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

[Box]

Does letting the clutch in and out make any difference? It seems lately a lot of members have had their 5S bottom end give out, so it could be that the engine is giving up the ghost. Either way I'd stop driving it if possible until you get it fixed. You should drop the oil pan and look for chunks of metal.

[Mattattack]

Does letting the clutch in and out make any difference? It seems lately a lot of members have had their 5S bottom end give out, so it could be that the engine is giving up the ghost. Either way I'd stop driving it if possible until you get it fixed. You should drop the oil pan and look for chunks of metal.

No difference at all, whether I'm in neutral or accelerating. But from what I know about rod knock is that it should always be a constant knocking noise no matter what rpm, this seems more sporadic, like it may stop for a split second, be quieter, be louder, etc. Sucks to hear other people are bitin the dust too

[Box]

Rod knock can be at certain rpms, at first. Then as it progresses it'll just be certain ranges, and then it's constant unless the rod flies out of the side of the block first.

Being the clutch isn't making an effect I wouldn't think it's the flywheel then. Another possibility could be valvetrain, but that'd be more along the lines of a ticking or clacking versus a thumping.

[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

[Box]

A really long flat blade screwdriver or the like works well as a stethoscope if you don't happen to have an actual one like mentioned, broom handles can be cumbersome and wood dampens the sound. The cams spin twice for each revolution of the crankshaft, which is what nick was saying. Our latest member to have crank/rod failure was PegsGTS and he posted a video or two of his motor running before it completely died. Had a thought, if it's a cracked flywheel the noise should change as the motor/flywheel heats up.

Really the only way to know for sure is to pull things and inspect. The motor sounds rebuildable now, but continued operation and you could end up like others with pieces of rod flying out the block. Pulling the oil pan will be easier than dropping the trans so I'd start there with my fingers crossed.

[Mattattack]

Thanks guys, couldn't ask for better responses and I appreciate that more than you know. gonna try the screwdriver thing and most likely drop the oil pan. Either way i think this ends in me retiring my 6gc, head was rebuilt less than 10,000 miles ago and i think I'm done dumping money into her.

[Box]

Well, weigh out the costs of doing a rebuild or swap versus selling the car for next to nothing and having to buy something else. From what I've seen a GT with a bad motor you do well to get a grand out of it. Just something to think about anyway, but I know how you feel though as I've been there and done that more times than I'd care.

[PegGTS]

Yup I was in your same boat a few months ago. I posted the video on your facebook post. Pulled the oil pan off to find it was full of metal shavings from the main bearings

I have another 5S on the way now though! 160k kms on it and should be here in a couple days