m42 timing

[///M42 sport]

So i'm replacing the lower timing case and didnt set the timing to TDC. How do I set the timing of the cams and the crankshaft?


I think on of the cams turned while messing with the timing chain

[roguetoaster]

Set TDC 1, cam lobes at one should be up, pointed at each other. Crank via the arrow on the timing case to the mark on the crank pulley tooth.

You can turn the cams via the squares at the back, which should be flat when timed correctly. You can also make an ersatz cam lock from wood or the two adjustable wrenches clamped together method.

[///M42 sport]

are the two dots on the squares at the end of the cams supposed to be facing up at tdc?

[bmwman91]

I don't 100% recall where the holes are supposed to be. The lobes for cylinder 1 (not visible in that pic) should be pointing up & inward toward each other. Assuming that this is a motor with stock internals & cams, the flat surfaces on the ends of the cams (seen in your pic) should be co-planar; you can use a ruler or piece of flat bar stock and lay it across them and there should be no gaps. I got 2 large crescent wrenches on the square ends and zip tied them together to hold alignment while reassembling the timing system.

When you are putting it all back together, get the cam sprockets into place but don't tighten the 4 bolts in them yet. Release the timing chain tensioner so the system is under tension and then get things lined up (or have someone press on the timing rail to put some tension in the chain). From there get the sprockets lined up, and on a stock motor the bolts should be centered in the slots. Tighten it all down and turn the engine 3-4 times by hand via the crank bolt. Turn it back to TDC and make sure that the crank and cams are still aligned. If so, you are good to go, otherwise readjust and repeat until the timing holds alignment.

[roguetoaster]

Just wanted to illustrate what bmwman said.

Cams when I first timed an M42 (ran just fine, didn't notice anything odd), but as you can see the cam squares are not flat.


Crank alignment, don't just trust this, make sure you are really TDC 1, check it with a screwdriver or similar:


TDC 1 from the front, also showing shadows on the cam gears where the bolts were, and cam sensor trigger post alignment, which is important and sometimes overlooked. BTW, do not wire your cam gears in place, it's just adding an unnecessary step.


Don't worry if it's not absolutely perfect (cam squareness, bolt center in cam windows), just check by rotating the engine to be sure there is no interference. If you then notice a difference in power you can always readjust as the cam gears can be moved with only the VC removed.

Also, M42s are super easy to work on, yay!

[bmwman91]

Also, M42s are super easy to work on, yay!

Which is fortunate, because you'll be working on your M42 all the damn time! It's a love-hate thing.

[///M42 sport]

thanks for the pics!!

[cody_eppler]

To make sure it stays timed you can use a special key that goes into your flywheel. This 100% locks your cylinders. Timing should be fine after. Im doing my head gasket right now and its pretty simple. My neighbor used to work for bmw so he had the special key already though.

[roguetoaster]

Good that you mentioned it as everyone skipped over that step.

Simply insert anything that fits snugly in the hole where you see the metal rod protruding below. If you are lucky there will be a plug that covers the hole which you need to remove prior to locking the flywheel/lower end of the engine.

[R1dd1ck913]

Man if you weren't so far away I have to cam tool for doing this.

[cody_eppler]

Yes! I didnt even know of this tool till my friend showed me.