![]() ![]() I can see a case for the balance shafts, but only for a broken chain. If it started when the transmission was installed or shortly there after, I’d be inclined to check the flex plate for cracks, which requires removal of the transmission. If so, and you complained about this to the dealer while it was under warrantee, they are still responsible for its resolution at no cost to you. ![]() If it has always been there, then it is quite possible that the balance shafts were not timed correctly when the engine was assembled. Has this always been a problem with the car or is this recent? Was the transmission change because of this or other reasons and if this is recent, did it start with the new transmission? The serpentine belt goes around the outside of the harmonic balancer so there would be other issues if that were the problem. They would go from a shaking to a buzz kind of feeling. I believe that the vibration caused by balance shafts will not go away above 2000 rpm, but their frequency could increase to the point that they are less noticeable. The tools do exist to diagnose the problem. As I stated, I don’t think proper analysis has yet been done. Couterbalance shafts would react to engine rpm regardless of whether the engine were under load or not. I think it’s safe to start with the assumption based on the description that the problem lies somewhere in the first category. Items that react solely to engine RPMs without regard to load:Īnything in the drivetrain or rolling stock past the flywheel Items that oerate differently under load: Isolating those things suggests perhaps a bad Exhaust Gas Recirculation system, That system allows a bit of inert (already burned" exhaust gas to be recirculated back into the engine when under load in order to keep cylinder temps from getting too high and causing preignition. Some things are different on an engine under load than an engine not under load. Since it vibrates no matter what gear it’s in, and I assume (correct me if I’m wrong) that means regardless of the car’s speed, it sounds like a resonance somewhere in or attached to the engine, but one that requires the engine to be under load. Since it only vibrates when in gear, it’s a good bet that the vibration is somewhere in the drivetrain. Any good shop should have this equipment. Using this technique, the source of a vibration can usually be isolated and definitively diagnosed. Numerous traces can be run simultaneously. ![]() The way linear accelerometers work is that they’re stuck (via a wax) to various key spots on an engine and drivetrain and send signals to an analyzer that converts the signals to “traces”, like on an oscilloscope. For that reason, I would like to know why he suspects the balance shafts in the first place. This is at least an all day job for one mechanic, maybe more so the labor cost is going to be high. The timing chain has to be removed and then the balance shaft assembly can come out for replacement. The balance shafts are located in the upper oil pan, so that means the valve covers have to come off, then the lower oil pan, then the upper oil pan and finally the timing chain cover/oil pump has to come off. In a shop, I would pull the engine out first. It can even be done with the engine in place but its no fun. Your dealer may not want to do the disassembly on this engine, but it can be done. If it is the balance shaft, you do not need a new engine. The stock flywheel is a dual mass flywheel and it is possible that it is worn out too but I’m not sure how that would affect the vibration, it does make using the clutch much more difficult. Is this a manual transmission? Another mod that will make it run rough at this RPM is an aluminum flywheel. Often after the CAI and fart can exhaust, the next modification on this engine is to remove the balance shafts, that frees up about 11hp. If it is a recent purchase, is there any evidence that the engine may have had some “performance” improvements done? I.e. Maybe the bearings? Maybe the chain broke? If the chain broke, I would think that it would make a lot of noise and possibly tear up teh oil pump. ![]() The balance shaft, two of them actually, are solid pieces of steel that are driven by a chain from the crank sprocket, so I am wondering what the dealer thinks is wrong with them. ![]()
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