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Old 03-01-2011, 04:17 AM   #1
cpatstone
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Default knock knock... what's that?

First an intro: just bought Gimp's car. Flew down to BWI and drove it back... long day, but well worth it.

Shortly before I bought it, the car developed a bit of a knock. This was fully disclosed. PO and his mechanic suspect rod knock. I'm not sure, or at least I'd like to eliminate other possibilities before pulling the motor.

Symptoms: essentially no noise at idle, and up to maybe 2500 rpm. 3000+ and it's there. somewhere around 3000, it sort-of hit or miss happens, but on a per-revolution basis, it's either there or not. So it's not like a ticking that gets progressively louder with higher RPMs.

CEL is on, but for an oxygen sensor which we think is unrelated. At the higher RPMs, it's not subtle... sounds really bad. I wasn't sure I'd make it from MD to MA, but I limped along and it did fine. Got great mileage, too. Not overheating. Don't know if it's lost any power, but the PO didn't seem to think so.

Motor has 184k, well maintained but not necessarily babied. PO changed the oil after this started happening, ran the oil thru a coffee filter, didn't see any metal particulate. I assume he used his pela oil sucker, so there might be a little junk in the oilpan that didn't get picked up with the oil. I guess the oil filter looked fine too.

Had a buddy over tonight and he did the dowel trick: one end on the motor, other by his ear. He thought the knock was more top-end. He thought there might be something glaringly obvious -- and the noise would make you agree -- but I just pulled the valve cover, and all looks fine. No metal particles at all. No visible scoring. springs seem fine. chain looks fine.

Fully disclaiming that I'm a complete noob to the M44, I'll throw out a couple of thoughts and I'd appreciate any comments.

* Timing chain guides are plastic, right? do they break (think M62)? if that happened and the chain was flopping around enough to really whack the engine case, wouldn't the chain skip teeth and become a really big problem?

* Apparently the valve guides can wear and/or break? If a valve guide was causing excess drag, would it cause the valve to not return as quickly as it should, thus not following the cam, and whacking the cam when the two caught up?

So? thoughts/comments/suggestions? Thanks in advance!
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Old 03-01-2011, 04:32 AM   #2
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That would be great if it wasn't rod knock.

Just adding - I originally thought it was chain slap from the tensioner, so I swapped it out. No change to the sound.

It doesn't make any noise between shifts when cold, but does when warmed up. I was assuming this was the tolerances on the bearings opening up due to heat.
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Old 03-01-2011, 05:07 AM   #3
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Rod knocks do not normally come and go. They are always there at their specific RPM as you stated and normally at all RPM. Also they tend to get worst with higher RPM and should be at their worst when the engine is first started.

Can you take a video with sound of you knock and post it? This might help us try to diagnose over the internet which is very hard to do.

Best, John S
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Old 03-01-2011, 11:51 AM   #4
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video - good idea. will-do.

had another thought: one of the crank bearings self-destructed and now resides in the oil pan. so, low rpms, little stress on crank, it flexes without that bearing but not enough to impact the block. at 3000 rpm, it's flopping around, sometimes hitting, sometimes not. 3500, hits solidly ever time. higher rpms, seems to go away a little, maybe because it's hitting the block sooner.

if that were the case, I'd need that part of the crank ground, and a new set of crank bearings. can this be done with the motor in the car? in terms of hours, easier to pull the motor?
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Old 03-01-2011, 12:49 PM   #5
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My mechanic said he could do the bearings while the motor was in the car. You would have to drop the subframe to do it.

I'm not sure about the idea of the crank bearing being gone all together. I would think that would make a terrible noise, even at idle (which is 700 revs per minute - pretty quick with no bearing)
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Old 03-01-2011, 01:42 PM   #6
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Quote:
Originally Posted by cpatstone View Post
video - good idea. will-do.

had another thought: one of the crank bearings self-destructed and now resides in the oil pan. so, low rpms, little stress on crank, it flexes without that bearing but not enough to impact the block. at 3000 rpm, it's flopping around, sometimes hitting, sometimes not. 3500, hits solidly ever time. higher rpms, seems to go away a little, maybe because it's hitting the block sooner.

if that were the case, I'd need that part of the crank ground, and a new set of crank bearings. can this be done with the motor in the car? in terms of hours, easier to pull the motor?
If the motor is running without a crank bearing I would think the crank journal would be so damaged that the crank would be destroyed. It would be groved so bad you could not grind enough material to get a fresh finish. Also the flex from runing it like this would most likely cause hairline cracks on the rod journals. I've not heard of a motor running for very long with a missing bearing on the crank. I would think you need to remove the motor. I've never heard of someone grinding a crank with the crank in the motor. Also I think the block would have damage on the bearing seat surface so to repair this the crank caps would need to be milled then torqued and line-bored. If you in fact are missing a bearing on the crank you will have serious damage inside that motor.

This is my opinion, John S
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Old 03-01-2011, 05:22 PM   #7
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Now I know nothing about the M44, but are they hydraulic lifters? I seem to think a sticky lifter would have been diagnosed long ago, but figured I'd throw it out there since I had one after doing the head on my M50.

Video will help tons, try to get that up ASAP
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Old 03-01-2011, 07:01 PM   #8
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Could it be clutch related? Thrust bearing going out? I know the thrust bearing is toast in my motor because it was from a 5 speed car.

