Flywheel Replacement???

[986Porsche986]

I will be changing the clutch on my 2002 S with 60,000 miles next weekend. Its not slipping but it is getting very stiff to push down. I have changed several clutches on other cars before, and usually have had the flywheel resurfaced. My question is, nowing that I cannot resurface the flywheel, what are some signs that it needs to be replaced, besides the obvious signs of cracks, uneven ware, burned marks, etc.. Should I save the $600.00 or just replace it anyway because I will already be there with the access to it. What is the average life of a stock flywheel?

Mark

[blinkwatt]

I'd say this is open for debate.

I've always been told to change out the flywheel with the clutch just to save time and money. But the flywhels on these cars are at least $700. When my clutch was changed out at 50k I also told the shop to replace the flywheel while in there(which they recommended).........I went to go pick up the car and they gave me the old flywheel back because they said it's in almost new shape.

If you want one order it from www.************************************************************ best prices around.

[Cloudsurfer]

I would suggest changing it while there to guarantee a good fix. For a marginal extra fee, you can upgrade to a lightweight flywheel, which really improves the rev response of the motor (and hypothetically reduces the propensity for RMS leaks).

Patrick

[insite]

there are a couple of reasons to change it out while you're in there. first, you cannot machine the surface on the OEM dual mass flywheel (DMF). this means that the friction surface will not be optimal when you install the new clutch; your new clutch probably wouldn't last as long. also, there is an elastomer on that connects the two halves of the DMF; as it decays, driveline shocks are no longer properly damped. this can affect a lot of things including comfort, noise and driveline longevity.

when i pulled my transmission, it was clear that my DMF was totally shot; the elastomer didn't perform as it should & there were hotspots all over the mating surface. i replaced the DMF with an Aasco lightweight aluminum flywheel and a custom spring centered clutch from Spec. total cost was about $200 more than if i'd have gone with a new OEM flywheel and Sachs clutch. the LWF is a nice performance upgrade; it does take some getting used to from a drivability perspective, but i love mine. as an added feature, if you ever do a clutch again, you can replace the mating surface on the Aasco FW for $100 (it unscrews).

[TimAustinW]

So if you were going to replace your clutch and flywheel would it be a good rule of thumb to put in a new flywheel seal (RMS)? My Boxster is nearing 83K miles and I was told six months ago that I'd probably need to replace my clutch in six months. I've read here that lower mileage cars are more prone to RMS failure so will a new clutch, flywheel and new RMS open the possibility back up to RMS failure?

[insite]

Originally Posted by TimAustinW

So if you were going to replace your clutch and flywheel would it be a good rule of thumb to put in a new flywheel seal (RMS)? My Boxster is nearing 83K miles and I was told six months ago that I'd probably need to replace my clutch in six months. I've read here that lower mileage cars are more prone to RMS failure so will a new clutch, flywheel and new RMS open the possibility back up to RMS failure?

flywheel or no, replace the RMS everytime you have the tranny off. $20 insurance policy. if you haven't done it yet, replace the IMS bolts and rear case bolts with the microencapsulated versions.

BTW, there are some people who think that if you're lucky enough to have one that doesn't leak, don't replace it or you risk a leak with the new seal. this is garbage; the leaky cars leak because of out-of round issues on the case.

[986Porsche986]

Thanks for all the great feedback!! I will definitely change out the flywheel and RMS. Never heard of the microencapsulated bolts. Is this a bolt upgrade from Porsche or an aftermarket upgrade? Where can I buy these?

[insite]

Originally Posted by 986Porsche986

Thanks for all the great feedback!! I will definitely change out the flywheel and RMS. Never heard of the microencapsulated bolts. Is this a bolt upgrade from Porsche or an aftermarket upgrade? Where can I buy these?

the bolts are from porsche. there are i think seven total: three IMS flange bolts and four rear case bolts. the service tech should know the ones i mean.

a couple of notes if you do this yourself (or if an indy does it): replace the IMS flange bolts while the oil in the car is DRAINED, otherwise it will leak out. also, replace the IMS flange bolts one at a time; if you remove all three at once, the IMS will be pulled out of place and you won't get it realigned without a special tool.

the case bolts are straightforward.

