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


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#1 HRH

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Posted 09 March 2016 - 09:26 PM

So I forgot to get the flywheel while extricating the 4 speed from the field car 280z the other day.  I can go get it, but it's an hour long journey one way on my day off, which means I'd rather use something else.  Looking up the clutch from a 280z, it appears that all the Z motors, KA motors, and L motor 4 cylinders or 2.0 or larger all fit.  Which means the flywheel, as long as it's a 6 bolt, ought to work fine, right?

 

Well, I talked to the Datsun guru and he swears he put a 4 cylinder flywheel on a 280z and they had a hell of an issue with vibration.  Changed the flywheel back to the correct 280z one, and problem solved.  What's more, when I look on the internet for a new flywheel, the interchange suggests only 280z.

 

I know there are different depths, but has anyone else had a vibration problem from swapping flywheels?  Not that I don't trust my guru, just never had any experience with that problem.  But I don't want to get the motor and trans in the race car only to have to remove it soon after.



#2 datzenmike

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Posted 09 March 2016 - 09:32 PM

The Z flywheel I weighed was 21 pounds. L20B were 29 because of their lighter cranks and spinning parts..


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#3 Lockleaf

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Posted 09 March 2016 - 09:46 PM

Could the fly wheels potentially be tested for balance on a tire balancer? I'm perfectly willing to be wrong here, but it seems like if you could have one of each balanced and they are both balanced, that would answer the question? But I suppose that requires access to both fly wheels and a tire balancer...

So perhaps this post is inane.

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#4 HRH

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Posted 09 March 2016 - 09:50 PM

I have a tire balancer and many flywheels.  Think I could probably arrange that.  But I'm betting someone out there has the definitive answer.  One of the things is the difference in weight.  But if that's the case, how would a lightened flywheel ever work?  If they are different depths from the crank, as in one sticks out farther to absorb different levels of vibrations, that would make sense.  If the moment arm is 1" from the rear crank face vs. 2" from the rear crank face, then yes, it would absorb different frequencies which could then be attributed to having different crankshaft lengths.

 

But I don't know.  Though it is an interesting subject.  I've only ever played with 4 cylinder cranks and flywheels, and yes, they are interchangeable.  Never had one balance issue.  But I haven't played with L6s much.



#5 Lockleaf

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Posted 09 March 2016 - 10:15 PM

I agree with the moment arm changing frequencies, but I wonder how much effect that is in the real world? I've seen many flywheel spacers used with transmission adapters and never seen a complaint about vibration caused by them. In my head, the spacer would equate to the same thing as the different flywheel depths, but perhaps I'm mistaken.

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#6 Ranman72

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Posted 09 March 2016 - 10:32 PM

I am using an L6 flywheel on my L20b with no issues 

not sure about reversing it but guru,s are guru,s for a reason 

do you feel like proving a guru wrong or doing the job twice because he was right  :devil:  :devil:  :devil:



#7 datzenmike

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Posted 10 March 2016 - 06:24 AM

I am using an L6 flywheel on my L20b with no issues 

not sure about reversing it but guru,s are guru,s for a reason 

do you feel like proving a guru wrong or doing the job twice because he was right  :devil:  :devil:  :devil:

 

I get accused of it all the time....

 

 

 

How can it be balanced differently? Heavy or light on one side like 3 o'clock? This would have to be to off-set some other imbalance found in the rest of the rotating engine parts. Then the wheel would be marked so it can only fit in that position and it would be impossible to swap it to another L6 which would probably be different.

 

It would be better for mass production to balance the crank and the flywheel perfectly  before putting them together. Everything is balanced and goes together without problems. 

 

Doesn't the L-6 have a harmonic balancer on the front pulley? 4 cylinders are perfect for balancing and don't use them. A six might?  


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#8 datzenmike

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Posted 10 March 2016 - 07:27 AM

Matt I guess the simplest thing is to ask him what he means. Maybe he means something else than what you took away from the discussion. (again, not being argumentative)


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#9 H5WAGON

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Posted 10 March 2016 - 09:21 AM

Nice to know the Z flywheel is 21 pounds VS 29....

Is it fully balanced? I know the L20 & L16 one's have drill holes on the edges where they are balanced from the factory.


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#10 LenRobertson

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Posted 10 March 2016 - 10:44 AM

I'm using a Maxima flywheel in my 510 on a stock L20b since it is much lighter than an L20 one. It seems to me it revs up noticeably faster than the stock L20b in my 200SX. But they are different cars and different weights so maybe I am feeling what I want to. I did a search since I couldn't recall the actual weight of the Maxima flywheel. I was thinking 18 lbs, but it is actually 19 1/2 according to my post #10 here:

http://community.rat...tened-flywheel/

I have a memory (probably bogus like the 18 lbs one) that some Maximas used a slightly lighter weight flywheel than 280Zs.

 

While searching for my flywheel weight, I found here in post #5:

http://community.rat...wheel-question/

Matt you mention Joe having a vibration problem with a Z24 flywheel on an L motor. Which isn't to say he may not also have had a problem with an L4 flywheel onto an L6.

