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Weird engine noise

pettaw on Thu July 07, 2005 12:23 PM User is offline

Year: 1986
Make: Volvo
Model: 360
Engine Size: 1986
Country of Origin: United Kingdom

So I did get the rebuild done etc. All back together now and fired up and running really well. I've done about 1000 miles now. I put that 'running in' oil in for the first 300 miles and then changed it for a Castrol semi-synth magnatec. After finally getting the tappet adjustment right, (don't you just hate those stupid shims?) its running smoothly with the pleasant whine of nice tight bearings.

Anyway, to my query. It does however have this annoying noise that sounds like something resonating. I did think it could be a big end noise, but it can't be because I pulled all the plug leads in turn and the noise was still there. Its also not belts because I took then off and also the timing belt cover off and it didn't make a difference.

Erm, it occurs twice in the rev range, but low down. First about 1200ish and then again about 1400ish. There is also an exhaust rumble, because I probably haven't put something on straight, but thats a much lower grumbling noise. This is a resonating higher pitch vibration. Occurs only when the engine's warm too, not from cold. Engine load makes no difference either, neither does dipping the clutch.


I made a recording of it. I'm just gently raising and lowering the revs, with the clutch depressed.

360noise.mp3

pettaw on Fri July 08, 2005 12:34 PM User is offline

harmonic balance prob sounds like the one. Is it gonna cause harm or do I need to strip down and redo everything.

I bought the rods in a kit of 4. The pistons come separately, but knowing Volvo dealer parts, are usually completely ready to go. Checked all the ring end gaps, didn't have to adjust one of them.

bohica2xo on Fri July 08, 2005 2:31 PM User is offline

Sounds like a grounding problem to me - not the electrical kind.

Do you have something touching body metal that is transmitting engine vibration? A hose, the exhaust system, a battery cable, anything like that can produce noises by drumming on the sheetmetal. A 4-banger has strong harmonics in those rev ranges, and can really be tough to isolate - are the motor mounts new?

If you have no unusual vibration from the engine at higher rev ranges, especially at the 2nd or 3rd order of the range you hear the noise in, then I would say the internals are fine. Always a good idea to match the rod and piston weights when assembling an engine though.

Your Harmonic Balancer is responsible for damping a lot of harmonics. If the rubber has hardened with age, it will not have the dynamic range to deal with the strong pulses at low rpm, but will do fine at higher speeds - this is usually noticable on inline 4's more than others.


.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

pettaw on Fri July 08, 2005 3:06 PM User is offline

Do you mean the rubber on the crank pulley? Would it still do it with all the belts disconnected? Apart from the timing belt obviously, but that goes on a gear, not related to the front grooves.

The motor mounts are original, but they're heavy duty ones and don't have a history of going. They're also expensive at nearly 200 USD each.

Edited: Fri July 08, 2005 at 3:07 PM by pettaw

bohica2xo on Fri July 08, 2005 6:17 PM User is offline

The harmonic balancer is active anytime the crankshaft rotates. It damps torsional harmonics by the reaction mass of the outer ring vs the inner ring, against the rubber.

I am not familar with your engine mounts specifically, but in general they tend to be an elastomer of some sort. Many mounting assemblies incorporate metal fitments that get closer to each other as the rubber compresses with time. On some mounts this results in the metal touching or "grounding", and the transmission of noise. At the particular rev range you are dealing with, the amplitude may be high enough to make contact.

Some of the really expensive mounts are liquid filled or so called "hydraulic" isolators. Many of these have a history of leaking and collapsing with age, and can result in annoying vibrations at idle and low speed.

Don't forget to check the transmission mount as well.


.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

pettaw on Sat July 09, 2005 2:30 AM User is offline

Quote
Originally posted by: bohica2xo
The harmonic balancer is active anytime the crankshaft rotates. It damps torsional harmonics by the reaction mass of the outer ring vs the inner ring, against the rubber.

Some of the really expensive mounts are liquid filled or so called "hydraulic" isolators. Many of these have a history of leaking and collapsing with age, and can result in annoying vibrations at idle and low speed.


Don't forget to check the transmission mount as well.

.


OK, so it prob means I should get a new damper then.

