I am replacing all the engine electrical components (Dyna III ignition, alternator, diode board and wiring) as well as replacing the timing chain, crankshaft timing gear and the crankshaft nose bearing and all the seals in the timing chest cover. You can read about how I removed the engine electrical components here:

• 12 BMW 1977 R100RS Replace Engine Electrical Components

You will need to remove these components to get access to the inner timing chest cover, so this procedure starts after the engine electrical components have been removed and the timing chest is accessible.

Parts List

Here are the parts I used for this work.

Part #	Description	Qty
11 21 1 250 198	SPROCKET (to 09/78)	1
11 31 1 250 258B	MASTERLINK CHAIN 1970-78  MAX BMW Part #	1
11 31 1 250 258 7	MASTERLINK FOR DUPLEX CHAIN  MAX BMW Part #	1
07 11 9 981 722	GROOVED BALL BEARING – 160 07	1
11 14 1 338 428	GASKET	1
11 14 1 338 429	WASHER-GASKET	2
11 14 1 262 282	CAMSHAFT SEAL – 20X32X7 (superceed by 11 14 7 705 086)	1
11 14 1 337 654	CRANKSHAFT SEAL – 28X47X7	1
11 31 1 256 861	TACHOMETER SHAFT SEAL – 7X16X7	1
11 14 1 262 644	POINTS SEAL STRIP 1976-1978 MODELS	1

There are three oil seals in the timing chest cover: the crankshaft, camshaft and tachometer shaft seals. I replace all three of these. I replace the seal strip that  fits in the groove of the housing that contains the points and ATU.

Tools

I use the same Cycle Works tools I used for the 1975 R75/6 work.

• 11 BMW 1975 R75/6 Replace Timing Chain, Crankshaft Sprocket, Nose Bearing: Tools

Disassembly Procedure

I previously did this much of this work on my 1975 R75/6 and where the procedure is the same for this 1977 R100RS, I provide links to the R75/6 procedure.

New work I did on the R100RS project includes replacing the tachometer drive cable and measuring the run out of the camshaft to see if it’s straight.

Remove Timing Chest Cover

Here is the front of the engine with the engine electric components removed from the timing chest cover. The crankshaft nose is covered by the Cycle Works puller nose.

I did this work previously on my 1975 R75/6 and the procedure is the same as required for the 1977 R100RS.  I use the Cycle Works tools to remove the timing chest cover. You can read about how I did this here.

• 11 BMW 1975 R75/6 Replace Timing Chain, Crankshaft Sprocket, Nose Bearing: Remove Inner Timing Cover

Note that the 1977 R100RS has (3) Allen head nuts and (9) Allen head bolts securing the cover.

I decided to use wheel bearing grease to lubricate the threads of the puller bolt this time.

Remove Oil Seals

I remove the three oil seals from the timing chest cover; the crankshaft, camshaft and tachometer drive.

I heat around the crankshaft and camshaft bores and remove the seals with a seal puller.

The tachometer drive has a helical gear that can be seen from the inside of the cover. The gear turns on a shaft in the bottom of the gear.

On the outside of the cover I can see the seal as the bushing the tachometer cable mounts in came out when I removed the cable.

I heat the case around the tachometer seal. I pull the gear to expose the shaft in the base of the gear. I use a screw driver and plastic mallet to gently tap the base of the helical gear to push it out. I don’t want to chip a gear tooth.

Here is the tachometer drive removed and it’s parts: the seal, a washer and the helical drive with shaft.

Add Timing Mark to Camshaft Sprocket

I position the crankshaft so the engine is at top dead center.

Since the camshaft turns at 1/2 the rate of the crankshaft, I carefully set the engine at TDC so what I think is the timing mark on the camshaft is at the 12:00 position. The timing mark is faint and I put some white paint on it. Note that it is not necessary to get this mark to the 12:00 position and you may not even see a mark on the camshaft sprocket. But it is very important to mark the valley of the camshaft sprocket that is straight up at the 12:00 position when the engine is at TDC so the relation between the crankshaft and camshaft timing is correct when installing the new timing chain and crankshaft gear.

