1988 R100RT - Bent upper shock mount

Greetings, very new here so please allow some space for my forum/jargon learning curve. Thankful for this community and all that help. Here it goes...
After cyber stalking almost every corner of the metric bike internet for about 5 years (move, new city, new job, new kids, etc), the pandemic motivated me to purchase not only my first Airhead but also first bike (1988 R100Rt). With nothing more than a basic rider course under my belt, I trailered home a Craigslist find (didn’t know what I was looking at) from Ft Smith, AR, almost 5 hours from my home in the DFW metroplex. Started acquiring tools and doing minimal basic maintenance as the work flow nudged me to get it running. Upon more detailed inspection I noticed the upper shock mount looked crooked. After asking around a bit, come to learn monoshock rubber mount bushings wear after 32 years. Time for a new shock & here I am unwilling to press this new shock onto the 2nd mounting bolt. Something is not right & need some advice from people who have/can work with metal. View attachment 79841View attachment 79842

Thanks in advance for any advice for suggestions on how to proceed!

Reils -

Welcome to the forum! I'm guessing you haven't been out on the bike yet. I'm not familiar with the mono shock model in terms of how the upper mount connects to the frame as well as what it connects across to the other side. Is there observed bends/creases in the right side frame ahead of the shock mount? If the frame is bent, then there must have been some major pothole hit at some point. Seems like someone who has experience with frames would know if it can simply be bent back to normal and/or if there's anyway to add structure to the frame to support it. I suspect that this has weakened the frame and without a proper fix, there's a chance it could break completely creating a hazardous riding situation.

Maybe you can show a few more pictures of other parts of the frame forward/below the upper mount so we might have a better idea of the extent of damage.

Kurt,
Thanks for the reply. Once I got it running, (Valves adjusted, carbs rebuilt, new starter due to a failed solenoid) in preparation for inspection and registration, I took it for a spin around the block as I started to get into tires and brakes which led me to the rear suspension. I don’t see any instances where the frame is bent, only damage I see is where the Left frame bracket attaches to the Left exhaust & scrapes on valve cover. Guessing you’re right, it was a major pot hole causing the upper mounting bracket to flare out to the right because if it were laid down on its left hard enough to somehow bend the upper shock mount right, the original swing arm would be beyond repair. I’d love to get an opinion on how to get the bracket squared up without loosing the integrity of the frame. Guessing a hair dryer & hammer aren’t gonna get it done!
I’ll post some more pics then defer to the experts. Thanks again!

Guess it's a little hard to see the details for this. I wonder if you shouldn't tap into the DFW Airhead crowd to get some eyeballs on this as well as get some suggestions. You could join the Airheads Beemer Club and then get a chance to contact other members in your region, even attend a TechDay although I haven't seen/heard of any Texas TechDays in a long time. In my signature line, the link provides a number of resources. There is a frame section and I believe there are some frame companies but they might all be on the west coast. Ted Porter in NorCal and Tom Cutter near Philadelphia are good resources...Anton Largiader in Virginia has a wealth of experience, too. All of those are miles away!

But checking with your local community would be more helpful. Also in the link is a link to "Airhead Friendly" shops...the list might be a bit dated, but you might see some shops with experience where you could begin asking questions.

Compare the top of the old shock and the new shock and see if there is any difference? The old shock might have had a ball joint type swivel at the top.

Thanks Paul, that makes perfect sense & would be ideal opposed to what I’m dreading. Unfortunately both shocks standard straight rods & loops with rubber mount bushing onto the fit pin. My 1st pictures show the mount of the new shock and 2nd post has pics of the old shock. Again, I’m a total newbie so please let me know if I’m not seeing something right.... my understanding is that during installation, both pins should fit into the new shock simultaneously rather than inserting one then pressing the opposite side & stressing the rubber mount for a crooked fit. I’ve been unable to find any pictures of a monoshock installed. Boxer2valve’s “1985 on R80” YouTube video showed it slipping right on cleanly as was expecting. Appreciate all thought, ideas or possible solutions!

Maybe someone with a similar bike who has access to this location could take a picture of a "known good" condition. So nothing connects the left-right side of the frame at this point?

I removed the battery tray for a more clear picture. Yellow is the welded piece of the frame that I believe has been flared out. As I’m typing I just realized the subframe probably has the nearest horizontal brace, which is broken at the weld!
Doubtful this is coincidental.
Thanks again & will gladly welcome any ideas/suggestions (other than ME stripping it all down and mailing to NorCal)!

