After installing the crankshaft, I’m ready to install the flywheel. Since the flywheel is off the crankshaft, I keep the crankshaft pushed to the rear, I use the the Cycle Works front main bearing carrier removal tool and hand tighten the puller bolt. This pushes the crankshaft up against the inside thrust washer so it won’t come off the pins while I’m installing the flywheel.

Parts

This is a list of the parts I used. I bought an engine gasket kit from Euro MotoElectrics that includes the flywheel hub o-ring. I show the part numbers for them below along with the EME part number of the engine gasket kit. If you don’t buy the gasket kit, you need to order the individual o-rings and rear main seal.

Part #	Description	Qty
GSK-EngineKit422	Engine Gasket Kit, Euro MotoElectrics	1
11 22 1 337 093	GASKET RING – 59X3MM (from 09/78), Flywheel Hub (In EME Gasket Kit)	1
11 22 1 262 060	M11 BOLT, COARSE, Flywheel	5

Video

Here is a short video summary of this work.

VIDEO: 1983 BMW R100RS Prepare and Install Flywheel

Preparing the Flywheel

There are a number of things I need to do to prepare the flywheel before I install it on the crankshaft.

Clean The Flywheel, Polish The Guide Ring

I clean the flywheel with engine degreaser removing the oil and clutch dust that has been baked onto it over the past 40 years.

Remove Grooves In The Guide Ring

I posted a question about what to do about the grooves in the guide ring to the Micapeak Airheads forum (if you haven’t joined, you should as several long-time airhead mechanics hang out there offering valuable advice).

Tom Cutter suggested if the grooves are shallow they can be polished out.  If not, then a new hub (part # 11 22 1 337 284) can be installed as it’s removable from the flywheel.

I used my finger nail to scratch across the grooves. My finger nail was catching on the grooves, so I concluded they were shallow and I should be able to polish them out. I started with 400 grit wet/dry paper and sanded all around the hub in a circular motion so the paper cut across the grooves to remove them. When I could see swirl marks across the grooves all the way around the hub, I switched to 600 grit paper sanding along the circumference of the hub until the swirls were gone. Then I used 1000 and finally 1500 grit paper to get a mirror finish on the hub.

After sanding out the grooves, I used metal polish with a blue shop towel and cleaned the hub until I didn’t get any black residue on shop towel. It looks like new again and I am optimistic that the new seal will seat and stop oil from leaking.

I polish the guide ring where the rear main seal runs on it before I install it back in the bike with the flywheel. I use metal polish to clean the guide ring and get rid of any debris from sanding out the grooves.

Remove Guide Ring From Flywheel

Later, I learned that the guide ring is supposed to come off the flywheel easily. But mine didn’t. You can read about how that happened, how I fixed it, and how to remove the guide ring from the flywheel should yours not come off easily.

• 11 BMW 1983 R100RS Remove Flywheel & Rear Main Seal
  • Remove Flywheel Guide Ring

Paint The Timing Marks

I like to add paint to the timing marks so they are easier to see. Before I paint them, I clean them with some brake cleaner to get any remaining oil out of the engraved timing marks.

I use different colors for each mark. Why? Because I can and it makes my flywheels “distinctive” 🙂

I use Testor’s plastic model paint: Yellow for top dead center (OT), White for the timing mark (S), and Red for full advance (Z). I use a tiny brush (or you can use the end of tooth pick) to fill in the engraved letters and let the paint dry. Then I lightly sand with 600 grit wet/dry paper to remove the over paint leaving the paint in the engraved areas.

Install Flywheel O-ring

There is a large o-ring inside the flywheel hub. I think mine was leaking as I could see small radial streaks of oil and clutch dust radiating from the bolt holes inside the flywheel hub on the back of the flywheel before I cleaned the flywheel. I use a screw driver to pop the o-ring out of its groove.

I bought a engine gasket kit from Euro MotoElectrics that includes the flywheel o-ring. But it’s in a bag with several others. I measure the new o-ring thickness as the one for the flywheel hub is 3 mm thick.

I put engine oil on the new o-ring and insert it into the groove in the hub with my fingers. I oil the o-ring so it won’t run dry when I first start the engine while it waits for oil to reach it.

Install Flywheel On Crankshaft

I use new flywheel bolts. Although these are the larger 11 mm bolts used on the 1981+ crankshafts, and in theory can be reused, I like to replace them after 40+ years “just because” I don’t want any surprises.

I use the locating marks I made on the flywheel and the crankshaft nose when I removed the flywheel to ensure I align the marked flywheel hole with the marked bolt hole in the crankshaft. Should I fail to align the flywheel bolt hole with the correct crankshaft bolt hole, ignition timing will be off and the bike won’t run or will run badly.

I put the flywheel on the crankshaft nose. I find it’s easier to install if you tilt it a bit so the top of the flywheel goes into the bell housing first.

I confirm the flywheel hole with the white paint witness mark is aligned with the flywheel bolt hole in the 11:00 position as shown in the picture.

Belt & Suspenders Confirmation That The Flywheel Is Mounted Correctly

WARNING:
If the flywheel is rotated by one crankshaft bolt hole from where it should be, the crankshaft will be out of synch with the flywheel by 72 degrees and the ignition timing marks on the flywheel will be out of synch by 36 degrees since ignition timing is defined by the camshaft which rotates at one-half the speed of the crank.

