The first engine start is always a major milestone on a project. I usually perform this earlier in the build than I am on this project. But, my gas tank and the other parts that I had painted have been delayed coming back, so I’ve done everything else I can do until I got the gas tank in hand.

First Engine Start Check List

There are details that have to attend to before I start the engine for the first time so I made up a check list to ensure I didn’t forget anything.

Verify Engine Oil Level
Verify Transmission Oil Level
Verify Rear Drive Oil Level
Verify Swing Arm Oil Level
Verify Fill & Drain Bolts Tight
Set Carburetor Jetting
Static Balance Carburetors
Install And Gap Spark Plugs
Test Coil & Plug Wires Resistance
Install Spark Plugs And Wires
Oil Pressure & Flow Check
	Install Oil Thermostat Bolt To Open Thermostat
	Remove Top Spark Plugs
	Remove Coil  Power Wires
	Crank for 5 seconds and then rest
	Verify Oil Pressure Light Goes Out
	Verify Oil Flows From Top Of Rocker Blocks
Verify Valve Clearance Set (I-0.006, E-0.008 inches)
Install Valve Covers
Connect Coil Power Wires
Statically Set Ignition Timing
Remove Thermostat Bolt & Install Original Bolt / Washer
1st Engine Start Sequence
	Fuel On Reserve
	Check Fuel Level In Float Bowls (28 mm)
	Choke On
	Start
	15 Seconds @ 3000 RPM
	45 Seconds @ 3500 With Blibs To 4000 RPM
	Engine Off
Ride For 10 Miles (15-20 Minutes) Vary RPM 3000-4000 RPM
	Back Off Throttle Then Accelerate Every Minute or So To 4,500 RPM

Video

Here is a summary video of the preparation for and first engine start.

VIDEO: 1983 BMW R100RS/RT First Engine Start

Check Fluids

I inspect the dip stick, remove the transmission, swing arm, and final drive fill plugs and verify they all have fluid.

Setup Carburetors

When I installed the carburetors, I changed the jetting since I increased compression from 8.2:1 to 9.5:1 and had the heads modified for dual spark plugs. This changes the carburetion. Here is how I did this.

• 13 BMW 1983 R100RS Install Carburetors, Cables and Air Box
  • Setup Carburetors

Install Spark Plugs And Plug Wires

When I had the heads modified for the second spark plug on the bottom of the head, I had Randy Long build up the surface the spark plug mates with so the reach of the plug (3/4 inch) is the same as the top plug so I can use four of the same size spark plugs. For the higher compression this engine develops, I use NGK BP7ES plugs used on the earlier 9.5:1 compression engines which are a step colder than the the BP6ES plugs that were used with the original 8.2:1 compression engine. I set the gap to 0.6 mm (0.024 inches) on the four plugs and install them.

I install new spark plug wires I got from Euro MotoElectrics. The wires need to be longer to reach the bottom plugs so they supply two different length wires. The stock plug wires come with the plug caps installed but the longer wires come with the plug caps separate so I have to install the caps on the ends of the wires.

Spark Plug Wire Routing

I use the shorter spark plug wire and route it from the front coil port to the top spark plug on the cylinder that’s on the same side as the coil. I route the longer spark plug wire from the rear coil port over the bottom spark plug on the cylinder on the opposite side from the coil. There are two reasons I route the plug wires this way.

Since both coils fire at the same time, one coil sees spark plugs with high compression fuel/air mixture and the other sees a very low compression mixture as the valves are open. A dense mixture requires more power for the spark to jump the gap. So by having each plug in a cylinder get power from a separate coil, more energy is transferred to those spark plugs as each coil is powering a second plug in a cylinder with less dense mixture. This improves combustion.

The other reason is that if one coil fails, the other coil fires one plug in each cylinder all the time, and so the engine will keep running, perhaps not as happily as it did before, but enough to get home. I like exploiting this redundancy to improve reliability of the ignition system.

Since I installed non-stock dual port coils the distance from the coil to the spark plug is shorter than for the stock coil. I trimmed the top spark plug wires and shortened them about 8 inches so they fit comfortably but don’t have too much excess wire to get in the way.

Verify Spark Plug Cap And Coil Resistance

The electronic ignition requires 5,000 (5K) ohm plug caps, not the 1K ohm caps used on the non-electronic ignition engines. I use my ohm meter to measure the resistance and they are nominally 5K ohms.

Then I measure the resistance from one plug cap to the other through the coil. I subtract the nominal resistance of the two plug wires and caps, (10K ohms), from the nominal resistance of 23K ohms I measured. The coils have an internal resistance of 13K ohms which is the specification supplied by Euro MotoElectrics for these coils.

Prime & Pressurize The Oil System

Before I start the engine for the first time I need to prime the oil system. I install a special bolt to push open the thermostat on the oil cooler so it will fill with oil when I crank the engine. Here is a description of how I use the bolt.

• 11 BMW 1983 R100RS Shim Oil Filter Canister, Install Oil Cooler & Filter
  • Filling The Oil Cooler Safely

I remove the top spark plugs. I make sure the GREEN-Blue and RED wires that attach to the left coil are disconnected so I don’t have any chance of damaging the electronic ignition system while I crank the engine with the plugs removed.

NOTE:
I’m likely okay since I have dual plug heads and the bottom plugs are installed and will discharge the coils, but I try to be careful I don’t inadvertently damage the electronic ignition system if I have the spark plugs out while cranking the engine.

I crank the engine for five seconds or so and then stop for 10 seconds and repeat so the starter motor doesn’t get overheated. After a couple of these cycles the oil pressure light goes out. After a few more cycles I get oil flowing out of the top rocker assembly pillow block on both cylinders. After I finish priming the oil system, I remove the special bolt and install the original bolt.