Not as familiar with the '80s monoshock airheads, but could the top shock mount actually mount inside of the frame versus outside? It's hard to believe it could be that far out of alignment. Also, I've seen the cross brace fractured on several airheads, not from some catastrophic incident. Sometimes from altering the seat or seat mount or from overloading. Good luck with your project. Hope you're on the road soon.
gp

I have an 86 Monoshock airhead and I just went out and took a look at the upper rear shock mount. First thing, my shock mounting bolt goes from the inside through the frame bracket out to the shock. The nut securing the shock is on the outside. I don't know if this is correct since the pictures on BMWs fiche seem to imply it should go from the outside in. I will say that having the bolt head on the inside allows better clearance when pulling the battery. Also, I noticed that the fiche implies that the lower mount nut is on the inside as well and that's just not possible.

The fiche picture implies that the shoulder on the bolt is the same size where it goes through the shock eye and the frame shock mount. Is this true for your mounting bolt? Is it correct to assume that your bolt is straight?

I installed the shock on mine long enough ago so I don't remember anything except it was a tight fit. It does not appear to have a ball joint at the top though.

The photos of your new shock make it look like it won't align with the lower mount. The photos of the old shock look like it does. Are the upper eyelets of the same construction and alignment?

6322 said:

Not as familiar with the '80s monoshock airheads, but could the top shock mount actually mount inside of the frame versus outside? It's hard to believe it could be that far out of alignment. Also, I've seen the cross brace fractured on several airheads, not from some catastrophic incident. Sometimes from altering the seat or seat mount or from overloading. Good luck with your project. Hope you're on the road soon.
gp

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Thanks Gary, I removed the shock from the outside of the mount, also all the Fiche show it mounting on the outside. This saga and my obsession continues!

Anyname said:

I have an 86 Monoshock airhead and I just went out and took a look at the upper rear shock mount. First thing, my shock mounting bolt goes from the inside through the frame bracket out to the shock. The nut securing the shock is on the outside. I don't know if this is correct since the pictures on BMWs fiche seem to imply it should go from the outside in. I will say that having the bolt head on the inside allows better clearance when pulling the battery. Also, I noticed that the fiche implies that the lower mount nut is on the inside as well and that's just not possible.

The fiche picture implies that the shoulder on the bolt is the same size where it goes through the shock eye and the frame shock mount. Is this true for your mounting bolt? Is it correct to assume that your bolt is straight?

I installed the shock on mine long enough ago so I don't remember anything except it was a tight fit. It does not appear to have a ball joint at the top though.

The photos of your new shock make it look like it won't align with the lower mount. The photos of the old shock look like it does. Are the upper eyelets of the same construction and alignment?

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Anyname,
Just looked at the fiche again, you’re right, clearly incorrect for the lower threaded bolt is fitted in the differential housing, so clearly the nut goes to the outside.
Amazingly both mounting bolts are straight. I noticed the issue when the rubber mount bushings were oozing 32 yo rubber from being so stressed. What I can clearly see & I’m not sure how easy it is to see in my previous pictures, the frame’s upper shock mount is curved about 5mm toward the Right/outside causing the poor alignment 410mm away at the lower mount. Is there any way to shoot a very “internet elusive” picture of your frame’s upper shock mount so I might be able to confirm mine Is bent rather than continue to wonder if my swingarm is crooked?
The old and new eyelets are the same dimension. They look different in the pics because I at one point pressed the old rubber mounts out of the old shock to replace with new ones, thinking that would fix the problem. Didn’t fix it and cost me a few days building a press tool that ended up mushrooming the new rubber mount. Live and learn. Thanks for your help, and a picture of your frame mount would lead me in the right direction with how to proceed. Thanks!

Photos of monoshock upper mount:



I don't know if these will help. It's really hard to get a useful view.

It does look like your mount, frame or both may be bent. I have to wonder how that could happen, especially given the thickness of the cast mount and the fact it's attached at a bend in the frame. That should be a very stiff location.

Anyname said:

Photos of monoshock upper mount:
I don't know if these will help. It's really hard to get a useful view.

It does look like your mount, frame or both may be bent. I have to wonder how that could happen, especially given the thickness of the cast mount and the fact it's attached at a bend in the frame. That should be a very stiff location.

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Any,
Thank you!!! It appears clear to me that your monoshock frame mount is straight while mine has a subtle yet significant bend (approximately 5mm). Seems as though my options are now to somehow straighten it or find a replacement frame. Still open for any ideas/solutions. Thank you!

The thought occurred to me that maybe we can compare measurements between the left and right sides of the frame such as the sub frame mounting points. As best as I can measure without removing the sub-frame, mine is 8 7/8" between the subframe mount points.

Anyname said:

The thought occurred to me that maybe we can compare measurements between the left and right sides of the frame such as the sub frame mounting points. As best as I can measure without removing the sub-frame, mine is 8 7/8" between the subframe mount points.

