This Alero had given its owners more than a hundred thousand miles of trouble-free driving and still ran good, but they began noticing a rattling noise coming from the engine area. It wasn’t vehicle speed related and it wasn’t always there. When it did occur, it always seemed to sound off on deceleration, but the transmission didn’t have to be in gear to hear the noise. The local GM service outlet (a small dealership) thought they had pinpointed the problem as a loose catalyst brick and replaced the catalytic converter with an aftermarket part to keep the cost low. The car seemed fine for a week or two, but then the sound returned. Another trip to the dealer proved fruitless. Nobody at the dealership was rude, but the Alero owners were shown the door. The dealer wouldn’t work on the noise any further. That in and of itself was a puzzling circumstance; most shops, dealer or not, would have at least tried to sell these folks an engine, but not this time. After all, the Alero wasn’t smoking and hadn’t overheated. It would seem feasible to attempt some sort of repair. One possibility was that the service department had been burned on one of these jobs before and didn’t want to go there again, but who can be sure? Listening Carefully An engine knock doesn’t always mean something is loose. Years ago I helped a roommate of mine rebuild the VW engine on his rail buggy. And while my dad worked on VW’s for 30 years and I had built quite a number of domestic engines at that time, I had only done one or two bug engines myself, and those were in bygone years. My roommate and I carefully disassembled the little air-cooled mill and just as carefully reassembled it with new parts. It ran like a scalded dog and would yank the front wheels about three feet off the ground on a jackrabbit start, but the engine was knocking, and I was puzzled; we had been very careful to measure and torque everything. Some of you old bug engine guys are already smiling, aren’t you? I called my dad and the first question he asked was which way the piston index arrows were pointing. I assured him that I had pointed them toward the front, and then realized that the front of a bug engine isn’t the crank pulley, it’s the flywheel. Duh! My dad did say that a bug engine with the pistons installed backwards will have a lot more power, and boy was he right about that! After we corrected our mistake, the engine ran quiet but wouldn’t pop wheelies any more. Anyway, there are more than a few engines that will knock if the pistons are installed backwards, but that wasn’t’ the case with the Alero because nobody had removed the pistons and besides all that, it sounded more like a chain than anything else. There are two chains in this particular engine, one to drive the camshafts and the water pump and another smaller chain to drive the balance shaft. As described earlier, mildly revving the engine and allowing it to return to idle would usually produce a rattling noise as the engine was slowing down that sounded like it was occurring at about twice the speed of the crankshaft. The odd thing was that I couldn’t hear the noise anywhere with a stethoscope probe, but it was as noisy as all get-out in the oil pan area with the stethoscope’s end screwed off and using the scope as a listening pipe. Digging for Information I like to stand on my own two feet in a situation like this, but to be honest, I wasn’t all that familiar with this 2.4, and rather than drawing vast conclusions with half-vast information, (the GM shop manuals and TSB’s had nothing at all to offer on a noise like this), I put in a call to Randy Wilson (another MA contributor who was working at a big GM dealer at the time), and he said they had replaced more than a few of the balance shaft assemblies in 2.4’s for the noise I was describing. The balance shaft is an interesting piece of hardware in and of itself. Ford Contours equipped with four cylinder engines had an annoying vibration at idle that was practically unfixable because of the dynamics of the engine and the way it was mounted. Ford published a TSB (97-11-7) with instructions to replace the radiator mounts, install a steering column damper, and make sure the A/C lines weren’t touching the upper radiator hose neck or the body of the car, but nothing worked. As a matter of fact, directly quoting from the Ford TSB, we read: “THE PROCEDURE CONTAINED IN THIS TSB ARTICLE MAY NOT COMPLETELY ELIMINATE ALL VIBRATION FROM THE VEHICLE. SOME VIBRATION IS INHERENT IN I-4 ENGINE DESIGNS, SUCH AS THE ZETEC 2.0L. THIS PROCEDURE IS DESIGNED TO REDUCE THE AMOUNT OF VIBRATION EXPERIENCED BY THE CUSTOMER.” Inline four cylinder engines are always jumping up and down by their very nature, and vehicle dynamics dictate that this intrinsic vibration is more noticeable on some cars than others. With only four pistons, and with one firing event per cylinder every 720 degrees of crankshaft rotation, there are 