Need advice from experience for an M42 rebuild

[JonsE30]

I loosened the front four bolts of the gear on the exhaust cam and tried to use and adjustable wrench to rotate the cam so I can level it with the squared off edge of the intake cam but It stopped. And I didn’t want to turn it more because I didn’t want risk snapping or breaking anything. Is this the resistance from the lobes pressing on the lifters? Should I just rotate with a little more force?

[bmwman91]

Ha man, no way. That is far too much work!

You just need to leave the flywheel locked at TDC as you showed in the photo, remove the valve cover (which I think you already have) and loosen the 4 bolts holding each cam to its sprocket. Get an adjustable wrench on the back of the cams to set the ends parallel with one another (and you are at least close since the faces that need to be parallel are the ones with the 2 small holes in them), and tighten the 4 sprocket bolts again.

Then remove the flywheel locking pin, turn the engine 3-5 times by hand, lock the flywheel again and double check that the cams are still parallel. It is normal to find them just a little off, so you might need to tweak them once more. If so, turn the engine again and check until they stay aligned.




The arrows and dowels on the sprockets are themselves almost irrelevant. They are good for a rough visual check to make sure you are in the ballpark, but the 3 things that actually matter are the flywheel lock pin and the 2 back faces on the square cam ends. That's it. Now, if you were off by a whole tooth you MIGHT be able to still get those 3 things aligned and be at an extreme end of the slots in the cams, but it would be fairly obvious since the factory configuration had the bolts centered in the sprockets. So anyway, if you do the steps above and find that the bolts are bottoming out in the slots when trying to get the rear edges parallel, then you need to remove the sprockets because they are off by a tooth. You can fix that in-place without pulling the upper timing cover, but it is a pain in the ass and you DEFINITELY want a magnet on a stick to prevent a bolt from falling in...it becomes a much bigger project at that point! You might be better off pulling the upper cover, but then you may need to replace the thermostat housing gasket again (most local parts stores can get Elring or Victor Reinz ones in 24 hours).

[JonsE30]

here is my plan of action: is this right?

remove the water pump, crank sensor and front timing cover so i can remove the gears, then remove the bearings caps, level the edges at the rear of the cam, reinstall the caps, then reinstall the cam gears aligning the dowel and arrow markers.

[bmwman91]

Yeah, the cams are visibly off in the photos if looking at the rear ends. I have also just used an adjustable wrench on the square ends to turn the cams and a small straight edge to visually verify that they are parallel after adjustment.

In your case, the intake looks advanced and the exhaust retarded. It's hard to tell if it is a whole tooth off, but with any luck they are just at the limits of their travel in the sprockets' slots.

[JonsE30]

got it. i will readjust the camshafts and the gears and post the pics as soon as possible.

[roguetoaster]

Bolts should ideally be centered, or as close as you can get to the center of the slot. It's not likely to be perfect without a cam locking tool, but don't sweat it. Remember, this feature adjusts actual valve timing.

The square bits on the backs of the cams should be flat relative to each other. As in, put a ruler across them and there should be little to no daylight visible. Start with aligning the squares and see where this puts the bolts in the slots. You may have it right on.

From memory I believe the dowels are in the right place presently, and IIRC the arrow pointing up achieves this. The one on the intake side does not matter as the cam sensor does not read it.

[JonsE30]

Do you mean the bolt should be in the center of the bolt slot of the cam gear? The square edges at the rear should be flat relative to the angle of the head casing? These are the dowels it’s probably hard to see but it without taking the front timing cover off, but with respect to the angle of the head casing the dowels are sitting at between 7 and 8 o’clock. The right gear maybe sitting more like 8 o’clock. Sent from my iPhone using Tapatalk

[roguetoaster]

You want to aim for centered in the cam windows and flat relative to each other across the back of the cam squares.

Perhaps I have been doing a no-no, but I've had good luck setting the chain in place, ever so slightly backing off the cam bolts and rotating the cam square with an adjustable wrench until flat, then tightening the bolts.

Also, I ignore the cam gear arrows and just remember to keep the cam position sensor dowel indexed as stock (down and left IIRC when voewed from the front).

[JonsE30]

So I hand cranked until I can get locking pin inserted: I checked the cam gear markers and they look like this:the one on the right maybe should be pointing a tooth more to the left? Cams look like this:

[JonsE30]

Sounds like a plan. I have a flywheel locking pin that i can use. And ill take some pics of the crank pulley and the cam gears and run it by here. Thanks guys!

[bmwman91]

Recheck that you have the E marked cam on the intake side. Check for timing mark agreement with cam position. Verify TDC 1 with a dowel down a plug well when aligned on the marks. Check your plug wire order.

Don't freak out.

Yup, always good to verify that the piston is properly at the top with a sharpie and dowel!




I'd not use the oil filter housing arrow for much besides rough alignment. If you have any 8mm rods or long-ish M8 bolts, you can also set the crank to TDC with the hole in the block that grants you access to the lock hole in the flywheel (assuming you still have a stock M42 FW). Still, as Toaster said, the dowel method is reliable and I'd double check things that way no matter what.

I'd just check the physical timing first before making any other moves. If it is not too far off then you could be fine, even with interference occurring.

[JonsE30]

I’ll check on those items tomorrow. Thanks.

[roguetoaster]

Recheck that you have the E marked cam on the intake side. Check for timing mark agreement with cam position. Verify TDC 1 with a dowel down a plug well when aligned on the marks. Check your plug wire order.

Don't freak out.

[JonsE30]

At this point, would it make any sense to redo the timing or did i just botch everything and the damage is already done and I am back to square one and gotta rebuild everything again?

[JonsE30]

From what I recall, i lined up the split tooth of the crank pulley facing the timing case marker by the oil filter housing. When i installed the cams, cam lobes closest to the cam gears point towards each other, with that rear of the camshaft sitting flat. i had the cam gear arrows pointing up with respect to the angle of how it sits in the engine bay with that slant.