It’s easy to confirm you have the flywheel in the correct hole of the crankshaft. Keep in mind there are five flywheel bolts, so each of them is 72 degrees from the other since 72 x 5 = 360 degrees.

With the flywheel and guide ring pressed onto the crankshaft nose aligned with what I think is the correct crankshaft hole, I check that the “OT”, or Top-Dead-Center (TDC), indicator on the flywheel is visible through the timing window.

And, in this position, the crankshaft throw should be centered in the cylinder hole and pointing at me as shown below.

The picture below shows how far the crankshaft throw is displaced if I make a mistake and mount the flywheel one bolt hole away from the correct crankshaft hole. It’s easy to see “something isn’t right” :-). This is a simple method to confirm you have the flywheel mounted on the crankshaft in the correct orientation.

Assured the flywheel is correctly aligned with the crankshaft holes, I install the five flywheel bolts with dry threads, but only finger tight.

WARNING:
BMW increased the recommended torque settings for the flywheel bolts and mention “lightly oiled” threads. Unfortunately, if you oil the threads, the stress on them increases by about 30% compared to dry threads at the same torque. Since it is hard to know what “lightly oiled” really means, and to avoid the disaster of stripped threads in the crankshaft or a sheared flywheel bolt, I use dry threads and torque to the “lightly oiled” thread torque value. This method is recommended by a long time airhead mechanic, Tom Cutter.

Center Flywheel On The Bolts

The flywheel and guide ring holes are larger than the flywheel bolts. And, the ignition timing marks are affected if the flywheel is not centered on the five bolts. I use a propane torch to heat the flywheel around the outside of the bolts so the guide ring will expand allowing it and the flywheel to rotate back and forth on the five bolts.

Now, I look down onto the edge of the flywheel from where the starter motor mounts. I gently rotate the flywheel and guide ring back and forth. I make sure the crankshaft is not rotating which is why I heated the flywheel and guide ring so they will slip easily on the crankshaft nose. I rotate the flywheel clock wise until it butts up against one side of the bolts and then rotate the crankshaft so the edge of a flywheel tooth is just past the edge of the starter motor housing. Then I rotate the flywheel counter-clockwise until iti butts up against the other side of the bolts. I do this a couple times to see how far it moves, and to ensure that as I do rotate the flywheel back and forth, the crankshaft isn’t turning. The free play in the flywheel bolt holes is just a tiny bit more than the thickness of a flywheel tooth.

I rotate the flywheel on the crankshaft nose clockwise until the my reference tooth is covered and then rotate the flywheel counter-clockwise until half the flywheel tooth is exposed.

Then I finger tighten all five flywheel bolts while keeping an eye on the flywheel tooth to be sure it doesn’t move. I use my 19 mm socket and ratchet handle and carefully tighten the five bolts being sure I don’t rotate the flywheel on the end of the crankshaft.

Flywheel Free Play Converted To Degrees of Timing

Since the flywheel moves about the thickness of a flywheel tooth when I rock it back and forth on the flywheel bolts, I wondered how many degrees of ignition timing is represented by that much free play.

I measured the diameter of the flywheel and got about 235 mm. The thickness of a flywheel tooth is close to 3 mm.  The circumference of the flywheel is Pi x 235 or about 738 mm. Therefore, 738 mm / 360 is the length of flywheel circumference that equals one degree of flywheel rotation, or about 2 mm per degree. Finally, the maximum change in ignition timing caused by flywheel free play on the bolts is 3 / 2 or 1.5 degrees.

The “S” mark on this flywheel is 6 degrees from Top-Dead-Center (TDC), so an error of 1.5 degrees in timing is pretty significant. I conclude from this that getting the flywheel centered in the bolt holes is important.

Torque Flywheel Bolts

I don’t have a tool that will keep the flywheel from rotating. So I used a large blade, flat blade screwdriver and slip the blade between two of the flywheel teeth and place the shaft against the left side of the bell housing to brace the flywheel.

Keep Engine Block From Turning Over

I don’t have an engine stand, so I strap the engine block down tightly on top of my workbench. But I can’t keep the engine block from trying to tip over as I get closer to 90 Ft-lbs of torque on the flywheel bolts.

I use some scrap wood to block the engine so it can’t tip over as shown in the pictures below.

I screw a piece of scrap wood, as shown by the red circles, into the top of my workbench up against the left side of the oil pan.

I use a 2×4 as a brace and butt it up against the side of the bell housing on the right side of the engine. I screw another 2×4 as a runner to keep the 2×4 brace against the bell housing.

This impromptu solution keeps the engine block from moving or tipping over as I torque the flywheel bolts to 90 Ft-Lbs.

WARNING:
BMW increased the recommended torque settings for the flywheel bolts and mentions using “lightly oiled” threads. Unfortunately, if you oil the threads, the stress on them can increase by about 30% compared to dry threads at the same torque. Since it is hard to know what “lightly oiled” really means, and to avoid the disaster of stripped threads in the crankshaft or a sheared flywheel bolt, I use dry threads and torque to the “lightly oiled” thread torque value. This method is recommended by a long time airhead mechanic, Tom Cutter, who has had no flywheel bolt failures using this technique.

Now, I can remove the Cycle Works front bearing carrier removal tool as the crankshaft can’t move forward enough for the inside thrust washer to come of the pins since the flywheel is installed.

Revisions

2020-01-08  Typos.
2020-02-01  Warning about flywheel bolt torque.