Noisy M40 after cam swap

Mon Jul 30, 2007 7:57 pm

Hi I've fitted a new cam and all the bits to my 89 m40 316i. However its still noisy! I've flushed it filled it with thicker oil, all to no avail. The strange thing is, its quiet on start up and after a couple of minutes running gets noisy. The noise is coming from the back, around No.4 cylinder area and sounds much louder under the car. I've spoken to an engine reconditioner who says that this engine is prone to developing piston slap on the rear cylinder if it overheats. It hasn't overheated for me but it does have a newish Rad fitted. Has any else come across this? I convinced it nots the tappets as they should be noisier on start up and this engine is spotless inside the rocker cover. Please help its driving me insane

Mon Jul 30, 2007 8:21 pm

Did you replace the hydaulic tappets?

Mon Jul 30, 2007 8:54 pm

Yes, and the rocker arms, spray bar, thrust pads, water pump, timing belt and tensioners! I'm now considering ripping the thing out and getting another 316i or even a 318i engine. Does anyone know if if I did get a 318i engine would it fit straight in? Would the exhaust still fit (it's new) and would it be a case of swapping the ecus and keeping the old loom or swapping loom and ecu?

Mon Jul 30, 2007 8:59 pm

Are you sure its not the injectors making the noise?
316-318 is a straight swap, just the ECU needs changing as well.

Mon Jul 30, 2007 9:04 pm

How loud can injectors get? this is noticeable from a good 30 to 40 feet away once warm and sounds horrific on a narrow street, but it still pulls well - as well as 316i can!

Mon Jul 30, 2007 9:55 pm

Noisy enough for people to think its the cam, Get a stethoscope or a long screwdriver and put your ear on the end (if you can on an M40).
The reconditioner is probably trying his luck and hoping you'll say "yeah ok mate, put a new one in and send me the bill"

I've never heard of them developing piston slap on one cylinder due to overheating. Dropping a valve and not being checked correcly when re-built yeah that i've seen.
If you can be bothered you could try swapping the injectors for a known quiet set, or just swap the 1 and 4 and see if the noise moves to the front.

How many miles on it?

Mon Jul 30, 2007 10:23 pm

Its done 96k with full bm history. All the valve springs looked fine and all were the same height when I swapped the cam. I even got two more new lifters and fitted them to no.4 cylinder. Have done the stethoscope thing and all I can tell is that the noise is around no.4. Can injectors really get that loud? The exhaust seems to amplify the noise.

Mon Jul 30, 2007 11:07 pm

If you end up ripping it out, stick a 325 in. At least you can adjust the tappets on that.

Mon Jul 30, 2007 11:24 pm

Injector noise is easy to check for.
Rev the engine and switch off the ignition. Injector noise will cease instantly; am related noises will continue as the engine stops.
Exhaust blow at the manifold is another possibility. Sounds very similar.

Tue Jul 31, 2007 6:33 pm

I suspected a manifold blow, but I can't feel anything around the manifold. some one else suggested that a manifold would get quieter as the engine warmed and expanded sealing the gap? Is the m40 prone to any bottom end problems?

Tue Jul 31, 2007 8:57 pm

might be a cracked manifold.. that might get louder when warm

Tue Jul 31, 2007 11:54 pm

An exhaust blow should sound louder when the engine is under load. i.e. when going along, bit awkward to check though

Wed Aug 01, 2007 6:50 am

I thought piston slap was supposed to be worse when cold also, until everything expands and seals the gaps. Mine does a similar thing-comes and goes but when bad it's a loud metallic "tink tink tink". Usually happens in the first half a second of startup in the morning, and then randomly after that, a quick blip of the throttle sometimes sees it off. I'd love to know what causes this-pretty sure it's not tappets or exhaust related.

Thu Aug 02, 2007 8:27 pm

Hi I just had a go at stethoscoping with a length of steel bar, the noisest place I could find was the fuel rail. So Brianmoore is right it is more than likely a noisy injector. But can these really get that loud? Would a decent Injector cleaner in the tank help? Or is it new injectors? How quiet were they new? Someone please help!