M42 making a diesel sound after replacing the timing chain tensioner

[cheezo.king]

M42 making a diesel sound after replacing the timing chain tensioner, what can the issue be. Please help?

[Nick_318is]

Did you expand the tensioner before you installed it? If not, it may need some revs to pop open and then quiet down.

[cheezo.king]

Hi, Yes I did. You see the thing is that a few months back the idoits at the filling station threw diesel in my car so I burnt a few valves. Had it replaced and then after a while the sound came. I then bought a new tensioner and put it in. But that sound is still there

[bmwman91]

The diesel sound is often pistons hitting valves. It is not necessarily the end of the world as the M42 is fairly tolerant of this. Reasons for this could be that the cam sprocket bolts are not tight and they shifted the timing by a few degrees (the sprockets are slotted), or because the chain jumped a tooth.

Another common reason is a failure of the deflector sprocket that guides the chain around the thermostat region. This can be checked for with a magnetic oil pan drain plug (you will find the bearings stuck to the magnet, or maybe a VERY strong magnet swept around the bottom of the pan from the outside to try to pull any debris to the outlet. There are 6 balls, plus plastic bits from the race that holds them. It is highly recommended to fish all of this out or it WILL end up in the oil pump, and that causes significant damage to the engine.

If it is the sprocket: This is a fairly large job to fix since you have to remove the crank damper to get the lower cover off, and at that point you may consider a full timing case rebuild if the parts are all the original stuff which got design updates later on. In that case, the best option is to switch to a 1994-1995 M42 timing case because it eliminates the deflector sprocket entirely in favor of another solid plastic guide. You have to drop the oil pans to swap cases, but you can do it without removing the head if you are clever and patient (I have done it a couple of times). Pulling the head is a safer way to do it, but it gets expensive since you have to have it machined flat.

When the sprocket bearings go, there is a good chance that the timing case gets damaged, and you can actually have the whole mounting post snap off a few thousand miles after replacing the sprocket (I learned this the hard way). Given that a replacement sprocket is like $200, it is a better deal to swap in a used late-M42 timing case. Just be sure to use the corresponding gasket between it and the block if you do this.
http://www.realoem.com/bmw/enUS/showparts?id=BE53-USA-04-1994-E36-BMW-318is&diagId=11_6003
http://www.realoem.com/bmw/enUS/showparts?id=BE53-USA-04-1994-E36-BMW-318is&diagId=11_1370

[cheezo.king]

Hi Thanks for the info. My mechanic said that the chain stretched
I had a lot of doubt in that, because it just happened after he did the valves, I bought the chain, but never has time to do the job.
Think I should save up some money and get a garage to check or do it.

[bmwman91]

I have a very hard time believing that chain stretch is significant enough to cause this issue. It would also not happen rapidly, and simply rehecking/adjusting the cam & crank timing would fix it.

My guess is that the cam gears slipped a little, or maybe the timing was not set quite right after the head was reinstalled. You can check everything yourself fairly easily by simply removing the valve cover.

If the engine is mostly stock, then you can lock the flywheel at TDC and make sure that the cams are correctly aligned (cylinder 1 lobes pointing up and in, and the square ends at the rear are perfectly co-planar). Just remember to always turn the engine clockwise when manually rotating it.

[cheezo.king]

Thanks man, you are a real big help. Looks like this guy is taking me for a ride. We replaced the chain and the tensioner and the noise is still there
I will buy some tools and try to do what you suggested.
Much appreciation with your interest.

[DesktopDave]

I had the same trouble with mine, was just me incorrectly installing the tensioner. I made sure to drain all the oil from the tensioner, then re-installed it compressed being careful to spin it properly so it engaged with the timing rail. It'll fill & open up without damaging anything if you rev it a bit. I suspect they can jam if installed in the open position.

The other related problem with the M42 that can cause a dieseling sound is the idler sprocket in the lower case. Get a camera down the case to check that out, the roller bearing can wear out & cause all sorts of havoc.

[ispierrot]

Hello,

look in the crankcase often the screws removed and the oil pump no longer work properly.