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L series Flywheels. 240/260/280 vs. L16/L18/L20

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#21 MRLQ2U



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Posted 18 March 2017 - 03:54 PM


#22 Xnke


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Posted 04 April 2017 - 04:15 PM

All L-series flywheels are neutral balance-none of the L-series (four or six) are externally balanced.


4 cylinder engines are NOT inherently balanced. Reciprocating balance only, no rotating balance.


6 cylinder engines ARE inherently balanced. Reciprocating and rotating balance.


It's not a harmonic "balancer" it's a torsional damper. It's there to help negate the twisting vibrations in the longer L6 crankshaft.


L series flywheels have an 80mm bore for the rear of the crank to seat into, and this is the locating surface. No "spigot" on the back for the flywheel to center up on.


RB and KA flywheels have the same bolt pattern, same clutch cover pattern, and are widely available in aluminum or steel down to 7lbs aluminum or 11lbs steel.


RB/KA flywheels have an 81mm bore for the rear of the crank to seat on, and that bore is NOT the locating surface. The 38mm spigot on the back of the crankshaft surrounding the pilot bearing bore IS the locating surface for the flywheel.


This means you can get an RB20DET chrome-moly flywheel in 11lbs, have your local machine shop turn a 80mm ID, 81mm OD spacer ring 6mm wide (they will hate you for this, so be ready) and press that into the flywheel-you can then use the 11lb RB20DET flywheel, a 250mm 350Z clutch, and have a flywheel/clutch assembly capable of 400ft-lbs of torque capacity.


You can also use the 200mm L-series flywheel and the roadster pressure plate, but be aware the lightest you can safely cut the stock 200mm flywheel down to is about 17lbs. Any lighter and you're risking your feet.


L-24 225mm flywheels can go down to 17lbs as well, but L28ET 240mm flywheels can't quite go that far-at 18lbs they are borderline. Stock L-6 flywheels are all 24lbs, L20B at 29lbs, RB20DET at 22lbs.


When turning the L-series flywheel, you need a 12" swing over bed minimum. You want to come in under the ring gear at a 45 degree angle, and cut the thick outer inertia ring out, but do not try to turn the flywheel thinner than the thinnest cast area. You want to just clean up the cast finish everywhere except the outer inertia ring, and you need to leave that 45* angle cut under the ring gear to make sure there's enough meat to keep the ring gear press-fit in place. I have a 200mm L-flywheel around here that I lightened but failed the crack-test afterward-make sure you get yours checked! The old cast iron is good stuff but there is always a chance of uncovering a little piece of shit in the casting or a bubble.

#23 distributorguy


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Posted 26 April 2017 - 04:21 AM

 The old cast iron is good stuff but there is always a chance of uncovering a little piece of shit in the casting or a bubble.


Actually, its cast steel, not iron.  I don't recall the specification, but the steel grade is cast into the flywheel face.  They are a relatively high grade steel, considering the mass.  I lightened my stock L20b flywheel to 16.5 lbs, and it passed a crack check as well as being corrected about 1/4 oz for a perfect dynamic balance.