cold start knock/rattle-30 seconds

[Russell]

Anyone experince a random cold start knock/rattle for the first 30 seconds? I almost think it is the exhaust/trany/engine hitting something as it does not seem to happen all the time. BTW, I have replaced engine and trany mounts.

[Tiger]

I think that is your VANOS rattling. Let other confirms it for you.

http://www.beisansystems.com/products.html

[Russell]

I think that is your VANOS rattling. Let other confirms it for you.

http://www.beisansystems.com/products.html

I had not thought of my vanos unit. rather have that than a rod or similar. Any idea of cost to fix?

[Russell]

any more thoughts?

[BennyM]

I generally get a lot of ticking noises with a cold start. I wouldn't describe them as a knocking per se, but I've come to accept it as just a charactaristic of the M50TU. My old M50 non VANOS also ticked when cold, but not to the extent. So, maybe it is a VANOS thing.

[Ross]

Another possibility is piston slap. As the bores wear and piston/bore clearance increases the piston rattles around a bit while cold until it warms and expands. Lots of old M20s do this.

[Tiger]

look at older vanos threads to get more idea if this confirms your symptoms. I highly doubted piston slap on modern engine.

[Russell]

look at older vanos threads to get more idea if this confirms your symptoms. I highly doubted piston slap on modern engine.

I have looked at some threads. I will do so again with more vigor :)

[Tiger]

http://www.bimmernut.com/forum/showthread.php?t=40900&highlight=vanos+rattle