[Jake Raby]

We have the only aftermarket flywheel bolts on the market, to my knowledge.. These are aerospace quality and made by ARP especially for us...

[insite]

Originally Posted by Jake Raby

We have the only aftermarket flywheel bolts on the market, to my knowledge.. These are aerospace quality and made by ARP especially for us...

we were talking IMS / Case bolts. there is a TSB that calls out replacement bolts w/ microencapsulation in order to prevent possiblel oil leaks.

FYI, if you buy an aftermarket flywheel (like Aasco), it comes w/ aftermarket low-profile bolts. these are required to clear the clutch disk.

[Frodo]

Quote:

"the LWF is a nice performance upgrade; it does take some getting used to from a drivability perspective, but i love mine."

Posted by insite.

I was curious about this. How does clutching/driving feel with the LWF? I assume that it's one of those things that, once you get used to it, you love it. But what's it feel like initially?

[insite]

Originally Posted by Frodo

Quote:

"the LWF is a nice performance upgrade; it does take some getting used to from a drivability perspective, but i love mine."

Posted by insite.

I was curious about this. How does clutching/driving feel with the LWF? I assume that it's one of those things that, once you get used to it, you love it. But what's it feel like initially?

if you try to drive it like you normally do, the car will shudder when you take off from a stop. you have to keep the revs higher as you engage the clutch to get a smooth take-off. the other thing that takes getting used to is the speed at which the revs drop when you press the clutch. the RPM's drop VERY rapidly; you have to shift the gears much more quickly or the RPMs drop too far for the next gear.

once you're used to it, the LWF coupled with a short throw shifter make for a very racy feel; i love it. it transforms the car from a GT personality to a more precise, mechanical feel.

[Frodo]

Thanks.

Makes sense: reduce the weight of the flywheel, you lose some rotational momentum, so you're more likely to bog down the engine when starting out. Ditto when you disengage the clutch to shift---low mass, low momentum keeping things spinning, so it's gonna lose revs quickly.

My kid (a budding shade-tree mechanic) found an Excel spread sheat program that calculates HP gains with FW changes. He says he would need to know the weight (OEM and LWF) and the diameter of each as well. I know I'm being lazy, but anyone know these off hand?

[insite]

Originally Posted by Frodo

Thanks.

Makes sense: reduce the weight of the flywheel, you lose some rotational momentum, so you're more likely to bog down the engine when starting out. Ditto when you disengage the clutch to shift---low mass, low momentum keeping things spinning, so it's gonna lose revs quickly.

My kid (a budding shade-tree mechanic) found an Excel spread sheat program that calculates HP gains with FW changes. He says he would need to know the weight (OEM and LWF) and the diameter of each as well. I know I'm being lazy, but anyone know these off hand?

you actually need to know the moment of inertia of each FW along with the weight. i ran the calculations awhile back and found that a 2nd gear sweep from 4800 revs to 6800 revs was good for a reduction of 21HP parasitic loss (~21HP gain) if i remember right.

i'll try to find the measurements. i still have an OEM FW; i'll weight it & measure it this weekend.

[Jake Raby]

Engine dynos test at steady state... even those that do a "sweep" of the RPM range are still sampling at steady state, just very quickly. Some chassis dynos can measure inertia accurately and may show some differences with lighter weight components.

This is why HP gains that are present from lightening components are very difficult, if not impossible to measure on an engine dyno, but they do show up very clearly on a stop watch in lap times.

The lighter components increase throttle response which gets a car out of the hole and off of a corner faster, increasing trap speeds..

Lighter parts will always increase acceleration and make any car feel faster, in a street car they cost drive-ability as the engine revs down just as fast as it revs up and that cost gas mileage as the driver is using the acclerator more and more up and down with the reduction in rotating mass.

