Due to the history of this bike, 83,000+ miles and an oil filter high pressure bypass valve that was loose and not sealing for an unknown period of time, I want to inspect the crankshaft main bearings.

I previously removed the electrical components under the front engine cover, the inner timing cover, the crankshaft nose bearing and crankshaft timing sprocket. You can see how I do that here:

• 12 BMW 1983 R100RS Remove Diode Board, Alternator & Electronic Ignition Sensor

To remove the camshaft requires removing the oil pump. I already removed that to replace the rear main seal, flywheel o-ring and oil pump cover o-ring. You can see how I do that work here:

• 11 BMW 1983 R100RS Remove Flywheel & Rear Main Seal
• 11 BMW 1983 R100RS Remove & Inspect Oil Pump

Tools

I use the Cycle Works Stage III engine tools to remove the crankshaft. The tools can also be used to remove the front and rear main bearings.

I need to heat the engine block around the front main bearing carrier before I extract it with the Cycle Works tools. I use two MAP gas torches (only one shown in picture below) to put enough heat into the front of the engine block to get the temperature around the bearing carrier to 275 F. I use an infrared non-contact temperature sensor to measure the temperature around the bearing carrier and two 1-1/8 inch box-end wrenches to tighten the puller bolt on the Cycle Works tool to extract the bearing carrier.

Video

I made a short video summarizing how I do this work.

Remove Camshaft

The camshaft timing sprocket is in the way of removing the crankshaft front bearing carrier, so I have to remove it. The obvious way is to pull the sprocket off the camshaft with a 3-jaw gear puller. BUT, it turns out the sprocket is stamped out of a thin piece of steel and the force needed to pull it will bend the sprocket.  SO DON’T GO THERE!!

WARNING:
The picture below shows you how to have a bad day, NOT HOW TO REMOVE THE CAMSHAFT SPROCKET.

I was warned about not using a 3-jaw puller from Tom Cutter at Rubber Chicken Racing Garage. He said he positions the camshaft sprocket holes to align with the camshaft bearing carrier bolts, removes the bolts, and then pulls the camshaft with the sprocket out of the engine block as a unit. Of course, the oil pump has to be removed since it attaches to the rear of the cam shaft before you extract the camshaft from the front of the engine block.

Remove Cam Followers

Before removing the camshaft, I remove the cam followers. The followers need to go back onto the cam lobe they came from, so I labeled the block with the side (“R”, “L”) and intake and exhaust (“I”, “E”) as a “belt and suspenders” approach for getting the correct follower on the correct lobe. Then I labeled four baggies appropriately.

I use a pick and insert the point into the hole in the center of the follower cup the push rod sits in and pull the follower out. I inspect the followers. There are no cracks, pits, or chips on the cup the push rod fits into. The slots in the side show no cracks. The face of the follower that rides on the cam lobe has a mirror polish to it and shows not pits, rust or scratches. The followers are in good condition. After I finish inspecting each follower, I put it in it’s baggie before pulling the next one.

Remove Oil Pump

I previously removed the oil pump. You can see how I do that here.

• 11 BMW 1983 R100RS Remove & Inspect Oil Pump

Pull Camshaft Out of Block

I rotate the camshaft timing gear to align the holes in the gear with the two bolts securing the front camshaft bearing carrier. I remove the two bolts. I had to tap on the rear of the camshaft that the oil pump mounted to to push the camshaft forward so I could pull it out of the block.

I had to tap the rear of the camshaft with a plastic mallet to push it out the front but the process was straight forward (no pun intended 🙂 )

I inspect the cam lobes for signs of nicks, rust, cracks or other signs of abuse. There is an uneven, and off-center, wear pattern on the lobes, but this is normal. The cam followers are off-center on the lobes so that the force of rotation of the cam lobe produces a torque on the cam follower and the push rod riding on top of the follower so they both rotate. The idea is to have uniform wear on the followers and push rods.

