Balancing DMF By Itself

I bought a new DMF for my M96-01, old one is toast. Engine was completely balanced a few months ago while it was in pieces. Two shops are telling me, can't be done without the crankshaft. One of them removed the DMF pilot bearing to get it on the mandrel and the machine kept reporting it was totally off, with or without the pressure plate bolted on. Am I crazy here that this can't be done with the DMF out of car? Certainly not, since plenty of folks have done this before. Is there some trick or does it pretty much require a crankshaft to bolt up to? Crap. Thanks in advance if someone can help.

Then that would mean that everytime a flywheel is replaced on a Porsche the engine is no longer balanced and therefore problamatic?? I think from a total integrated assemble everything shouild be balanced as a package; however, there is no reason the FW cannot be spun and balanced as a single component.

Certainly ideally it would be balanced with the crank/etc... but life isn't always perfect, wish I would have had the funds for this in December when the engine was apart. Still reading about it, apparently it can be done, but most run of the mill balancers aren't setup for it. Short on details still. Perhaps it requires a shop with a 0 balance crank to bolt it up to?

I didn't know you had to balance a DMF?? I would have assumed it was balanced out of the box

Yes and no. Brand new they do come balanced to within a certain tolerance which is probably acceptable to some degree and for most applications, possibly even mine. And the dual mass soaks up some of that imbalance of course. I could probably just bolt it up and be dumb about it, but I spent tons of time and money on the engine balance and rebuild, so I certainly want to do it right. Talking to the guy that did the balancing he 0 balanced everything on it's own, crank, etc. He assured me I could buy a flywheel later and then have it 0 balanced with the pressure plate, bolted up and life would be good again. Now in the moment he's telling me his balancer is saying the new DMF is way off and can't balance it. I called another shop and they say they can also try, but haven't done a whole lot of DMFs and after I described with the first shop tried, they said it would probably end in the same result. I guess maybe it's a case of finding the right shop? We are going to eliminate the possibility that the new DMF is bad and we are going to see if the old DMF will balance this afternoon and see if it does the same thing on his machine. I'm guessing it probably will. He's also telling me it shouldn't be match balanced since he 0 balanced all of the engine components individually. But this is a little strange if he is telling me this, how did he balance the orig FW, maybe he 0 balanced crank, bolted on FW and then found imbalance and corrected it...

If I remember correctly Jake made a special fixture to balance flywheels .Mightr be worth a phone call

Thanks, I posted the question on his forum. I think he has given up this type of work, or at least he made a post recently that he won't accept balancing jobs any longer and is only doing elective work. Maybe that is just for old air cooled stuff no longer in production. "What we have learned on our most recent experiences has proved that we simply can't do these jobs from this point forward. Our balancing services are now limited only to our turnkey engines. " If he can't do this work I'm certainly open to suggestions if someone knows of a shop. Thanks.

The old flywheel turns true on the balancer. It was balanced on the crank after the crank was balanced. The brand new flywheel one does not turn true, and he doesn't want to begin balancing it since the machine is telling him it is already too far out to balance. But he's also not certain of his method and doesn't want to say the new one is bad since he doesn't do a lot of DMFW balancing. Anyone know of a shop that has done this before? I've tried calling around my local area, none of the shops have this type of experience, and I'm getting the cold shoulder. Either I'll have to just bolt it on and maybe hook up a dial indicator to see how far off it is or maybe send it off somewhere. Thanks in advance.

Try BBI in Huntington Beach, CA

Quotes source post: 9328483

If the new DMF does not turn true that's not a balance problem, but a run out problem and the shop was right to refuse to 'balance' the DMF. Either the DMF was not properly seated to the balancer hub/mount or the DMF is defective or possibly has a burr or something similar that prevents it from seating properly. A good automotive machinist though should always check for that and decline to even mount unless the burr can be removed (stoned down). I have not looked at DMF but other FWs (IIRC -- it has been a few years...) generally have balance holes (shallow holes!) drilled into the FW at various places or weights spot welded on to bring the FW into balance. Does the new DMF have any of these? Sincerely, Macster.