NOTE:
The crankshaft sprocket has 19 teeth. Therefore the camshaft sprocket must have 38 teeth so it turns 1/2 as fast. This means the timing mark on the camshaft sprocket is in a valley while the mark on the crankshaft sprocket is on a tooth. But with the timing chain installed, you can’t see the mark on the crankshaft sprocket tooth. I show it later when I install the new crankshaft sprocket.

Remove Timing Chain Tensioner

The timing chain tensioner on the 1977 R100RS is the same design as the one used on my 1975 R75/6 and comes off the same way.

Before I start, I use a shop towel as a napkin to prevent the C-clip for potentially falling inside the engine through one of the holes on the front of the block.

Here is how I removed it on the R75/6.

• 11 BMW 1975 R75/6 Replace Timing Chain, Crankshaft Sprocket, Nose Bearing:  Remove Timing Chain Tensioner Arm and Spring

The rubber rubbing block is in good condition so I don’t replace the tensioner arm nor the spring as I did on the R75/6.

Remove Timing Chain

The original timing chain is continuous loop without a master link. I cut the chain using a bolt cutter. The new chain uses a master link.

On the 1975 R75/6, I used a cutoff wheel to cut through the plates of the timing chain. But that created a lot of shrapnel and debris as shown here:

• 11 BMW 1975 R75/6 Replace Timing Chain, Crankshaft Sprocket, Nose Bearing: Remove Timing Chain

I rented the bolt cutter at my local rent-all place. I got a very big one with 41″ handles. I almost couldn’t fit the jaws into the available space. I suggest getting one with 24″ handles. I took me two minutes to cut the plates on the double row chain and fracture the pins on one of the links so I could remove the chain.

Remove Crankshaft Sprocket & Nose Bearing

I use the Cycle Works tools to remove the crankshaft sprocket and nose bearing at the same time. Here is how I did this on the R75/6 and the procedure is the same for the R100RS.

• 11 BMW 1975 R75/6 Replace Timing Chain, Crankshaft Sprocket, Nose Bearing:  Remove Crankshaft Nose Bearing and Sprocket

Note that the two aluminum puller halves have a wide and a narrow shoulder inside. The narrow shoulder goes behind the crankshaft sprocket.

My son bought me some 1-3/8″ box end wrenches for this puller so this is their inaugural use.

The sprocket teeth are not badly worn, so the mileage on the odometer is likely accurate at 37,000 miles instead of 137,000 miles. Nonetheless, I’m replacing the sprocket and nose bearing while I’m in here. And, no signs of rust on these parts unlike on the other side of the timing chest cover, so that’s good.

Check If Camshaft Nose Is Straight

Since the Dyna III magnet on the ATU showed it had been rubbing on the left pickup, it’s possible the camshaft nose is bent. With the timing chain removed, it’s time to check and see how straight it is. I use a dial indicator with a goose neck that attaches to a pair of vice grips. I got this set at Harbor Freight.

I attach the vice grips to the left side timing chest cover stud and adjust the goose neck to the probe of the dial indicator rests on the tip of the camshaft.

Here is a short video of the measurement.

CLICK VIDEO TO RUN: Checking Camshaft Nose Run Out

The camshaft is not bent, so the rubbing must be due to misalignment of the pickup plate itself. I’ve ordered a new Dyna III ignition.

Installation Procedure

I refinished the timing chest cover to remove the corrosion and bring the finish back to as close to original condition as I can. I install new metal diode board mounts to replace the original rubber mounts.

I install a new timing chain, crankshaft sprocket and nose bearing and timing chest cover gaskets. The procedures are the same as what I documented for the R75/6.

Install New Crankshaft Sprocket

• 11 BMW 1975 R75/6 Replace Timing Chain, Crankshaft Sprocket, Nose Bearing:  Install New Crankshaft Sprocket

Install New Crankshaft Nose Bearing

• 11 BMW 1975 R75/6 Replace Timing Chain, Crankshaft Sprocket, Nose Bearing:  Install New Crankshaft Nose Bearing

I marked the crankshaft sprocket teeth behind the timing mark so I can see the mark when the timing chain is installed.

I moved the timing chain one tooth off to show how much misalignment occurs between the timing mark on the crankshaft and camshaft sprockets.

