How to remove cap on outside of differential

[maverickbluer1]

Hi,

I want to remove the round cap on the outside of the differential housing on my 1983 R80ST. I aim to build a spindle that will fit through the differential and allow me to use a single-sided swingarm paddock stand.

I guess there's not much reason to remove this cap so I can't find any information on how to do it. I've banged on it a little and it seems firmly planted. I don't want to damage it so seeking guidance.

Attached is a pic of the cap I want to remove. It's right in the center of the housing.

Any advice greatly appreciated. My ultimate goal is to measure the ID of the diff to determine the size of the spindle I need. Also does this cap serve any purpose other than aesthetics and to keep the inside protected?

 

[20774]

Welcome to the forum! I see that you've already been to Brook Reams' site as that is the picture of the housing from his thread on an R80ST build. I've never been close to one of these, and didn't realize that there was a center cap. But according to the fiche, the cap is part number 33111241955. No idea how it's held in place, but suspect it's pressure fit. As for purpose, I'm thinking it's there to keep the dirt on the outside...lots of critical seals and gears in there.

Can you access that cap from the other side? Will it tap out from the inside? And once you get it out, use your stand, how do you get the cap back in to stay and protect the insides while the bike is in use?

Is this the only form of paddock stand that could be used? Plenty of bikes out there with various shock and swingarm combos. I wonder if there's something else that might be used. But I'm sure you've done your research!!

 

[AntonLargiader]

Won't work without a lot of modification. The Twinshock system had a hollow ring gear to allow the axle to pass through, and the small ring gear needle bearing was large enough to give space for that axle. The Monoshock system doesn't have a hollow ring gear and the tapered bearing is smaller. Also the Monoshock lacks the inboard seal that the Twinshock has, keeping oil out of the hollow area because the Monoshock has no use for it.

Bottom line is, just because it's the casting that the Twinshock used, this doesn't mean that the internals are compatible. They really aren't.

 

[AntonLargiader]

As follow-up you can see the parts on Brooks Reams' website: https://brook.reams.me/bmw-motorcyc...-index/33-bmw-1983-r80st-rebuild-final-drive/

The ST actually still has the needle bearing design like the Twinshocks, not the later tapered bearing (they changed that when the center cap went away a year or so later) but there's still no hollow axle for your support to go into and there's no exposed stub on the axle against which to put a seal.

 

[maverickbluer1]

I've used a rachet extension and socket to try and remove it from the other side but it doesn't move. It apparently is press fit.

 

[maverickbluer1]

As follow-up you can see the parts on Brooks Reams' website: https://brook.reams.me/bmw-motorcyc...-index/33-bmw-1983-r80st-rebuild-final-drive/

The ST actually still has the needle bearing design like the Twinshocks, not the later tapered bearing (they changed that when the center cap went away a year or so later) but there's still no hollow axle for your support to go into and there's no exposed stub on the axle against which to put a seal.

I'm not technical enough about bearings (or Airheads, it's my first) to know what problems it would cause if I inserted a shaft in there. It seems to be hollow and the opening seems to be 24mm or so all the way through to the cap in question.

 

[maverickbluer1]

Welcome to the forum! I see that you've already been to Brook Reams' site as that is the picture of the housing from his thread on an R80ST build. I've never been close to one of these, and didn't realize that there was a center cap. But according to the fiche, the cap is part number 33111241955. No idea how it's held in place, but suspect it's pressure fit. As for purpose, I'm thinking it's there to keep the dirt on the outside...lots of critical seals and gears in there.

Can you access that cap from the other side? Will it tap out from the inside? And once you get it out, use your stand, how do you get the cap back in to stay and protect the insides while the bike is in use?

Is this the only form of paddock stand that could be used? Plenty of bikes out there with various shock and swingarm combos. I wonder if there's something else that might be used. But I'm sure you've done your research!!

I've searched extensively but haven't found one. If anyone knows of one, I'd be indebted to know about it.

As far as a replacement cover, was thinking I could fabricate one from delrin or some material like that.

 

[kbasa]

I'm not technical enough about bearings (or Airheads, it's my first) to know what problems it would cause if I inserted a shaft in there. It seems to be hollow and the opening seems to be 24mm or so all the way through to the cap in question.

Given this level of knowledge, you sure you want to start mucking around and redesigning a final drive?

Can I ask why you're interested in this when these bikes all came with centerstands? Kinda curious. I've got an R12RT and had a PitBull rear stand for my 916, but since the RT had a centerstand, it didn't see especially useful.

 

[maverickbluer1]

I don't want to muck around with the operation or mechanics of the drive unit, just put a spindle through it. The bike doesn't have a center stand. It was removed before I bought it.

 

[kbasa]

I don't want to muck around with the operation or mechanics of the drive unit, just put a spindle through it. The bike doesn't have a center stand. It was removed before I bought it.

If it's an airhead, you can buy a used centerstand for less than a hundred bucks and not have to bore a hole through the final drive.

Just sayin'. Unless you like leaving the house from a second floor window, that's probably easier. Does your bike still have the mounting points? If so, this one is all of $75 before you buy some spray point, the springs and a couple nut/bolt sets. https://www.ebay.com/itm/2660456119...heldOC6n6pg46d7Q8%3D|ampid:PL_CLK|clp:4429486

It's gonna be a whole lot cheaper than trying to not only bore a hole in your final drive, but seal it effectively so it doesn't inhale crud and leave you stranded.

No worries if you're dead set on doing this, but it seems like reaching over your shoulder to scratch your butt - a lot harder than it needs to be.

