That "tinking" sound from cooling engine

[SmithSwede]

All the air-cooled bikes I've owned, certainly including the Guzzi, make a distinctive "tinking" sound after you turn off a really hot engine and let it cool.

Why?  I've always loved the sound--just curious why.

None of my water-cooled bikes do it.   

I don't think it's as simple as a hot metal cooling off.  You don't hear this sound from hot pots and pans cooling off (or from liquid cooled engines).

I'm thinking maybe something to do with the cooling fins, which have to have a huge heat gradient and are capable of making plenty of noise.

Does it make the same sound when you start a cold engine and it warms up, but you don't know it because you can't hear it over the engine noise?

[oldbike54]

 Think it is just a normal sound amplified by the cooling fins . I've owned several old Brits with cast iron cylinder heads and barrels , the sound was different and not as pronounced , probably due to the rate of cooling , and the difference in weight .

 Dusty

[Sasquatch Jim]

 It is the engines' version of post exercise sweating.

[Yeahoo Whoyah]

The sound came from heat shields on the exhaust system on several different bikes I've owned that made those sounds when cooling.

[Triple Jim]

Yeah, any place where two pieces of metal are in contact, there can be relative motion as they cool and shrink at different rates and/or in different directions.  The ticking is the metal parts sliding a little and then sticking, repeating.

[rboe]

At one time folks (so I've been told) thought it was the cooling fins but I'm inclined to side with the sheet metal on the exhaust as several cars I know do the same thing (and they have plenty of exhaust shields).

[ITSec]

It's happened on motorcycles (both air and water-cooled) and sports cars I've owned. I'm of the schools that says it's likely cause by seismic movements where two unlike metals are in contact (heat shield with block, block with head, head with valve cover, etc.). It was loudest on a Dodge Daytona Turbo Z  my wife insisted on buying back in the 80s. Three years later she begged me to sell the piece of junk. Biggest depreciation bath I ever took...

[Penderic]

The tinkeling sound can be eliminated by making the cooling fins on the cylinders thicker nearer the barrel and thinner near the outsides.

So I have been told.

[Triple Jim]

The tinkeling sound can be eliminated by making the cooling fins on the cylinders thicker nearer the barrel and thinner near the outsides.

So I have been told.

How does the person who told you that think fins make noise when cooling?  Unless there are two parts in contact, moving relative to each other, there's no noise.

[Penderic]

It was a tech note I saw on the newer Triumph Twin engine changes and one of the changes made was to 'taper the thickness of the cooling fins to reduce the crinkling sounds made when the engine is cooling off".  Or was it 'to make the fins uniform in thickness to reduce the .....'

This was about a year or so ago, so maybe I remember wrong. 

One of the two.





 

[Triple Jim]

I guess even the guys writing tech notes can be confused.   

[Huzo]

Dunno, but damn good topic. A beautiful sound and the smell of hot aluminium that comes with it, defines a lifestyle that I'm sorry for anyone who hasn't shared in. Good one SS !

[oldbike54]

I guess even the guys writing tech notes can be confused.   

 Actually Jim , and don't ask me to give an engineering treatise here , but I have also read that . Seems the reason is that making the fins thicker at the base reduces the amplification provided by the fins .

 Dusty

[Huzo]

One of the guys mentioned differing shrink rates, he's gunna be real close I reckon. If he's right and I think he is, will it be the moving of the metal relative to the fasteners, 'cos it's similar to the "tink" sound that you get when you crack a dry bolt loose holding a thin heat shield or such. The sliding of the metal under the bolt head or the two flat plates moving against each other as stated earlier.

[Triple Jim]

Actually Jim , and don't ask me to give an engineering treatise here , but I have also read that . Seems the reason is that making the fins thicker at the base reduces the amplification provided by the fins .

 Dusty

No argument there, but a noise amplification effect at the fins is different from causing the noise.  I'm very familiar with the fins on my H2's cylinders and heads making any piston slap noise very audible.  But the fins aren't making the noise, the pistons banging on the cylinders are.  Yamaha put blocks of rubber between fins on some of their 2-strokes to make the engine quieter.

[oldbike54]

No argument there, but a noise amplification effect at the fins is different from causing the noise.  I'm very familiar with the fins on my H2's cylinders and heads making any piston slap noise very audible.  But the fins aren't making the noise, the pistons banging on the cylinders are.  Yamaha put blocks of rubber between fins on some of their 2-strokes to make the engine quieter.

 True . Someone mentioned earlier that his car exhaust made a tinking sound , I'm betting that the heat shield being of thin metal is amplifying the sound .

 Yeah , the rubber blocks probably were to reduce the "ringing" on aluminum cylinder 2 smokers , which while caused by a different thing was also amplified by the finning . The tinking sound caused by cooling are percussion waves creating noise .

