 grams off it is just from uneven wear. have your flywheel planed before reinstalling it. you should in any case. you will be fine.

tom w
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #4  
Old 08-22-2005, 12:47 AM
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Well, it is not just the weight ... it also makes a difference how far off the center it is....and that is also multiplied by the 2000 ro 4000 rpms which it will be turning...
Being off can really wear out those new bearings quickly and may also be felt in the seat of your pants.... but except for that " flywheel to flywheel " instructions I don't know what to suggest.
My VW turned over 2 million revolutions just going from Dallas to Houston one night...that is a lot of wear if the parts are very far from balanced.
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  #5  
Old 08-22-2005, 06:56 AM
t walgamuth's Avatar
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the only

way it would be off center is if it is built off center. there are no markings on the flywheel or crank. we have converted automatic cars to stick. we looked and looked for marks. there are none. the flywheels and cranks are not balanced together.

an auto flex plate weighs 12 pounds. a 240 flywheel weighs 38 pounds. how you going to transfer a special balance from one to the other?

if this guys flywheel was off 250 grams, it was from eneven wear. plane it and it will be balanced.

tom w
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #6  
Old 08-22-2005, 01:33 PM
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What do you mean by planed

When you say plain do you mean to have the flywheel Resurfaced or to have the machine shop rebalance the flywheel. Thanks for the quick reply.
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  #7  
Old 08-22-2005, 02:26 PM
t walgamuth's Avatar
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yes

resurface. should not need balancing.

tom w
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #8  
Old 08-22-2005, 02:54 PM
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Metals , when cast , are not completely homogeneous. So differences in density occur which translate to different weights...
The " off center" i was talking about referred to the distance from the center than any potential weight anomoly occured... the total weight difference could be the same between two flywheels... but if it is right near the middle on one as compared to being near the starter ring gear it makes a huge differnce in the vibration which it causes...
The concept is like ' torque arm' though that may not be the exact word for it. The assymetrical weight times the distance from center times the rpm is a close description of the total damage potential.
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  #9  
Old 08-22-2005, 04:19 PM
t walgamuth's Avatar
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all that

you say is true. but the flywheel is balanced at the factory. it really shouldnt need to be rebalanced.

tom w
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #10  
Old 08-22-2005, 04:32 PM
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This subject seems to come up from time to time, especially when someone is doing a stick conversion on an automatic.

Here has been my experience with it:

When I first installed the 616 in my Rover it was a standard engine and came with a flywheel already on it. In my haste, I removed it and never made any marking on my own. When the time came to reassemble it, I looked and looked and looked and could never find any factory marks. I spend a few days calling everyone I know and consulting with some old-time Benz guys and they all said that these engines are internally balanced and don’t need to the flywheel to be timed to the crank. So I took their advice and bolted the flywheel on any-old place. The engine was fine for 4 years until I changed it out.

The second motor that went into the truck was from an automatic. Just for the hell of it I put the old motor to TDC, marked the flywheel, put the new motor to TDC and put the flywheel in the same position. That motor feels just as good as the old one.

As far as 82-300td’s flywheel being 250 grams neutral, I can’t explain that. 250 grams is almost ½ pound and a hell of a lot of weight at 4000rpms!

As I’m writing this, I’m surfing the manuals and came up with this.

Linky

Read the text on the first page about how the different engines are balanced. Kinda explains why some flywheels are neutral and why 82-300td’s isn’t.

Logic leads me to think that on automatic tranny engines the balancing would have been done somewhere other than the flywheel as it doesn’t carry enough weight to help a whole lot.

All this leads back to the original question as to whether there are markings on the flywheel and crank. I think there must be and that you need to find them.

And:

If the crank is from a manual car, you need to find the original flywheel, find the marks and install it back where it was.

If the original engine was an automatic, I would send your flywheel out and have it balanced to neutral.

Hope I didn’t confuse you. I know I confused myself a couple times!!

