Technical What might be causing a light metallic rattling noise in the engine?

[smart51]

The other day the car was making a light metallic rattling noise starting at 3000 RPM and getting louder above that. I thought I'd got it when I saw a missing screw from the that bolts to the rear valance of the car. A test drive today showed that it wasn't that. Then there was a snap and the rattle got worse, sounding like something was loose and rattling round. Nothing is visibly loose and everything I can poke with a stick seems firmly attached. I drove home very slowly and carefully. What would you guess could be the cause of the noise?

 

[jolly500]

The other day the car was making a light metallic rattling noise starting at 3000 RPM and getting louder above that. I thought I'd got it when I saw a missing screw from the that bolts to the rear valance of the car. A test drive today showed that it wasn't that. Then there was a snap and the rattle got worse, sounding like something was loose and rattling round. Nothing is visibly loose and everything I can poke with a stick seems firmly attached. I drove home very slowly and carefully. What would you guess could be the cause of the noise?

How about the fan? Either coming loose or starting to come apart?

Steve

 

[smart51]

Yep.

 

[fiat500]

...light, metallic rattling noise? Surely, understatement of the year?

 

[smart51]

Yeah, before the bang.

 

[AnthonyH]

Cant see whats going on because the picture is too close in.

 

[smart51]

OK, so I've removed 50 million bolts from the fan housing, and 3 that hold the generator to the block. The thing isn't budging. If its not an odd question, where are the fastenings I can't find?

To make it easier, I'd taken out loads of M6 bolts round the edge, 4 M10 bolts holding the shroud to the block, and the 3 M10 nuts holding the generator to the block. There aren't any under the sump connector thing are there?

 

[fiat500]

OK, so I've removed 50 million bolts from the fan housing, and 3 that hold the generator to the block. The thing isn't budging. If its not an odd question, where are the fastenings I can't find?

To make it easier, I'd taken out loads of M6 bolts round the edge, 4 M10 bolts holding the shroud to the block, and the 3 M10 nuts holding the generator to the block. There aren't any under the sump connector thing are there?

Check that you've removed the one (maybe two) that are in the dished area above the generator. You will need to remove that piece that caps over the sump.

 

[Goldnrust]

Ouch! At least you found the issue!!

While it might all be a bit fiddly, it should at least be a fairly straight forward fix once you’ve got a new fan.

 

[smart51]

Turns out there were 4 bolts holding the alternator, one hidden by the fuel pump. All the tin ware is off now. It's surprising how much thick greasy gunk was in there.

It's all been cleaned, and has had rust treatment applied. When that dries, it will be time for paint.

 

[smart51]

The new fan has arrived and is binds against the tinware. I've fitted the big washer between the fan and the alternator. Is there some fitting needed or do I just have to make a thicker washer until it clears?

 

[fiat500]

The new fan has arrived and is binds against the tinware. I've fitted the big washer between the fan and the alternator. Is there some fitting needed or do I just have to make a thicker washer until it clears?

Are you meaning a steel, shim washer or the thin, fabric ones?
In some setups, I've found one or two very thin steel shims of the same diameter as the clamping discs, that are fitted to stop the impeller brushing against the front side of the casing. I'm not sure what you could do if it was hitting the rear side.
There might be some distortion of the cowling after the incident, or maybe the new impeller has a different geometry. You might even have to remove a washer to make it good.

 

[smart51]

The thin shim needs to be a bit thicker. I guess the new fan isn't quite the same shape as the original.

 

[smart51]

Two steps forwards, one step back. The new fan is fitted, partly with the help of the new spacer, partly with the help of a hammer. In refitting the cowling, I noticed that the fan started to scrape when I tightened up one bolt, but stopped when I tightened another. It all seems to be good now. Except that I started to smell petrol. I just assumed that I'd disturbed the fuel pump hoses somehow. Until I put my head under the car to tighten up a few bolts. The fuel line seems to have been fractured just forwards of the engine bay bulkhead. That's not how I expected today to go.

 

[Goldnrust]

I’d see that as a blessing in disguise.

The fuel line must have been already very weak, much better for it to break on the drive than to break out on the road and at best cause break down and worst cause a fire.

 

[smart51]

I’d see that as a blessing in disguise.

The fuel line must have been already very weak, much better for it to break on the drive than to break out on the road and at best cause break down and worst cause a fire.

Very much so. Moving the fuel pump will have twisted the copper pipe slightly. That's all it took to crack it, and it cracked almost all the way round.

I've just had a look in my 'Tools That Might Come In Handy Again' box and found the pipe flaring tools I used when building a kit car 19 years ago. I nearly got rid of them a few years back when I moved house. Looks like they'll get a second use now.

 

[smart51]

Well I didn't enjoy that job much, but I've fed a copper pipe through the transmission tunnel to the fuel tank and then through the engine bay to the fuel pump. The car starts and the fan doesn't rub. Terrific. Except I've lost the bolt that holds the seatbelt clip to the floor. I know they're an odd size, but I can't remember what. Do any of you know off hand?

 

[fiat500]

Well I didn't enjoy that job much, but I've fed a copper pipe through the transmission tunnel to the fuel tank and then through the engine bay to the fuel pump. The car starts and the fan doesn't rub. Terrific. Except I've lost the bolt that holds the seatbelt clip to the floor. I know they're an odd size, but I can't remember what. Do any of you know off hand?

Try 7/16" UNF....seems to be almost universal.

 

[smart51]

Yep, 7/16 UNF. I had one in my car stuff that might one day be useful box. The car is now back together, but I'll leave a test drive for a drier day.

 

[smart51]

Three days, three test drives. Everything's back to normal again. Except that its not. It sounds slightly different in a way I can't put my finger on. I guess the fan makes a noise and a different fan makes a slightly different noise. It also starts better since I've replaced the fuel pipe, as in instantly. It used to crank for half a second before firing. Now its running before I've fully lifted the lever. And its a sunny day. All is right in the world.