Engine rattle upon deceleration

[75BMW2002]

I have a noise in my M42 (91 318iS) engine that I "think" is timing chain noise but not certain. It sounds like a loose chain rattling as the engine is reving down in RPMs. I don't hear the noise at higher RPM or at normal highway speed but I do hear it when I shift gears, etc as the motor is getting lower in RPMs. Again it sounds alot like chain rattling but as I said, it goes awya when you rev the motor.

Could it be something as simple as the tensioner or something more severe or maybe something really simple like an exhaust shield or?

Thanks

[EN318isPDX]

A friend of mine put a nice 3 inch pipe on his DSM and he has a sort of drone noise when he lets his rpms build down So if its similar to that, It could be an exhaust leak or more likely could be the tensioner. I'd say have a exhaust shop look at your exhaust and see if it leaks (normally free).. if not a timing chain tensioner is always a good idea on a timing chain driven car.

[75BMW2002]

I had forgotten that the PO had put a header on the car so it doesn't have the exhaust shield

[colin86325]

Are you sure the PO put a header on the car?  It has factory headers w/o much of a heatshield in the headers area.

Could be a weak timing chain tensioner.

[75BMW2002]

Could be a weak timing chain tensioner.

While I can do brakes and general mechnical I am nto so sure I feel comfortable tackling the chain tensioner replacement.  I know the kit isn't very much but how many hours of labor do you think a mechanic will charge me to do this?

BOB

[nicknikolovski]

The timing chain tensioner takes less than 1/2 an hour. You need a 19mm socket and a 3/8" or 1/2" drive ratchet, thats it!

The tensioner is located just above the A/C compressor. You loosen the 19mm plug, and pull out the tensioner piston. Put the new tensioner piston in the cap and replace the washer. Insert the tensioner back in the timing case. Tighten the 19mm bolt to spec. Then get in the car, start it - expect the chain to rattle briefly. Then rev the engine to 3,000 rpm for 15 seconds and thats it. Take the car for a drive, listen and compare the noise.

If it's gone - all good, if it remains check out the exhaust manifold for leaks and cracks. (common). If the manifold and exhaust system checks out ok, I would think the timing chain system may be worn out.

Good luck

[75BMW2002]

Well if it's that easy I will do it myself.  I will order the tension kit from bavarian today.

Another question - assuming worse case scenario it needs the timing chain replaced - how difficult is that and how many hours labor?

Thanks

[nicknikolovski]

Timing chain can be complex if you have not done a timing belt or chain before but there is a really good site which explains the procedure in depth. The M42 chain replacement is not to hard actually. Also if you replace the chain, you will need to replace all the guides, all the sprockets, gaskets and seals. Parts come to about $600.

http://www.esatclear.ie/~bpurcell/318istimingchain.html

Labour time is about 5-7 hours.