engine knock
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engine knock two bolt 400 CID developed a wicked knock over the last day or so. Started at 3k rpm but quickly moved into the lower ranges until it can be heard at idle. Somewhat intermittant. I have several ideas of what it could be but I'd like to see if anyone could point to something specific. Knock may be coming from mid to high on the front side of the engine, but it's hard to say. Here is a video that may help.
http://www.youtube.com/watch?v=IleBauFOnS4
http://www.youtube.com/watch?v=IleBauFOnS4
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#1 and #5 rod bearing spun for sure. Initially I thought it was likely due to a clog. Now, I'm wondering if it's due to the engine's slant. It is off level with the front higher by about 5 degrees, maybe less. Could this be the reason? I'm thinking that if the oil pump is functioning properly that it should not matter, I'm just wondering.
a 5 deg slant would not do anything, nor should a 30-degree slant. If either were the case then anybody who has ever parked or drove on a hill should have spun bearings.
the first question is- was the oil level always reasonably full?
what was oil pressure typically, when cold and when hot?
do you know who installed the oil pump, pickup tube and screen?
oil pumps generally never fail, they're too simple. What happens is the pickup tube wasn't securely mounted and vibrates off the oil pump, this is why many weld the pickup tube to the oil pump, but if this happened you would have no oil pressure. Another potential source is not mounting the pickup tube down near the bottom of the pan in the middle. If the wrong pickup tube was used or something, and the pickup was at one end of the block and not low enough then a severe slant and low oil level could result in the oil level dropping below the pickup tube.
What I think you should do first is rule out oil starvation as being the problem, which should be easy to do.
I'm not familiar with the oiling system of the 400, i don't think its designed to always feed the mains first, known as priority main oiling. So maybe looking into that will help figure out the cause of the problem. And if you had too much oil in the pan and the crank whipped into it, that can aerate the oil and allow the oil pump to suck up air (if the pickup screen was unreasonably high) resulting in intermittent losses of oil pressure which could kill bearings. best of luck.
the first question is- was the oil level always reasonably full?
what was oil pressure typically, when cold and when hot?
do you know who installed the oil pump, pickup tube and screen?
oil pumps generally never fail, they're too simple. What happens is the pickup tube wasn't securely mounted and vibrates off the oil pump, this is why many weld the pickup tube to the oil pump, but if this happened you would have no oil pressure. Another potential source is not mounting the pickup tube down near the bottom of the pan in the middle. If the wrong pickup tube was used or something, and the pickup was at one end of the block and not low enough then a severe slant and low oil level could result in the oil level dropping below the pickup tube.
What I think you should do first is rule out oil starvation as being the problem, which should be easy to do.
I'm not familiar with the oiling system of the 400, i don't think its designed to always feed the mains first, known as priority main oiling. So maybe looking into that will help figure out the cause of the problem. And if you had too much oil in the pan and the crank whipped into it, that can aerate the oil and allow the oil pump to suck up air (if the pickup screen was unreasonably high) resulting in intermittent losses of oil pressure which could kill bearings. best of luck.
i believe this is the oiling system you have, but don't quote me on this, get some assurances first.
but if this is what you have, not a priority-main, then what can happen is all the oil can go into the top of the heads through the rockers instead of to the mains, resulting in bearing loss. This can happen if there's not a significant enough restriction in the lifters if they are hydraulic and all the oil goes to the top end. Or the lifter bores are worn out and all the oil flows around and past (not through) the lifters resulting in loss of oil pressure, same with cam bearings. If you notice in this diagram, the rods are the last to see oil pressure. So if you had a worn top end and even worn mains and low oil pressure, you're gonna lose rod bearings.
i also forgot to ask, how many hours/miles on engine?
Last edited by 1 FMF; Sep 12, 2010 at 09:00 PM.
