m42 engine prob

[tim_s]

Hi guys,
my m42 has developed a noise over the weekend. I took her all round wales and to london and back to bristol at the wkend, a good 500 miles which was when it developed the noise. its a 'metallic' kinda noise get it occasionally at high engine speed but low speed, and get it at 75-80mph+ about 50% of the time, easing off the throttle and accelerating up again sometimes rids the problem. thought it was prob timing chain related, but the tensioner was changed about a yr ago (gen BMW item) and i briefly checked it today and it popped out with quite a lot of force suggesting its doing its job. have bought another chain and tensioner today regardless, but i'm not 100% this will rid my problem. revving the engine a little on my drive i couldn't hear anything too amiss, and driving her around town etc it seems fine. any ideas?i'm quite worried about this as its not exactly healthy! apart from the noise the car is spot on, performance and economy, oil cumsumption and temperature etc all fine, no other indications of anything wrong.
cheers
tim

[stuartgallafant]

sounds like chain-slap on the timing cover to me. thats what i had. the timing chain and tensioner had been done 10'000 miles ago, but i swapped the tensioner, and things seem to be ok now.

you said your tensioner was a genuine BMW part? if so, and you still have the invoice for the part, providing you bought the tensioner from a BMW dealer, you can get a two-year fitted part warranty. all you have to do is book your car in at the dealership, and they'll replace your tensioner for free...

also, check valve clearances and operation of hydraulic tappets. if the valve clearances are too big, the rocker will 'smack' the tappet. if the tappet is f*cked then obviously this will happen too...

hope you get everything sorted tim

also, while im here, can i ask what your iS drives like with a 3.91 LSD. coz im putting one on mine and just wanted a bit of info before i did it. also, did it go straight in or did you have to f*ck about with different driveshafts and allsorts?!

[Geeman]

Sounds like it 'could' be a sticking tappet. They get clogged up with dirty oil and become sticky...

Might be that.

Giles

[stuartgallafant]

yeah, common symtom too

try engine flush or engine gunk. the best one is the stuff you put into your engine, then do 250-300 miles with it in, and then drain your oil and renew oil and filter. stuff works the nuts!!

[tim_s]

cheers for the help fellas, i'm sure all will be revealed soon enough, have ordered a gsf chain and tensioner, will get the rest of the parts and do a chain job at the weekend. the tensioner seems ok, definitely has a good amount of spring in it, probably guides or the chain itself that is worn. i don't believe in engine gunk stuff, not fond of detergents in the engine. would prefer to have the tappets out and clean/replace.

I've thought about tappets too, i really don't know. if it is a tappet, it must be properly fcuked! its strange though as its intermittent, which somehow in my mind i reckon is more likely to be a tappet problem. i think i'll do the chain, and if that doesn't resolve it, then have a go at the tappets. am glad i'm singing from the same score! is a pretty dramatic noise for a tappet though i reckon.

I'm just worried that its neither of these, but can't for the life of me think of anything else it could be. its definitely not bottom end related. wondered if it might be an ancilliary making the noise though, mb water pump or something?


as for the 3.91 lsd, to fit its ok. it doesn't bolt straight up, the prop needs shortening - don't panic though as this doesn't require a new prop, just adjusting the existing one by loosening the collar in the middle then pushing it in. when i did mine in the end i took the prop out, fitted a new centre bearing (takes 2 mins while the prop is out), loosened the collar (easier while out of the car), then reassembled and tightened the collar once i had the diff and prop in and connected together. its a good few hours work to do on a drive, but isn't too tricky. its 100% worth it though, i'm very happy with mine. the ratio makes very little difference - if you're like me you'll notice it the first time or so you drive it because you're aware of it, then forget all about it! it makes a slight difference to revs on the motorway etc but imo its probably a bit better on the road with a slightly longer ratio. and having an lsd is ace, its a lot of fun, and inspires a lot more confidence in the car.
hope that helps!
cheers
tim

[stuartgallafant]

nice one Tim...

shouldn't take me that long coz i'll do it at work on my ramp.

i just heard that you had to use the output flanges from your original diff, on the new one, coz the 3.91 is a large case and the one on iS's is a small case???

i'll find out soon enough though!

hope your engine gets better!!! however, try this:

-take a fairly large and long flat-head screw driver.
-when the engine is idling, place the head of the screwdriver on the waterpump, and put your ear to the handle
-if there is a horrible grating noise, or unsmooth revolutions, there could be a problem with the bearing on the shaft inside the pump
-same goes for the PAS pump

whatever happens, keep us all posted

[tim_s]

no worries! the output flanges are definitely the same, well at least mine were. i'm not sure what year the diff came out of, but i bought it off karan last yr. only other thing i didn't mention on mine was that the speedo connector was different, so i used the connector from the small case diff. shouldn't take you too long on a ramp to swap over, its not a tricky job, access was the only problem doing it on the drive.

will have a go at putting a screwdriver to the waterpump. have a pretty new spare water pump from the engine i'm rebuilding, so may put that on when doing the chain. i'm a bit annoyed i'm going to have to do all this work before the engine swap, would be so much easier outside of the car! but don't want to leave it like this.
am trial fitting the throttle bodies on it tonight hopefully with a mate, and will get his opinion on whats wrong with it. the chain's done 60 or 70k, but over about 10 yrs, so it wouldn't really harm to change it i've decided.
will let you know how it all turns out in the end anyway.
cheers

[Demlotcrew]

Dude the spring in the chain tensioner is not what pushes the rail against the chain, its the pressure from the oil pump which flows into the tensioner and pushes the two pistons appart thus creating tension over the rail/chain.

Andrew

[tim_s]

yeah cheers andrew, should've thought that through a bit better.

regardless though, have fixed it!!!! don't believe what it was! was the heatshield around the ignition leads on the head, under heat and age it had split making it rattle a little, but was only rattling when the car was moving, which was why i couldn't figure it out when the car was stationary!
don't believe such a small problem can sound so worrying!
now have excess timing chain bits, but will change it anyway for peace of mind.
cheers for the help though fellas!

[Geeman]

Glad you found it before ripping the engine to pieces!

[stuartgallafant]

that was lucky!!

could've been a lot of hassle. i'll let you know if i get any probs with the diff...

[TheDutch]

This is another one of those 'is it something really simple or really complicated' scenarios, luckily it was the former and found out in time.

[Cava]

Sorry, I was going to suggest this but thought it might sound a bit stupid when everyone was talking about timing chains and sticking tappets. I had mine replaced years ago when the car was still being serviced by the main dealer after i had complained about the noise.

[tim_s]

lol, no worries! at least its all sorted now!