Technical Metallic Rattle

[FR85]

Folks,

Latest one, 126 650 engine, I get a strange metallic rattle when you go above idle that simmers out at high revs and then comes back into it when passing "a point" to return to idle. There is obviously a frequency/vibration level that is met to trigger this.

Have fitted a rebuilt carb recently and I've done the valve clearance a couple of times as it was backfiring and still is (think it's timing) when it's decelerating so it to me isn't valve clatter.

Tomorrow when it's cooled down I'm going to take the belt off and see if it's something in the fan housing/tinware. I've tightened everything tinware related that I can get a socket on.

Not sure if the video will attach or if it does if it's clear audio wise.

Ta muchly!

 

[lazylobster]

Have you checked the tin work, missing bolt and it rattles like a rattlesnake !

 

[Ant Knox]

Check the thermostat flap. I had similar, it turned out that the nut that attaches the flap to the thermostat actuator arm had vibrated free, leaving the flap swinging freely and rattling like a coin in a tin can whilst driving.

 

[FR85]

Have you checked the tin work, missing bolt and it rattles like a rattlesnake !

I've been through the tinware and I don't see anything missing and I tightened up anything that was in sight. Engine was hot last night so I couldn't go much further without getting the burn cream involved so I'll give it another going through tonight.

Cheers

 

[FR85]

Check the thermostat flap. I had similar, it turned out that the nut that attaches the flap to the thermostat actuator arm had vibrated free, leaving the flap swinging freely and rattling like a coin in a tin can whilst driving.

The stat is solid, it's opening and closing itself so I think it's all connected as it should be.

If it was up to my ear I think it's between the carb and the fan, that to me is where it's most audible but I'm not 100% certain what's in there or if it's just an open air channel?

Thanks for the suggestion all the same but I think it's more centrally located!

 

[giardini]

At this remote, and much else having been eliminated, if it was mine I'd check that the dynamo strap is tight, and/or for signs of the fan blades
contacting the housing.

 

[FR85]

At this remote, and much else having been eliminated, if it was mine I'd check that the dynamo strap is tight, and/or for signs of the fan blades
contacting the housing.

I don't think it's the fan as at idle it's fine and at high revs it also seems fine. It to me sounds like loose bolts as when it hits a frequency/pitch it comes in and then goes away again. I work in music so it's the only way I can describe it, sympathetic resonance if you follow me. It would be like fret buzz on a guitar.

 

[fiat500]

I don't think it's the fan as at idle it's fine and at high revs it also seems fine. It to me sounds like loose bolts as when it hits a frequency/pitch it comes in and then goes away again. I work in music so it's the only way I can describe it, sympathetic resonance if you follow me. It would be like fret buzz on a guitar.

I think you've just coined a euphemism for the infamous noise output of even a well-adjusted Fiat 500 engine, " Sympathetic Resonance".

 

[Toshi 975]

It might be wise to inspect the fan. They have a strange type of construction in that the separate vanes fix to the back and front plates by simple pips that go through slots are just given a little twist to keep them in place so no welding. With age and perhaps a little corrosion the vanes can come loose up to the point where the fan will self destruct. Also within the fan housing there is a thin sheet steel divider that I believe is there to direct cooling air more to the cylinder head. Held on the front side by two M6 bolts above the Dynamo or alternator but it is fixed to the back fan housing by just a couple of spot welds that often break away leaving one side free to vibrate.

 

[fiat500]

It might be wise to inspect the fan. They have a strange type of construction in that the separate vanes fix to the back and front plates by simple pips that go through slots are just given a little twist to keep them in place so no welding. With age and perhaps a little corrosion the vanes can come loose up to the point where the fan will self destruct. Also within the fan housing there is a thin sheet steel divider that I believe is there to direct cooling air more to the cylinder head. Held on the front side by two M6 bolts above the Dynamo or alternator but it is fixed to the back fan housing by just a couple of spot welds that often break away leaving one side free to vibrate.

Yes, I had one that was really crusty-rustythat I soaked in acid to tidy it up.. Although pitted, it then otherwise looked like new, and in ignorance, I assumed I had done a good job. A few hundred miles later it had to be replaced because every single peened-in blade had rattled loose.

 

[FR85]

I think you've just coined a euphemism for the infamous noise output of even a well-adjusted Fiat 500 engine, " Sympathetic Resonance".

It should be quoted in the workshop manual!!

 

[FR85]

It might be wise to inspect the fan. They have a strange type of construction in that the separate vanes fix to the back and front plates by simple pips that go through slots are just given a little twist to keep them in place so no welding. With age and perhaps a little corrosion the vanes can come loose up to the point where the fan will self destruct. Also within the fan housing there is a thin sheet steel divider that I believe is there to direct cooling air more to the cylinder head. Held on the front side by two M6 bolts above the Dynamo or alternator but it is fixed to the back fan housing by just a couple of spot welds that often break away leaving one side free to vibrate.

I was delighted to see yourself chiming in here! What is the best way to inspect the fan and in theory if I have to go in deep am I best off to just buy all new components and just fit them and have the lot fresh?

Mine has an alternator so is there a difference in fans?

Thanks!

