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  #1  
Old 09-14-2006, 12:41 AM
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617 turbo/ 240D flywheel Idle

My stock 240D idles quite smoothly, while my turbo 240 idles like a bulldozer rattling in the interior. When revved slightly it seems to smooth out. I have yet to install the engine shocks, which I am hoping will reduce the vibrations. Should I try any other fixes such as the rack damper pin, or is this normal for a 617 with a 240D flywheel?

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  #2  
Old 09-14-2006, 01:15 AM
ForcedInduction
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Originally Posted by bgkast View Post
while my turbo 240 idles like a bulldozer rattling in the interior. When revved slightly it seems to smooth out.
...
or is this normal for a 617 with a 240D flywheel?
Mine does the same. While it's possible to swap out a manual 300D FW, I like the extra acceleration a lighter flywheel allows. I can live with some vibration at idle. If I wanted a smooth engine, I'd get a 280CE.

From http://www.se-r.net/engine/light_flywheels.html
"Neil's comments are right on the money, and describe the effect well. No one ever said that a lightened flywheel would increase horsepower, but it sure does *decrease* acceleration times. Herb Adams, in his book CHASSIS ENGINEERING, says that "..the effect of reducing rotational inertia on driveline parts has 15 times the benefit of just reducing the weight of the car." I have been intrigued with this statement for months, and wish that I had followed his suggestion a long time ago and gone to a lightened flywheel. I am not an engineer (obviously), but I do have enough seat time to have a fairly refined butt dyno, and I can tell you that the difference in how the engine spools up is not subtle, but positively sensational. I wish that I had done some quarter mile times (yeah, sure, I go to the drags all the time) before I installed my lightened flywheel, so that I could provide reliable, numerical evidence. I didn't, so believe what you choose, but I can think of absolutely no reason NOT to go to the lightened flywheel. It is the single most important modification that I have made in quite a while, and I have made quite a few.

As far as perceived acceleration goes, your engine sees the mass of your car as a point stuck way out on some lever arm that it has to twist. If your engine is direct drive (i.e. no gear reduction), and you have an M3, you'd need quite a bit of torque to get that 3175 lbs moving faster. So somebody invented gears, which has the effect of changing the length of the lever, as far as the engine is concerned. In an M3, for example, first gear is 4.20:1 and final drive is 3.23:1 so what looked like 3175 lbs to the engine out at the end of that lever without gear reduction now looks more like 234 lbs (3175/13.57), assuming your rear tire has a radius of one foot give or take a few inches.

Suppose you had a magic flywheel with all the mass concentrated at the outer edge. Now the flywheel is stuck directly to the engine, so you can't reduce its effective moment via gearing. The only way you can reduce the moment is by lightening it and/or changing its mass distribution. If you could somehow remove 10 lbs from the rim of the flywheel, and the flywheel's radius was also one foot, then that would have the same effect on acceleration in first gear as reducing the mass of the car by 10x13.57 or 135.7 pounds. Now I am guessing the flywheel's radius is more like six to eight inches or so, so 10 pounds off it's outer edge would have the same effect as reducing the car's mass by more like 70-100 pounds (in first gear). Only you can't take that much weight off the edge, and moments of disks look more like 1/2mr^2, etc. etc. Point is that in first gear, the mass of your car appears to be only 20-30 times that of 10 pounds out at the edge of your flywheel, as far as the engine can tell. So the reduction of weight of the flywheel begins to be pretty significant. Expect bigtime effective acceleration improvements in first gear for proper flywheel lightening, similar to what you'd expect from reducing the weight of the car by anywhere from 70 to 100 lbs or more. The benefits decrease in higher gears in proportion to whatever the ratio is.

Obviously, the lighter your car is to begin with, the bigger an acceleration improvement you'll see since the flywheel mass represents a larger portion of the perceived mass of the car."

I compensate for the faster RPM drop between gears by adjusting the idle knob on the dash. I set it to a point that the RPMs drop to where I want them based on how long it takes to change gears (Along with engine temp, oil temp, and others that affect engine response time.)

Last edited by ForcedInduction; 09-14-2006 at 01:20 AM.
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  #3  
Old 09-14-2006, 09:33 AM
Waitn For The Bus All Day
 
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I would not only replace the engine shocks but the motor mounts too. Look at them to see if they're collapsed.