In most any case a car with a lightened rotating mass will be faster than it was with stock weight parts, despite what the dyno says. This is why we run small 4" clutches with a reduces diameter, lightweight flywheels and even whittle 4 pounds off the crankshaft of our E and F production race engines.

Most lightened flywheels are also "single mass" meaning the factory harmonic dampening effect of the dual mass set up is eliminated. The factory flywheels were also balanced with the engine at the time of assembly as an indexed assembly, changing the flywheel removes this absolute balance- not good.

I have a 996/X-51 engine here at my shop now, it has a broken crankshaft and I feel VERY certain that this was caused by the lightweight flywheel that was used on the engine that could not be indexed to that engine as it was installed after the fact. Often times changing a flywheel creates imbalance and then removing the dual mass eliminates harmonic dampening. Double negatives that cost this 996 customer a 3,500 buck crankshaft- (we are replacing it with our billet unit to eliminate future occurrences)

(FYI- We also have IMS retaining bolts that feature a different design to that of the Porsche units and they also guard against oil leaks, especially when coupled to a sealant that we live by) We make all these as low profile as possible for interchange with as many different components as possible.

[insite]

there were a lot of LWFs out there that weren't balanced well in the first place (fidanza comes to mind). the aascos are supposed to be balanced very well. one could always take it to a machine shop and have it checked prior to installation.

as for the dual mass flywheel? jake is right that just swapping to a single mass removes the elastomer damper from the engine / driveline interface. most cars use a sprung centered clutch disk rather than a sprung centered flywheel. when i installed my LWF, i had a spring centered clutch made for my by Spec. this protects the driveline / motor from excessive shocks.

one wierd problem some of the 997 GT3 guys have experienced, and i can't really figure out why, is that when they go to a LWF, their crankshaft pulley unscrews and essentially falls off the car. not a problem on the boxster.

[Jake Raby]

One thing my CN controlled balance machine has taught me is that rotating masses must be balanced as units.. I can hang a perfectly dynamic balance flywheel onto a rotating mass assembly and to correct the "plane" 2-3 grams of material will have to be removed from that flywheel to bring the entire mass in an .5 ounces per inch or below. Stabbing an new part onto an assembled engine is never optimum as you can't correct the plane differences as the engine is assembled. Reducing the component weight further impacts the balance differential that the mass will see with a component swap with the rest of the engine assembled.

We even balance index pressure plate bolts and washers.. @ 6"+ radius everything is critical..

I have seen 3 Boxster engines with loose crank pulleys so far, one did fall off...

The sprung center disc is a great addition to the driver and tranny, but does very little to absorb the harmonics within the engine. I am working on a harmonic balancing crank pulley that could be added to the engines that have lightened flywheels for some dampening, something set up like a Chevy is the current prototype.

[insite]

wow, jake. i think i speak for all of us when i say i am VERY glad you found this board. great info.

[Jake Raby]

Originally Posted by insite

wow, jake. i think i speak for all of us when i say i am VERY glad you found this board. great info.

After my post this morning I put some time into the harmonic balancer development... Should have a prototype in 3 weeks. I'd like to implement a kit that includes the harmonic balancer, sprung center clutch disc and the lightened flywheel as an assembly... Selling someone just a lightweight flywheel is kind of asking for issues with these engines, and we try to be problem solvers, nt creators.

Thanks for the compliments, it's great to be hanging out here and having interface with the Boxster drivers.

Wait till you guys see what we have in store for 2009, the Boxster engine has done a 180 degree barrel roll!!

[Cloudsurfer]

Jake-

This is very interesting information. So, for those of with Aasco LWF's, you feel we have a higher probability of potential issues? I had always thought that the reduced mass of a LWF was a good thing?

Hypothetically, if one were to purchase an engine from you, with LWF, would you dynamically balance the whole rotational mass?

Also, I"m sending you a PM on an outside idea of mine

Patrick