Engine whine at mid RPMs

#1
After I rebuilt the engine on my 1968 2000 TC, I have a whine at mid RPMs that I do not recall from before the project. It persists regardless of the gearbox or clutch "position". It happens sitting still and when in motion. I removed the fan belt for a short run to eliminate the possibility of it being the water pump, fan or alternator. Nothing changed. I checked the top chain tensioner and it looks fine. I have attached a zipped .wav audio file of the noise. You can hear that the noise starts as the engine speed goes above idle and then fades as the engine speed increases further. It returns as the engine speed drops through the same speed band. If anyone has any ideas, I would be grateful.
 

Attachments

Demetris

Well-Known Member
#2
This is really strange. What i would do is, with the fan belt removed, use a stethoscope / long screwdriver and try to locate it in the distributor / oil pump / auxilliary drive area. I know, easier to say than to actually do it, but perhaps it's a step forward.
 

chrisw

Well-Known Member
#3
Check your clutch pedal adjustment.. and check that the noise isn't coming from the front of the gearbox, rear of the bellhousing.
 
#4
Check your clutch pedal adjustment.. and check that the noise isn't coming from the front of the gearbox, rear of the bellhousing.
The noise definitely is not originating from the gearbox clutch area. I have been able to eliminate that as a possibility listening through a stethoscope (hose) and by the fact that there is no change with the clutch engaged or disengaged. I am beginning to suspect that it is chain noise but caused by worn chain wheels, either on the cam shaft or the aux. drive.
 
#5
I processed my audio file with a spectrum analyzer to see if I might get some more information on the frequency of the "whine" to support my camshaft chain wheel hypothesis. The analysis shows the noise mostly centered just above 500 Hz with harmonics at 1.2 and 1.7 kHz. I should say that this was using a freeware spectrum analyzer, so the data is not as accurate as it might be. Assuming an engine speed of approximately 2000 RPMs when the noise is bad, the crankshaft rotation frequency is 33.3 Hz. The cam would be turning at half that speed, so 16.66 Hz. I am guessing that there are 32 teeth on the camshaft wheel sprocket. I will have to verify that later, but it is close. One would then expect any chain/gearwheel frequency to have a base frequency of 533 Hz. That is close to what I am seeing in the frequency plot. So nothing to disprove my hypothesis. If the noise was from the crankshaft sprocket wheel, the frequency would be half of 533 Hz. I don't know the number of teeth on the aux. drive chainwheels, so that still remains a possible source of the noise although I think they have significantly less than 32 teeth. The next step is to remove the cover and inspect the chainwheel teeth closely for any significant wear.
 
#6
My recently-rebuilt engine does much the same thing at the same frequencies, albeit not as loudly as far as I can tell, and was quiet before the rebuild. I replaced both chains: one new one is made by AE, the other by Rolon, can't remember which is which. The tensioners are new Rolon items, which seem to have stronger springs than the Renold orginals. Perhaps the whine is from a slight mismatch of a chain to its sprockets, or from extra tensioner pressure. I don't think it's much to worry about, and the whine is reducing as I add miles (now about 2500 since rebuild). There have been problems with the Rolon tensioners in the past, with the rubber pad becoming detached, but I haven't managed to find any recent reports of this (thank goodness).

The sound of yours does seem to have a bit more of an 'edge' to it than mine, but that might be the frequency balance of the recording. Unless your unseen bottom tensioner has lost its rubber pad, but I think the sound would then be very loud indeed. Sdibbers on this forum will know – I believe it happened to his engine.
 

jp928

Active Member
#7
As an aside, but related to chain wear...many many years ago (60s-70s) I met a man with a 1937 14hp Rover. No, not for sale. I gave him my phone no just in case. Years later he called asking for help with the car - wont run, garage no help, diagnosed broken crank. No movement of the valves indicated something to do with cam. Front cover off showed a broken cam chain, badly worn cam gear. And I mean BADLY - once removed it had to be handled with gloves on, as the teeth were VERY sharp, due to the flanks being very badly worn. What now? Took the old chain (duplex even then) to a well known shop in Melbourne, keeping a straight face, not expecting success, but hopeful. They pulled a box straight off the shelf, 'There you go'. Gear? MMMM looks familiar - same teeth, diameter and keyways as a P4, but the hub was thicker - needed 1/4" faced off the back. Crank gear same as a P3. Success!
I suspect that chains and gears need bedding into each other. If they dont, check for a tooth with damage. 512Hz is high C isnt it?
 
#8
My recently-rebuilt engine does much the same thing at the same frequencies, albeit not as loudly as far as I can tell, and was quiet before the rebuild. I replaced both chains: one new one is made by AE, the other by Rolon, can't remember which is which. The tensioners are new Rolon items, which seem to have stronger springs than the Renold orginals. Perhaps the whine is from a slight mismatch of a chain to its sprockets, or from extra tensioner pressure. I don't think it's much to worry about, and the whine is reducing as I add miles (now about 2500 since rebuild). There have been problems with the Rolon tensioners in the past, with the rubber pad becoming detached, but I haven't managed to find any recent reports of this (thank goodness).

The sound of yours does seem to have a bit more of an 'edge' to it than mine, but that might be the frequency balance of the recording. Unless your unseen bottom tensioner has lost its rubber pad, but I think the sound would then be very loud indeed. Sdibbers on this forum will know – I believe it happened to his engine.
Unfortunately I do not recall the manufacturer of the replacement chains I used in the rebuild. I also used replacement Rolon tensioners and replaced both chain guides/dampers. I did not replace any of the chain wheels as they seemed OK. I read about the issues with the Rolon tensioners after I had installed them and disposed of the old ones. I generally have a rule of never disposing of any old parts but broke my rule on them for some reason. Hopefully it is not something I will come to regret. It is good to hear that your noise is reducing over time. It sounds like I need to put a few more miles on and see what happens before I start digging into the engine again.
 

sdibbers

Well-Known Member
#9
I had a Rolon tensioner fail in the bottom of the engine within 500 miles. The sound came from just next to the alternator. When I drained the oil the were swirls of aluminium from where the foot’s baseplate had been eaten by the chain. Not fun to replace either.
 
Top