Cheers,

Bill
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  #4  
Old 09-14-2006, 10:19 AM
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Motor-mounts are brand new. Engine shocks are not worn out, but are not installed yet. The '79 240D I put the engine in needs some brackets made and welded in place to allow me to mount them.
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  #5  
Old 09-14-2006, 05:51 PM
t walgamuth's Avatar
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the 617 hops normally when idling. it is pronounced on an automatic equipped car.

a 617 with a proper 617 flywheel on it idles as smoothly as a six.

this i can state from personal experience.

and a 617 with a 616 flywheel would shake and hop a lot more than a 240.

tom w
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..I also have a 427 Cobra replica with an aluminum chassis.
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  #6  
Old 09-14-2006, 06:10 PM
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Whats diff between FW on 240/300? Weight? I am looking at doing the ultimate upgrade finally (turbo/intercooler). Cant you just get the 300 lightened?
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  #7  
Old 09-14-2006, 06:27 PM
ForcedInduction
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Originally Posted by winmutt View Post
Whats diff between FW on 240/300? Weight? I am looking at doing the ultimate upgrade finally (turbo/intercooler). Cant you just get the 300 lightened?
In the automatic, a good 80%+ of the mass is in the torque converter and fluid. I'm looking at the auto FW from my TD right now and you could only take about 2-3lbs off it without affecting the structural integrity.

For manuals, it's faster and cheaper to use the 240D FW insted of lightening a manual 300D FW. I'm sure a few lbs could also be taken off the 240 FW, but it's pretty light for an OM617 as-is. Much more than a few lbs and it would probabley start to negatively effect the daily driving quality. The difference between the 240/300 manual is about ~8lbs.
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Old 09-14-2006, 07:25 PM
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Quote:
Originally Posted by ForcedInduction View Post
In the automatic, a good 80%+ of the mass is in the torque converter and fluid. I'm looking at the auto FW from my TD right now and you could only take about 2-3lbs off it without affecting the structural integrity.

For manuals, it's faster and cheaper to use the 240D FW insted of lightening a manual 300D FW. I'm sure a few lbs could also be taken off the 240 FW, but it's pretty light for an OM617 as-is. Much more than a few lbs and it would probabley start to negatively effect the daily driving quality. The difference between the 240/300 manual is about ~8lbs.

Thanks for passing along the great write up.

I believe the 300 fw weighs 7# more than the 240, wouldnt put $100 on it but thats the number I have in the back of my head.
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  #9  
Old 09-14-2006, 08:01 PM
t walgamuth's Avatar
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i have personally weighed the automatic fw: 18#
the 240 fw is 28#

i read here that the 300 is 38#.

although i had a 300 na stick fw i never weighed it personally. i would have guessed it was closer to the 240 fw but dont know from personal experience.

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 09-20-2006, 01:51 AM
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I bumped up the idle and it is a quite a bit better at idle now. I still do get vibrations when revving or driving in gear at around 1500-2000 RPM. Should the engine shocks take care of that, or is there a chance the machine shop did a bad job on my flywheel?


Hey FI just out of curiosity do you have the old silver rack damper pin or the newer gold one in your car?
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1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine
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  #11  
Old 09-20-2006, 07:07 AM
t walgamuth's Avatar
dieselarchitect
 
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with a five you will get vibes at certain rpms that will not be possible to eleminate. it will just shudder at some rpm. no big deal. normal.
so all the shocks and mounts etc. ...

and after that it will just serve as a reminder of your good work.

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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  #12  
Old 09-20-2006, 01:01 PM
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Thanks. Good to know. It's my first 5 cyl engine.
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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine
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  #13  
Old 09-20-2006, 06:37 PM
ForcedInduction
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Hey FI just out of curiosity do you have the old silver rack damper pin or the newer gold one in your car?
No clue. When (if) I ever pull the back panel to adjust the max load screw, I'm going to replace the damper and shut-off valve anyway.
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  #14  
Old 09-20-2006, 07:53 PM
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You don't have to pull the rear panel I don't think. The rack damper should be exposed.

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1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine
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