"Resonance'

[grt]

Hi Everyone

I need some assistance.  I have a FIAT Abarth OTR 1000 coupe which is based on the FIAT 850 coupe.  When I rev the engine there is a resonance or ringing (rattling) from about 3200 to 4500 rpm.  I have been trying for a long time to find out what it is so that I can fix it.  It's very annoying.  It sounds like something is rattling or ringing when the engine is in this rev range.

What have I done to try to find it?
X   It's not transmission or running gear related - it occurs in neutral, with clutch in or out
X   Changed exhaust - NO CHANGE
X   Changed starter motor - NO CHANGE
X   Checked engine bay - everything seems secure
X   Tightened nuts securing the ram tubes - NO CHANGE
X   Taped up regulator so it couldn't rattle - NO CHANGE
X   Handbrake on/off - NO CHANGE
X   Carby expert said it's not the carbys
X   Removed loose choke cable bolts from carbys - NO CHANGE
X   Checked tightness of nuts holding fuel tank straps - NO CHANGE
X   It's not the brake pads rattling and vibrating with the backing plates - the noise continues if brake pressure is applied - checked while driving
X   Removed drive belt to alternator and water pump - NO CHANGE
X   Checked:
o   Undertrays - OK
o   Water pump - OK
o   Bolts holding the alternator - OK
o   All venturies including rear carby - OK
o   Rear shock mounts - OK
o   Flywheel cover – OK
o   Carbys for ringing when engine is going - OK - weighted carbys with hand when ringing heard - NO CHANGE - also used stethescope
o   Brass floats in carbies - OK
o   Oil pick up - OK - used stethescope
o   Windage tray - OK - used stethoscope
o   Rocker cover - no noise source detected using stethoscope or with oil filler cap off.

Does anyone have a suggestion of where to look next?

With thanks

Graeme

[guy moerenhout]

did you look to distribition Chaine ?Take of belt and let turn whitout ,after that you are sure from this .

[grant gauld]

Graeme,
            G'day.A great idea is to get a small diameter hose about 2 meters long and put one end in your ear and the other wave around the engine bay until you get closer to the noise.Sounds silly but works well.Probably more effecient with rear panel removed ?

I do not know what 'chain' Guy is reffering to ? I thought you had gears instead of a chain.

My wild guess is the windage tray,despite you having already checked this.They are notorious for coming loose and for that reason are often missing.

Good luck ! Cheers,Grant

[guy moerenhout]

OT  1300/124 have gears.1000 OT have a chain

[grant gauld]

OT  1300/124 have gears.1000 OT have a chain

Both you (Guy) and I have owned both motors.
Graeme's car has gears and no chain I believe.

[guy moerenhout]

all OT cams shaft that I have seen and have have the teeths on onther turnside and chain.You find each day something new

[grt]

Hello Guy and Grant

I've removed the belt driving the alternator and water pump and the noise is still there.

My engine has a timing chain - single row only because the timing chain cover is thin and will not allow a duplex chain to be fitted.  I understand the TCR is the same.

Thanks for your help, Graeme

[guy moerenhout]

yes,but have gears and other camshaft.OTR have chain and special camshaft for Otr,not so race cams

[trevor]

Graeme,
Left field:  distributor weights / loose shaft splines/ worn upper dist bearing  / resonance veries with on/off throttle change in the resonance rpm range ??
Good luck
Trevor

[grt]

Hi Everyone

I've tried the hose and the mechanic's stethescope again with no luck.  Also removed the dipstick and no change.

Yesterday I dropped the sump and the windage tray is firmly secured in place.  I hadn't come loose.

So, the rattling noise starts at about 3200 rpm, is not dependent on road speed (it occurs also while stationary), is not affected by clutch in or out or gear engaged or not, is independent of the throttle being open or closed, and nothing I can find or see is loose.  Local experts are confident it's not in the engine and there is nothing peformance wise to suggest that's the case.

I guess I'll check out Trevor's suggestion now regarding the distributor.  When we had the car on the dyno there was variation in the timing that would suggest wear in the distributor.

Whereelse should I look?

I should say however that the car is fantastic to drive.  It has an amazing amount of torque and power for a 1 litre car, and it handles very well.

Cheers and thanks

Graeme

[viotti600]

Graeme,

The only other thing not mentioned that I can think of is perhaps the oil pump gears? Or maybe the bronze bushing in the engine block for the oil pump/distributor driveshaft is worn & the shaft is wobbling under load?

Just throwing ideas out there... ;)

[Pantdino]

I had a horrible rattling sound in my 850TC replica which was much louder at certain revs.
I had replaced the starter with the Subaru-based one from Paul van der Heiden and it was touching the sheet metal of the body.  I had to cut away some of the sheet metal, which cured the problem.

check out the sheet metal for shiny areas where the paint has been rubbed off.