I need help ID'ing a knock...

Hi all, long-time lurker, first-time poster :rolleyes: and all that jazz...

And also a recently-acquired Metro owner - a 91, standard G10 engine and manual transmission. The little bugger's been running very well up until recently, getting me about 42-44 mpg and saving me a fortune as I have a 110 mile commute each way, 5 days a week. Yeah, I know: :screwy: But my sanity in taking on this commute aside, I have a problem now and need some advice.

Last Friday I was driving home and stopped once on the way down. I'd had the radio on so I don't know when it actually started (other than on that trip), but when I started the car back up to finish my trip, I noticed it had developed a pretty loud knock. I'd checked the spark plugs a little while ago and cylinder 3 had some oil fouling - I knew the car burned oil already, but not very badly. Well, the knock's in cyl 3 too. It sounds similar to baseball_playa's knock in the video he posted, I'd say. So my first assumption is rod and/or bearings. I can't get a good lock on where the sound is coming from, other than the one cylinder. And the weird thing is that the sound drops off a lot, or even disappears, when I'm coasting at speed (65-70 on the highway). It does seem to be quieter when the engine is hot (ie idling after a long chunk of the commute), but it doesn't go away completely. I haven't noticed any loss of power, there's no misfiring, and since it's my only source of transportation, I've had to drive it in spite of the knock.

So here's what I'm wondering:
1. Is there any way to tell whether it's a lifter, the piston, the rod, or the bearings, just by when the sound is louder/quieter/gone? I tried the "mechanic's stethoscope" bit, but I couldn't get it localized any better than that cylinder.
2. I went ahead and picked up a set of rod bearings just in case. If all I'm doing is replacing the bearings, how difficult a job can I expect this to be? I've been following the exploits of DOCTORBILL and it sounded like removing the bearing caps and replacing the bearings wasn't too bad, once he actually got them shipped. It's just a "hope it's either lifters or bearings and nothing else because I don't have the time/money to swap engines" kind of desperation move on my part :emo:
3. If it was something as bad as a bent rod or cracked piston, how fast would the engine become useless? Under duress from my boss, I've now put another 400 highway miles on the poor car. The knock's exactly the same as it has been, no worse and no quieter (except when coasting or maintaining speed). If it was one of the "terminal" scenarios, shouldn't the thing have gone :newburn: by now?

If I had the time and cash, I'd be following in DOCTORBILL's footsteps right now, but as it is, I just want to keep the lil' bugger running as best I can. Am I just tilting at windmills at this point or is there hope for the wee bairn after all?

Two other quick notes:
1. The knock is about half the engine rpm's - around 400 /s at idle

2. I've been using 20 weight oil, up until I read about it causing the valves to stick. I'm using 5 now, but that's only since the last oil change.

Oh yeah, and my insurance does cover towing. ;)

Take a long screwdriver and put the handle part against the outside of your ear the put the business end to different parts of your running engine. this works pretty well at figuring out what sounds are coming from where. Good Luck!

Now I need help finding parts - or rather, an engine. :uhoh: Once I got the oil pan off and heard rattling, I knew there'd be a problem. Sho' nuf, I not only found the decimated rings from the piston in cylinder 3, I found chunks of what could only have been the piston itself. Shining a light up in 3 confirmed it - the connecting rod looked fine but the lower 3rd of the piston was basically missing. The thin part around the bottom of the piston is the skirt, right? That's what the chunks were in my oil pan. :crying: Luckily I saw a company that sells used G10's for 295, and they're up in Santa Ana, not too far from here, so I don't have to have the engine shipped. Thanks for the suggestion anyway, sbiddle, too bad it wound up confirming my worst fear.

Sorry to hear about the demise of your engine. When you get your new engine (I assume its JDM (japanese domestic market)) remember you will need to trade over the intake/exhaust manifolds and their respective sensors/wiring from the old engine to the new. Search the forum and you will find all kinds of information. Good luck on your swap!

Ahhh...so that's where the initials JDM come from. I'd just assumed it was a company name. And yeah, the engine's JDM.