Those sound like the ones. I heard hydraulic mentioned. Might well be why the ehaust insists on vibrating slightly all the time, although I have to say the engine doesn't 'look' like its got loose mounts. So I prob need new mounts as well.

Its strange that the harmonic balancer is active even if there are no belts on the pulleys, beyond my understanding....

The transmission is a transaxle system that sits over the rear axle and is connected to the engine with a propshaft, housed inside a metal torque tube, which means although the design is good, the g/box/rear diff are absolute hell on earth to get in and out. Its a two day job for me although prob the 'professionals' would book about 6 hours, so fingers crossed.


Thanks for the tips Bohica.

bohica2xo on Sat July 09, 2005 2:17 PM User is offline

Pettaw:

Before you spend a bunch of money, look for any grounding that may be making the noise.

Collapsed "hydraulic" mounts are mostly a nusiance. You say the engine mounts seem "firm", and that may be exactly why you have the vibration - the engine no longer dances around on squishy mounts. Not a big issue, not unsafe - you can probably run those mounts another 200,000 km's

Quit driving the poor thing like it is an MG or a tractor - spin it up to about 3k and it will be happy....



Nick:

The harmonic balancer is actually more than you see at first glance. The story about breakawy is nonsense - even a 1.6L honda makes enough torque to snap a serpentine belt without straining.

The damper relies on the hysteresis of the rubber to kill harmonic vibrations in the crankshaft. Many racers have found out that replacing one with a solid unit results in a broken crankshaft. If detroit could replace them with a 2 dollar stamping, they certainly would. Some engines with natural balance (flat opposed 4's and 6's) do not need a damper.


.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

pettaw on Sat July 09, 2005 5:24 PM User is offline

thanks for the heads up. Have already checked for wires etc touching the body and found none.

A new crank pulley/harmonic damper was only 70 quid, (about 130USD) which frankly is cheap for Volvo. The new mounts come in at 90 quid (about 170USD) which is darn expensive, but the entire engine does hang off only two mounts, with any tilt to the rear being supported by that torque tube/gbox mounts I talked about earlier.

I don't pussy foot around, but unfortunately when pulling off in traffic, which you're always doing in London, you always end up going through that range. This engine likes being revved though, the camshaft timing is such that the max torque is at about 4K although, being high compression it does have a good lower down torque too.

bohica2xo on Sat July 09, 2005 7:39 PM User is offline

Nick:

That is precisely the reason for the damper - to emulate the effect of a 40 pound chunk of iron 16 inches in diameter, without the bulk or weight.

Most american V8's have dampers, and the belts are not involved with the damper ring. The Volvo is unusual in the fact that it adds the accessory drive mass to the ring.

If you were to take the failed damper from your ford, and press the ring off, clean off the rubber - and reinstall it you would be unhappy with the result. If it was not necessary, nobody would buy a new one. Here is an excerpt of an SAE Paper on Crankshaft Torsional Harmonic Control. The references to the SAE paper are at the bottom, you can read the whole thing if you are an SAE member.



Pettaw:

Good to see you will do it right. Since your damper drives the belts as well, replacing it is a good plan - having one fly off at 5500 rpm is never fun. New motor mounts will probably make the car smoother on the road. I was of course only joking about driving it like an MG. A torque peak around 4k makes them nice to drive in traffic, sounds like a fun car.


.


.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

pettaw on Thu July 14, 2005 10:30 AM User is offline

Well, I changed the damper and also the mounts.

Strange thing, when I shook the old mounts I could hear the oil sloshing around inside, and when I shook the new ones I couldn't hear anything. Also the new mounts are slightly shorter than the old ones, meaning the engine sits higher in the bay. Its a good thing because its now clearer from the front axle member. So those hydraulic bits were definitely worn out.

New damper went on too.

The car is definitely smoother all round and less rumbly. Unfortunately that harmonic twice in the rev range 1200 and 1400 ish is still definitely there. Any other ideas guys? The new mounts, expensive as they were, were definitely worth doing, but I still need the source of this dang noise. I also checked carefully to make sure nothing's touching the engine.

pettaw on Thu July 14, 2005 4:30 PM User is offline

You're probably right Nick. Thing is thinking about it I kinda remember when I put the other engine in from the scrapped car, that had some noise right around those revs too, but that engine had other issues around the fan belts and I associated that noise as being belt noise but maybe its an inherent resonant Volvo block issue.