 

[Toshi 975]

I was delighted to see yourself chiming in here! What is the best way to inspect the fan and in theory if I have to go in deep am I best off to just buy all new components and just fit them and have the lot fresh?

Mine has an alternator so is there a difference in fans?

Thanks!

No difference in fans, just out of interest a few years ago I bought a couple of new fans and immediately had them powder coated for protection and to give them a little more integrity. On more recent engines I have tended towards the alloy fans. Have you ever had the fan housing off your engine? On my high mileage 500L engine I had to remove the complete housing and I have in the past found small spaners, a socket, a spark plug and assorted nuts and bolts inside the housing but my 500L was so dirty with oily grime. I cleaned it all up and painted it before assembling. It was almost like I had an air freshener in the car when driving, no more horrible oily smells coming into the cabin.
I would think about removing at least the rear fan housing and maybe the top.
New components? Well I would just check the condition of the fan and for any loose vanes.

 

[FR85]

No difference in fans, just out of interest a few years ago I bought a couple of new fans and immediately had them powder coated for protection and to give them a little more integrity. On more recent engines I have tended towards the alloy fans. Have you ever had the fan housing off your engine? On my high mileage 500L engine I had to remove the complete housing and I have in the past found small spaners, a socket, a spark plug and assorted nuts and bolts inside the housing but my 500L was so dirty with oily grime. I cleaned it all up and painted it before assembling. It was almost like I had an air freshener in the car when driving, no more horrible oily smells coming into the cabin.
I would think about removing at least the rear fan housing and maybe the top.
New components? Well I would just check the condition of the fan and for any loose vanes.

I have never had it off at all but I know where you are coming from, I have had to fish out a spark plug in the past.
You could be onto something though, previous owner cross threaded the rear plug and put a helicoil in there so that side of the engine has a history, something could have dropped in. Also, before I bought it he had replaced bearings in the alternator so there could well be something in there rubbing.

I'll pull the belt off and run it for a minute to eliminate the fan. If it is the fan I'm not looking forward to that job......with a 5 month old in the house that could take a few weeks to do from start to finish!!

 

[FR85]

Hi All,

So the previously mentioned 5 month old hasn't let me out of the house to play in the shed! If he wants to inherit it he may give me an hour or two alone!

Going to remove the fan belt and try and get to the bottom of the frequency induced rattle. Then am going to look at valve gapping again using the rule of 5.
Finally timing, she's backfiring through the exhaust when I come off the power or am down shifting. From experience, which way do I need to turn the cap, clock or anti clock? Reason I ask this simple question is the car is running so just needs to be sweetened. Timing never slipped, I had an electronic ignition go dodgey and I've reverted back to points, someone has marked the distributor with tipex so I have a reference if I go completely out.

Thanks all!

 

[FR85]

So the metallic noise is valve chatter. Went through it quickly tonight, did clearances quickly and now they are even more chattery. Must admit I was in a bit of a rush.

Also, had a look at timing, adjusted it with a test light, closed everything and it wouldn't start. Tried again, loud bang....ears ringing and soiled trousers, I realized I'd put the plug leads back on the cap in reverse. Reversed the reversal and went to the old timing marks and it started but the valve chatter is too much.

Tomorrow is another day and efforts will be doubled.

I much prefer my 850!

 

[FR85]

The saga continues, went through it again tonight, did static timing (retarded it a bit) and redid the valve clearances a few times using the rule of 5 that has been mentioned a few times. Went back and forth over them so I'm at .20 on the inlets and .25 on the outlets. At idle with the timing done it's silky, ticking over beautifully and seems to be a lot more responsive. Rev it up and let it return to idle and I'm now clear of the backfiring through the exhaust. Happy days.
But the metallic noise comes into it above idle and then goes out of it again when it returns to idle.
I ran it for a minute with the fan belt off and it's still the same so I assume the fan section is ok.
Its metal on metal vibrating and for the life of me I cannot find it.
I think I'm going to pull the tinware off the top of the fan side and have a look, something silly is sitting somewhere silly and it's driving me demented.

 

[fiat500]

The saga continues, went through it again tonight, did static timing (retarded it a bit) and redid the valve clearances a few times using the rule of 5 that has been mentioned a few times. Went back and forth over them so I'm at .20 on the inlets and .25 on the outlets. At idle with the timing done it's silky, ticking over beautifully and seems to be a lot more responsive. Rev it up and let it return to idle and I'm now clear of the backfiring through the exhaust. Happy days.
But the metallic noise comes into it above idle and then goes out of it again when it returns to idle.
I ran it for a minute with the fan belt off and it's still the same so I assume the fan section is ok.
Its metal on metal vibrating and for the life of me I cannot find it.
I think I'm going to pull the tinware off the top of the fan side and have a look, something silly is sitting somewhere silly and it's driving me demented.

Check underneath that the metallic connecting tube for the heater isn't loose or contacting the body or the exhaust.

 

[RalphM]

Backfiring is often connected to air leaks in the exhaust system,
so it may be worth a good look round that.

 

[FR85]

Check underneath that the metallic connecting tube for the heater isn't loose or contacting the body or the exhaust.

I'll be going in under it on Tuesday with mirrors and the whole shooting match. It really sounds like its between the fan and carb.