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2022-07-19 Barrie's 1990 BMW R100RT

dcarver's picture
published by dcarver on Mon, 07/18/2022 - 13:08
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2025 Miscellaneous

Me: “Oh look, a grenade. I think I’ll jump on it!”

 

Another way of saying I decided to help my bud Barrie with his RT.

 

As they say, “Hold my beer, watch this!”

 

Barrie bought the bike new. Almost 300k miles and she was puking oil out the crankcase breather. As in a lot of oil. Sometimes he could had a quart, or two, and it would stop puking… then after xxxx amount of miles and time, start puking again.

 

So he took it to a local independent shop, a ‘on the side’ job, where it was determined to have excessive leak by. Imagine that.

 

A known good short block was purchased for ~700 USD, then the typical stuff <supposedly> done… Bored to accept new pistons, rings, valve work…

 

I say ‘supposedly’ because the mechanic decided to quit, leave the shop and area, overnight. Hmmm. 

 

The RT is 90% together, supposedly the only remaining work was install carbs, some electrical.. which the shop owner, who isn’t a tech and has no techs, completed the work.

 

Barrie went to pick it up… she started, ran ok, note just ‘ok’, then started smoking (from where I don’t, exhaust or residual oil on headers) then got to point of barely running.

 

Soooo, after 8 months at the shop, it will be on my lift tomorrow, ASSuming AAA tows it.

 

Barrie is our local Wed/Sat fearless leader, he’s in his 80’s now, and was/is sooo dejected. 

 

So, Oh look, a grenade!

 

Gonna start with basics.. Compression, leak down tests. Fresh battery. Mechanical carb sync to get it close… I may fail miserably, but honestly, the patient is already dead, so why not try?

Submitted by dcarver on Thu, 07/21/2022 - 11:17.

Well, no good news yet.

 
  • Bike arrived.
  • Pushed up the hill to lift
  • Hmm, shop owner stated ‘running perfectly’ yesterday
  • Fire it up. Sounds like shit, stumbling, barely running. Starter motor sounds like shit too.. clanky loud, grinding sounds WTFO? Engine surging from 1,200 to 3,000 rpm. Max vacuum leak?
  • Ride it up on lift, barely makes it
  • Turn it off
  • Pull spark plugs. RHS extremely lean, LHS only ‘dangerously’ lean
  • Fiddle and fart around.. 
  • WTFO? Rubber boot for drive shaft has no freaking clamp! Leaking oil directly on exhaust plenum. That shop is the shits. Really. At least you didn’t ride it and damage the u-joints drive shaft, tranny output due to lack of lubricant. Most likely the smoke cloud you described earlier…
  • Attempt to fire it again. Nothing. No starter motor. Key on, hit button, click click click says the starter motor relay, no starter action. Great.
  • Put on battery charger, leave overnight. It’s hot out, 104F, done for the day
  • Next day hit starter button and voila, it turns over but doesn’t continue running. Hit start button again, nada, zip, zilch.
  • Hoping it’s something simple, loose cable at starter motor, battery, or ground.
Barrie, no offense, but I’ve never seen anything this bad from a so-called shop in my life. They should have paid you $1,800 for the pleasure or provided a hooker or something? :)
 
Fortunately, I have a friend who is an AirHead Xpert… I’ve been picking his brain for airhead tips and tricks. When it cools down I’ll be after it again this evening.
 
Have a good pine mtn ride, 
 
D

Submitted by dcarver on Thu, 07/21/2022 - 11:20.
Don, 
 
For an unknown Airhead which isn't running correctly - Do the following: 
 
