11 BMW 1983 R100RS Remove & Inspect Oil Pump

Access to the oil pump requires removal of the transmission, clutch and flywheel. You can see how I do that here:

Video

I shot a short video of highlights of the procedure documented in this write-up

VIDEO: 1983 R100RS Remove and Inspect Oil Pump

Remove Oil Pump Cover

The oil pump is behind the cover at the bottom of the bell housing behind the flywheel. It is secured by four M6 bolts. The top edge of the oil pump cover is beveled. The cover bolts are not symmetric so the cover can only mount in the correct orientation. This is necessary due to the cavities machined into the cover that must be in the proper orientation to the internal pump parts.

Remove 6 mm Oil Pump Cover Bolts

Remove 6 mm Oil Pump Cover Bolts

The Beveled Edge Of Cover Goes UP

The Beveled Edge is The Top Of the Cover and Points UP

The pump cover o-ring is installed in a groove on the back of the cover. A leaking oil pump cover o-ring is a source of oil leaks from the rear of the engine.

Oil Pump Cover Has O-ring in Groove On Back of the Cover

Oil Pump Cover Has O-ring in Groove On Back of the Cover

The two rotors are mounted inside the oil pump cavity that is machined into the engine block. The inner rotor attaches to the rear end of the cam shaft and has four lobes while the outer rotor has five.

Inside The Oil Pump: 4-Lobe Inner Rotor and 5-Lobe Outer Rotor

Inside The Oil Pump: 4-Lobe Inner Rotor and 5-Lobe Outer Rotor

As the cam shaft spins the inner rotor, the inner rotor turns the outer rotor inside the oil pump cavity. As you see in the picture above, the gap between the inner and outer rotor vary around the circumference of the inner rotor. As oil enters a large cavity, it is compressed as that cavity gets smaller increasing the oil pressure.

Oil Pump Measurements

There are several measurements to make in order to assess the condition of the oil pump. In the case of measuring clearances, I use feeler gauges, but mine are in 0.001 inch increments with the equivalent metric measurement in mm shown on the feeler. The specifications state a range for the acceptable clearances in mm.

I start with the feeler gauge closest to the smallest clearance in the range in mm and work my way up until I find the gauge that is very tight or won’t slip into the gap. I write down that gauge and the one that was just smaller as the measured range for the actual clearance.

Outer Rotor-to-Case Gap

I use feeler gauges to determine the size of the gap between the outer rotor and the case. The allowable range is (0.100 – 0.171 mm ). I found the gap to be between (0.152 – 0.178 mm).

Measuring Clearance Between Case and Oil Pump Outer Rotor

Measuring Clearance Between Case and Oil Pump Outer Rotor

Inner-to-Outer Rotor Clearance

I use feeler gauges to determine the clearance between the inner and outer rotor lobes. The allowable range is (0.120 – 0.200 mm). I found the clearance to be between (0.152 – 0.178 mm).

Measuring Clearance Between Inner-to-Outer Oil Pump Rotor

Measuring Clearance Between Inner-to-Outer Oil Pump Rotor

Rotor End Play

The outer and inner rotors are slightly recessed inside the engine block pump housing which provides some end play for the rotors so they aren’t grinding on the pump cover. I use an Allen wrench as a gauge block across the engine block and the face of a rotor.

Use Allan Wrench As Straight Edge

Use Allan Wrench As Gauge Block

Flat Face on Back of Allen Wrench

Flat Face on Back of Allen Wrench

I place the Allan wrench so the foot faces outward and the flat face on the back is flush against the body of the oil pump housing in the flat surface of the pump body housing.

WARNING:
If you aren’t careful, you can end up with the edge between two flat faces of the Allan wrench against the pump housing. This will result in an incorrect reading with too large an end-play gap measurement. Be sure a flat face of the Allan wrench is placed across the pump housing with the rotor underneath that face as shown below.

Allen Wrench Across Outer Rotor Lobe with Foot Facing Out

Allen Wrench Across Outer Rotor Lobe with Foot Facing Out

I slide the feeler gauges beneath the Allan wrench face and the outer rotor until I find the one that won’t slide into the gap.

Measure Outer Rotor End-Play with Feeler Gauges

Measure Outer Rotor End Play with Feeler Gauges

I remove the outer rotor and put the inner rotor on the cam shaft and make the same measurement for the inner rotor.

WARNING:
Avoid putting the Allan wrench across the end of the cam shaft as it is proud of the inner rotor and your measured gap will be wrong and much too large.

Using Allan Wrench To Measure Inner Rotor End Play

Using Allan Wrench To Measure Inner Rotor End Play

The allowable range is (0.020 – 0.070 mm). I found the clearances to be:

Outer Rotor End Play: Between (0.064 – 0.076 mm)
Inner Rotor End Play: Greater than (0.076 mm)

Outer Rotor Thickness and Diameter

I pulled the outer rotor out of the pump body with my fingers. I used a vernier caliper to measure the outer rotor thickness and diameter.

