BMW 535i Knocking Sound when Revving


I just bought a used 535i with 98k miles. It was knocking when revving it up. I took it into a shop and they said I need a new engine. The showed me some copper shavings in the oil filter. Said it was broken bearings. Offered a 95k engine replacement for almost 10k. I asked if I’d be getting the same problem and they said they didn’t know as they don’t inspect the engine. OEM engine is 21k.

My question is can I replace the bearings instead? Seems like the same odds as having a replacement with same miles and potentially same problem.

Once some bearings go bad, it’ll cost more to do the engine rebuild than the used engine replacement. LOTS of work to rebuild a modern twin cam BMW engine.

What year?

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It is a 2012.

So, I was quoted about 10K for the replacement engine with similar miles. Replacing bearings costs more than that? And wouldn’t I be rolling the dice on the new engine having the same problem?

Just bought a car and motor knocks? Missed that on test drive? I would go back to seller and have a talk.

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It never showed up on test drive. Bought private party so I’m going to get a shrugged shoulder.

Yes they do.

Why, because the engine must come out, be taken apart, the crank gets sent off to be re-ground. The rods get measured to see if they’ve been pounded out of round. The block gets checked for straightness and bearing saddle damage and if you are really lucky no block or rod machining is needed. You flush out the block as best you can and hope no metal particles got past the oil pump (which you must replace for that reason) and it all goes back together measuring every clearance for the replaced parts.

Assembled, of course with the rest of the parts that have 98K miles on them. Then it gets re-installed. Hopefully no metal particles got up into a spot not easilt cleaned out since you didn’t spend the extra time to strip the head down and clean it. That is mostly labor and will run close to $10K PLUS you have an engine that might need the head rebuilt in 50-75K miles. All assuming the mechanic didn’t screw something up because this is not normally part of their work.


I would imagine having right skills, time and determination … in a few months you will get it cheaper and better and whatever… but it does not sound like the case here.

New bearings for your engine cost maybe $100-150… installation however, will easily exceed 10x that amount.

Kind of like Piston Rings…


You bought a $10k car
Needs a $10k motor.
Will be worth $8k when done.
Kinda like life.

This is, of course, what you must officially do to replace worn-out bearings in an engine. If you are a professional mechanic, doing this work on other people’s cars for money, you better do it by the book. On the other hand, as a DIY’er, you can probably get away without doing any measuring other than a “wiggle test” to check for gross wear or out-of-round.

If you stopped driving the car soon after the engine began to knock, it is possible that the crankshaft journals might be round enough that new bearings will last long enough to be worthwhile. Of course, if it was driven with a knock for a long time, and/or if someone already tried replacing the bearing(s) once already, that is likely not going to be an option.

I am going to tell you how I rebuilt the short block in a car which had a rod knock. I originally wanted to replace the bearings from below, but found by doing the “wiggle test” that all of the bearings had excess play, and one crankshaft journal was ovaled out. So I pulled the motor and replaced the crankshaft with a used one, and installed all new standard size bearings. No measuring, other than performing a “wiggle test”, ok, no noticeable play in any of the bearings, looks good.

I did not replace the oil pump either, just took off the pickup tube and cleaned the metal shavings out of the screen by putting the pickup tube at the end of a garden hose and blasting water through it while tapping it on a wood block to dislodge any debris. I did, however, do a lot of cleaning with carburetor cleaner (to remove oil sludge, grease residue, etc) and compressed air (to remove particulate matter). I can’t wait to reinstall this engine and see how well it runs/how long it lasts. If it blows up after a short time, whatever, I’ll just do the job again, this time with a complete used engine.

My point is that if your alternative is to spend $10k on another engine, you really don’t have anything to lose trying to repair this one yourself. You don’t need to spend thousands of dollars on measuring tools, either. There are plenty of Youtube videos which show people removing the oil pan, performing a very rudimentary cleaning, and installing new bearings from below. As long as the crankshaft journals aren’t too badly damaged, this probably lasts for a long time.


Cheaper to find a known good used engine and install it…if the vehicle is in nice enough condition and or you cannot part with said vehicle and must re-power it.

Can it be repaired? Of course…are you able to do that work yourself? If not, it is not going to be cost effective. Rebuilding any engine with a “I hope this works” type of attitude will produce widely varied results. The only way to guarantee that it is done correctly and stands a chance at a long life is to go with precise measurements and clearance checks. It is simply “how its done” there are no mysteries here. Can you get lucky with “wiggle tests” sure…you can…all depends on the damage at hand and your ability to recognize and correct it.


I know that it is not proper for me to cast aspersions on the integrity of a seller that I do not know, but if I were to bet, I would bet that the seller put some STP or Motor Honey in it to quiet the knock for the test drive. Such additives accelerate the damage but at that point, it did not matter because the damage was done.

6 cyl BMW engines don’t often lose main or rod bearings, so I would suspect that this one may have an array of problems besides the bearings. I would not try to rebuild it.

I would think that if you shop around, you could find a competent mechanic who would do an engine swap for less than $10k. I spent $4500 for the junk yard 6 cyl BMW engine and installation, including a new clutch and several other parts. (I have since put 100k miles on that junk yard engine) Yours would be somewhat more, but I would not expect it to be that much more. You might even find a junk yard engine with fewer miles on it if you shop around…


I would safely bet that the crankshaft journals are damaged. They are probably scored and/or out of round or tapered. If so, new bearings won’t last long.

Before spending one dime on bearings in the hope that it may fix this problem I would run a compression test on it. If the top end is worn to some degree then bearings would be pointless. If the compression turns out to be good then it would be possible to buy rod and main bearings (300 bucks give or take), remove the crankshaft, and have it reground. Say a 100 on a regrind plus gaskets/fluids.

That it still labor intensive and also carries the assumption the crank is in good enough condition to be reground.


Pull the motor to repair crank/bearings vs install used motor? Both are expensive. But, saving a few grand might be nice. When all is said and done.

Mustangman is right in his reply. If I wanted to keep the car I would only consider 3 engine options = A new crate engine; a factory rebuilt engine; or an engine from a like car with low mileage that was totaled in an accident (a wrecking yard can search for such an engine). Keep the car, pay the price, drive it for years - or sell the car and let it be known the engine was blown. Someone with an engine might give you a decent price for the car. You got a bad deal. Make the best of it and move on. Sometimes you’re the bug and sometimes you’re the windshield.

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This forum has been extremely helpful. I wanted to give an update. There is a group in Oklahoma that rebuilds the engine I have (N55 I think). There is a local mechanic that specializes in BMW/Audi who will get the motor and install it. The motor is a rebuild with a 2 year warranty. Out the door it’s about 8,000. Seems like the best option considering the warranty.

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Nothing wrong with what you are considering if you really like the car and it is in good shape.

I guess you really have to like the car. Me? I’d probably get a completely different car for that 8K rather than another engine. 8K can get you a nice used car with low miles.

I completely understand your opinion and I’ve thought hard about it. To that end, I’m having my mechanic look at the car and determine if the rest of it is in good working order (cosmetically it’s in mint condition) and then we’ll move forward. After all, the engine will be completely rebuilt with a 2 year warranty. That’s more of a guarantee than I would get with a new used car.

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