And I guess I just got lucky with mine!!

jim
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  #11  
Old 08-22-2005, 04:36 PM
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Quote:
Originally Posted by leathermang
The concept is like ' torque arm' though that may not be the exact word for it. The assymetrical weight times the distance from center times the rpm is a close description of the total damage potential.
F=1.77 x MRN²/1000000

F=Force in pounds
M=Mass of unbalance in ounces
R=radius of unbalance in inches
N=RPM
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  #12  
Old 08-22-2005, 05:56 PM
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"Logic leads me to think that on automatic tranny engines the balancing would have been done somewhere other than the flywheel as it doesn’t carry enough weight to help a whole lot."

Half the torque converter is bolted to that plate... that should bring the total rotating mass up to pretty close to a manual flywheel.
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  #13  
Old 08-22-2005, 06:39 PM
t walgamuth's Avatar
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leather

have you personal experience with putting a stick in an automatic car? can you find anything in the factory manual saying that the flywheels and or flex plates are balanced with the crank?

there are a lot of folks out there who haven't had personal experience telling folks who are contemplating a swap that the flywheel needs balancing or balancing to the crank.

i have done it and i invite any of you non believers to come look at my non turbo 300d motor idling and tell me that the flywheel is out of balance. it is so smooth you would swear it is a six. me and my machinist researched and examined and could not find any evidence of special balancing (with the crank).

so if you can show me hard evidence i will buy you a six pack of your choice of beer.

otherwise there are a lot of folks out there who might spend money on a balancing to have the balancer to tell them "its balanced already".

tom w
__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #14  
Old 08-22-2005, 07:05 PM
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Quote:
Originally Posted by t walgamuth

i have done it and i invite any of you non believers to come look at my non turbo 300d motor idling and tell me that the flywheel is out of balance. it is so smooth you would swear it is a six. me and my machinist researched and examined and could not find any evidence of special balancing (with the crank).
I have no personal knowledge of whether this flywheel is balanced with or without the crankshaft.

However, you cannot use the performance of the engine, at idle, as a measure of whether the flywheel is balanced properly, or not.

If you utilize the above formula, you will find that the force, in pounds, for a typical flywheel unbalance (5 oz-in) is less than 3 lb. at 600 rpm.

The only way that an unbalanced flywheel could be felt by the engine and the driver is at very high rpm's. It would manifest itself as a slight buzzing. I have my doubts if even this unbalance would be noticed above the road vibrations.

You are speaking of a very small unbalance level and, basically, on an automobile engine, it's effectively a moot point whether the flywheel is balanced by itself, or with the crankshaft.

If the Germans specified that it should be balanced with the crankshaft, it's an example of typical overkill by an engineer who is operating on theory without any practical experience.
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  #15  
Old 08-22-2005, 08:48 PM
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T-Walgamuth, right from the manual:

For engine 615 and 616 the crankshaft, balance plate and flywheel are balanced as one assembly.

In contrast, engine 617 is balanced as a whole, i.e. the entire engine is balanced on a balancing machine.

Since this balancing operation cannot be executed in a repair shop, and as engine balance has to be maintained as well as possible, it is necessary to adjust the balance of a new flywheel to that of the old one. This applies equally well to new flywheels for engines 615 and 616.


It seems in most cases the flywheels may be balanced to neutral. In my case I believe that’s the case as both engines ran smoothly at all rpms. And I never marked the flywheel at all.

In 82-300td’s case, I think if he were to put a 250 gram “off-balance” flywheel on an automatic car I think there would be trouble.

“Half the torque converter is bolted to that plate... that should bring the total rotating mass up to pretty close to a manual flywheel.”

That mass isn’t as important as the fact the a torque converter will by it’s nature help balance an engine.

IMO, it’s not whether the flywheel is balanced or not…it seems that some are and some aren’t. It’s the fact that on a 240 the flywheel should stay with the original crank shaft and if it doesn’t, you need to match the balance of a new flywheel to the old one.

If David can’t find the original flywheel for the crankshaft he has, the next best thing would be to balance the one he’s got to neutral and hope for the best.

jim

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