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Stock '81 R100RT seat not latching properly

dovfrankel

New member
I've been having problems with my seat, but haven't been able to find any solutions yet. The closest I came to someone having my problem was this thread, which was with an aftermarket seat: http://forums.bmwmoa.org/showthread.php?14067-Opening-stuck-seat-on-R100RT

I'm the second owner of the bike, and the original owner had an aftermarket seat on it for many years, but kept the original. I want to try using the original, since I like the way it looks more, and it seems like it wouldn't be terribly uncomfortable (time will tell).

Here's the situation, though. When I fit in the swing hinges properly and close the seat, it doesn't latch. If I slam it a few times, it eventually latches, but only because the hinges become dislodged. At that point, it then becomes nearly impossible to reopen the seat, requiring a lot of pushing down and shimmying, to eventually get it loose enough to pull open. Has anyone else experienced something similar? What should I be looking for to diagnose the problem, and what might a suitable solution involve? I'm a fairly new rider, so any advice would be greatly appreciated.


Thanks for anything you might have to offer,
Dov
 
If my memory serves me right from the last time I put a new seat on an airhead (1995 RT), I had to remove the pin that goes into the latch from the stock seat and install it in the Corbin I bought. This pin also has a rubber "cone" over it that slips off. This pin screws into the seat. If you unscrew it a bit to make it longer it will go into the latch further, making it easier to lock. Also, there are rubber bumpers on the bottom edge of the seat. When I replaced them on my stock seat on my 1978 RS I found they came in two thicknesses. I do not remember where the small ones went vs. the taller ones, so you may want to look at a parts diagram to see. They will compress over time and make it easier to close the seat too.

Wayne

edit
Photo stollen from Ebay shows a pin and cone I am talking about.
 

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  • seat pin.jpg
    seat pin.jpg
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Thanks for the replies, so far. toooldtocare, that's definitely what my pin looks like. I'll take another look, and try extending it if necessary. If that doesn't help, I'll report back with pictures of the frame and seat.
 
I also like looking at the presence (or absence) the rubber bumpers. When the seat is latched in placed, it's actually supported by the bumpers, not the latch.

I had a missing rubber piece on my R12R's seat recently, and the slight change in alignment made the seat more difficult to place and latch. Perhaps you could compare yours to another bike of similar seat and vintage.
 
I tried loosening the latch pin with a vise-grip, but had no luck. I also noticed that yes, it does have three rubber bumpers (one of which fits over the latch pin). When I'm trying to get the seat pressed shut, the rear bumper makes contact with the frame, but the front one does not. I've posted a couple of pictures below showing the overall setup and a closeup of the latch pin with the rubber bumper removed from it.

Any tips on how to twist that latch pin out of there? I'd also like to verify whether it does, in fact, come out (the picture certainly looks like it) before I tear into the metal any more than I already have. I also added grease to the inner workings of the latch mechanism, so that should stay smooth.

Seat and frame:
Seat and Frame.jpg

Latch pin:
IMG_0552.jpg
 
On the bikes that I have replaced the seat with a Corbin, the pin would unscrew. Those were mono-shock bikes. On my R90S and 78 Motorsport I left the factory seats on, but I BELIEVE they also unscrewed. Right now I am between airheads, so I cannot look. But, remove the cone bumper and see if the seat latches. It sounds like the bumper or latch is keeping it from latching. Maybe someone else could look at their seat to see if it unscrews an dual shock bikes. You can also try some penetrating oil on it too overnight.
 
Sorry, on the pin. I do not see threads, so either it is screwed all the way in, or it is welded. Maybe the oil will loosen the pin.
 
The WD-40 product you sprayed on is a LUBRICANT (grease), not a "penetrating oil". I would be surprised if it was able to actually work it's way into (penetrate) the threads and loosen the parts.

product-lithium.png



These are "penetrating" oils. There are others.

WD-40
wd-40-image.jpg


Kroil
IMG_0968.jpg


PB Blaster
PB_Penetrating_Catalyst.jpg


Liquid-Wrench
96987331-260x260-0-0_Radiator+Specialty+Gunk+L116+Liquid+Wrench+Super+P.jpg


You will want to spray the penetrant around the base of the stud where it enters the seat base; it will wick into the thread by capillary action. It won't be an instantaneous fix and will probably need to sit over night at the least. Re-apply the oil occasionally

attachment.php


#11 is stated to be a hex nut. If so, then the seat cushion may need to be removed to get a wrench on it. > http://www.ascycles.com/Illustrated...seat/52_1009?gclid=CMumpI3fp7cCFWSCQgod1FEAmA

MicroImage.aspx
 
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I just looked again at Max BMW parts listing and do not see the seat pin for your bike like I do for the mono-shock bikes. I then looked at the Corbin seat for the RT and see that it comes with the seat pin. Gives me reason to doubt that your pin is removable. No way of telling unless you remove the fabric. Did you try it without the cone bumper yet? if it works, you may be able to trim it down a bit to get it to latch.

Wayne
 
The WD-40 product you sprayed on is a LUBRICANT (grease), not a "penetrating oil"

Thanks for clarifying what a "penetrating oil" is. I'll try some WD-40 (original) on it, and see if that works some magic overnight.

Did you try it without the cone bumper yet?

Unfortunately, yes, I did try without the cone bumper and it made no difference.

I think that at least part of the problem may be the right hook (#14 on the parts diagram Lew posted above) on the seat. When the left hook sits all the way over the pin on the frame that holds it in place, the right one sits a little to the right. I need to look at that more closely and see if I can possibly straighten it or something.

Also, I found the parts catalog (fiche) from A&S (slightly different than the one shown above, but correct for the '81) and MAX BMW, which shows an image of the "cushion" (below). As Wayne pointed out above, it looks like the pin may be permanently attached to the seat (although that photo also shows only one hook). If so, I'll have to look at the hooks and bumpers, and see which of those may be misaligned.

Again, thanks for all the help, you guys. I greatly appreciate it.

52531237834_3_B.jpg
 
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Sounds like you are on to something. Could also be a bent subframe, not uncommon. My old R90S had one which prevented the bag mounts from bolting on. It was easy to straighten with a couple 2x4's once I had a good bike to take measurements.

Wayne.
 
I haven't forgotten about this or given up yet, but on my last ride I noticed my rear brake is non-functional, so that's taking my attention instead (and I'm dealing with the 3rd-party seat). I'll send another update after I analyze the frame and seat to see where the misalignment is.
 
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