8 replies to this topic

[whawes]

For a week or two I have been hearing a loud clacking/tapping noise coming from the top of the engine (1275 A+) at the rear. It's noticeable at idle and gets louder under load, but dies away on the overrun or when holding the car at a constant rpm. Performance isn't noticeably affected. The noise sounds very similar to a fan blade hitting something, but definitely isn't coming from the fan area.

I have checked and can eliminate the following:

Valve clearances - checked and re-checked using "rule of 9", all definitely ~0.30mm
Fan blades hitting radiator housing (or anything else)
Carb/exhaust hitting the bulkhead
Loose inlet/exhaust manifold - both checked and re-tightened, no difference

It occurred to me that perhaps a cam follower could be to blame, although I'd have thought this would still be heard when decelerating or holding the rpm constant. Also this noise appeared overnight rather than developing gradually, which doesn't seem consistent with something wearing out gradually.

In any case, having spent 15 minutes under the bonnet last night with a long screwdriver held against various parts of the block and ancillaries, I'm pretty certain the noise is coming from either the HIF44 carb itself, or the downpipe underneath.

I've had carbs apart for cleaning before and can't immediately think of anything that would make this noise. Any ideas?

Edited by whawes, 03 May 2007 - 07:58 AM.

[Silicon Skum]

In any case, having spent 15 minutes under the bonnet last night with a long screwdriver held against various parts of the block and ancillaries, I'm pretty certain the noise is coming from either the HIF44 carb itself, or the downpipe underneath.

I've had carbs apart for cleaning before and can't immediately think of anything that would make this noise. Any ideas?

In the carb, the ONLY thing I can think of is the butterfly valve being loose and flapping with the intake charge pulse.

Could it be a fault on the mechanical fuel pump or associated bits? This is also at the back of the engine.

Dunno about any other causes, out of my depth on this one.

SS

[whawes]

In any case, having spent 15 minutes under the bonnet last night with a long screwdriver held against various parts of the block and ancillaries, I'm pretty certain the noise is coming from either the HIF44 carb itself, or the downpipe underneath.

I've had carbs apart for cleaning before and can't immediately think of anything that would make this noise. Any ideas?

In the carb, the ONLY thing I can think of is the butterfly valve being loose and flapping with the intake charge pulse.

Could it be a fault on the mechanical fuel pump or associated bits? This is also at the back of the engine.

Dunno about any other causes, out of my depth on this one.

SS

Thanks for reply.

Will check the butterfly valve later, as you mention I can't really think of anything else in there that would make this noise :/

I can pretty much eliminate the fuel pump, as it's brand new. It's also a bit further down and to the right (as viewed from front of car) than where the noise is coming from.

[_Ad_]

This sounds exactly the same as what mine has just started doing!!

http://www.theminifo...showtopic=47038

Trying a new manifold gasket today to see if that does anything.

[whawes]

This sounds exactly the same as what mine has just started doing!!

http://www.theminifo...showtopic=47038

Trying a new manifold gasket today to see if that does anything.

Keep me posted then!

Although as I mentioned, I don't think it's coming from the radiator side in my case, it's more central around the carb area.

Could be cam-related, which would be something of a b*stard having only had the engine out a month ago.

Not sure about big end failure as someone suggested to you, IIRC that would usually result in a knocking noise rather than a rattle.

[Leonard]

sounds like manifold gasket

[whawes]

sounds like manifold gasket

How would that create the clacking sound though? Or do you think it could be fuel igniting that I'm hearing rather than two objects hitting one another?

[fikus01]

sounds like manifold gasket

How would that create the clacking sound though? Or do you think it could be fuel igniting that I'm hearing rather than two objects hitting one another?

it does, trust, its like a taptaptap with each explosion of the engine, it'll be the centre one thats leaking, almost 100% its that if u have an LCB as the seperate centre branch has the capability to move if the lower manifold bracket fails or moves or if its not there at all!

with the engine running feel for air movement in that central area, its usually above it that it blows so you shud feel it!

[whawes]

sounds like manifold gasket

How would that create the clacking sound though? Or do you think it could be fuel igniting that I'm hearing rather than two objects hitting one another?

it does, trust, its like a taptaptap with each explosion of the engine, it'll be the centre one thats leaking, almost 100% its that if u have an LCB as the seperate centre branch has the capability to move if the lower manifold bracket fails or moves or if its not there at all!

with the engine running feel for air movement in that central area, its usually above it that it blows so you shud feel it!

Leonard & fikus01, kudos to you both. Last night I used some Firegum to seal along the top edge of the inlet manifold and lo and behold, the noise is gone!