is my M42 dying?

[LivingLegend06]

I posted this in m42 technical also but I'm looking for some more input so this is a copy paste.

OK, so my m42 has just recently developed a fairly loud knocking sound that is proportional to engine speed. The motor has 142,000 miles. I'm running royal purple full synthetic 10w30 that has just a touch over 2000 miles on it.

I think the problem may have come from this last weekend. I went on a fishing trip and on the way back i decided that i would be able to get away with using the extra gas that we didn't put in the boat to fill my car. I put 6 gallons of regular into my tank that was a little less than half full(premium). I've always used premium and when I was running the regular/premium mix (close to half and half i would expect) it seemed to studder slightly in higher rpms under heavy throttle (i noticed it best in 4th gear around 80mph), I didn't think much of it at the time but this is the only thing that I have to suspect.

Is this rod knock, am I fucked?

Edit: Video

[smonkbmw]

lower octane fuel will only cause pinging. unless it was very old fuel in the boat. id rule the fuel out.

[LivingLegend06]

It wasn't bad gas and it had only sat for a few days. It was outside in a can and might have gotten a little sun, but i wouldn't expect anything that would hurt it too bad.

[T Verdier]

doesn't mixing 91 and 87 make it 89?

[3E0panda]

mine had that same thing as well. filled her up with 91 and after a while it was gone.

[shutter]

If you haven't changed your timing tensioner in awhile or you're not sure when it was last done, I'd put one on. It's a pretty easy and quick job. I'd probably pull the valve cover and check your sprokets, and pull your lower pan to check for timing debris. Something like this is almost always the chain.

[stevofthahill]

You say knock, but are you referring more so to a ticking noise that is rpm dependent? Make sure your oil is topped off, they like to make a racket when low on oil, ask me how I know. Secondly, change out your chain tensioner if it's never been done. If that doesn't fix it, then you've got a couple more things to be looking for. For instance, it could very well be time to inspect all your timing chain components.

As another note, I'd recommend on your next oil change switching to some Mobil 15w50 full synthetic. I've noticed the m42 will run much quieter and smoother on a heavier weight oil. But I also run it because during the summer our temps get ridiculous in AZ.

[LivingLegend06]

I wouldn't describe the sound as a ticking, it sounds like a louder and harder sound than I would expect the valvetrain to make. Doesn't really sound like a timing chain rattle to me either. I'm going to try to drive it 100 miles to get from school to my house this weekend and ill have my mechanic look at it. In the meantime ill be engine shopping (swap time?).

[Van Westervelt]

Get some 92 octane in there and run a tank through. Sounds more like it was a fuel problem, my m42 in my first 318 was really tempramental with fuel grades.

Timing chain tensioner is also a nice lil fix dependant upon the noise. Grab a video, and post it up.

[shutter]

The chain can get pretty damn loud if it's slapping up against the guides... Go to m42club.com and search on the topic, there are some videos up there so you can hear what it sounds like when nasty. Drop the lower pan too to check for timing components and upper pan bolts in the pan. Retorque your upper pan bolts, metric mechanic goes +20% for what it's worth. Also pull your VC to check to see if your sprockets are pointy and replace the tensioner with the updated m44 tensioner.

It could be the gas thing, but all of the above is necessary maintenance to having a healthy m42 IMO. Especially if you haven't done any of it yet, or know when it was last done.

edit: I wouldn't drive it 100 miles till you know the timing chain isn't going to jump a tooth on you... At least do the tensioner, it takes 5 mins. Put it in extended and you're set. The caveat being that if the sprockets are bad, it could make them worse, but it should buy you some miles. Also, if it has junk in the pan, it could be blocking your oil pick-up screen.

[LivingLegend06]

Video of the noise


if that doesn't work just let me know and ill try to figure something out.

[bergie_318is]

wow i was gona say a fuel problem, but ive never had that noise, and my m42 has run over 300.000 km's, but ive always, without fail put the best fuel in it.

[tjts1]

Have you checked your oil pan gasket bolts yet?

http://www.m42club.com/forums/showthread.php?t=594

Also inspect your timing chain and change the tensioner if you haven't already.

http://www.m42club.com/forums/showthread.php?t=2925

[LivingLegend06]

I replaced the lower pan 2000 miles ago (broken pan) and everything appeared to be in place and there were no debris in the bottom of the pan, everything looked really clean. I'm not sure when the tensioner was last replaced but its hard for me to imagine a timing chain making that sound.

[Van Westervelt]

Pull the valve cover. I had one make a similar noise right before a cam snapped. Loose bits was the cause. Worth a look.