How to Pre Bleed BMW Hydraulic Lifters Before Installation, Install Tappets
Most BMW DOHC (Double OverHead Camshaft) engines (except some ///M engines) use hydraulic valve lifters (or tappets) in order to eliminate the service requirement of periodic valve clearance adjustments. The hydraulic lifters fill with oil and are pressurized by the oil pump. A hydraulic piston in the lifter is then able to make full contact with the camshaft and the valve stem and, in effect, vary the “thickness” of the lifter. As the parts (valves, lifters and camshaft) heat up and the distance between the valve stem and the camshaft decreases, the hydraulic lifter is able to keep full contact yet not bind and prevent the valve from fully closing against its seat, as a mechanical lifter or rocker arm would do if there were no clearance adjustment.
It’s not uncommon for the hydraulic lifters to begin to fail as they age. Oil varnish build-up in the oil feed holes, worn/weak pre-load springs and worn lifter pistons can contribute to lifters that will not stay “pumped-up” with oil pressure. This causes valve tapping, just like a mechanical valve lifter or rocker arm that is out of adjustment. The cure is to replace the lifters.
Prior to installation, the lifters should be pre-bled in order to remove air from the lifter and fill it with oil. This makes the final bleeding of the lifters, after installation, much quicker. Here are the basic steps to pre-bleeding the hydraulic lifters. In this case, we are using a Mityvac vacuum pump to pre-bleed the lifters. In this example we will be bleeding the flat tappet style lifters as used in the BMW M50, M52, M54, M56, S50 and S52 6-cylinder, M24 & M44 4-cylinder and the M60, M62 and S62 V8 engines. Other style hydraulic lifters, such as those used in the later BMW Valvetronic engines, can be bled using this method as well.
* New replacement hydraulic lifters (ID vehicle and search “lifter”):
* Motor oil; type being used in the engine or any compatible type:
* Magnetic pick-up tool:
* Vinyl or Nitrile mechanics’ gloves:
* Dymon Scrubs-in-a-Bucket hand wipes:
* Mityvac vacuum pump kit
* Container to hold the bled lifters, fully submerged in oil
* Small washer to place in Mityvac cup
* Paper towel or clean rags
1) Fill the lifter holding container with enough fresh motor oil to fully submerge the quantity of lifters that will be bled prior to installation. In the case shown, we will bleed 12 lifters at a time and install them in either the intake or exhaust lifter cages (cam carriers).
2) Place the washer in the bottom of the Mityvac vacuum cup. This will keep the lifter from “sticking” to the bottom of the cup after the vacuum process, making it easier to remove the lower lifter with the magnet tool.
3) Place two or three lifters in the Mityvac vacuum cup and cover with fresh oil.
4) Connect the vacuum pump and apply as much vacuum as it will generate. You will see air bubbles being drawn from the lifters’ oil feed holes.
5) Release the vacuum and repeat, until there are no more bubbles being pulled from the lifters’ feed holes or until only a few small bubbles continue to show. Note that the vacuum will actually cause the oil to aerate, generating air bubbles within the oil itself.
6) Remove the lifters, using a magnet pick-up tool, and place the lifters in an oil bath that fully covers the lifters.
7) Once the full set is pre-bled, they are ready to install.
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