So one last quick question - even though I'm almost definitely going to do a swap (and thanks for the :2cents: btw), is it even feasible to just buy a single piston/ring set from partsdino or another company and spend a weekend reaming/reboring cylinder 3 and replacing the damaged piston and rings instead of swapping the whole engine? Or will the cylinder itself have been damaged? I inspected everything thoroughly last night after I'd pulled things apart and cleaned them, and the rod and bearings look like they're ok - it's just the piston itself apparently. And the other two cylinders' mechanisms are in incredibly good shape for being 15 years old. Heck, after I put the thing back together, other than the knock from the already damaged piston the engine sounds great. It almost offends my senses of thrift and fairness :evillol:. I'm curious mostly, although DOCTORBILL's experience seems to suggest it's possible and I'd love the experience and satisfaction of doing open heart surgery on a car (I'm a biology scientist by trade). But if we're talking about something that would take more than a weekend (assuming 2 full days to work on it) I'd rather donate some blood and sperm and just pay to swap the engines. :p

Zed,
You've got the same exact prioblem as I. I put a reman head on convinced it was a lifter. Anyway, I'm going to do the JDM thing now and keep the old engine for spare parts (like the new head if I need it).
My friend told me their taxes go thru teh roof in Japan if they keep a car until it's old. Is that why they have these JDM engines for sale?
I need to find out what the difference is between G10L, G10A, G10V & whatever. I see all these letters in the ads. Mine is an XFi model and I think they have different stuff in 'em. Someone said they only have 2 rings instead of 3, for fuel economy. It probably will make little if any difference but I want to find out.

Ted

Part of Japan's emmission program is to replace the entire engine every 30,000mi or so.

Consider what kind of miles these would be with so little open road.

If you knew you had to replace your engine at 30K, how often would you change your oil?

Also consider with so many people and cars navagating such narrow roads, it is not uncommon at all that new cars are envolved in accidents almost as fast as they are sold.

I have never heard someone complain about a JDM engine. I can recall at least two brand new American replacement engines that had problems.

Syndrome Zed;
I'm quite certain you could just replace the piston and rings in cylinder 3, but I think in the long run you would wind up pennywise and pound foolish. I once took 3 different subaru engines and pirated the best parts off each to make a whole one, I matched the wear on them as close as I could and went with it. While I'm sure no self respecting engine builder would sanction such a thing (and who knows about longevity, although I had the suabru for two years and 45K miles after the "rebuild") when you are young/poor you do what you have to. As a matter of fact I'd be willing to bet you could go to a local wrecking yard and get a "replacement" piston for really cheap. The downside of doing just one cylinder would be the possible effect of uneven wear/stress on the rest of your rotating assembly. And you will have at least some money involved in the gaskets, rings, miscellaneous parts and of course your time. I really think you'ld be better of swapping in a JDM engine or doing a real honest rebuild. Of course if you are just plain overtaken by that forever present scientific question "What if...?" then have at it.

Syndrome Zed;
I'm quite certain you could just replace the piston and rings in cylinder 3, but I think in the long run you would wind up pennywise and pound foolish. I once took 3 different subaru engines and pirated the best parts off each to make a whole one, I matched the wear on them as close as I could and went with it. While I'm sure no self respecting engine builder would sanction such a thing (and who knows about longevity, although I had the suabru for two years and 45K miles after the "rebuild") when you are young/poor you do what you have to. As a matter of fact I'd be willing to bet you could go to a local wrecking yard and get a "replacement" piston for really cheap. The downside of doing just one cylinder would be the possible effect of uneven wear/stress on the rest of your rotating assembly. And you will have at least some money involved in the gaskets, rings, miscellaneous parts and of course your time. I really think you'ld be better of swapping in a JDM engine or doing a real honest rebuild. Of course if you are just plain overtaken by that forever present scientific question "What if...?" then have at it.
I've decided to do what Chilton's calls a "freshen up" - basically rebuild the bottom half of the engine and replace the piston at the time. Money was one factor, time and equipment another, and since I'm a scientist by trade, you're right that there's definitely some curiosity at play. :grinyes:

So I'll try and document everything as much as possible a la DOCTORBILL. I doubt I'll be able to do as good a job as he did, but I'll give it a go.

Anyway, one question. Chilton's says to take the piston to a machine shop to have the pin removed and the new piston installed to the connecting rod. But Chilton's also says to go to a machine shop or pro for most everything I plan on doing to my engine. So how does the pin come off - is it a dowel-tapping thing similar to removing the piston from the cylinder? Hell, at this point I could probably just use my Dremel to cut the old piston off (just kidding, don't worry...:naughty: ).

ZED;
I don't have a piston readily available but if I remember corrrectly the wrist pin is a press fit. Definitely somehting I'd take to a machine shop and have done. Check out the affected cylinder to make sure the walls aren't so scored that they wouldn't clean up with a light honing. If vertical scratches are left behind after the honing the rings will not seat as well as they should giving you a reduction of compression and allowing excess oil to migrate into the combustion chamber. Also have the machine shop check the condition of the other pistons/rods as they too might be cracked. Oh and congratulations on holding the curiosity somewhat in check....