The machinist remounted the brand new DMFW and spun it several times, each time with the same result; according to the machine it was too far out "out of balance" to be balanced. Because of his inexperience, he is not sure if that is because of his balancing equipment and the way he has it attached, or if the brand new DMFW is actually too far out of round to balance. He was not certain if his mandrel and shims were causing the problem, or if it was due to the balancing method with a DMFW, the springs/etc causing a discrepancy. He was very surprised when he attached the old DMFW using the same method and it was nearly perfectly balanced according to the machine (this is the DMFW he had balanced while the crankshaft was outside of the engine). He doesn't feel comfortable working with it at this point, and I'm going to collect everything from him tomorrow. I will inspect the brand new DMFW for burrs when I pick it up. It looks basically spotless and fresh from the factory. But factories don't always do things correctly and sometimes the craftsmanship of brand new items is less than desirable. I called another shop and explained the situation, and they told me they would use the same method and balancing machine to attempt the work, so I don't think I will bother with the time or expense. I'm hesitant to ship the brand new DMFW to any shop if they have not done this work before. The new DMFW comes from the factory balanced within a certain tolerance. Various lengths of material along the outside perimeter of the flywheel surface at the outer most point are ground down to achieve balance. I am not sure what that tolerance is, and I cannot find that information anywhere. There are no balance holes to accept weights. Of course, the inherent nature of a DMFW is to soak up some imbalance. The new flywheel surface does rotate approximately 14mm in either direction while the ring gear below it is held stationary and returns back to it's original location very promptly. The springs inside the new DMFW seem to be significantly harder and difficult to rotate compared to the old DMFW with appx 78,000 miles of service. The springs on the new DMFW do not make any noise, whereas the old DMFW springs creak and the flywheel surface doesn't always return to the same location once released; in addition it rotates approximately 18mm, which is 3mm beyond spec. The brand new DMFW surface is unused, whereas the old DMFW has very apparent heat related damage, and a deep groove where several clutch discs have worn into the surface. I have spoken with two machine shops and they refuse to resurface the old flywheel. I'm not sure what to do at this point.

Can you return the new one and let them inspect it?

I assume the shops you are talking to are doing dynamic balancing. This is where they rotate or spin it and a machine tells them where and how much weight to place to bring it into balance. I think you need to find a shop that truly understands static balancing. This is is done without a machine using a perfect centering device like axle that is placed on knife edged rollers or 2 perfectly straight parallel planes. The heavy spot will always fall to the bottom. Either weight is added at the lightest area or the heavy points are drilled until the flywheel can be placed at any point on the rollers and stay stationary. This if done properly is extremely accurate with no possibly for error as while balancing is being accomplished, the results are continually being checked and verified. This is how motorcycle wheel and tires are balanced for roadracing including World Superbike and GP. It is more accurate than the electronic balancers and good for 200+ MPH. Many motorcycle cranks and components that spin at high rpm are done this way also. I have successfully balanced components for decades using the static method.

Not sure the new flywheel is out of spec .The trick is to find the spec .Luk is shipping 6 million of these annually which would require very rigorous quality control .Some of their units have built in compensation-without knowing Porsche specifics it's just guesswork. Further I believe that your old engine idled fine -one major change is the flywheel balancing which has to be suspect .

It's hard to change a mindset once you've already done everything a certain way. But.... I'm contemplating just bolting it on and not worrying about it, I bet 99.99% of the units they ship are done this way, and you point out I'm sure there is rigorous quality control. Sure I might lose a few percent of horsepower if it's not perfectly balanced, but I'm not building a race car, and even if it's off by a few 10's of grams oh well, that's part of the DMFW's job. The rest of the engine is balanced to the 9's, so it will be soaking up it's own imbalance, whatever that is. Even if I find the specs, I can't measure the radial run out, since the perimeter has been ground in various spots (apparently the factory balance job) ... I think it would have to be done statically as Nick points out. These skills are quickly going the way of the dinosaur as I'm finding out. After spending time on the phone and in a shop, at this point I have 0 confidence in anyone's ability to do this balancing unless they've actually done it before. Jake says he accepts M96/7 balancing work on a case by case basis, but I don't want to have my car on stands for another month or more, including all the back and forth, shipping, etc.

Understand your dilema .One thing for sure- the engine is far more balanced than the factory builds .Doubtful that they go thru the steps you have taken .Everything today is just in time and rely on the supplier for QC with a few random samples taken along the way . I'd bet a six pack it will be fine .

Theory??? The old DMFW was worn out so when it was spun up the springs were 'relaxed' and the 'sprung' part rested against its 'stops'. This allows the unit to act as 'one' piece and then it can be balanced. With the new FW the springs are not worn out so the 'sprung' piece does not rest against its stops and has a bit of springy movement which the balancer detects and it cant read properly.... So if my theory is correct the new FW did its job and could not be balanced because it was absorbing vibrations... Wanna take the old one apart and shoot some pics? At this point I would bolt it on and go - if it is still not right, well you are pretty quick in and out with the motor/gearbox any way. Really rooting for you to end up with perfect motor - you deserve it, great job in the build. Hoping to be the proud owner of a 3.4 911 in the very near future.

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I'm not sure about that rigorous quality control. Sometimes a factory will cut back on inspection/gaging after a while relying upon their processes to deliver quality product. This works very well, until it doesn't. When it doesn't, the customer ends up being the quality control for the manufacturer. Sincerely, Macster.