Excessive vibration

[supershaft]

Originally Posted by Horsehockey

Thank you Professor Disston. Maybe this explains the big difference I noticed in how difficult it was to remove and reinstall the wrist pins the three times I've done that on an airhead. Sometimes easy, sometimes harder n' hell. Sounds like the alignment on them things can be off by more than I thought.

That phenomenon is mostly not about the twist in the rods. It's varying interference fit in the pistons and varying pin/bushing fit and bushing bevel. I have sized enough wrist pin bushings on a Sunnen rod honing machine to know for sure that if you get that down to .0003 or .0004" like it is suppose to be sometimes you would swear the pin is never going to go in with the rod and pin right there in your hands! Then you try and try again and it falls right in with plenty of room to slide back and forth.

[headtube]

Originally Posted by DaveBall

Headtube, As this is your first Airhead, what other bikes have you ridden?

Been riding motos for years now. Owned a few Nippon bikes in the 70's and 80's. More recently I have restored/rebuilt and ridden a 72 Triumph Bonnie and a BSA Royal Star. The BSA I continue to enjoy. Always wanted the Beemer RS model so I decided to grab it when it came my way.

Riding British bikes have made me quite familiar to vibration. But this a is a different kettle of fish. My foray into BMW territory is new for sure, but the principles are the same, right? I'm not used to feeling the right to left tidal wave motion of two opposing pistons fighting against each other. That's how it feels. Very pronounced at idle to about 4000, then everything smooths out nicely all the way to 7000.

BTW... I though two hydraulic discs up front would be far better than my 1970 dual leading shoe drum brake. Not by much. What's with that? Time for a bleed.

Thanks for the tips guys. I'll try to hook up with some other airheads

[DaveBall]

You will definitely feel that side to side vibe at idle and up to about 2000RPM. Beyond that, you probably need a carb balance.

Those twin disks should work very well. If you have the original rubber brake hoses, replace them with some quality braided stainless. Speigler makes a pretty nice kit, that includes the line for the rear disk as well. Change out the original fluid and reverse bleed the system. You will find a HUGE difference. Won't be as good as some of the new bikes, but will definitely improve over the stock OEM setup.

[disston]

The Airheads do vibrate more than I think they should. But they all do it I think. Since I have only ever been on any Airhead that was mine and that I tuned, except once, I've always been paranoid that this is a personal problem. Well, I decided a long time ago I wouldn't let that stop me and so i ride the bike I built and tuned.

Mine vibrates mostly between 3000 and 4000 rpm. And idle is not always very smooth, but sometimes it's better than others. If I get tired of the racket the trans makes in neutral at a light I will pull the clutch in. But mostly I just let it rattle away.

You should of heard them when we had the Turkey valves. On top of the rattle at idle there was a honking noise from the engine breather.

I think the /2s were truly smooth.

Check the eccentric adjustment of the caliper mounting. The pins also need to be cleaned and greased. The pins are extracted from under the cap on the bottom of the fork tube. The eccentric is held in place by a stout spring. To get it out after removing the cap and the spring a small bolt (8mm maybe) is threaded into the end, it's drilled and threaded for this, and the eccentric is pulled out. If it's been a long time since these were pulled the grease can be very dry and the part hard to remove. Use ordinary wheel bearing grease.

The adjustment is explained better in the manual than I think I can tell it but I don't do it the way the manual says to anyway. The manual has something about an involved process of marking the rotor and adjusting the eccentric so the brake pads wipe the markings off. All really nice I guess. I just watch how the parts are moving and set the caliper to it's closest position. My method may not be correct.