Measure Gap Between Camshaft Shoulder and Camshaft Sprocket

Tom said to measure the gap between the face of the camshaft shoulder and the back of the bearing carrier as sometimes the camshaft sprocket moves forward. The gap should be no more than 0.005 inches. I found my gap was 0.004 inches so the sprocket has not moved.

Remove Inner Timing Cover Gasket and Two Doughnut Gaskets

I use a single edge razor blade to carefully get under the inner timing cover gasket so I can remove it. It’s easier to start from the inside of the gasket. I take care to keep the edge of the blade flat with the sealing surface on the engine block so as not to nick or gouge it. I also use the blade to remove the two doughnut gaskets at the top of the engine block.

Remove Starter Motor

Since I have to heat the front of the engine block near the starter motor to 275 F, I remove the starter motor so I won’t damage it. It is secured by a bracket on the front and two large bolts on the rear.

The rear bolt heads are captive in the starter motor bracket so you can remove the nuts from the rear and the bolts won’t turn. After I remove the left nut, I can pull the bolt to the front and get it out of the stater motor. The right bolt head is hidden, so when I remove the nut, I can’t extract the bolt, but I can tilt and pull the starter motor forward to get it free.

Remove Crankcase Breather Cover & Hose

Since the engine block will get hot near this, I remove it.

The breather hose is cracked under the hose clamp so I will replace it.

Remove Front Main Bearing Carrier

There are three nuts left securing the front main bearing carrier that I remove. The lower left nut (facing the engine) was removed when I removed the timing chain slider

I assemble the Cycle Works tool for removing the front main bearing carrier.

I put on my welding gloves and I use two MAP gas torches to heat the side of the engine block around the bearing carrier. I sweep the flame of one torch on each side of the engine block on the cylinder side of the carrier and above and below the carrier. The bottom and sides of the block heat up slower than the top so I move more slowly over those surfaces. It takes about five minutes to apply enough heat to the front of the block to get it up to 250 F. Then I use the two 1-1/8 inch box end wrenches to tighten the Cycle Works puller bolt and the carrier starts coming out of the block.

When it comes free, I use my gloved hands to remove it and the cycle works tool from the nose of the crankshaft.

I pull the crankshaft forward and it slides easily out of the rear main bearing. I center it in the hole and rotate it so I can get the front journal counterweight out of the hole in the front of the block. Then I tilt the crank a bit as I rotate it the other way so I can get the rear journal counterweight past the hole.

Inspect Main Bearings

The bearing carrier has the front bearing inside the bore along with the high pressure oil relief valve at the top left of the carrier. As shown in the picture below, I put a Sharpie triangle mark next to where the seam of the front bearing goes in the carrier. The seam is located here so it avoids the maximum thrust on the crankshaft from the connecting rods.

The front bearing is discolored and I can see minor grooves in it. The center slot with cut outs aligns with the oil passages drilled in the crankshaft main journal. There is a small hole in the bearing near my thumb in the picture below that sends oil to the valve train on one side. There is another hole on the other side of the bearing in the following picture to lubricate the other cylinder’s valve train. Note the seam between the two bearing halves in the picture below has a cut out across the seam which is normal.

The rear main bearing shows a similar level of wear.

 

Inspect Crankshaft Main Bearing Journals

There is a discolored band around the circumference of the front and rear main bearing journals that align with the oil passages drilled into the journals and line up with the center groove of the bearings. I believe this is normal and not an indication of crankshaft main bearing journal damage.

I shine a light into the oil passages connecting the main journal with the connecting rod big end journals to see if they are dirty or partially blocked. They are both clear. I use a soft bristle bottle brush and clean them out just to be thorough.

On the front main journal there is a rectangular recess in the middle of the polished journal.

It acts to cyclically pump a small flow of oil from the main journal oil passage through the two holes on the left and right sides of the front bearing. Those holes are connected to passages in the engine block that go to the holes the top cylinder studs screw into. This oil lubricates the rocker assembly in the heads. By providing a pulsating, lower pressure oil flow for the rocker assembly, the head gasket and base gasket are better able to seal without having to overcome high pressure oil. IMHO, this is a clever feature of the crankshaft design.