Verify Valve Clearances

I set them when I installed the top end, but I want to verify the clearances haven’t changed since the engine has sat for several months and the head gasket may have compressed a bit in the meantime. I leave the valve clearances a bit loose for the first 600 miles or so on the engine: 0.008 in. (0.20 mm) exhaust; 0.006 in. (0.15 mm) intake. After that, when the valve clearance stabilizes, I will set the clearances to the normal values: 0.006 inches (0.15 mm) for the exhaust and 0.004 inches (0.10 mm) for the intake valve.

I rotate the engine until the bar above the “OT” mark, which is top-dead-center, is aligned with the groove in the left side of the timing window. I put the transmission in second gear and rotate the engine by turning the rear wheel in the normal direction of rotation. I loosen the tappet retaining nut and check the clearances. They have not changed.

Statically Set Ignition Timing

I have to set the ignition timing statically prior to the first engine start. Afterwards I’ll use a timing light to dynamically set the ignition timing.

I remove the battery ground cable. As an added protection against inadvertent grounding I slide the ground terminal inside a plastic sleeve. Then I remove the front engine cover. If it touches the diode board,which it will, the cover will short out the diode board if the battery is still connected.

I remove the oil cooler bracket and hang the cooler off the fairing middle bracket so it’s out of the way. I remove the two Allen bolts that secure the front cover to expose the Euro MotoElectrics optical trigger unit mounted to the alternator rotor.

Then I attach the GREEN–Blue coil power wire to the left outside terminal along with the RED optical-electronic ignition wire to power it and reattach the battery ground cable.

The optical ignition module from Euro MotoElectrics that I installed uses a timing wheel which is circular plate with a slot that rotates between two arms of an optical sensor to act as a crankshaft position sensor.

When the slot is in front of the optical sensor, the optical sensor sees light and turns on. The ignition control unit (ICU) interprets the sensor turning on as TDC. The slot is a fixed number of degrees wide and when the trailing edge of the slot obstructs the sensor light, the sensor turns off. The ICU uses the time the trigger was on and the number of degrees the slot is wide to compute the RPM. Based on the RPM, it selects the amount of ignition advance to use from an the ignition advance map stored in memory.

There are three advance curves to choose from. The #2 curve has a maximum advance of 28 degrees BTDC with an idle advance of 8 degrees BTDC which is what I will use.

NOTE:
The idle advance maybe too much advance and it could affect the carburetor adjustments at idle and how smoothly the engine accelerates off idle. I’ll have to see what happens and adjust things accordingly.

To statically set the ignition timing, the engine needs to be at top dead center. I put the  engine at TDC to adjust the valves so it is already set. I loosen the two small Allan, screws securing the timing wheel to the sleeve and rotate the timing wheel clockwise so leading edge of the slot causes the LED to just turn off. I tighten the two set screws on the timing wheel to hold it in place.

Install Gas Tank And Seat

I install the gas tank and cut new fuel line to connect to the carburetors. Then I put gas some gas in the tank, turn the petcocks to reserve and fill the float bowls. I turn the petcocks off and carefully remove the float bowls. I use a caliper to measure the depth of  the fuel in the center of the float bowl. If the floats are set properly, the fuel depth should be 28 mm, which is the case with both float bowls.

I slide the seat hinges on the pins and close the seat so I can complete the first engine start procedure which includes 10 miles of riding to help seat the rings.

Starting Engine

It’s Labor Day morning, 2020. So here goes. I put the choke 1/2 on and hit the starter button. The engine fires after about three revolutions and I back off the choke as much as I can and open the throttle gently and then close the choke. I increase the RPM to 3,000 and hold that for about 15 seconds. Then I increase the RPM to 3,500 with a couple blips to 4,000 for 45 seconds. Then I turn off the engine.

The idea is to force the new rings into the cylinder wall and score the rings from the small scratches put into the cylinder wall by the cylinder hone. The scratches are what seal the rings and prevent the engine from burning oil. I live at 5,500 feet elevation so I use a bit higher RPM during the first engine start since the cylinder pressure is about 10% lower than at sea level.The higher RPM ensures the rings mate with the cylinder wall immediately.

10 Mile Ride for 20-25 Minutes

After the first engine start I put on my riding gear and ride for 10 miles holding the RPM at 3,000 – 4,000 with some blips to 4,500 RPM. Several times a minute, I close the throttle and let the RPM drop to 3,000 and the accelerate back to 4,000 RPM. Just before I close the throttle again I blip it to 4,500 RPM. I ride the bike this way for 10 miles in my neighborhood and on a couple feeder roads which takes about 20 minutes.

I had to lower the idle RPM on the ride as it became too high, but I expected that and brought a screw driver in my jacket pocket, since I set the throttle stop screws at 1-1/2 turns to make sure the engine would start and idle with little need for the choke.

When I got back from the this first ride, I checked for any oil, gear lube, gas, or brake fluid leaks. Everything was tight with no leaks. Then I drain the engine and transmission oil to get rid of the assembly lube and to remove any metal filings that typically are produced during the first engine start. The transmission magnetic drain plug has some steel whiskers that are typical when new gears are installed.

I also remove, open and replace the oil filter to check for any obvious debris. There is always some small bits of aluminum, gasket and seal rubber in the filter, but nothing to worry about. This is why I like to drain the oil and the transmission after the first 10 miles to remove this debris

So, this is a project milestone. The engine runs, the transmission shifts, the optical-electronic ignition ignites, the brakes stop, the forks work and nothing fell off or leaked. Onward to complete the project.