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Flywheel weight reduction  Rating:  Rating
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 Posted: 10-16-2013 11:35 pm
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Frank Schwartz
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Somewhere I read that it was advantageous to have the flywheel turned to remove some weight.   Can anyone elaborate on this and also tell me the advantages of this??
We have a spare late 75 engine we are cleaning up and plan to keep as a spare...so at this point, I have the flywheel removed and the engine on a stand....

Therefore, if I do have it shaved down, I need information, please.

Thank youi.

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 Posted: 10-17-2013 12:12 pm
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Dan (Florida)
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I had 19444 down a couple of years ago for overhaul and did the flywheel in a freinds shop with a 8 inch or so swing lathe.  We removed a lot from the outer edge both front and back and did  a good cut across the surface.  Another freind resurfaced the wheel on a surface machine (transmission shop) . We saved and weighed the shavings which came to over three pounds.  More could have been taken  but I didn't want to take up his whole day.  The balance was not affected and it gained power mostly on the bottom end where it was needed. A lightweight clutch would help further.    I am glad I did the job.    One note  on the machining is to get the flywheel chucked up in the lathe we turned the chuck jaws around so that they would grip outward on the shoulder where the crankshaft attaches. It provided just enough grip area to take small cuts without slipping.

hth Dan

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 Posted: 10-20-2013 02:34 pm
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Jensen Healey
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A flywheel stores rotational energy. It helps smooth the power output and maintain constant cruising speed.
In a stock engine the pistons and rods are not all the same weight. Even the crankshaft isn't perfectly balanced. An aluminum flywheel would allow you to feel these imbalances.
It does take some of the available torque to spin up the flywheel during acceleration. This is why racers use lightweight flywheels. They don't care about smoothness or maintain a constant cruising speed.
By the same logic, if you rev the engine to 4000 rpm and dump the clutch, the energy stored in the flywheel will be added to the available torque. Good for smoking the tires.
There can be a seat-of-the-pants improvement in acceleration in 1st gear at lower rps's. Since the 907 is weak in this range, a modest reduction in weight makes for a nice improvement in drivability. An aluminum unit will probably be to touchy for normal street driving. Lotus used a steel flywheel on later engines that weighed in at 13lbs which is ideal for a modified and balanced street engine.
Order one from Mike at Lotusbits.com if you intend to race.

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 Posted: 10-20-2013 03:34 pm
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Frank Schwartz
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Hmmmmm...well, since I do not intend to race the engine, I can see it is best to leave things alone...going with the old adage, "If it ain't broke, don't fix it..."

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 Posted: 10-20-2013 04:43 pm
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Jensen Healey
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Hi Frank,
As I stated, it will improve drivability off the line in a stock engine. If you're going to surface the flywheel anyway, there's no reason not to remove a few pounds and balance it.
Just make sure the machinist has experience has experience in this area. Or just get one at the Club Store:
http://www.jhps.com/mm5/merchant.mvc?Screen=PROD&Store_Code=jhps&Product_Code=SLW&Category_Code=

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 Posted: 10-20-2013 07:36 pm
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Frank Schwartz
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Good idea...will save the running around and scratching for a professional....will save the pennies and maybe buy it for Xmas present to myself...

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 Posted: 10-23-2013 03:47 am
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atgparker
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Hi Frank,
I nabbed a Flywheel two weeks ago that was lightened and blanchard ground in the area of the clutch disk. The weight was removed from the engine side where approximately 3 pounds were turned into chips beneath the area where the ring gear is pressed on. The depth of cut was tangent to the as cast surface and then the removal of cast iron proceeded to venture up toward the ring gears mounting surface and flange. But enough material was left so that the ring gears press fit is not compromised. So the OEM flywheel is 20.4 pounds and the one I have is 17 pounds. The actual weights are not the key though. It really is were the mass is removed that matters in that the radius of gyration is what you want to be making smaller to attain the most effect in lightening a flywheel. So this effort was about an 18% reduction in rotational mass and from the brief driving stints for before and after equating to less than 200 miles in each case I can tell you the car seems quicker in first and second gear and the 1-2 and 2-3 gear changes seem more effortless in both up shifting and down shifting. In fact the engine braking and acceleration seem a bit faster from what I remember with the OEM flywheel. Basically the flywheel is there to smooth out the gear changes and smooth out the engines tolerances that make for imbalanced rotating components. With a smaller radius of gyration for a given application the car will speed up and slow down faster because the energy that is not in the fly wheel is transferred to propelling the chassis of the car down the road where the engine has good mechanical advantage over the chassis weight. That is were the final drive axel ratio comes into play as do the lower gears in the transmission. Thus for an 18% reduction like I have done the lower gears are were the effect seems the most.

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