Tick / grinding noise at 0.36x crank rpm.,
05-15-2018, 11:18 AM
#1
Tick / grinding noise at 0.36x crank rpm.,
My engine (3.4) developed a tick/grind noise especially when cold. It’s audible in the cabin as well as under the car. At 780rpm idle, the tick seems to be 290rpm. Definitely not 0.5x crankshaft, but slower (i can tell cause i also havea noisy lifter everynow and then, definitely the lifter is faster.
I’d upload the soundbite but my iphone doesnt let me.
Ratio to crank seems to be 0.36:1, anyone have an idea?
I’d upload the soundbite but my iphone doesnt let me.
Ratio to crank seems to be 0.36:1, anyone have an idea?
05-17-2018, 07:01 PM
#2
Seems like this topic only got approved after it was well and truly buried. Anyway, I figured out what it was by carefully listening to the tick.
listened and recorded the sound, measured the periodicity of the grind and determined it to have a 'frequency' of 316 RPM.
Now, nothing in the car syncs up with 316 RPM. Idling, my engine runs 780 rpm. Camshafts go 1/2 that, so 390 RPM. The IMS shaft goes 0.67x crank, so 523 RPM. Couldn't think of anything else spinning at this weird fraction, until it hit me; the ***** in a bearing go 1/2 the speed of the races, while the ***** also have a shorter distance to travel because they're on a lower radius (more towards the center, smaller circle than the outer race), so complete 1 revolution 'faster'.
Correcting for the lower circumference the ***** have to travel compared to the outer race, which is a factor 1.24, I came out on the ***** inside the IMS bearing rotating with a frequency of 523 (shaft RPM) divided by 2 (***** go twice as slow) times 1.24 (distance in travel between outer race and ***** itself) = 324 RPM. Which is very close to the 316 I measured from the sound.
So it's the IMS going. Sounded like this:
listened and recorded the sound, measured the periodicity of the grind and determined it to have a 'frequency' of 316 RPM.
Now, nothing in the car syncs up with 316 RPM. Idling, my engine runs 780 rpm. Camshafts go 1/2 that, so 390 RPM. The IMS shaft goes 0.67x crank, so 523 RPM. Couldn't think of anything else spinning at this weird fraction, until it hit me; the ***** in a bearing go 1/2 the speed of the races, while the ***** also have a shorter distance to travel because they're on a lower radius (more towards the center, smaller circle than the outer race), so complete 1 revolution 'faster'.
Correcting for the lower circumference the ***** have to travel compared to the outer race, which is a factor 1.24, I came out on the ***** inside the IMS bearing rotating with a frequency of 523 (shaft RPM) divided by 2 (***** go twice as slow) times 1.24 (distance in travel between outer race and ***** itself) = 324 RPM. Which is very close to the 316 I measured from the sound.
So it's the IMS going. Sounded like this:
05-17-2018, 07:39 PM
#4
Well I already solved it, it was coming from the IMS and the periodicity of the sound corresponds to the rotation rate of the ***** inside the bearing which is unique in the motor. Nothing else spins at 324 RPM. I just figured I'd post back with the results for anyone looking for it in the future 
I'm pulling it apart as we speak.
I'm pulling it apart as we speak.
05-17-2018, 08:06 PM
#5
Burning Brakes
Well I already solved it, it was coming from the IMS and the periodicity of the sound corresponds to the rotation rate of the ***** inside the bearing which is unique in the motor. Nothing else spins at 324 RPM. I just figured I'd post back with the results for anyone looking for it in the future I'm pulling it apart as we speak.
I'm pulling it apart as we speak.
05-17-2018, 08:08 PM
#6
Haha, that's exactly what a friend said who was in my workplace with me when he saw me crunch the numbers after making a spectograph of the sound on my PC. "There must be a way to make an app for that, "IMS Failure Detector" or something".
Haven't found one yet, but sure would be useful.
Haven't found one yet, but sure would be useful.
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05-17-2018, 08:36 PM
#8
Yeah I started it with the belt off, suspected the water pump at first. Same sound. Ferritic metal grit and larger debris (1-2mm) in the filter which is only 300km old. All pretty clear :P
05-19-2018, 10:23 AM
#10
I can't believe you ran the car that long hearing that noise. Shut it down and tow it to the shop. Sounds like a bag of marbles in there, which coincides with your IMS theory. Side note, nice work on the math, detective. LOL
05-19-2018, 10:29 AM
#11
Should have been more clear about that; the vid is not mine but someone elses. I linked it as it's the same sound. Car's been stationary after hearing the sound, and is not going to be started before the IMS is fixed.
05-19-2018, 10:32 AM
#12
PHEW LOL. Well I can't believe that guy ran his car sounding like that. Every rotation is damage. 780rpm Idle, almost a one minute video, he basically was taking a hammer and chisel to his motor 700 times to post that lol. Not smart.
05-19-2018, 10:42 AM
#13
Rennlist Member
Interesting. Let us know what you find. The video (while not yours) kinda sounds like 1/2 crank speed to me, or at least I would have assumed that. I would never have figured out 1/3rd RPM like you did. If you tear the whole thing apart and it’s the IMS, let us know.
05-19-2018, 10:57 AM
#14
Definitely will, should be coming out this week. But I am really confident in this analysis :P
I went all Audacity on my recorded soundfile, and got the frequency from the spectogram. But if you tap along with the vid here, you'll get a general measurement of how many beats per minute (= rpm): https://www.all8.com/tools/bpm.htm
I went all Audacity on my recorded soundfile, and got the frequency from the spectogram. But if you tap along with the vid here, you'll get a general measurement of how many beats per minute (= rpm): https://www.all8.com/tools/bpm.htm
