Why are my intake camshaft bolts broken on my BMW?

Why are my intake camshaft bolts broken on my BMW?

This is a design defect, and well know in professional BMW service circles. You can see on the photo below, that VANOS (variable valve timing system) to intake camshaft bolts have broken and backed out, 3 of the 4 bolts are damaged and loose.

What causes a camshaft to be broken in an OHC engine?

If the cam timing is lost during high revs (broken chain or gears) the con rods will contact the camshaft causing the cam to be broken. Other serious damage can occur at the same time causing the block to be unserviceable. OHC engines break camshafts usually after a seizure of a cam journal in the head.

What causes a camshaft to break in a pushrod engine?

When a camshaft breaks it is generally the result of another component failure. In the case of pushrod engines contact with a broken con rod is the usual cause. This is only resultant damage and has no bearing on the condition of the camshaft.

What causes the cam to move back in the block?

If the end play is excessive, it will cause the cam to move back in the block, causing the side of the lobe to contact an adjacent lifter. Broken dowel pins or keys. The dowel pin or woodruff key does not drive the cam; the torque of the timing gear bolt, or bolts, against the front of the cam drives the cam.

If the cam timing is lost during high revs (broken chain or gears) the con rods will contact the camshaft causing the cam to be broken. Other serious damage can occur at the same time causing the block to be unserviceable. OHC engines break camshafts usually after a seizure of a cam journal in the head.

This is a design defect, and well know in professional BMW service circles. You can see on the photo below, that VANOS (variable valve timing system) to intake camshaft bolts have broken and backed out, 3 of the 4 bolts are damaged and loose.

If the end play is excessive, it will cause the cam to move back in the block, causing the side of the lobe to contact an adjacent lifter. Broken dowel pins or keys. The dowel pin or woodruff key does not drive the cam; the torque of the timing gear bolt, or bolts, against the front of the cam drives the cam.

When a camshaft breaks it is generally the result of another component failure. In the case of pushrod engines contact with a broken con rod is the usual cause. This is only resultant damage and has no bearing on the condition of the camshaft.