sudden engine knock ???

alfaal164l · #1 (**permalink**) 04-09-2008, 07:00 PM

i was driving the other night at a constant 75 mph for about and hour when i finally came to a stop the motor sounded louder than normal. I quickly pulled over and checked it out. At idle the car is fine at about 2500 rpms i can hear what sounds like a bottom end rattle. also sometimes noe at start up for a brief second it does it as well. I noiced my oil pressure light has been coming on briefly then turning right back off. I have checked the oil plenty in there. Could it be the oil pump? Any help would be great as this is my daily driver and have to keep it going for now...

ChazzyD · #2 (**permalink**) 04-09-2008, 07:19 PM

Hate to say it, but that sounds like a crank or connecting rod bearing has or will be spun in the very near future, you will know for sure when it happens, believe me (but by then it's too late). My car flashed it's oil pressure light when hot for about a month before it spun bearings (one con rod and one crank). That engine sits in my garage now and I'm running a used engine that has been running great. You should park the car if you don't want it to tear up it's crankshaft or block from a completely spun bearing. Wish I would have done this myself as my old engine block/crank is probably too trashed to do much with. Can you put an oil pressure gauge on it to see where your at, both cold and hot? You can't really tell much by the gauge in the dash, but the light coming on, is not good at all. Sorry, but don't do what I did. If it's already trashed, don't make it worse and completely ruin what could still be a rebuildable engine.
Charles

**Richard2** · #3 (**permalink**) 04-09-2008, 07:22 PM

And the oil pressure is....? Or do you have the failed oil sender syndrom? Is there molasses type substance in your oil fill cap, indicating coolant leak into the oil?

jontg428 · #4 (**permalink**) 04-09-2008, 07:39 PM

I think the light is always more reliable then the gauge, and given the stories of main bearing failures on the #3 bearing (I think thats the one) it seems that it is susceptible to failure without enough oil preassure. I would not drive the car, in order to try to save the crank.

**Richard2** · #5 (**permalink**) 04-09-2008, 08:43 PM

The rod bearing failure is on #4, ask me how I know

Fortunately I got mine apart in time to save the crank

Del · #6 (**permalink**) 04-10-2008, 12:08 AM

Even if the crank throw is buggered/torn up, the crank can be easily fixed. They weld up that throw, grind it, and if needed it can be nitrided again, although for street use, nitriding is not necessary, as very few engines these days (or even in the past) have nitrided cranks. It's just not necessary. My friend who repairs Ferraris has this done when needed. He even has new cranks for old Ferraris made in Detroit, and says they are really beautiful. Of course, I don't know the cost for THAT.

colo164 · #7 (**permalink**) 04-12-2008, 02:03 AM

Exactly the noise mine made when the rod bearing spun. My crank was pretty messed up but they did grind, weld, and resurface it no big deal.

MrT · #8 (**permalink**) 04-12-2008, 07:13 PM

Chiming in here for your amusement....Wife's car's P.O. had timing jump on him (broken tensioner) and he ran it for 30 miles knocking badly. #5 rod bearing pounded paper-thin and crank journal trashed. He'd included a spare crank, so I have the impaired one in the garage awaiting some need.

alfaal164l · #9 (**permalink**) 04-15-2008, 05:52 PM

well it finally went not all the way still running but lost power on the way home and the oil light stays on now. so it is parked time to put the used engine in it. so had to go buy a new car this last weekend so i will make the alfa my new project

MrT · #10 (**permalink**) 04-16-2008, 04:51 AM

I really ought to add here that the wife's car is an S, with the 10.0:1 compression. The car we bought for a daughter a few years ago came to us with one tooth advanced timing on both cams. I've heard that two teeth advance can be an audible interference on the 9.5:1 compression 12V engines, but also may not trash the valves. The two teeth advance on the wife's S did in the rod bearing and journal, as well as bending (just a little bit) 8 of the 12 valves. Engine still ran, but knocked badly, even when re-timed. I didn't do a compression check, but the shop that re-did the heads said the visibly asymmetric valve seating was their flag to change out those 8 valves.

I guess it doesn't take a lot of interference to cause the bearing shells to deform, giving them clearance to start moving.

Michael