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flywheel lightening at home


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23 replies to this topic

#1 archemitis

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Posted 13 October 2003 - 11:56 AM

so i was about to start drilling holes into a motorcycle hub, to chuck my flywheel into the lathe, when two of the old time mechanics here tells me its a stupid idea. they say the flywheel is balanced with the crank and all that.

but the thing is, i have swapped flywheels between subaru motors all the time, without balancing, with great results.

should i respect my elders ideas, and leave the flywheel stock, or turn that b!ch till she wheighs 10lbs?

#2 bushbasher

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Posted 13 October 2003 - 12:04 PM

If you lathe it perfectly straight, then the weight balance would be the same, one side will still have the same % more weight than the other. Unless there are added weights tacked on. Just tell the mechanics that subaru parts are perfectly balanced, because they aren't cast and machined crappily like american parts are.

#3 calebz

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Posted 13 October 2003 - 12:12 PM

Balanced with the crank?.. my engine is out of an auto car.. with a flywheel from another car and a tranny from yet another.. no balance problems that I can tell.... I say go for it

#4 Setright

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Posted 13 October 2003 - 12:41 PM

No way is the crankshaft balanced in conjunction with the flywheel!

The crank is balanced, the flywheel is balanced. Separately!

If the crank is poorly balanced and you then try to correct this by attaching a misbalanced flywheel which you attach so as to counter the crank imbalance, you are asking for trouble. If anyone does this, their engines won't last long.

Let's say the crankshaft imbalance is at the front of the engine. Now attach a misbalanced flywheel on THE OTHER END?? Any thoughts on how long the crank bearings will last?

Skim the flywheel down, but don't forget that your idle will be rough and you will need a lot of throttle for a smooth take off. But ahhhh, what fantastic throttle response!

#5 electryc_monk

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Posted 13 October 2003 - 02:04 PM

for what I remember from those that have "skimmed some poundage off their FLywheels" the idle throttle was never brought up as a negative issue, so if SKip (and Bbitner?) and those who have done this before care to update Setright on this and correct me if i'm mis-remembering the theads of your?

#6 XSNRG

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Posted 13 October 2003 - 03:22 PM

It seems I recall the old chev 400 small blocks had the flex plate and crank balanced together, it's the only one I recall, there may be others.

Subaru flywheels and clutch covers have a mark on them that indicates the heavy side of the part (after balancing) the marks are to be offset from each other as much as possible.
(from the FSM)

I have mixed and matched many Subaru cranks, flexplates and flywheels with no ill affects...

#7 Caboobaroo

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Posted 13 October 2003 - 03:26 PM

you're right Mark but not all Chevy 400's were like this. Also the 350 was externally balanced and the 305 was internally balanced. It all depends on the motor and the company of it. Can we all tell that I'm a Chevy guy?:brow: But like everyone else is saying with Subarus, I've mix-matched parts before and nothing has gone wrong. Just tell the guys at the shop "Its a Subaru thing....you wouldn't understand":D

#8 XSNRG

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Posted 13 October 2003 - 05:40 PM

Always nice to meet a Chevy guy, I'm one too. Don't know alot about the 400's though, Siamesed cyclinder wallls have always been a turn-off for me:brow:

#9 electryc_monk

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Posted 13 October 2003 - 06:53 PM

well i had a 400/400TH in a 3/4ton 4WD it was fun (while it lasted) but that crank and flywheel wasn't that big of a deal for us in autoshop class in junior college.

The subaru flywheels actually have a oddity that makes me giggle when I read the "FSM" reference you used above.

the bolt pappern of a flywheel is a "one way only" install there is a spacing between like 3 of the bolt holes that make it a "fool proof" install if your going to use all the bolt holes - that is.

at least thats with all the EA82(T)'s that I've tinkered with.

(hmmmmm, makes me wonder what's up in the EA81 and the EJ's..

#10 PHATBRAT

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Posted 13 October 2003 - 08:12 PM

Yep, Skip is the one that has done this a few times and he has never mentioned having problems. It's true, You have to get it perfectly even all around otherwise you will be extremely disappointed. You're wife/girlfriend may like the car then though.:lol:

#11 electryc_monk

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Posted 13 October 2003 - 09:03 PM

(evil grin) that reminds me of a story that I witnessed first hand...well mostly anyways.

A gal got a piercing (who used to work where Mom did down in Battle Creek, MI) and she drove a "severely mod'd RX-7.

yeah... the story will leave you glassy eyed...(LOL) just not like her. :santa:

#12 archemitis

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Posted 13 October 2003 - 09:05 PM

i figured it would be just fine, its a lathe, and as long as it is chucked relatively straight, it should work great. kinda like resurfacing it, just on a big scale.

#13 XSNRG

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Posted 13 October 2003 - 10:48 PM

monk, you didn't read what I was saying, my fault, I was changing the subject a bit.

I did say the flywheel and clutch, not the flywheel and crank. The pressure plate will go on the flywheel in more than one position. Even though these parts are balanced individually, they are not perfectly balanced and the procedure I described intends to offset this slight imbalance. I will included the complete passage from the FSM I referenced for your benefit.