If you do move forward with the hole thing, be sure to send pictures. I'd be curious to see how it works.

 

[20774]

So obviously, you have a side stand. Is the need for this paddock stand for the purpose of doing maintenance? There are versions of bike lifts that can be wheeled in to support the bike which would then allow for wheels to be removed, etc. I guess another alternative would be to purchase a used center stand.

I wonder if you could push a hole through the center, is it possible that the wall thickness of the final drive is too thin to support the weight that alternative stand might see?

 

[88bmwjeff]

If it's an airhead, you can buy a used centerstand for less than a hundred bucks and not have to bore a hole through the final drive.

Just sayin'. Unless you like leaving the house from a second floor window, that's probably easier. Does your bike still have the mounting points? If so, this one is all of $75 before you buy some spray point, the springs and a couple nut/bolt sets. https://www.ebay.com/itm/2660456119...heldOC6n6pg46d7Q8%3D|ampid:PL_CLK|clp:4429486

It's gonna be a whole lot cheaper than trying to not only bore a hole in your final drive, but seal it effectively so it doesn't inhale crud and leave you stranded.

No worries if you're dead set on doing this, but it seems like reaching over your shoulder to scratch your butt - a lot harder than it needs to be.

If you do move forward with the hole thing, be sure to send pictures. I'd be curious to see how it works.

A quick search of the parts fiche indicates that the center stand for the ST has a different part number than the monoshock bikes. It's also different from the early R80 GS & G/S, according to the parts fiche. I don't know what other bikes, if any, use the same center stand as the ST. But, I would double check before purchasing. New ones, albeit a bit pricey, seem to still be available from BMW.

 

[52184]

A quick search of the parts fiche indicates that the center stand for the ST has a different part number than the monoshock bikes. It's also different from the early R80 GS & G/S, according to the parts fiche. I don't know what other bikes, if any, use the same center stand as the ST. But, I would double check before purchasing. New ones, albeit a bit pricey, seem to still be available from BMW.

OP may want to check with Stoner’s Beemer Stash (Larry Stonestreet) Ca.stoner@yahoo.com. I think Larry recently parted an R80ST and may have a centerstand.

Best,
DeVern

 

[rich]

Why not use a simple scissor lift? Or do you need something you can wheel the bike around on?

https://www.homedepot.com/p/VEVOR-M...bGAopneyNCEXjO81GOCBJs4zipUpih1SNLhuM8Qid0-rc

 

[stevenrankin]

scissor lift

I will butt in here with a caution about scissor lifts. In my experience a lot of those that are on the market are to put it mildly crap. I purchased a Home Depot unit, not the cheapest one but supposedly a good one. The third time I used it, it failed in the up position. the main screw stripped while I was lowering it.

The only jack I have found that works is the Handy company jack. While I do not own one, my airhead shop lets me borrow theirs from time to time. (I am waiting to get one from Tucker company that is another long story). The shop uses theirs quite a bit and have never had an issue.

You get what you pay for however, this jack is listed at the Handy shop for near $500. My shop is trying to get one at his cost from Tucker supply.

Not to shill for Handy but I can say, there are not many out there that are worth the price. Good luck, St.

 

[20774]

Many varieties of small lifts:

https://www.harborfreight.com/1500-lb-steel-atvmotorcycle-lift-60536.html

 

[maverickbluer1]

If it's an airhead, you can buy a used centerstand for less than a hundred bucks and not have to bore a hole through the final drive.

Just sayin'. Unless you like leaving the house from a second floor window, that's probably easier. Does your bike still have the mounting points? If so, this one is all of $75 before you buy some spray point, the springs and a couple nut/bolt sets. https://www.ebay.com/itm/2660456119...heldOC6n6pg46d7Q8%3D|ampid:PL_CLK|clp:4429486

It's gonna be a whole lot cheaper than trying to not only bore a hole in your final drive, but seal it effectively so it doesn't inhale crud and leave you stranded.

No worries if you're dead set on doing this, but it seems like reaching over your shoulder to scratch your butt - a lot harder than it needs to be.

If you do move forward with the hole thing, be sure to send pictures. I'd be curious to see how it works.

To put this in perspective, I bought this bike to build a custom "brat" bike. The previous owner had built it into a sort of cafe racer so I guess that's why the center stand is gone. Part of the fun of this project is coming up with cool and elegant ways of doing things. So, "leaving the house from a second-floor window" is not all bad in this situation.

I do have a scissor stand that I can use for maintenance (the bike's on it now with the rear wheel off) but just looking to do something a little different. And I don't really want to put a center stand back on it.

 

[ccolwell]

Pitbull has a number of rear stands that work without spools.

Other than a fun project, why do you want the single sided stand?

 

[maverickbluer1]

Pitbull has a number of rear stands that work without spools.

Other than a fun project, why do you want the single sided stand?

It's a single sided swingarm so nothing else will work.

 

[kbasa]

To put this in perspective, I bought this bike to build a custom "brat" bike. The previous owner had built it into a sort of cafe racer so I guess that's why the center stand is gone. Part of the fun of this project is coming up with cool and elegant ways of doing things. So, "leaving the house from a second-floor window" is not all bad in this situation.

I do have a scissor stand that I can use for maintenance (the bike's on it now with the rear wheel off) but just looking to do something a little different. And I don't really want to put a center stand back on it.

Got it. I'm caught up.

Thanks for the reply. I appreciate it. Good luck. If you do it, I'd love to see how it comes out.