  1. Pull the spark plugs. 
  1. Pull the valve covers.
  1. Pull the negative terminal off the battery so there is NO possibility of power to the bike.
  1. Pull the front cover of the engine. Should be 3 screws one short one at the bottom and one on each side about 1/2 way up the cover. 
  1. You will see a rubber timing plug on the Left side of the engine (as you sit on the bike) behind and slightly above the Left Carb. Remove that and the flywheel will be visible. 
  1. Using a relatively thin long bladed screwdriver, and a flashlight to see in the hole, rotate the engine in the clockwise direction (flywheel moving down from the top)  a tooth at a time with the screwdriver. As the flywheel rotates you will eventually see an F or a Z in the window (depends on model), keep rotating and you will see the Letters OT etched on the flywheel.   The left side of the window (on the block) has a V etched in it. Line up the OT with the V in the window of the block. 
  1. Check the valves by moving them by hand,  one side should be loose, the other side should be tight.   One side is on TDC the other side is on BDC (Boxer Engine).  
  1. On the "Loose" side, try to move the rocker arm up and down.  There should be a tiny bit of clearance (.001 thousand's) in the up and down movement of the rocker arm. IF NOT, you will see two head bolts which hold the rocker arm in place (15 mm I think).  carefully and slowly loosen them (top and bottom of the rocker arm) and squeeze the two mounting parts together, thereby taking up excess slack.  You need three hands here hold the rocker arm mounts tight and tighten the head bolts. Sometimes I use a big C clamp and a couple of short sockets as spacers. Light pressure don't get crazy here. 
  1. Tighten the two head bolts in increments of 5 ft. Lbs.  to 25 ft. lbs. NO MORE THAN 26 ft. lbs. with a known good torque wrench. 
  1. Once the rocker arm slack is adjusted properly, check the valve clearance for .006 thousandths on the INTAKE valve (Carb side of the Head) and .008 thousandths on the Exhaust valve (Exhaust pipe side). 
  1. Once the valve clearance is correct. ROTATE THE ENGINE 180 degrees (using same method used before) until the OT shows once again in the window.  NOW the opposite side valves to what you just worked on should be loose.  
  1. Follow the same procedure to set the Rocker arm slack and the Valve Clearance as before. 
  1. Replace the valve covers.  IF the gaskets are torn, replace them to prevent leaking.  I always use a tiny "smear" of wheel bearing grease on the surface of the covers.  Seems to help prevent leaking. Don't over torque these bolts they are small. 
  1. ONCE you are sure the valve clearance is set correctly, (you did remove the front cover and removed the NEGATIVE battery leady right?).  ON the front of the engine and down low toward the front crossover exhaust pipe, you will see a "Bean Can"!  This is the electronic ignition which runs off the camshaft. There are 2 ea. 4 mm set screws to hold it in place. 
  1. Timing is set by loosening the 4 mm sets screws and rotating the Bean Can,  to get the proper display in the timing window (where you were turning the flywheel with the screwdriver). Rotating it Clockwise will Retard the timing!  Rotating it Counterclockwise will Advance the timing. 
  1. The timing can be set statically but it is best to use a timing light.  HOWEVER, since the bike was running somewhat, timing should be close.
  1. Once you are assured the valves are set correctly.   Please read the attached file, 4 times and compare the photos to your carbs!!
  1. This Carb Sync and Adjustment procedure I wrote has been used, checked, and critiqued (then modified) by Airhead folks all over the World.  TRUTH! 
  1. Having the valves set correctly, then set the Carbs initially settings, (as recommended by my Carb adjustment procedure). 
  1. Cable slack first, (3-4 mm of free play), then the air/fuel idle mixture screw 1 turn out from seated, AND the bike should start and run. Maybe NOT well but run. 
  1. NOTE: There are a LOT of things about the Bing Carbs which can be set up wrong!! Such as: 
            A. Needles in the wrong positions. 
 
            B. Bad Diaphragms. 
 
            C. Worn/broken "O" rings inside the carbs on various Jets. etc. 
 
            D. Float Levels set incorrectly. 
 
            E. AND other things. A Bing Carb Manual is a big help here. 
 
Hopefully this will get the bike started and running fairly well. 
 
There are a few other things to check, the Ignition module needs to be removed from the heat sink (Aluminum plate with fins under the tank on the right side of the bike) the old heat sink compound cleaned off and new applied. Check the resistance of the plug wires from one side to the other THROUGH the coils, etc., but those are things for later, once you get it running. 
 
This should be enough to confuse you for tonight, getting late here. 
 
Me tired. 
 
dj
 

 

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