Anyway, when it ceases to become my daily driver, I'll be taking that sucker apart and getting a machine shop to balance everything in sight, including flywheel, harmonic damper and all the rods/pistons.

Thanks for the help, the car certainly drives smoother, even if the noise is still there!

Edited: Thu July 14, 2005 at 4:32 PM by pettaw

TXAB on Thu July 14, 2005 8:23 PM User is offline

Quote
Originally posted by: pettaw

Anyway, when it ceases to become my daily driver, I'll be taking that sucker apart and getting a machine shop to balance everything in sight, including flywheel, harmonic damper and all the rods/pistons.

Don't forget to have that crank balanced as well. I've had many stock cranks that were poorly balanced to begin with.

-------------------------
"Don't get stuck on stupid!"
---- Lt. Gen. Russel Honore

bohica2xo on Thu July 14, 2005 8:47 PM User is offline

Balancing a performance engine build is always a good idea. The engine may well have a natural vibration at that speed, but a good balance will certainly minimize it.

The hydraulic mounts work well, but they do wear out. The new mustang has a bunch of liquid filled suspension bushings - can't wait to see what those cars are like in a few years....


You can do a lot of the balancing yourself. Matching Piston weights, and Con Rod weights is easy. End for End balance on the rods is also not too hard. All you need is a decent balance, something that will resolve a tenth of a gram. If you send a good balance shop a set of rods and pistons that are matched, all they have to do is the dynamic work on the rotating parts.

Make sure you send it all - the crank, balancer, flywheel (with bolts), rods, pistons (with pins), timing drive, keys, etc. The balance shop will want to weigh your rods and pistons, but if they are matched, they will not work on them. The add bob weights to the crank throws, and spin the assembly - they need the piston & rod weight to calculate the bob weights. Once they spin it, they can dynamically balance the whole rotating assembly.


.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

pettaw on Sun July 17, 2005 1:26 PM User is offline

It wasn't really a performance build. More just a restoration to a family car, but I take your points.

Erm, the weird thing is I don't seem to hear this noise at any other revs, and I've had the car up to the redline a couple times now. Maybe the engine noise is drowning it out, but wouldn't the amplitude get bigger?

bohica2xo on Sun July 17, 2005 1:44 PM User is offline

pettaw:

I still don't think it is an imbalance. Like I said before, it should get worse at the second or third order if it is just rotating mass. Perhaps every one of those engines has that vibration. Most inline 4 bangers have some sort of low speed harmonic.

You have taken great care with this car, based on all of your posts over the past months. I posted the balancing information for you because it looks like you will be doing that just because you want every last bit of vibration gone.

I had a customer that was a perfectionist - I delivered a flat 4 to him fresh off of the dyno several years ago, and I KNEW the balance was perfect. The rod & piston assemblies were within a tenth of a gram, and the end to end balance on the rods were within 2 tenths. The rotating assembly had been dynamically balanced, this engine was smooth. He got it in the car, and it had a vibration. The higher he spun it, the worse it got. He pulled it out, and we put it back on the dyno. Could have put your coffee cup on the block @ 6500 rpm. He looked at me with a surprised look, then went home and got the clutch cover. His clutch cover was out of balance, and not a lot.

I think if you have a rotating mass error, it is small.

.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

pettaw on Thu December 08, 2005 1:28 PM User is offline

heh, well Bohica I ended up tearing the whole thing apart and getting the whole assembly balanced......The noise is still there, so I guess I'll just have to live with it. Had the guy listen to it at the machine shop, but they're machinists, not engine builders or techies so he didn't really have much clue what it was, although he thought it wasn't a serious thing. Its a shame we don't have the kind of places you have over there where you can find a guy who can hear a rod knock from down the road....those people are hard to come by here in the UK, well at least I haven't found one yet. I also got a few of my Ovlov friends to listen to it and they didn't know what it is either.

Never mind. I'll do a new recording at the weekend and you can see if its changed at all.

Edited: Thu December 08, 2005 at 1:30 PM by pettaw

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