QUOTE:

"a. When installing the clutch cover on the flywheel, position the clutch cover so that there is a gap of 120 degrees or more between "0" marks on the flywheel and clutch cover.
("0" marks indicate the directions of residual unbalance)"

This is from section 2-10, page 9 or the 1987 FSM.

#14 calebz

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Posted 13 October 2003 - 11:42 PM

Hey.. my 88 FSM says the same thing.. Go figure.. Good advice too.. makes for a much smoother clutch and a smoother running motor

#15 electryc_monk

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Posted 14 October 2003 - 12:33 AM

thanks XSNRG.....

i saw - yes- as you corrected not what was written ... hmmm selective reading on my part? mostlikely the ADHD playing more of a role though...

#16 Russ Hill

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Posted 14 October 2003 - 11:12 AM

The only problem I can see with lightening the flywheel is the it will reduce your rotating mass. The engine will spin up faster but it will fall back out of it's torque range faster too. Subys aren't very "torquey" so they have heavy flywheels.
As far as balancing the engine goes....
A boxer engine is as close to naturally balanced as you can get. There are always two pistons moving in oposite directions to balance each other.

#17 ballitch

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Posted 01 January 2005 - 08:03 PM

if you take away from the normal amount of rotating mass that your car has you will have to use more gas and slip the clutch more to get the car moving, but it will help your engine rev faster and you may even be able to attain higher speeds by reducing drivetrain drag, but arent subaru flywheels cast iron? wouldnt that be a bad thing to lighten a cast irn flywheel? i dont know.

#18 calebz

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Posted 02 January 2005 - 01:12 AM

if you take away from the normal amount of rotating mass that your car has you will have to use more gas and slip the clutch more to get the car moving, but it will help your engine rev faster and you may even be able to attain higher speeds by reducing drivetrain drag, but arent subaru flywheels cast iron? wouldnt that be a bad thing to lighten a cast irn flywheel? i dont know.


Its been successfully done by a number of people.

Wow this is an old thread.

#19 Qman

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Posted 02 January 2005 - 03:35 AM

if you take away from the normal amount of rotating mass that your car has you will have to use more gas and slip the clutch more to get the car moving, but it will help your engine rev faster and you may even be able to attain higher speeds by reducing drivetrain drag, but arent subaru flywheels cast iron? wouldnt that be a bad thing to lighten a cast irn flywheel? i dont know.

That is a negative. I have lightened flywheels in both my Brats. No clutch slipping neccessary. It does rev faster. The gas milage thing I don't know. Mine are both built up motors and weren't really built for gas mileage. I get 20-24 in my little Brat. It has the bigger of the two engines. Estimated 150hp and has zero issues with the clutch slipping. I used XT6 clutch parts though. The flywheel in this Brat weighs about 17lbs. The stock XT6 flywheel weighs about 19lbs and the stock EA82 is about 21lbs.(if my memory still works)

Wow this is an old thread.

Been alot of these lately. I guess the search functions works!

#20 TomRhere

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Posted 02 January 2005 - 08:49 AM

Only actual problem this one can invision with someone shaving down the flywheel is getting it to thin in the area of the clutch surface outter edge. What I'm talking about is the intersection of a line drawn from the clutch surface outwards to the outer circumfrance of the flywheel, (y'al following me?). If this intersection was turned to thin, it could be, well, interesting. :eek: Not saying , "don't turn the flywheel", just trying to point out a possible problem for someone trying this themselves, and taking of to much meat in that area. Just something to be mindful of if you're thinking of putting your flywheel on a diet.

#21 Skip

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Posted 02 January 2005 - 09:11 AM

Tom is talkin turkey here -listen to the wise man.,

When the flywheel is machined at the factory
There is a section near the hub that is app. 0.5" thick

when I turn these I use this as the minimum crossectional
thickness at any point on the unit.

For accurate chucking in my three jaw
I use the factory pressure plate ledge - no adapter


Note the crown in the hub area on these pictures
The clutch side has a recess in this area where
the unit bolts to the crankshaft
Posted Image

#22 scrap487

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Posted 16 January 2006 - 05:37 AM

are these pictures of the same flywheels in varrying stages of weight loss or what am I looking at it? sorry for bringing back a thread so old but I'm curious, thanks
trevor

Tom is talkin turkey here -listen to the wise man.,

When the flywheel is machined at the factory
There is a section near the hub that is app. 0.5" thick

when I turn these I use this as the minimum crossectional
thickness at any point on the unit.

For accurate chucking in my three jaw
I use the factory pressure plate ledge - no adapter


Note the crown in the hub area on these pictures
The clutch side has a recess in this area where
the unit bolts to the crankshaft
Posted Image



#23 Skip

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Posted 16 January 2006 - 08:18 AM

Trevor.
Please excuse the confusion, you are correct I should have labeled the picture.

What you see on the top row is
the turned XT 6 unit-----the factory XT 6 unit

the second row is
the turned XT 6 unit-----the factory XT 6 unit -----the factory EA82T unit

the third row is the second row in profile

The bottom picture is the factory XT 6 down side up
on the turned unit for profile comparission.

Hope that clears it up

#24 scrap487

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Posted 16 January 2006 - 07:06 PM

cool that helps alot... so essentially theres a whole crap load that can be taken off of a stock unturned flywheel




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