Deja Juju

Five months ago Marc finished overhauling the engine in his Toyota Tercel. New pistons, bearings, rings, the works. Now it has developed a tic. This isn't good. It only shows up when the clutch pedal is depressed. Let off the clutch and the tic goes away.

What could this be? You

• push on the clutch pedal, 
• hydraulically it pushes on the lever 
• that pushes on the throwout bearing, 
• that pushes on the retraction fingers in the pressure plate (assembly), 
• that pull the actual pressure plate away from the clutch disk.

I wrote up an explanation of how a clutch works, just in case you want to know. You can read it here.
  The throwout bearing, the pressure plate and the disk are all rotating with the engine, so if pushing on the clutch pedal caused something to stick out, and there was anything for it to hit, well, that could be making the noise. I give this a low probability because 1) all the clutch parts are new, and 2) I've never heard of such a thing happening.

However, there is another, worser possibility, and that is that whatever bearing(s) are holding the crank in place, that is, that keep it from sliding end to end, have failed. When you step on the clutch pedal, and that mechanical chain reaction starts, it ends with the throw out bearing pushing on the clutch. If the clutch, which is mounted on the end of the crankshaft, is free to move along it's axis, that is what will happen. The bearing will push the clutch, and instead resisting the force of the bearing and forcing the pressure plate to disengage, it will just move away.

Underside of main bearing number three of Toyota four cylinder engine with main bearing cap removed.

So if these suspect bearing(s) have failed, then when you push on the clutch, the crank should slide end to end, and when we tested it, it did in fact move. Marc had cut a three inch hole in the right side inner fender so he could reach the bolt in the center of the crankshaft. If  you push against the end of the crank (we used a two foot length of pipe, engine not running, please) and have someone step on the clutch, you should not be able to feel it move. Mind you, you have to push against the crank pretty hard. The first time I did it I could feel a little tic when Marc stepped on the clutch. Marc tries it and then tells me to really lean into, and when I do and he steps on the clutch I can easily feel the crank move, I would say about an eighth of an inch, which is about a zillion times more than what the spec says.

Once upon a time, about a zillion years ago, when I lived in Austin I had a friend named Ayron who had a Toyota Corolla wagon, and he rebuilt the engine in that car. And sometime later the engine developed a problem, which turned out to be because the thrust bearings had failed.

It seems that on either side of the number three main bearings, there are flat surfaces that serve as thrust bearings to keep the crank from sliding end to end. For these to work properly, the matching surfaces on the crankshaft need to be a certain distance apart. When Ayron first took his crank to the machine shop, they neglected to check this critical measurement, and went and ground the rest of the bearing surfaces as specified. I am afraid this is the same thing that has happened to Marc. Toyota must be the only manufacturer that makes their engines like this.