WARNING:
You maybe tempted to remove the outer rotor with a magnet. I would avoid that as it will magnetize the rotor and it will attract and hold any steel fragments circulating in the oil which attract the metal bits to the face and lobes and increase the wear on the rotor. Over time as the rotor gets heat cycled, it will loose it’s magnetism, but I think it’s good practice to avoid magnetizing it at all.

Thickness of Oil Pump Outer Rotor

Thickness of Oil Pump Outer Rotor

Outer Diameter of Oil Pump Outer Rotor

Outer Diameter of Oil Pump Outer Rotor

The allowable range for thickness is (13.955 – 13.985 mm). I found the average thickness to be (13.953 mm). The allowable range for diameter is (57.075 – 57.100 mm). I found the average diameter to be (57.083 mm ).

Inner Rotor Thickness

I pulled the inner rotor off the end of the cam shaft with my fingers. I used a vernier caliper to measure the inner rotor thickness.

Just Pull To Remove Oil Pump Inner Rotor

Just Pull To Remove Oil Pump Inner Rotor

Flat Machined on Nose of Camshaft For Oil Pump Inner Rotor

Flat Machined on Nose of Camshaft For Oil Pump Inner Rotor

Flats Machined Into Hole of Inner Rotor-NOTE Scoring On Face of Inner Rotor

Flats Machined Into Hole of Inner Rotor

Thickness of Oil Pump Inner Rotor

Thickness of Oil Pump Inner Rotor

The allowable range is (13.955 – 13.985 mm). I took three measurements and found the average thickness to be (13.956 mm).

NOTE:
This inner rotor, (part# 11 41 1 335 194), has flats that mate with flats on the end of the cam shaft. Earlier rotors up to 09/1978 have a slot with Woodruff key that fits into a slot in the cam shaft. There are two different slotted inner rotors with different Woodruff key dimensions: the 2.5×3.7 mm Woodruff key rotor is (part# 11 41 1 253 294) and the 3×5 mm Woodruff key rotor is (part# 11 41 1 258 971). I believe the smaller Woodruff key version was used on early /5 series engines. The clearances and size of these three different rotors are the same.

Pump Body Depth

I used a vernier caliper to measure the pump body depth as shown in the picture below.

Measure Pump Body Depth

Measure Pump Body Depth

The allowable range for the depth is (14.010 – 14.025 mm). I took three measurements and got an average depth of (14.143 mm).

Visual Inspection of Rotors

I used a strong light and inspected the inner rotor. There are grooves at the ends of the lobes. The inner and outer faces of the inner rotor also showed circular grooves caused by metal bits going through the pump. This is likely since shortly after I got the bike, I found the oil filter high pressure check valve was broken which allowed unfiltered oil to circulate through the engine. And I also found scores in the connecting rod main bearings from metal bits that circulated in the oil.

Flats Machined Into Hole of Inner Rotor-NOTE Scoring On Face of Inner Rotor

Scoring On Face of Inner Rotor

Scoring On Face of Inner Rotor

Scoring On Face of Inner Rotor

Scoring On Lobe of Oil Pump Inner Rotor

Scoring On Lobe of Oil Pump Inner Rotor

Scoring On Lobe of Oil Pump Inner Rotor

Scoring On Lobe of Oil Pump Inner Rotor

Scoring On Lobe of Oil Pump Inner Rotor

Scoring On Lobe of Oil Pump Inner Rotor

Scoring on Face of Oil Pump Outer Rotor

Scoring on Face of Oil Pump Outer Rotor

Scoring on Face of Oil Pump Outer Rotor

Scoring on Face of Oil Pump Outer Rotor

Scoring on Face of Oil Pump Outer Rotor

Scoring on Face of Oil Pump Outer Rotor

Condition Assessment

Here is a table of the oil pump components allowable range of measurements and what I got when I measured my components.

Measurement                  Range             Actual                               Status
Outer Rotor OD 57.075-57.100 mm 57.07, 57.08, 57.10:
AVE 57.083 mm
GOOD
Outer Rotor-to-Body Clearance 0.100-0.171 mm Between 0.152 – 0.178 mm GOOD
Outer Rotor Thickness 13.955-13.985 mm 13.95, 13.96, 13.95:
AVE 13.953
MARGINAL
Outer Rotor End Float 0.025-0.070 mm Between 0.064-0.074 mm MARGINAL
Inner Rotor Thickness 13.955-13.985 mm 13.96, 13.96, 13.95:
AVE 13.956
MARGINAL
Inner Rotor End Float 0.025-0.070 mm > 0.074 mm BAD
Outer-to-Inner Lobe Clearance 0.120-0.200 mm Between 0.152-0.178 mm GOOD
Pump Body Depth 14.010-14.025 mm 14.12, 14.16, 14.15:
AVE 14.143
GOOD

The end gap of the outer rotor is almost at the limit and the end gap of the inner rotor is past the limit.

Combined with the scoring on the lobes of the inner rotor and on the faces of the two rotors, I will replace the oil pump rotors and the cover.  I’m glad I took the time to measure and inspect the oil pump parts since oil pressure failure is usually found out after serious damage to the engine has already occurred.

Revisions

2019-11-20  Edits, Typos.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.