Rod knock or Cracked flywheel? Options

[Mattattack]

So today is a sad day and I'm trying to figure out whether the knocking I'm hearing is rod knock or a cracked flywheel. Anyone experienced either? For the past few months, even after swapping in new mounts, I've had trouble from time to time getting out of 1st gear without the entire car shaking. Knocking first started today at just around 2k rpms and was very subtle. The next time I started it is when it became more apparent and was loud throughout the entire rev range. Also noticed while driving it home revs would drop about twice as fast and had lost at least 25% of power. If anyone can throw in their 2 cents it would be greatly appreciated

[texasnick]

First step, bottom end or top end? As Box mentioned top end noise is usually more of a ticking noise, while bottom end is much deeper sounding. A good way to diagnose for sure is by determining whether the noise is happening once per motor revolution, or twice. If the problem is camshaft/valvetrain related you should hear it happen twice per revolution, if that makes sense. If it is a bottom end issue ie rod knock, spun bearing, etc. you would only hear the knock happen once per revolution.

Step two, isolate the noise. Listen around in the engine bay. Try to get a general idea of where the noise is coming from. Once you get a decent idea, take a mechanic's stethoscope, or if you're cheap like me, a broom stick handle, screw driver or anything solid (make sure it's long enough to keep your important body parts away from moving parts) and move it around the engine listening for the knocking. If you can narrow it down to one cylinder, pull the plug wire out of that cylinder and see if that changes the noise. If the knocking goes away or gets quieter, that is the rod you are having issues with. If it doesn't go away, it could be a main bearing.

Don't forget to use the "stethoscope" on the bell housing to see if that's where the noise is coming from (or if it is louder there). I am thinking that it could be a flywheel based on your description of the shaking and how the rpms are dropping, but you will have to do some diagnosing to know for sure. A cracked/fubar'd flywheel could make noise regardless of whether the clutch is engaged, as it spins when the crank turns. If the noise sounds like it could be coming from the flywheel, pull the starter motor off and try to inspect the teeth on the flywheel for damage.

If you still can't isolate the noise after that, you should drain your oil, look for bits of metal, drop the oil pan and check it as well. While you have it off you can check the rod caps or any part of the crank assembly for play. Cutting the oil filter open could reveal bits of bearing as well.

HTH, good luck

edit: do you have access to an oil pressure gauge?

This post has been edited by texasnick: Jul 28, 2015 - 10:17 AM