 Dusty

[Triple Jim]

True . Someone mentioned earlier that his car exhaust made a tinking sound , I'm betting that the heat shield being of thin metal is amplifying the sound .

Yes, I'm sure the biggest sources of the noise are things like exhaust heat shields and exhaust system joints, but I'm sure it's possible that hard mounted engines could move slightly against the frame mounts as the temperature changes, and make noises too, for example.  Heck, my waffle iron makes similar noises as its thermostat turns the heating elements on and off.

[CalVin2007]

One of the guys mentioned differing shrink rates, he's gunna be real close I reckon. If he's right and I think he is, will it be the moving of the metal relative to the fasteners, 'cos it's similar to the "tink" sound that you get when you crack a dry bolt loose holding a thin heat shield or such. The sliding of the metal under the bolt head or the two flat plates moving against each other as stated earlier.

     This is it.    My wood stove makes the same sounds as it cools,and also as it heats up. Listen closely and the heating/cooling sounds are enough different that one can tell if the temp is rising or falling. See what heating a house with wood for 35 years will make a person notice? 

  Terry

[oldbike54]

 Back to the original question , the Swede points out that his water cooled bike doesn't make the sound . We are in agreement that the lack of fins , and the muffling effect of the water jacketing probably makes the sound inaudible . ("We" being The Swede and me)

 Dusty

[Triple Jim]

Maybe his water cooled bike doesn't make the noise, but I bet there are owners of water cooled bikes on this board who hear ticking sounds from their exhaust system as they cool.  After all, the exhaust pipes aren't water cooled.   

[oldbike54]

Maybe his water cooled bike doesn't make the noise, but I bet there are owners of water cooled bikes on this board who hear ticking sounds from their exhaust system as they cool.  After all, the exhaust pipes aren't water cooled.   

 Wait , they aren't ?

 Dusty

[rocker59]

It's the exhaust.  Cars do it, too.

[Huzo]

Back to the original question , the Swede points out that his water cooled bike doesn't make the sound . We are in agreement that the lack of fins , and the muffling effect of the water jacketing probably makes the sound inaudible . ("We" being The Swede and me)

 Dusty

And maybe the the engine temp is more uniform so differences aren't as great, so less relative motion ???

[oldbike54]

And maybe the the engine temp is more uniform so differences aren't as great, so less relative motion ???

 Yeah , we discussed that idea also , more uniform heating and cooling .

 Dusty

[sib]

Yamaha put blocks of rubber between fins on some of their 2-strokes to make the engine quieter.

C'mon, guys/gals, were supposed to be Guzzi-familiar, here.  Small block Guzzi's have had rubber dampers between the cylinder fins for ages.  They're supposed to dampen vibrations of the running engine, I doubt the're there to suppress the tinking of a cooling engine.

[Triple Jim]

C'mon, guys/gals, were supposed to be Guzzi-familiar, here.  Small block Guzzi's have had rubber dampers between the cylinder fins for ages.  They're supposed to dampen vibrations of the running engine, I doubt the're there to suppress the tinking of a cooling engine.

Hey, don't blame me for not knowing that!  The only Guzzi I've owned is my Mille, and I rarely see a small block in person, other than from a distance.   

I'm sure you're right about the reason for the rubber dampers, since the tinking is almost certainly from the exhaust parts and has nothing to do with fins.

[SmithSwede]

I don't see how it can be the exhaust.  A water-cooled bike has essentially the same exhaust system as an aircooled engine.  Yet water-cooled engines don't make that tinking sound (or not nearly as much as an aircooled engine.)

I'd bet the temperature of exhaust headers and exhaust gas is the same. 

Somebody needs to bring a hunk of an old engine to a rally.   We'll stick it in the fire, fish it out, and see how it tinks.   Then we could loosen all the bolts a bit and see how that affects tinking.

[Nic in Western NYS]

Yet water-cooled engines don't make that tinking sound (or not nearly as much as an aircooled engine.)

Not sure the group agrees that this assertion is true.  Or if true in certain cases, that there isn't a confounding variable. Fascinating topic - I've had some cars that tinked pretty loudly.

[Triple Jim]

Right, your particular motorcycles support your hypothesis, but aren't representative of all motorcycles.  My H2 doesn't tink at all, yet my Mille does a little bit.  Both are air cooled, of course.  Most cars I've owned tink quite a bit if you lift the hood and listen, and they're all liquid cooled.  My wood stove tinks a lot if you build up the fire, or cut off the air intake to cool the fire.

[oldbike54]

 I agree with the Swede . Pretty sure when you are hearing an exhaust tink it is do to a heat shield being attached . Now , it may be coming from the header pipe/cylinder head contact points , steel into aluminum , but as I said before , my old cast iron head Brits didn't tink , at least not very loudly .

 Dusty