Crankshaft Journal Measurements

I measured the crankshaft front and rear journals. The journals don’t look abused, but it’s worthwhile to me to learn what the measurements show.

I use a 2-3 inch micrometer. I use a reference length to calibrate it. At 0.0000 inches, it reads 0.0004 inches so I will subtract that from all measurements I take. I make measurements at the top and bottom of the journal and at 90 degree angles. That gives me four measurements per journal. I take 3-4 measurements per measuring point and average them. I put all the information into a spreadsheet as shown below.

Based on what I read in the Clymer’s manual, the journals match up with the “Red” main bearings for both the alternator and flywheel journals. I don’t see any ovality (alternator 0.0000″, flywheel 0.0000″) and almost no taper (alternator 0.0001″, flywheel 0.0001″) in the journals, so that is good. It leads me to conclude the crankshaft journals are in good condition.

The engine block is looking pretty empty at this point.

Replace Oil High Pressure By-pass Spring & Plunger

Due to the miles and age of the bike, I want to replace the spring and plunger inside the oil high pressure bypass valve. It is easy to do this while the front main bearing carrier is removed. It’s not as easy if it’s in the engine due to a stud that’s near the end of the housing preventing it from being unscrewed all the way.

I use a pair of vice grips to turn it and then a pair of pliers to unscrew it from the front bearing carrier.

Once the housing is removed from the front main bearing carrier, I remove the plunger and the spring from the body of the high pressure bypass valve.

I measure the original spring and the new spring, and the diameter of the original plunger and the new one. The original spring has collapsed some, as I expected and the plunger diameter has not changed.

I replace the spring and the plunger. Here is the new plunger next to the old one.

But as a very experienced airhead mechanic told me, the oil high pressure bypass plunger is the best lubricated part on an airhead engine so it shouldn’t be worn. Nonetheless, I replaced the plunger with a new one as its inexpensive so why not.

Verify Condition of Bearings & Crank

I took the block with the rear main bearing, the crankshaft and front bearing cover with the front main bearing to see Matt Parkhouse. I wanted someone with experience to look things over, and if the front bearing had to be replaced, had been there and done that more than once before.

Based on what I read about replacing the front main bearing, there is “art” to staking it correctly and the penalty for failure is likely a new crankshaft. So I don’t want to take that work on myself.

Matt’s visual inspection of the main bearings and crankshaft did not show any reasons for real concern. He measured the crankshaft main journals and the inside diameter of the bearing shells. He pronounced the crankshaft main journals and the front bearing are within specification, but found the rear one was too loose. So he replaced it with a new “red” bearing.

NOTE:
You see the rear main seal and the rear thrust washer in the pictures above. I had installed a new rear main seal before deciding that I really ought to pull the crankshaft. Matt pulled the thrust washer out past the rear main seal to do the work. I replaced the seal later since I did not want to chance damage to the seal lip causing it to leak. That’s the cost of a change in plans. 🙂

The maximum clearance for the crankshaft main journal bearings is (0.026 in, 0.066 mm). The table below shows the measurements used to compute the clearance between the crankshaft main journals and the bearing. The alternator (front) bearing clearance is (0.0018 in, 0.047 mm) and the flywheel (rear) bearing clearance is (0.003 in, 0.070 mm). The rear clearance is just past the maximum.

For the flywheel journal main bearing, you can see the difference between the original clearance and the clearance with the new red bearing installed (0.019 in, 0.047 mm). With the new bearing, the clearance for both crankshaft main journals are just about the same.

The rear bearing runs hotter since the rear of the engine is not in the air stream. And the oil from the oil pump first goes to the front bearing before getting to the rear bearing. If the oil level gets low, the rear bearing gets less flow than it should. In short, the rear main bearing suffers more than the front.

This could explain the slightly smaller flywheel journal diameter and the greater wear of the rear main bearing.

Revisions

2019-12-20  Add oil high pressure bypass valve section, main journal inspection, journal notch explanation.
2019-12-23  Add high oil pressure bypass and front bearing seam pictures. Edits.