Having become concerned with the long time (10 seconds) required for my 1971 BMW oil pump to develop pressure, I decided to replace it with the newer design pump. Although this pump can be installed using the original oil sump for pre - '72 engines, I would highly recommend the newer design sump, as it contains baffles to prevent oil starvation during sudden stops and extended high G turns.
The shop manual procedure, though brief, adequately describes the change process. I do have a few suggestions. Prior to starting the job, ensure that you have a new oil pan gasket, an 8-mm allen wrench (to remove sway bar) and, most important, a supply of oil pump shims to correctly tension the oil pump drive chain.
Although the shop manual says to remove only the lower alternator bolt, the job is far smoother if you remove both alternator bolts to permit access to the power steering support bracket which also must be removed. Likewise, the clutch slave cylinder support bracket should be completely removed prior to sump removal. Once all hang-on components are out of the way, the many sump bolts can be removed. Although the manual says that the engine should be rotated until connecting rod number six is above the sump joint line, it does not say that you may experience interference from the crankshaft counterweight if you try putting number six piston at TDC position. You should be prepared to rotate the engine with a 36-mm socket on the harmonic balancer nut while jockeying the oil sump out of the way. The sump comes out quite easily if you have the crankshaft rotated to the correct position. Installation is simply a reversal of the removal procedure.
Before removing the old pump check the chain tension on the pump drive. It will probably be possible to deflect the chain about one-half inch. This is too much N one-eighth inch is more like it. At any rate, add enough shims to achieve a relatively tight chain. (My pump required .6-mm worth of shims.)
While the pump is off you could pull a few bearing and connecting rod caps off to spot-check your engine's bottom end. My mains showed 30% wear after 62,000 miles, rods showed only 5% wear. While you have the alternator and power steering pump off, it would be a good idea to replace these drive belts.
I was pleasantly surprised at the output of the new pump: 15 psi increase at idle, 20 psi increase at 3000 rpm, in addition to the advertised quicker pressure buildup upon starting.
*Not required unless new type sump is to be installed.
- Shop Manual
- 1141 1 256 305 New-type oil pump
- 1141 1 250 562 0.1-mm long shim
- 1141 1 250 563 0.3-mm long shim
- 1141 1 250 521 0.1-mm short shim
- 1141 1 250 522 0.3-mm short shim
- 1141 1 256 710 oil pump rear support
- 11141 1 255 646* new-type oil dipstick
- 111 3 1 250 090 oil sump gasket
- 1111 1 256 355 base for rear support
- 111131 256 121 new-type oil sump
Be sure to use new connecting rod nuts if you pull any connecting rod caps off, and be sure to tighten to factory specs. Although the parts list seems fairly extensive, the process is uncomplicated. As with any engine work, cleanliness is vital.
Author: Steve Brenneman