An R100RS Build: The shiny crumpet

[xavier296]

So, this is how she looks right now:


I am in the middle of the "big tube" swingarm conversion. This uses an 81-84 swingarm, which has a much larger cross section of the tube that the driveshaft goes through. This greatly increases its resistance to bending, and thus keeps the wheel in line with the bike when exerting side loads during cornering. It is easy to see the difference:


This is a direct swap in except for the perch for the rear brake switch. The end of the perch touches the swingarm and needs to be cut about 1/4". I used a grinder and a dremel:
Original:


Interference:


Modified:


This is also requires modifying the mounts for the brake switch, as the switch needs to be positioned closer to the exhaust mounting ears. I had two holes already (separate from the threaded holes, so I just made one larger and drilled another, then used small bolts and nuts to mount it. I thought I would have to modify the brake pedal arm in order to touch the switch, but the end of the bolt still presses in on the switch. Excellent!

[xavier296]

Taken a minute ago, sans transmission and rear end:


I removed the air box and tranny in order to figure out my plan of action for the very cracked up end plate around the output flange. Really easy with the swing arm removed. Air box, 4 bolts, reverse connectors, shifter, speedo cable and off she comes.


I thought to myself, lets take off the end plate. First, remove the nut on the output flange. Check. Hmm, how do I get the flange off? I do not have the 75 dollar tool from Northwood airheads. Is there any other garage solution to this problem? Many some heat with a torch and a harmonic balancer puller? Ofcourse the bolts are super fine thread. Help appreciated!!

I definitely have either a rear main or oil pump cover seal leak. Parts have already been purchased.



But transmission splines look good:


On a more successful note, I cleaned up the final drive.
From this:



To this:

[xavier296]

So, started the day with the goal of removing the output flange. I found my harmonic balancer puller, and then used the clutch removal bolts. Turns out they are the same fine thread M8s as the driveshaft bolts except much longer. My original setup bent both of the bolts out, as there was a curve at the mating point, so I faced the tool. I believe this puller cost less than 20 dollars, so this puller, a grinder, and 2 fine thread bolts is all you need.




I made sure the bolts were the same length on both sides, snugged everything up, then hit it with the air impact. A few seconds later, it popped off. I left the nut on the end of the output shaft to ensure I did not hurt the splines. Then I used the impact to zip off the nut.


I read everything I could about removing the rear plate and the use of heat, and decided that a torch would be the best method. I tried to heat it evenly to a point where I could barely touch it with a bare finger. I hit the bosses a few times with a dead blow hammer and it came apart. Alittle more work with two screwdrivers wrapped with a rag finished the job. The input shaft bearing stayed in the cover, so I heated that area again and removed it.



The internals looks great, with no metal flakes or shiny wear areas. The bearing also move beautifully with no drag. But... it looks like the end plate is not repairable. In addition to the cracks on the outer flange, there is a substantial crack on the inside bearing surface of the output shaft. I have no idea what happened to this rear plate, but it must have been a heck of a shock. I am no expert, but this does not look repairable to me:



Alright, off to remove the clutch and flywheel.

[fishkens]

Great thread! Looking forward to the rest.

[Wirespokes]

If it hasn't already been said - block the front of the driveshaft to prevent any moven't forward!!!!!! Do not remove the flywheel before blocking it!

I've seen rear covers broken like that from accidents. The output flange rides very close to the flange and when the engine is still spinning and the rear wheel suddenly isn't, the forces twist everything out of shape momentarily. Enough so that the ujoint output flange contacts the case and breaks it. One was bad enough the output shaft was bent.

With a new cover the tranny will need to be re-shimmed. You'll be looking at some fun on that score!

[DoktorT]

Originally Posted by xavier296

Alright, off to remove the clutch and flywheel.

Please do not repeat use of the RTV sealant on the rear cover. Follow factory procedures/specs. Good to replace that rear plate and be done with that. The RTV means someone who was guessing was in there. Verify everything, know the procedures, buy the tools, or send it to someone who has done hundreds of Airhead trannies. Building them right is expensive for skill, re-do is expensive with lack of skill.

[DoktorT]

Originally Posted by Wirespokes

If it hasn't already been said - block the front of the driveshaft to prevent any moven't forward!!!!!! Do not remove the flywheel before blocking it!!

That would be the CRANKSHAFT. Block that for sure.

[xavier296]

Thanks for the advice, crankshaft is blocked on the front using a nylon bolt.

Reshimming was the reason I wanted to have my cover repaired rather than replaced, but it looks like I won't be able to avoid it now. I will start doing my research now.