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Any, great idea, the measurement between the subframe mounting points is 8 1/8”. That 1/4” is about the difference I expected. Another update... a conversation with and a couple pictures sent to the North Dallas BMW airhead expert who shared with his tech in the shop. Their response was (I’m paraphrasing) - This bend is somewhat normal on monolevers & not much to be concerned with... the rubber mounts in the OEM shock has thicker rubber than some aftermarket shocks, I could either mount what I’ve got or press out and swap the aftermarket shock (yss) rubber mounts with the BMW part.

I hope I’m not being overly particular with ZERO bike experience, but I’m afraid prying on a brand new shock to fit the bottom mount would create a lateral tension on the shock (yes, the rubber mount would absorb most) that could cause increased wear.

I’d love to hear from a monolever owner to confirm that this bent frame shock mount is somewhat common.
Thanks again!

Hmmm, there are a number of specialist shops listed on Google that straighten motorcycle frames. I also had the kind of depressing thought that the bracket and frame look pretty stout so if that's tweaked, something else may not be straight as well.

I always fall back on the Max BMW shop in North Hampton for advice on Airhead stuff since they still do a lot of work on them including restorations of old BMWs. They are generally pretty helpful with advice.

reils50 said:

Another update... a conversation with and a couple pictures sent to the North Dallas BMW airhead expert who shared with his tech in the shop. Their response was (I’m paraphrasing) - This bend is somewhat normal on monolevers & not much to be concerned with... the rubber mounts in the OEM shock has thicker rubber than some aftermarket shocks, I could either mount what I’ve got or press out and swap the aftermarket shock (yss) rubber mounts with the BMW part.

I hope I’m not being overly particular with ZERO bike experience, but I’m afraid prying on a brand new shock to fit the bottom mount would create a lateral tension on the shock (yes, the rubber mount would absorb most) that could cause increased wear.

I’d love to hear from a monolever owner to confirm that this bent frame shock mount is somewhat common.
Thanks again!

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I have a ‘91 R100 monoshock. The upper rear shock mount is a fairly robust casting that’s welded to the main frame hoop. I wouldn’t believe that the mount is “commonly“ bent without a pretty serious drop or crash—a bit of speculation which may be borne out by your broken sub-frame and MIA fairing. I wouldn’t assume that the bent shock mount and broken sub-frame are the end of the frame damage without a real expert’s eyeball and perhaps some careful measurements in a frame jig. Send your photos to Tom Cutter at the Rubber Chicken Racing Garage for his feedback. No one wants to throw cold water onto an eager new airhead owner, but the reality may be that you’ve bought a parts donor, not a rider.

Frame measurement

Having had two airheads involved in major part bending accidents, I agree with the advise to seek a frame shop to have the over all frame checked out before riding. My first bike I hit a deer with resulted in a bent steering head tube on the frame, at the time, the cost to strip the bike have the frame repaired as well as replacing the damaged fork systems, fairing and such was far in excess of what the bike was worth, so it was written off and became a parts donor.

On the second bike, I was hit by a car from the side. It was stripped down to bare frame which was given to a frame shop. It was evaluated and determined to be all right. From there, I had the bike put back together donor parts and the cost was still higher than the bike is worth. The only reasons, I spent the money to rebuild the second bike was I really liked it and it was a low number model bike. If that had not been the case, I would have purchased a good replacement bike.

From the pictures and texts, I myself would be Leary with this particular bike. To do that kind of damage is not just a pothole or a bad shock problem. Who knows what else is out of true, I would not like to find out the steering head tube is off center and causing handling problems while riding at any normal highway speed. I do know, this could be a worse case scenario but, it can happen.

Unless the bike was purchased at a VERY reasonable price, or is something special to the owner, is a very rare model, I myself would not bother anymore than to find another bike in better condition, and part this one out. There are a lot of low mile well cared for bikes on the market.

Sorry, you had to learn a lesson on what to look for when buying a used airhead. Don't let the experience sour you on them. They are great bikes for what they are and I have never ridden anything but.

Good luck with what ever you do, I hope you do find a frame shop and it won't cost you a whole packet of money to fix, that would be great if you do, be sure to post the name of the shop. Cheers, St.

Oh yeah one more thing

Sorry, just one more thing.

When my first bike was damaged, my dealer set the bike up in his shop on a level floor and proceeded to use strings, wood doweling and reference marks drawn on the floors and such to check out the damage. No special jig.

Sadly, this was back at the end of 1984 and of course airheads were still the new bikes. I don't know if a local dealership would have the knowledge as to how to do this, if they still even work on airheads. Not all BMW dealerships do these days.

St.