Ominous noise quiz

[Andy]

Any ideas what this noise could be? I'll describe it as best I can.
I came home from work a couple of weeks ago and as I got out of the car, engine still idling, I could hear a regular knocking sound from the engine. Not a deep rumbling sound, but more like a regular "clack-clack-clack" sound about 2 to 3 times per second at idle. I hadn't really noticed the noise when driving, and the instruments showed nothing unusual.
It was too cold and dark to do anything then, so I put the car in the garage and left it for another day.
Yesterday, I tried to diagnose the noise. First, I removed the alternator belt to feel for play in the water pump, but there was none. I then removed the timing belt cover but couldn't see anything wrong. I then changed the oil, because the change was due anyway, and I even filled the new filter with oil before fitting, to be extra careful. Finally, I tried to start the engine. The engine was very cold and a little damp,so it didn't fire immediately, but that's normal after a couple of weeks standing. Turning the engine on the starter motor I could hear the noise, but it was only faint at first. After several attempts at starting the engine, the noise was becoming much louder, which suggested to me that the increasing oil pressure was making things worse. The car fired and died, as usual, and would soon have started in its normal way, but I stopped trying at that point, because I'd heard enough!
So, how bad is it, doctors? Any help would be much appreciated.
The car is an 1800 coupe.

[Hamish]

It sounds like big end bearings... what sort of oil pressure was engine showing at the time of noise? Or was it constant whilst engine running?

[Randy Adams]

Big ends should be at least somewhat load sensitive. Does it get worse when you ask for some torque from the engine?

[Andy]

Unfortunately, my oil pressure gauge is the standard hopelessly unreliable model. It usually reads normal on start-up, but as soon as the oil reaches normal temperature the pressure gauge cuts out and only comes back to life for brief spells, e.g. when accelerating hard. However... during a long journey a couple of weeks ago, the engine lost a LOT of oil. The oil pressure light never came on, the oil temperature stayed normal and I wouldn't have known any better had I not checked the level the following day and found NO oil on the dipstick. Since the noise wasn't yet audible I just topped up the oil and drove the car as usual. I didn't notice the noise until I'd done a couple of hundred more miles. Add to that the fact that I live on a mountain, so even without driving like lunatic the car gets a daily dose of sump-draining hairpins, which tends to confirm your diagnosis, doesn't it. But can I really have knackered the bearings that fast, on an unmodified engine that's done barely 50,000 miles from new? I'm just surprised that the noise appeared so suddenly, as if the bearing just broke from one day to the next, with no gradual increase in noise.
Randy, you ask about the effect of extra torque, but is it wise to drive the car to test this? Am I not likely to do even more damage by driving it gently to a garage (which I'd like to do, since I don't see myself pulling the engine with my limited facilities)? Thanks for the help, guys.

[Hamish]

Andy,
I hate to tell you this but all betas show what appear to be wildly erratic pressures on the guage, but that doesn't make it unreliable it can serve as a useful tool in engine fault diagnosis. In my experience most Betas which have shown LOW pressure once warm (ie: warning light coming on or in the low red) do have a problem or when the engine has been apart evidence of worn bearings or oil pump explain the pressure reading. In light of what you've said about the negine running pretty damn low on the oil front I would not drive it anywhere before getting it checked out by a skilled mechanic. If you are so minded it's possible to take the sump off with the engine in situ to have a look at the crank/bearings in place.
To answer the question "But can I really have knackered the bearings that fast, on an unmodified engine that's done barely 50,000 miles from new?" I'm afraid so, especially if it's run on very little oil for any period. Sorry.
If you do take it apart and even if it is standard PLEASE fit a baffled sump! It makes a lot of sense and could save the engine for a long, long time... I speak from hard earned experience and all my Betas now run Guy Croft type baffled sumps.

[Andy]

Hamish, when you say the sump can be removed with engine in situ, doesn't that involve hoisting/jacking up the engine? I thought the combination of crossmember and oil pickup made it impossible to drop the sump without some fairly involved manoeuvring. But I bet you've done this often enough to know the tricks!
Ideally, I'd like to remove the engine (sub-frame and all) to make a serious attempt at curing the oil leaks, but I don't really have room to leave the car in pieces for any length of time, so if the bearings can be replaced "on the car" that would be better.
I was aware of the benefits of a GC sump, but that was something I was considering doing if and when the engine had to come out. Didn't have to wait long... Did you make your own sumps to a GC pattern, or does the man himself supply them these days?

[Hamish]

Andy,
You can do with everything in the car - but it's tricky! You need a spare pair of hands and trolley jacks... but it can be done! if you have everything ready to go it's not impossible to whip the engine out (on the subframe as you say) do the gaskets and pop it back in a day.... just depends on state of bottom end i guess.
GC will make you up a baffled sump or you could buy a copy of his book and make one youself (or get someone to make it for you) lamentably my welding skills aren't proficient enough to make one myself!

[Randy Adams]

I have to agree with Hamish that if the motor's been run extremely low on oil, it's probably in real trouble now. If bad bearings are the reason for the engine making such a racket, I would not recommend just popping in new bearings. The crank will probably have taken a bit of a beating too and will probably need polishing if not grinding. Best of luck.

[Randy Adams]

I just thought of something else. Your report of running extremely low on oil is suggestive. I assume (hope) that you were keeping an eye on the oil level prior to this incident. Bad bearings do not make an engine use excessive oil. It is possible that you have a cracked piston. This can make the "clack clack" sound that you describe whereas big end bearings usually have a heavier metallic sound. And a cracked piston will let the oil into the combustion chamber in a big way. Of course, dropping the sump will not be sufficient to fix that problem. But, if you drop the sump and find the bearings to be in reasonable shape, your problem will be further north in the engine. Again, best of luck.

[andy]

Randy, I have to say that I don't know what a bad bearing sounds like, but I always hear it described as a low-ish rumble, unlike the sound I have, which is a kind of brighter hammering noise.
I'm usually very careful about checking my oil level but, as I moaned in a previous post some months ago, my engine seems to have started leaking appallingly ever since I put fully synthetic oil in it. There was some doubt amongst forum members as to whether that was really the cause of the leaks, but I stare at the evidence every day. I changed the gaskets for the cam box covers (the easy ones), and that helped stop some of the leaking onto the exhaust manifold, but if anything it's just accentuated the leaking from the cam box-to-head gaskets, which now fill the spark plug wells fairly regularly. Running the car for about 90 miles per day, the oil loss wasn't particularly bad, and the occasional top-up was enough to keep a normal level. Also, the engine has never been smoky, which makes me wonder about the broken piston theory. The massive oil loss only happened when I did a 1500 mile round trip, but even then the oil temperature remained normal and there were no signs of anything wrong when I was driving.
Either way it sounds like the engine will have to be taken apart.
Hmm. Another thought springs to mind: I tried several times to start the car this weekend, but it wouldn't fire. Although it's very cold here at the moment and the car hasn't run for about 2 weeks, I've never failed to start it in the past, and cracked piston = no compression = no start... doesn't it?
Time to ask you folks about engine removal procedures, but I guess it might be helpful to start a new thread on that topic.
Cheers.
Andy