I have a 1981 r100rt that runs almost as smooth as my k75s, I picked up a year ago a 1988 r100rt for a price I could not walk away from. It is in excellent condition,except it has always had excessive engine vibration IMO.This year I wanted to take my road trips on it but I needed to rid the bike of the nasty vibration. I thought I could could get rid of the problem by setting the valves , sinking the carbs, and checking the timing. I have done all of that and to my surprise the the bike is very quick and quite fast but the nasty vibration is still there. It is like the vibration on a old Honda cb750, puts your butt and hands to sleep but will smooth out @ 4200rpm plus. what vibration that is still there is still unacceptable to me.
I have had a bmw mechanic ride it and he said he has ridden smoother, but it is not the ruffist one he has ridden, and in his opinion the vibration is in the engine and to start with the top end or just ride it. I have read somewhere that the r100's with the small valves and 32mm sings run rougher , this I don't believe. I am going to put it on the lift and pull the pistons and connecting rods to balance them. Before I do that I would like to know or get input if I have missed any thing that could cause this like poor ignition spark or something.
Thanks guys
I have a 1979 RT that is dead smooth. Like you, I purchased a 1988 RS that had an annoying vibration.
I am no BMW specialist, but can tell you that a detailed balancing of the carbs and correctly setting the ignition timing smoothed out my '88 to where I actually prefer the later bike now. Here's the extra steps I took that made all the difference....
► Timing. Some of the manuals will tell you to strobe time on the "S" mark at idle. To me that's a mistake, becasue that's not where you ride the machine. You'll want to strobe time at very high RPM using the "F" mark.
► After a full warm up ride, come back and balance the carbs at idle (~1000 RPM). Here's the second part a lot of people forget.... Now, while the gauge is still in place, you need to balance the carbs at 1500-1800 RPM using the cable adjusters. Finally, check for throttle cable outer sheath free-play at the twist grip of at least 2mm.
► Install new NGK 5000 Ohm spark plug caps.
► Install new NGK BP7ES plugs.
► Install new metal core spark plug wires.
► Check and replace the carb diaphragms as required.
Other Ideas
At the core of your engine balance theory might be the idea that a little old man in lederhosen polishes each rod until they all weigh exactly (say for instance) 500.000 grams, and that on Friday after a good lunch at the Hofbrauhaus, sometimes 470.89 or 517.12 grams will just have to do. That is simply not the case.
Modern engines are assembled so that all the pistons and rods are weighed right after production. Then depending upon their finished weight, they are matched with an identical twin. The factory achieves the same objective of good engine balance by building engines with pairs of matched weight parts. So unless your engine was blown and built back up by an absolute novice, there is hardly any way rods or pistons can be causing your vibration issue. Therefore, taking the top end apart IMHO would be a very expensive exercise to accomplish very, very little.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Torque engine mounting bolts.
I will try your sugestions I really dont want to take the bike apart thank you for your imput ,I have not heard of that tuneup proceedure and would not have known of it if it were not for this form once again thanks alot!
Thank you for your input. I have not heard of that tuneup procedure....
► To which procedure are you referring ?
► One minor clarification....
• On the plug caps, I should have said "replace the OEM plug caps becasue they are 30 years old, if that hasn't already been done." Recently replaced NGK plug caps aren't due to fail for another 30 years ! So it's not necessary to replace good parts.
• On the plugs, I should have said "replace plugs older than 1 year, if that hasn't already been done." Even good looking plugs can be partially fouled, and the major reason these days is running the bike on stale fuel left in the tank or float bowls over the winter, or other extended non-riding season.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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