View Full Version : Possible Main Bearing Knock....what to do?

03-04-05, 03:04 AM
I think a bearing(s) for my crankshaft is starting to fail. I've had this knocking sound for some time now, but has been somewhat difficult to narrow down to a specific source. I now know, that it's not a pully, and it's not the valvetrain. It's seems to be coming from within the engine itself, which makes me think it might be a bearing, or something along those lines. What I'm wondering, is if I can remove the engine, pull the oil pan, remove the cankshaft, and replace it with new bearings without removing the heads. I don't have any problems what so ever with the heads, and would not like to develop one by removing them. I'm also not in the mood to spend the money for a Timesert kit if I don't have to either. I would replace the crank witha brand new one, as I have read it is very hard to resurface the old one, and have it be as reliable as new. I guess my real question is, has any body doen just the bottom end of the engine before, without the need to remove the heads. I don't want to have to take apart more of the engine, than I need to. I have my factory service manual to help me also. Thanks in advance.

03-04-05, 12:08 PM
As robust as the Northstar lower end is proving to be it is highly unlikely that a main bearing is "failing" on your engine. Just doesn't happen....

Have you run the engine without the serpentine belt to make sure that the noise you are hearing is not in the accessory drive or an accessory??? That would be the first step.

To do what you are describing is pretty difficult. You would have to tear the lower end down and take the timing drive completely apart to get the crank out. It is possible to do without disturbing the heads but it is a lot of work...just to find the main bearings in perfect condition....

03-04-05, 12:48 PM
I'll have to try that this weekend. How long would you recommend running the car with out the belt. I don't want to kill the battery, or damage the car. I take it from what you said about just doin the botom end, is harder without removing the heads then. The only reason I think it's in the bottom end, is because of the nature of the sound itself. At idle, it isn't very fast, and it's relativlely low in pitch. It is also very loud. You can here it from about 25-30ft away from the car. I also here is on both sides of the car too. You hear it the loudest near the wheel well, just about where the crank sits. I'll try the pully think, but I have a feeling, I'm going to have to take it apart at somepoint in the future. Thanks Bbob, I'll let you know what I find.

03-04-05, 03:34 PM
A couple of things to consider in your diagnosis:

1) First, is this a heavy "clunk" type of noise that is rythmic with engine speed?
Lower end noises are pretty distinctive - once you've heard one you recognize it immediately.
2) Is it worse under load or without a load on it? A rod will knock all the time where as a main is sometimes unnoticeable unless under a pull.
3) Does the harmonic balancer move in and out with the engine running?
I've seen broken crankshafts keep on running smoothly, but noisey.
4) Are the torque converter nuts loose?
Take the inspection cover off underneath and bar the engine over with a screwdriver in the flywheel teeth to check ALL FOUR nuts for tightness.
5) And finally, removing the surpentine belt as others mentioned might reveal something too. That would be one of the first and easiest things to do to locate a noise you're not sure of.

It's hard to say without hearing the noise myself. Take it to a mechanic - he won't charge you anything just to listen to it and give you an opinion. Good luck, my friend!

03-04-05, 03:45 PM
You can run the car for quite awhile without the main accessory belt. The water pump is driven separately so the engine will not overheat. The battery will be ok for 10 or 15 minutes easily. You won't have power steering if you drive it but otherwise there is nothing to hurt.

Checking the torque converter bolts is an excellent idea.

One more thing to do before you rip the engine out of the car is to get under it and remove the 4 torque converter bolts. Slide the converter away from the crank so that it clears it and start the engine. This will uncouple the trans/torque converter from the engine so as to take it out of the loop. If the noise goes away with the torque converter disconnect then the noise is in the trans or the flex plate.....a cracked flex plate could make that kind of noise and is much more likely than a lower end problem.

03-05-05, 12:34 AM
mechanix, thatnks for the info. The noise sounds like thunk, thunk, thunk...over and over again, ina constant rythi directly related to engine speed. It is less noticable when accelerating, but comes right back at ilde. It sounds the exact same no matter what the engine temp is either.

Bbob, I'l try and to open that access panel, and see what I can do with the torque converter. I'll also try the belt thing too. I might have to get it next week though, since I'm helping my Auto-tranny teacher tomorrow with an open house at my school. Maybe I'll get lucky, and no one will show up, so I can use the shop. I guess I'll have to wait and see.

Thanks again for the advice. :D