I figured an accident was the reason for the damage also. One of the rubber foot pegs is pretty torn up from an obvious slide. Poor thing.

[xavier296]

My powdercoater wants all the bearings removed from the wheels and swingarm. Without sounding too cheap, is it possible to reuse the wheel/swingarm bearings after they are removed? I know, I know, but they really are in great shape and do not require replacement. If I can avoid buying 6 new bearings (~150 dollars worth), I will. I would much rather just replace some seal rings.

[xavier296]

After getting the clutch and flywheel off (with crank blocked!), I jumped into cleaning. This stuff was nasty! I still have black spots on my hands, and I wore gloves for most of it.



After what seemed like an eternity and lots of rags in the trash:


I copied the technique seen on this forum to remove the rear main seal. This involves drilling holes on each side of the seal and screwing in course thread self tapping screws:


Then I used a pair of 90 deg pliers against the block:


Using very little force, she popped right out. Detail of screw install:


I replaced it with another new style seal using the seal installer purchased from northwoods. No problems at all.

I also replaced the oil pump o-ring. All the bolts came off easily with a 1/4" ratchet, and I replaced both the seal (old one had squared off) and the bolts. I used blue locktite and torqued to 88 inch-lbs. Much better:



I am not completely convinced that either of those seals was actually leaking. I am starting to wonder whether the breather hose above the starter gear was doing it. The hose just comes out and terminates right above the starter gear. I think it might have been depositing oil down into the recess for quite a while, as the entire inside of the bell housing was nasty. I will rectify that also.

Thanks for reading!

[Airhead Wrangler]

Originally Posted by xavier296

I am not completely convinced that either of those seals was actually leaking. I am starting to wonder whether the breather hose above the starter gear was doing it. The hose just comes out and terminates right above the starter gear. I think it might have been depositing oil down into the recess for quite a while, as the entire inside of the bell housing was nasty. I will rectify that also.

Man, somebody REALLY let that go. I'll be shocked if your clutch still works and isn't a giant oil sponge. Just because there's oil EVERYWHERE don't assume it's not the rear main seal. If one of those gets leaking pretty well, the flywheel will sling oil all over the place. That's one the nastier ones I've ever seen. Wow.

Might as well change out the oil pump seal while you're in there and inspect the oil pump for wear.


EDIT:
On second thought I think your rear main seal was definitely bad due to the concentration of oil immediately below the seal as well as the very outside of the bell housing as if it was being slung off by the flywheel.

[fishkens]

The hose just comes out and terminates right above the starter gear.

Yuck. What a mess.

[fishkens]

Originally Posted by Airhead Wrangler

Might as well change out the oil pump seal while you're in there and inspect the oil pump for wear.

The OP replaced the oil pump o-ring but didn't mention measuring for wear. Good point on that.

[Houseoffubar]

Originally Posted by Airhead Wrangler

Man, somebody REALLY let that go. I'll be shocked if your clutch still works and isn't a giant oil sponge. Just because there's oil EVERYWHERE don't assume it's not the rear main seal. If one of those gets leaking pretty well, the flywheel will sling oil all over the place. That's one the nastier ones I've ever seen. Wow.

Might as well change out the oil pump seal while you're in there and inspect the oil pump for wear.


EDIT:
On second thought I think your rear main seal was definitely bad due to the concentration of oil immediately below the seal as well as the very outside of the bell housing as if it was being slung off by the flywheel.

Get with it man, all the cool kids are running wet clutches these days!

That is one hell of a mess, I'm afraid to see what mine looks like now!

[DoktorT]

Originally Posted by DoktorT

The more I look at it, the more that tank looks too big. Don't need that much fuel for a cafe. Thinking more like a small /6 tank or a toaster would be more practical and make the machine look 20 lbs lighter. A narrow Benelli tank is used for lots of UJM cafe builds. Room for clip ons. Got any Benelli's in Italy? .

Search this on eBay: BMW Airhead R50/5, R60/5, R75/5 Fuel Tank

There is one on there now, small /5 with rubber knee pads and delovely badges. The non-toaster /5.

This is a type of tank to look for. If you go with the M/C handlebar upgrade, the /5 would fit right on. The small /6 tanks would fit right over the undertank M/C.

Anyway, when you settle on a tank solution, then modify the seat to fit.

You are a frankenbeemer so consider all airheads as donars for enhancing your options.

No one would fault you if you found a metal crafter to mount that custom tank properly. If you think you will be doing lots of miles roaming, the bigger tank is the only way to go.