got the R90 out in the sun

[8ninety8]

Here's what PO left inside engine with two cracked lifters. Likely caused by a rush teardown and misaligned chain sprockets. Almost parted it out. Had a BMW airhead mechanic at dealer install new cam and my crank in a good used block.

As for performance, I rode it only about five miles when I knew there were major problems. Had several other bikes, so I kept it as a project. With new cam it came alive, still hesitated under 3k rpms. Installed venturied inlets. Hesitation solved, IMO. The tapered inlet manifold accelerates the mix. Some would say it also limits WFO rpm if racing on a two and half mile oval. Don't spend much time over 7k as I want to keep riding this bike. Like all airheads, 4/5k is saweet.

These being real world rider bikes, bikes which we can ride across the country in relative comfort/speed/reliablity, throttle response roll-on from idle jets to mains is improved with the venturied effect, in my opinion. The Dels squirt that fuel, the narrowed inlet accelerates it, and the 64 degrees of overlap of 336 sucks it right out the rear end. All the best to your efforts keeping another airhead on the road. Had no idea over twenty years back that this bike would be such a source of fun times.

Caveat, I'm not expert in any of these areas, just an amateur wrench, loves to use the hands, and does a lot of research before going in.

[8ninety8]

Before assembly with sealant dripping, since pushrod rings were drifted down approx. 3mm, (go figure, no wonder they always leaked) and to avoid stomping around garage waving arms in exasperation having to remove wrist pins again for whatever problem, decided the seemingly mundane task of checking, before assembly! And remarkably they snugged up after compressing almost a quarter inch! Remove immediately with slight rubber tap, good to go as soon as Loctite 51031 is in grasp. Don't rush, use brain instead of feelings. And ride the bicycle. Garage floor is still sweating.

[8ninety8]

Can almost see how far out of spec. those rings were, there's about 2mm of shiney tube showing now.

[8ninety8]

Thanx to 20774 for magnificent job, and for excellent diagram on how to measure pushrod tube ring with straight edge and cylinder base. Most would agree, we are all in great debt to this website and the indefatigable efforts of BMW motorcycle owners of A and who, apparently, selflessly perform their duties.

[20774]

Thanx ....for excellent diagram on how to measure pushrod tube ring with straight edge and cylinder base.

I'll give credit to Oak for this. I received his version on an email a number of years ago when he was discussing it on the Airhead list. I requested his figure and he sent me one. Rather than just straight publish his work, I transformed it a bit to create my version. Still, it is Oak's knowledge that is in this figure.

[8ninety8]

After the fact it may have been prudent to mark yer stuff before the fact, where it's not noticed. Later stuff can be identified. Best when apart. Another brainless cold Saturday. Or, if you've got an immaculate stock copy, don't? Kinda like a golf ball? So you can find it.

[20774]

898 really knows how to mess up the next owner...they're going to come on this forum and ask what "898" means on the heads!!

[8ninety8]

It's really fun working on the bike. I'm paranoid when I leave anything with a shop. Like to get back the parts I left. A couple markings aways help out in these siterations. In the case of theft, the thief never knows where a mark may be hidden, in case of recovery. Next owner?, when you pass over, you lose all concern for temporal possessions. And, everybody will know about old 898. Strange, way back some said that 900s were the worst bikes BMW ever made. Strange, I think they were the best.

[barryg]

Strange, I think they were the best.[/QUOTE]

Yes, you are correrct. They were, was, and are the best.

[8ninety8]

You are a prince and a scholar, and further, the next owner, (probably my son) will be stunned the first time he cracks the throttle on this old bike. Still waiting for a proper ring compressor. Thousands left something on the table, don't know fer sure, the '84RS sort of moaned and rushed ahead. This 900 kicks its heels in a different way. Pays yer money, takes yer chances. Good night, and good luck.

[8ninety8]

Hard to believe, 23F degrees this morning, may as well take care of another small but annoying problem. Take apart choke apparatus, clean, apply some heat shrink and a short "straight" piece of brass tubing, tightening the ferrule, reassemble. Anal but a corrected straight pull.

[8ninety8]

See how it works out, needs more lube.

[Walking Eagle]

These choke assemblies are SO cool, aren't they? First time I had one apart, I found it so appealing that BMW would put all these wonderful parts into a choke assembly. . .many "simpler" designs are probably out there - like running a naked cable over a hemisphere, but that wouldn't be The BMW Way, and hurrah.

GREAT job on this repair. The Bavarian Elves would be proud.

Walking Eagle

[8ninety8]

Those bent cable ends were getting into my psyche. Made the bike look, it's hard to say, dumb. Now shoot some major grease into the end of the housing. Talkin about good design, they put grease holes in the back of housing! Holes everywhere on these bikes. Doesn't really work too well. Squirt in grease, move lever, out comes grease. Should be greased before reassembly. Holes must be for relieving pressure when racks move to and fro.

Tapered ring compressor should be in soon, time to push the pistons home, git that pink stuff out, not doing it until the block is warmer than 50 degrees. Think I'll have another guy give the valve guides one more check. Don't fergit to mark advance plate if amplifier/points/dual ignition are used, and may have to reset timing when amp inevitably fails on the road.

[8ninety8]

8ninety8 can't forgit to tie a dedicated chasis ground back to negative terminal thus bypassing all the various joints from the diode board, all the way back through the block/transmission, and then to the battery. Saw this somewhere? It's a slow day out here. Got the Proform stainless ring compressor today, have to modify it bit, looks like a winner.