Metallic rasp/rattle under acceleration 2500rpm

[swindler]

Hi all

I’ve developed a metallic rasp/rattle which comes on under load (1/2 to full throttle). Car otherwise running well. I thought it might be knock which I’ve not experienced before so don’t know exactly what to listen to. However I have a 123 distributor so was able to retard timing significantly to the point power is down but the rattle was still there unchanged. So I’ve returned the timing to previous setting. I can’t see any other obvious issues: any thoughts ? Car is 3.8, oil pressure reading 60psi at 3000rpm hot, no significant smoke, starting fine etc but I do have oil leak from rear - main seal?

Any thoughts??

Thanks in advance
Mark

[MarekH]

... but I do have oil leak from rear - main seal?

Is there a thick black trail of filth all down the underside of the car?

Even if there is, that has nothing to do with acceleration.

kind regards
Marek

[Jack the lad]

It might help if you could tell us which part of the car it is coming from. My first thoughts would be loose baffles in the silencers. Drive along with the drivers and passengers side windows open and you may get a better idea of what it could be. I had a similar one a few years ago that turned out to be a metal petrol pipe vibrating against the body, 2 mins with a new clip fixed it. cheers John.

[chrisfell]

I've had something similar. I found the cause was the deterioration of the gearbox mount bush due to hot oil. The sound was the spigot rattling against the gearbox mount.

Other possibilities are the exhaust downpipes rattling against the engine frames.

[swindler]

Thanks these are helpful tips. It's definitely load/throttle related so the baffles could be a possibility though it seems to be coming from the engine itself/further forward.

I was wondering if a failure of the main seal could be so bad as to allow crank pressure to vent out of it (noisily) under load? Or they may be totally unrelated.

M

[Jack the lad]

Hi Mark, the crankcase should have negative pressure in it to help prevent oil leaks, ie. air in and not oil out it is worth checking your system for a blocked filter at the top between the two camshafts and the associated pipe-work though. Could you record the noise so we could all have a listen? I'm sure someone on here will have had this problem before. John.

[malcolm]

It's always tricky locating a noise - it can transmit along metal and seem to come from other places.
Two noises I had that sound similar:
One was exhaust as mentioned above
the other was the fixing at the bottom of the air filter canister!