And here’s how the timing marks look when they are correctly aligned.

Install New Timing Chain with Master Link

The procedure is the same as I followed for the R75/6. This time I used masking tape to cover the holes in the engine case. I want it a bit sticky, but not too sticky so I can remove it easily. The trick is to rub the sticky side across my pants leg a couple times before sticking it on the engine case.

Note that the master link chain comes with two C-clips to secure the plate on the master link. These are very small and harder to install than a fish clip. I purchased a second master link with a fish clip. The link looks like the one that comes with the C-clips, but it is different. The grooves in the ends of the pins are wider. I got them mixed up and couldn’t get the fish clip to go on. I removed the link and found this difference in how they are made.

Install Timing Chain Tensioner and Spring

Although the following procedure shows installation of a new timing chain tensioner and spring, it’s the same procedure for installing the original parts on the R100RS.

• 11 BMW 1975 R75/6 Replace Timing Chain, Crankshaft Sprocket, Nose Bearing: Install New Timing Chain Tensioner Arm and Spring

Clean Timing Chest Cover & Engine Block

The timing chest cover has corrosion around the top, sides and on the outside.

I decided to clean the cover using bead blasting followed by an experimental home brew vapor blaster I have access to.  Here is the result; the corrosion is gone and it looks like new again.

Install Crankshaft Front Seal, Camshaft Seal and Tachometer Seal

I didn’t replace the tachometer drive seal on the R75/6. Here’s how I replaced the crankshaft and camshaft seals in the timing chest cover.

• 11 BMW 1975 R75/6 Replace Timing Chain, Crankshaft Sprocket, Nose Bearing:  Install Crankshaft Front Bearing Seal and Camshaft Seal

I install the tachometer drive with the parts in the following order.

I put a bit of engine oil on the circumference of the seal and I use a socket and extension to drive the tachometer drive and seal into the bore from the front side of the timing chest cover. I didn’t heat the seal bore and the assembly went in smoothly.

Here is how deep the seal goes and how it looks inside the drive housing.

Install New Metal Diode Board Mounts

I removed the original rubber diode board mounts and ground wires. I install new metal mounts from Euro MotoElectrics.

Install Timing Chest Cover

The procedure is the same as I followed for the R75/6.  It’s important to clean the gasket mating surface of the engine block and the rear of the timing chest cover before mounting the gaskets. Here is the procedure.

• 11 BMW 1975 R75/6 Replace Timing Chain, Crankshaft Sprocket, Nose Bearing:  Install New Inner Timing Cover Gasket and Two “Donut” Gaskets

I’ve had good success by heating the cover in the oven to 275 F. The cover slides on the crankshaft nose bearing easily, so I have not needed to use the Cycle Works tools. I installed new stainless steel bolts from a bolt kit in the four bottom holes which are outside the front engine cover and used the 5 of the original Allen bolts and 3 Allen nuts and torqued them down.

NOTE:
This time the nose bearing did not seat all the way into the bore of the timing chest cover. I did not find that out until a day later when I tried to rotate the engine by turning the flywheel in preparation for removing the flywheel to replace the rear main seal. It was very hard to turn the engine. I had installed all the engine electrical components on the timing chest cover, so they had to be removed. Then I loosened the (9) Allen bolts and (3) nuts and the flywheel easily turned the engine again. I heated around the front crankshaft seal with my heat gun until it was 190 F, used a plastic mallet and a socket extension and tapped around the ridge in the timing chest cover surrounding the seal. When I torqued the bolts and nuts again, the flywheel remained easy to turn.

So, an easy test to tell if the nose bearing is seated all the way in the bore is to try turning the flywheel when you have the bolts and nuts torqued and it should be very easy to turn (assuming the spark plugs are out).

Here is engine with the new timing chain, crankshaft sprocket, nose bearing, refinished timing chest cover with new crankshaft, camshaft and tachometer drive seals. They should be good for another 40 years.

The next work is to install the new engine electrical components and wiring harnesses. You can read how I do that here:

• 12 BMW 1977 R100RS Replace Engine Electrical Components

Revisions

2019-12-06  Edits and typos.