John, I know it's not a bimmer, but I ran my old grand marquis essentially without any bearings for quite a long time. Noisy as hell, and I beat the crap out of it. I eventualy just swapped the motor....It never blew it apart. When the motor was disassembled, the crank looked like an old audio scroll and the bearings were paper thin. It had less than 10psi oil pressure at highway speeds
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Old 03-01-2011, 07:53 PM   #9
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I spun a rod bearing on my motorcycle before, it knocked like hell at all rpms. There's a couple of other things that will give you a similar sound, but may not be as serious as a rod knock. First one that comes to mind is water in the fuel or too low of octane. Usually you can feel it misfiting if this is the case. This can be cured by running 1 can of seafoam to 8 gallons of clean 91 or better octane gas. The seafoam will mix with the water and make it combustable so it will eventually be burned off. The second thing I could think of would be a faulty or loose knock sensor, but I believe this will shut the engine down. And finally an intake or exhaust manifold leak. An intake manifold leak will allow unmetered air in, causing a misfire and a CEL. An exhaust manifold leak will sound EXACTLY like a rod knock only you won't feel any misfiring and there won't be a CEL.
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Old 03-01-2011, 08:20 PM   #10
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I did seafoam the oil and gas before the car was sold, thinking it was a sticky lifter or maybe water. There was no change.
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Old 03-01-2011, 09:52 PM   #11
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Quote:
Originally Posted by gimp View Post
I did seafoam the oil and gas before the car was sold, thinking it was a sticky lifter or maybe water. There was no change.
Oh, come on. Give it up. Which tool got sucked into the intake?

I know what bad gas sounds like. This knocking is big and bold. I mean, taking this thing on a 400 mile road trip is something only a college-age liberal arts student would do. 'course then he'd blog about it and probably make a million.

Video will be posted TOMORROW. I'll also probably drain the oil (from the oil drain plug) and see what sparkly things come out. Or maybe just nice clean Mobil1 5W-30???

(edit - will post a vid tomorrow - still need to get the car together and don't want to wake up the neighborhood with the knocking and loud-and-proud exhaust)

Last edited by cpatstone; 03-02-2011 at 02:03 AM.
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Old 03-02-2011, 07:20 AM   #12
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If any bearing destructed the motor should be torn completely down.
You don't know where the shrapnel went. Likely if you ran it after
bearing went the motor is a core at best.... These are very very close tolerance engines.

I'd pull the motor and stop messing with it so you can maybe save the block and crank.

Its not worth it in my opinion to try and remove the crank
(It has to be removed to polish the bearing surface) with the
engine in the car, you still would have to pull the timing chain
and unbolt the transmission. I've never seen a engine with a
main bearing gone without a badly damaged/broken crank.
The bearing cannot "get out" without being ground to small bits.

I have on rare occasions seen a stretched rod cause knocking
that comes and goes with different speeds. But the head comes off to
attempt that repair, once yoru in that deep the gasket set is too
expensive to NOT do a basic rebuild at a minimum. If your that tight
on cash, just go find the lowest mile motor you can and do a r&r.
These are starting to show up in U-pullit yards in my part of the country.


Dave


Quote:
Originally Posted by cpatstone View Post
video - good idea. will-do.

had another thought: one of the crank bearings self-destructed and now resides in the oil pan. so, low rpms, little stress on crank, it flexes without that bearing but not enough to impact the block. at 3000 rpm, it's flopping around, sometimes hitting, sometimes not. 3500, hits solidly ever time. higher rpms, seems to go away a little, maybe because it's hitting the block sooner.

if that were the case, I'd need that part of the crank ground, and a new set of crank bearings. can this be done with the motor in the car? in terms of hours, easier to pull the motor?
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Last edited by pdxmotorhead; 03-02-2011 at 07:28 AM.
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Old 03-02-2011, 08:24 AM   #13
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I'm not sure about the idea of the crank bearing being gone all together. I would think that would make a terrible noise, even at idle (which is 700 revs per minute - pretty quick with no bearing) Its not worth it in my opinion to try and remove the crank
<link removed> <link removed>
(It has to be removed to polish the bearing surface) with the
engine in the car, you still would have to pull the timing chain
and unbolt the transmission. I've never seen a engine with a
main bearing gone without a badly damaged/broken crank.
The bearing cannot "get out" without being ground to small bits.
<link removed>

Last edited by 1996 328ti; 03-02-2011 at 07:05 PM.
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Old 03-02-2011, 09:24 AM   #14
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Default Having the same issue with mine!

I decided to not even play around with the motor in my 318ti and went and found one with a mere 77,000 miles on it to swap out!
Sounds as though I spun a rod bearing and you can't shim these as I was told. Better to be safe than sorry and just swap out.
*Sidenote*
Got the trans. with the motor from the same car. All for a whopping $1575! : )
This babies gonna run for a long time to come. Gonna do a minor refresh to this engine with new seals, gaskets and timing set and new filter and fluid for the trans.

All this in the past two weeks. Had to buy a car in the meantime, VW, now I've got a Eurotrash driveway! lol! : )

Looking forward to that video and if you need it, I have the service manual I can send you pdf. Just need your email.
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Old 03-02-2011, 09:02 PM   #15
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Price everything carefully before you tear in tot he motor, I've gotten quotes north of 600 bucks for a gasket set! The "timing set" is also cubic dollars. Shop carefully!

Service the cooling system piping on the motor before you install it, its a service item see the forum for details.

Dave
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