Put an aluminum lightweight flywheel on my car and now has a slight vibration especially during idling. I'm assuming its because I lost the momentum from the OEM flywheel which was twice the weight. My question is if theres anyway to counter balance this without taking the transaxle out again and putting an OEM flywheel?
Make shore all your engine and transmission mounts are good and tight first
April, 26, 2012 AT 9:36 PM
Yes I did that when I put the transaxle back on. I even replaced the front motor mount which eliminated some other problems I was having unrelated to what we are talking about.
April, 26, 2012 AT 9:52 PM
Hi guys. You also have to consider that brake master cylinders are now made of aluminum rather than cast iron. The reservoirs are made from plastic. Sheet metal is made so thin it will warp from sand blasting. Bumper frames are made with styrofoam, then covered in plastic. Now spare tires are even considered an option. All of this is to reduce weight. The engineers have gotten carried away with the weight savings, so you can be certain they would have installed a lightweight flywheel at the factory if it could have been done without generating customer complaints. If your vibration is gone at higher engine speeds, that rules out a mismatch with an externally balanced engine and a flywheel without the counterweight attached. Four-cylinder engines naturally vibrate more because there's fewer power pulses per crankshaft revolution, and the mass of the flywheel smooths those pulses out. The only thing a lightweight flywheel will gain you is faster short burst acceleration. That's important on the racetrack but won't enhance daily driving.
April, 27, 2012 AT 3:31 PM
Yea vibration goes away when speed starts picking up. Yes and I knew about how an 4 cylinder opposed to a 4 will make a smoother crankshaft rotation but my question was is there a way to fix it without putting the OEM flywheel back in. I really don't want to drop my transaxle again. Can I throw a balance weight on the engine or anything?
April, 27, 2012 AT 7:52 PM
Look at your old flywheel to see if there's a weight welded onto it near the outer edge. If there is, your engine is "externally balanced" and there will also be an extra section cast into the harmonic balancer on the front of the engine. That is because with some cast crankshafts, it's real hard to cast some of the counterweights so they just add them later on the flywheel and harmonic balancer. I couldn't find a photo of your flywheel, but I found a photo of the harmonic balancer, but they just showed the backside and made no mention of it being externally balanced. Since you buy flywheels for a specific application, the manufacturer would have known what your engine needed, still, it's worth mentioning. In those applications there will be an offset bolt hole to let you mount the flywheel only one way to the crankshaft so that weight is in the correct orientation.
The whole point of my first reply was to point out the manufacturer would have lightened the flywheel if at all possible without causing a problem but they knew they couldn't. You did, and it's causing a problem. The only solution is to add a lot of mass. You can't do that by adding additional weights. First of all, there isn't enough room. To add big chunks of steel, they would have to be so big that they'd hit the transmission bell housing. Second, you'll find small holes drilled into most flywheels to balance them. A few ounces out-of-balance would be very noticeable. You'll never achieve even close to the same balance with add-on weights. There's way too many variables. Weight of each chunk of steel, distance from center of crankshaft, weight of bolt or weld bead. When they're manufactured, they are spin-balanced just like a tire and wheel on a spin balancer, not like on the old static balancers. A tire, or a flywheel that has one ounce of additional weight at the outer edge can be static balanced with two ounces on the other side halfway out from the center, but that would create a miserable vibration when it's spinning.
As you can see, there is no practical way we can add additional weight to a flywheel, and it's that additional weight you need to smooth out the power pulses. You need to reinstall the original heavier flywheel to get rid of the vibration, assuming, of course, nothing else was done inadvertently to cause that vibration. Djcl mentioned engine mounts. Be sure the two metal brackets on each one aren't touching as that will transmit normal vibration into the passenger compartment. Also check the exhaust hangers for the same thing. They all will have some type of rubber isolator to prevent transmitting vibration. Some applications have dampening weights in various places. Fords are famous for these hanging off transmission tail housings and welded to exhaust pipes. Those are targeting a specific vibration at a specific speed or condition, and one of those could be at idle speed.
Also be sure the engine is idling at the correct speed. It's computer-controlled but on many cars the Engine Computer won't know when to be in control of idle speed after the battery was disconnected or run dead until it relearns "minimum throttle". For Volkswagens, that requires a tow to the dealer to have them unlock various computers but for most other cars a simple set of conditions must be met while driving for that relearn to take place.