Loud clatter/ chatter when warmed up 1975 R90/6

Sounds like a general project, but a nicely sorted R90/6 is a good ride and well worth resuscitating--essentially all of the useful power of a 90S, but without fussiness of too-cool-for-school paint.

fxray said:

The Airheads Beemer Club continues to print one of Oak Okleshen's previously unpublished articles every month in the Airmail Magazine.



OP said in his first post that the noise does not occur above 1500 rpm, and is most noticeable when idling at a stop sign or light.



Yes, except that is hard to do when the stoplight turns red, and he has to sit and listen to the clatter and chatter while waiting for the green light.

Click to expand...

The search for perfection must be a total frustration...…...Acceptance of reality is serenity...…….God bless.....Dennis

The crankcase breather valve has become my 1st suspect. Would like to update to new version. Problem is base of breather valve is frozen to the engine casting. Removed clip, spring, and washers. Have tried a punch and small hammer to break loose and rotate, no luck. Heat gun, same punch and hammer, no luck. Small torch flame, punch and hammer, no luck. Tried to work sharpie blade between vent base and casting no luck. Caution is needed, looks like any debris goes right into crankcase. Studied parts diagram, looks like it should just be seated and easily removable. Plus needs removed to install new vent. Any info or advice would be appreciated.

Try a slide hammer. Loop some stout wire around the old breather and hook to a slide hammer. Heating around the base would be helpful as well.

Good thought, I do have a slide hammer. Now....... where is it.

Found issue to be wire large enough to take impact of sliding hammer, did not want to loop and thread upwards to be used as a link for the sliding hammer to attach to. Ended up using doubled up orange baling twine around each of the three sections of the base. This did allow me to hammer away with considerable upward force. But after 20 to 25 blows, no movement at all. Negative part of using baling twine is I can't apply too much heat or it will melt. Sprayed JB Blaster on base seam and taking a lunch break. STRIKE TWO.

Time and penetrant are your friends...plus hot-cold cycling to help suck the fluid in. As stated on the forum before, the best penetrant is a 50-50 mix of acetone and automatic transmission fluid.

Have both for that mixture.

The smallest, cheapest slide hammer from Harbor Freight includes a hook that will fit inside the slots on the breather base. If you put it in one slot, hook the edge, give a couple light taps with the slide, then repeat in the next slot, and work your way around, the breather will pop out in less time than it took you to read this. Afterwards, the slide hammer is bound to be useful in the future for lots of other situations.

Thanks fxray, May have found the problem but need wheels back and a test ride before I can report success or failure.

While cleaning the engine found right rear portion of air cleaner assembly not aligned correctly. It was making contact at the rear, but as I followed the seam to the front there was a 1/8 gap. This followed to the top where it was above the starter cover by the same 1/8 inch. After I corrected the position of the assembly I thought I had maybe found my noise problem. Before if I started the bike and let it idle for about 6 min's the noise would begin. After I correctly positioned the assembly, I ran the engine to the ten min time frame about 5 times over a 3 day period. Not A sound, none. Finally installed the the wheels with new tires last night and took my 1st test ride this morning. After 15 mile ride things were sounding good, no noise. Two hours later took another ride and D--nit, it's back. So will return to air vent updating.

Nice find.

There always seems to be a learning period with a newly acquired machine.

Well ... noise definitely being caused by crankcase vent. Removed cover, got bike to operating temp till noise was at full volume. Removed vent cover, when I held fiber disk up or held down the noise immediately disappeared. Tried Snowbum mod with 3/64 inch hole drilled into vent cover. It had minimal affect on the noise. Guess Im ordereding the new reed type updated vent.

This is an advance apology to Snowbum. When I read the instructions for modifying the crankcase vent. I, at the time could not imagine drilling a 3/64 inch hole in the disk itself. It would be like drilling a hole through the heart during heart surgery. I drilled a hole through the vent case instead. After it didn't work, I reviewed in my mind his instructions. Drill the hole at the 50% radius position. Will not describe the contortions I went through trying to figure out the 50% radius position of the vent CASE. Nor will I lament how desperate I desired a picture that had a red arrow that said DRILL HERE. This evening I had the shocking thought, what if he did mean drill a hole in the disk. How much simpler his directions became. Even I, can determine the 50% radius position of a circle. So.. thats what I did. Hopefully test ride in the morning. Drilling a hole in the disk would seem to release some of the pressure under the disk, preventing it from establishing a harmonic pressure that resonates through out the crankcase. Says the bear of little brain. Wish me luck.

Drilled a 3/64 inch hole in the disk, but after 20 miles or so the noise was back. It helped some what maybe 10 to 20%. Since I want to eliminate the noise I'll have to try the newer breather, hose, and cap.Thanks everyone for your suggestions and involvement.

All you really need is the reed type breather. You can use all the other existing parts. A little dab of JB Weld would plug that extra hole you drilled in the cover.

Had sealed the hole I'd drilled in the cap with permatex when I had drilled the hole in the disk. Also considered ordering just the reed base. But decided I liked the look of the upturned hose fitting on the new cap, as well as the sinusoidal look of the new hose. Have such a distain for the noise I could imagine the impediment to noise and oil ladened mist the whole new set up might give. So... close to $130.00 dollars on the credit card and within a week all should be on it's way. Only to take a 40 mile ride this morning stopping and idling at 20 or so stop signs or lights, not a sound. No chatter, clatter, warble, gobble, nothing. Perfect ride. They always need to let you know who is in charge,don't they.