Yo Z:
How many miles on this machine?
Even if you have someone check the other pistons for cracks, do you really want them back in the engine and possibly blowing chunks a few miles down the road? From what I've seen of my #2 piston, I wouldn't trust the other two, especially after 180k miles.
Even if "a few miles down the road" turns out to be a few thousand, you're doing 2,000+ miles a month. If you're going to this effort and plan to keep racking up that kind of mileage, I would at the very least replace all three (but that's another C note easy). In fact I would do the JDM thing (what I plan to do). If your bore is messed up (see previous post) you definitely will want to think JDM.
Then again, if you really do like to experiment, I've found that we do our best learning when things blow up in a really bad way...

Reading about your situation, I agree with the other guys. you should price a JDM engine, inspect your motor mounts and shop Ebay for them. You wrote that you don't have a lot of time. Patching your engine together is more likely to become an unreliable nightmare that you can't afford.

Thanks for the advice, everyone. I do appreciate it. I priced some engines and even found a couple places in the LA area where I could potentially drive up and pick up a JDM for replacement. The engines ran about $300 US, the cheapest I found for installation by someone else was $400 more for the labor, and if I did it myself I'd have to invest in a hoist, so it'd run me about $450 (total) for me to do it myself.

Fixing this engine will run me less than half that, or about half if I replace all 3 pistons. But I took a really close look at the other two cylinders and they look *really* good. The engine's got 114K miles on it right now, so not a whole lot for a 15 year old by any stretch. If this turns out to be a mistake and I'm under the gun, I can swap engines later on down the road (no pun intended) when I'm not paying for my wedding (2 weeks from now) any more. I may be changing jobs in a month too, with the commute being cut to about 90 miles round trip instead of 220, and that'd ease the load too. Even so, I could get the other two pistons overnighted for a Ben Franklin and still finish up by Tuesday. I'm already committed to doing the rings on all 3, so taking a couple more pistons to the machine shop wouldn't add too much to the list. The possibility of an engine swap is still there, and would make for a good complementary thread to DOCTORBILL's rebuild :), but if I can "rescue" this engine from a seriously short life span and get a few more months (or more) out of it before I have to do that, I'll take the experience I gain and the mileage as making it worth it in the long run. Just wish me luck!!! :) And keep answering my questions! ;) Thanks again for all the help and advice - this forum is a Godsend.

PB Blaster is an impotant tool that prevents injury and saves siezed up hardware. In the case of your head bolt, get a longer pipe and turn the bolt until it comes loose or breaks the bolt. Hopefully the bolt will break off at the head so you have a chance of turning it with vise-grips after soaking the threads with PB Blaster. If the bolt breaks and you can't loosen it with Vise-grips, you will have to cut the bolt close to the deck surface of the block without damageing the deck and drill the bolt out without damaging the deck or threads. Removing a broken bolt would be another reason added to your list of why in your situation the smartest most economical way to proceed is to rent an engine hoist and replace your engine. No doubt you can hardly wait to encounter your next obstacle.

Yep - I got some PB and used my torque wrench as a "cheater" bar, and finally got the bugger loose. Made some interesting discoveries too - no thermostat in the car, and I don't know when the last time that #3 piston actually worked from the look of it. But 1 and 2 are both in good shape, a little carbon-y but nothing a bit of elbow grease couldn't get rid of. And more surprises - no ridges to ream, bearings and rods all look great, and the bore for #3 is amazingly smooth. Even on close inspection I couldn't find any serious scoring from the damaged piston. It honed to a nice crosshatch and the ring gaps are well within spec. I took some pics as I went and will post them soon. I've still got to get the connecting rod off the wrist pin at the machine shop, and the UPS people missed their target date by a day with my head gasket and valve cover gasket.

Oh, and had the bolt broken, I would have said screw it and replaced the engine at that point. But I never could find anyone around here who rents hoists, only specialty tools. :( But boy, when this engine turns over again tomorrow (gotta have confidence ;) ), I'm gonna dance a jig that'll make that Lord of the Dance goober wet himself. :)

Man, you dodged a bullet on those cylinder walls! At least luck is on your side :grinyes: . I'm anxious to hear how she runs after the work. Looks like you might beat DrBill to the finish line, lol.

The race is on!
Around here the same outfits that rent garden tools, party supplies and the like rent engine hoists. In my case when I checked if I kept the hoist for more than 3 days it was cheaper to just buy one which is what I did, managed to get a package deal on an engine hoist, engine stand and jack stands.