180 degrees of crank movement between each firing event. Some I-4’s are smoother than others, but in order to take care of this intrinsic wiggle, GM’s 2.4 is outfitted with a chain-driven oil pump/balancer assembly with two parallel weighted shafts that spin at twice crankshaft speed. The 4 cylinder engine Chrysler uses in their PT Cruiser has the same setup, with the exception that the Cruiser balancer housing is aluminum instead of cast iron. Another factor to be considered was the price. At about $400, the balancer purchase wasn’t to be taken lightly; we pulled the timing cover and started the engine to watch the timing chain, but the chain was nice and tight, the noise was absent during this time and there were no visible signature marks where the chain might have been flopping, so we went with the balancer. Special Procedures Removing the oil pan on the Alero required draining the cooling system because one of the coolant pipes goes under the pan. And you don’t just pop the balance shaft assembly on there; it has to be timed properly. GM has a special tool that locates the two shafts that spin in the assembly (one is directly driven by the crankshaft chain and the other is driven via a set of gears like the camshafts on a Toyota Camry engine). The bolt that retains the balance shaft driven gear has left hand thread, presumably because it would screw itself loose if the threads were of the right hand variety. The chain is tensioned by an adjustable nylon-lined tensioner of a rather familiar design, and what we discovered early on is that if the chain is too tight (or too loose, obviously) it’ll make noise. With the lineup tool installed on the balancer (see illustration), and the engine turned 90 degrees away from #1 TDC in either direction, the balancer assembly can be installed and sprocketed to the engine. The GM shop manual calls for a .040 inch BRASS feeler gauge to be inserted between the chain tensioner and the chain (a steel feeler gauge won’t work because it isn’t flexible enough) and for 3 pounds of pressure to be applied to the tensioner before torquing the bolt. Well, that’s just peachy, but there is no brass 0.40 feeler gauge available anywhere from anybody I could find, including the major tool vendors; the closest they could come was 0.035. I even attempted to order some brass shim stock to build one and came up short there too. Finally we cut a piece of plastic from a hand cleaner jug that measured 0.040 and used that. With the engine reassembled, after a few bouts with getting the chain tension just right (the pan was pulled and reinstalled about four times) the noise was gone and it stayed gone for about three months before the car came back with what sounded like exactly the same noise. Round 2 The second time around we went back in and checked the chain tensioner and readjusted it to no avail. The nylon tensioner lining was showing some wear, so we replaced it. No good. We repeatedly worked on getting the chain tension just right. No good. We pulled the engine and replaced the gears and the chain, having discovered that some shops had fixed the noise that way. The crank gear is a stiff interference fit and was quite an adventure to change; we had to heat it like a flywheel ring gear to get the new one in place. We couldn’t initially tell whether or not the gears did any good because the timing chain was rattling so loud. The GM shop manual says to reinstall the timing chain facing the right way or it’ll make noise, so I had the students reverse the chain; they hadn’t marked it previously, but it was during this process that we discovered a sticking timing chain tensioner. The tensioner is a little two-stage oil piston has to be ‘cocked’ in order for it to be installed; when you push the tensioner all the way in, it remains that way while you install it and then you push the piston again with it installed, the tensioner is uncocked and the internal spring shoves the aluminum nylon-lined chain tensioner (similar to the smaller one on the balance shaft chain) against the chain. What we noticed about the tensioner was that this one was sticking at about the halfway point. We couldn’t take a chance on it, especially since this silly engine was so prone to make noises, so we replaced it, and in so doing, we haven’t heard the original noise since. Conclusions One of my graduates works at a shop down in Florida and he says he has heard at least three Aleros making the same noise in the same way, but they didn’t come in to have the noise repaired and knowing something about the trouble we went to on this one, he wasn’t about to try and upsell a fix. Was the noise the result of a sticking timing chain tensioner the whole time? It’s really hard to tell. One way or another, the next time we tackle one of these, that’s the first place we’ll look.
Posted on: Tue, 01 Oct 2013 09:43:46 +0000
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