 

Anyway, seems to me autocross would be where a lighter flywheel would be very desirable if it allows reaching higher revs quicker. I think Reg's Pratt & Whitney lathe is big enough to turn an L flywheel. There are probably some tricks and safety warnings about DIY flywheel lightening to investigate. One thing may be using a round-nose tool for the inside corner of the cut. I recall reading that a sharp inside corner is where cracking can start. Joe probably knows all this stuff.

 

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#11 HRH

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Posted 10 March 2016 - 09:25 PM

Well today was busy enough I didn't get any more research done.  I know the Maxima flywheel is the lightest of the 6 cylinders, but not yanking Ugly Betty's out for the Z.  ;)  It makes sense to me that the flywheels are balanced separately, in which case it shouldn't matter which flywheel goes on which engine.  However, I'm not one to poo poo a guru unless I have two other sources that say otherwise.  Consequently, I have another fellow to call tomorrow who most probably knows the answer to my question.  And I may just go grab that one out of the field car because I'm paranoid now. Lol.



#12 scooter

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Posted 10 March 2016 - 09:47 PM

When I balanced my motor the crank and rods wernt far off, but the flywheel was out tons! Over 40 grams from what I remember. You guys may be able to chuck it up in a brake lathe and turn all the meat off the back side of it. That will lighten it up tons. Or you can use a lathe and take out more. Make sure you balance it after as it WILL be out to lunch

#13 scooter

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Posted 10 March 2016 - 09:48 PM

And the tire machine might not be accurate enough. Most balancing machines will now go down to .1 of a gram.

#14 datzenmike

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Posted 11 March 2016 - 01:57 PM

When I balanced my motor the crank and rods wernt far off, but the flywheel was out tons! Over 40 grams from what I remember. You guys may be able to chuck it up in a brake lathe and turn all the meat off the back side of it. That will lighten it up tons. Or you can use a lathe and take out more. Make sure you balance it after as it WILL be out to lunch

 

That's abut 1.3 ounces! At 6K that's 541.29304 pounds.

 

 

 

Someone check that math... maybe 54.129204 pounds.


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#15 HRH

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Posted 12 March 2016 - 09:17 PM

So I talked to another guru today, and he think my other Datsun guru probably had a bad flywheel as he's mixed and matched them and never had issues on Datsuns.  I'm fairly confident he's right.  However, since I'm heading down to the flatcat bbq tomorrow, and the field car is on the way, we'll just swing by and grab it so I have the matching flywheel for the motor anyway.



#16 Stoffregen Motorsports

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Posted 12 March 2016 - 11:15 PM

All six bolt L series flywheels should be interchangeable, but beware that there are three different clutch diameters. When the flywheel is out and you're replacing the clutch, that is the time to have the flywheel and clutch cover zero balanced. It doesn't cost much and can make a big difference.

 

As far as the weight being the variable, possibly causing vibrations, I say no. A heavy flywheel will help dampen out the vibrations, assuming nothing else is wrong with the rotating assembly.

 

There is a possibility that the person who suggested the flywheel made the vibrations had one that had come loose at some point. When that happens, the metal on the mating surface (where it bolts to the crank) will ball up and gall leaving high and low spots. If not cleaned up, this flywheel would not bolt on straight and would certainly cause vibrations. The only reason I bring it up is because I've seen it happen a few times.


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#17 datzenmike

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Posted 13 March 2016 - 08:22 AM

F= M X V2 / r

 

Mass.............. 0.040 Kg or 40 grams.

Velocity.......... 95.77 KPH .... 305mm diameter flywheel. Circumference = 305mm X Pi = 9577mm or .9577 M X 6,000 RPMs = 5746/60 = 95.77 Meters per second.

r...................... .1525 M diameter 305mm/2 = 152.2mm or 0.1525 Meters

 

F= 0.040 X 95.772 / .1525 = 2405.74 Kg/M2  or Newtons X 0.224809 = 540.8325 POUNDS

 

 

Wow, 540 pounds spinning at 6K is going the shake noticeably.


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#18 scooter

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Posted 13 March 2016 - 08:55 AM

That's right Mike, before the rebuild everything would vibrate loose. I was quite Suprised how well the crank I used was though, the z22 crank was only out a few grams. I've put lots of North American v8's on the balancer and the Olds and a Pontiac motors were the worst. The counterweights looked like Swiss cheese when I was done, I think the worst one I did was out 180 grams.. do the math on that.. no wonder why blocks and cranks break.

#19 datzenmike

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Posted 13 March 2016 - 01:27 PM

Probably there were other throws out that would cancel some of those 180gr. But for the hell of it say you put a 180 gr weight on one of the throws.

 

Would need to know the diameter of the crank to work out the velocity in M/sec. For arguement sake 8" or 200cm?

 

180gr at 6K RPM would have a weight of .... almost 8 tons.


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#20 scooter

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Posted 14 March 2016 - 07:20 AM

Pretty sure it was a 400 pontiac crank. That balancer measures from the front journal and the rear journal. The front wasnt out soo much, but the rear was out to lunch.
Those things have roughly a 4 inch stroke so it would be less than that, but thats still bad.

Balancing the pressure plate is a good idea, theyre out sometimes too, but not usually that bad.