You'll do just fine! Nice work on the speedo, by the way. Just keep water from going down the reset button!
But I like the 80's look with the black orig. clamshell pissy light and i n s r u m e n t s. You gotta set limits on how much you modify or you never get "there" I dont want to put any more into the G/S - just maintain it from now on.
hopefully an early R80G/S (PD) is in my future. have seen higher fifth gear mentioned several times. odds are that I will be going in the tranny anyways. what an excellent source of info on this topic
Definately a great improvemet to your G/S. Here is a foto of mine, whith a 1,000cc engine, long 5th gear an oil cooler (can be seen behind front fender). All those mods make a more usable bike everywear. Runs great and "no problemo" so far. The increase of speed is not spectacular but noticeable. I would definatelly recomend it. Saludos from Spain !!!
Slightly higher gear ratio. It goes on the out put shaft. Drops RPM at top speed by a couple hundred. In the world of gear design the gears in the trans are a certain diameter and number of teeth. They make this gear the same diameter but a different number of teeth, I think they add one tooth, not sure though. It seems to work and there are many fans. There are plenty of purest though that say you can't be doing that. By changing the number of teeth you have to change the angle of those. It can't be good, must be Black Magic. There have been changes in the transmissions through out the years of Airheads. One change was the introduction of the X gears. The X gears have a different angle to their cut. The old is 15 degrees and the X is 17.5 degrees, I think I got that right. There are 3 angle cut gears in our trannies. One on each shaft. Since the final gear of 5th gear is one of these you have to get the higher gear to match your box. They used to be available in either X or non-X but not sure they still are. Have seen that the X gears are still available. There were also several different manufacturers and some are favored for some reason but I don't know which one is which really. I forget what year starts the X gears somebody will tell you though if you need to know. You can use the X gear in the older box if you change a few other gears with it. 600 posts. I have to slow down. I'm going to make a mistake sooner or later. I may have screwed up this entire post for that mater. Just saying...
Thanks, from you I'll take that as a great compliment. The trip meter reset button was a real stuff around (not to mention the trip meter itself!). It was broken in a couple of spots with the top missing. I found a good grommet that fit the glass and then glued the stub of the reset button together, drilled it out and turned up a new metal (monel actually) button for the top that threads into the original stub. It is a tight fit into the grommet so that I actually need to keep it a little oiled for it to move freely. I doubt much water will get through there but I'll keep an eye on it. A replacement button would have been a great thing, and a replacement speedo probably better. Now, back to the higher 5th gear. As my plan for this was part of a bigger picture- 1000cc siebenrock kit- after a bit more research I've pretty much decided not to do it at this point- at least the bigger picture part. I may still rebuild the gearbox but for my use in stock form I wonder if the higher 5th has much point...? the reason is that next year I'll be taking the bike up into SE Asia and probably a bit beyond and from my research it does seem like raising the compression that much is not a good idea for the fuel I'll encounter- even if I went to the trouble to twin plug as well (apparently siebenrock recommended running this kit not less than 94, and not less than 92 if twin plugged). I'm a little dissapointed, but probably at least a couple of grand richer too. Adding in twin plugging to the to-do list of things in this picture just took it over the edge. Which means I'll probably just be keeping the engine and gearbox in stock form for this next big trip. If/when the top end and/or the gearbox wear out, and if the expected use of the bike is primarily within developed regions, then I'll readdress the issue of the siebenrock kit. For now and before the bike gets pulled down to the frame I am going to fix the shift linkage and then give the gearbox a good test while I am testing my new front end and try to figure it it needs a rebuild. Thanks for the advice.
BMW mechanic, Ray Peake, has built up a number of GS` with Siebenrock kits. His personal R `80` GSPD (1000cc, twin plugs, 5%lower first, 5%higher fifth, etc, etc) regularly runs on 91, or ethanol without any drama`s.
Interesting. I am a little confused about what octane fuels will be available where and what might be made to work- let alone where I might end up. SE Asia for sure. India, Central Asia, Africa, all possible. My R90/6 starts pinging on crap fuel when it is loaded down and worked hard- I've never pulled the top end off that but have the original heads and barrels in my spare parts that came with the bike- with my better mileage (and awsome power) I get with my 90/6 bike compared to a lot of other camparible airheads (75's 90's and 100's I've compared it to in side by side running) I am beginning to suspect that things may not be quite stock under the valve covers- maybe higher compression? Dunno. Whatever it is it works very well, but doesn't particularly like Regular' and hates dodgy Regular. I suspect you are quite right and the G/S power-up could be done so that it would run fine on low octane, but from the impression I could get it would probably just require a bit too much work for me at this point- the head work is the main thing putting me off, the variables, the complications, and just having to trial and error a bit. I'm not leaving for a year or so, but I've got enough on my plate to finish building this bike and save up cash and all that. I like the siebenrock 1000 kit for its plug and play. Needing to go dual spark plugs just seems to open up too many variables... Later though, for sure, I am very interested in this upgrade. 1000cc Power up kit and higher 5th for sure. Personally in all the hairy dirt roads I've taken it I've never felt the need for a lower 1st on my 900, would have been nice in some bits but then probably quite annoying on the road in traffic as shifting out of 1'st seems to require enough short shifting already. Anyway, at least that is how I feel this weekend. KISS. there will be time to complicate things later. P.S. I think I've got an old reciept or two from Ray Peak in my 90/6 file (from PO's).
The 90/6 top ends were the most efficient BMW ever put on an airhead. They actually have a more aggressive squish shelf than the heralded '77 R100S and RS's. Decoking the heads and pistons makes a dramatic difference in how well they run under steam. If you've never done it, I bet you a donut it's a mess.
I have two sets of R90/6 heads. I've done the top end. Didn't notice a squish area. Was I not looking close enough. The heads were hemispherical and round all the way to the edges. What am I missing. Tell us more.
Here's a '74 R90/6 combustion chamber: The flat portion around the periphery is the squishband. There's a corresponding shelf on the top of the piston. Here's a '77 R100S "squishband" combustion chamber: Note the radiused inner edge compared to the R90/6's sharper edge. I'm guessing BMW decided this aided turbulence at the expense of aggressive squish effect? Or maybe it reduced the tendency of carbon to collect on the edge? Or maybe they never gave it that much thought and it was just easier to machine?
Cheers, I never knew that, very interesting to know. (EDIT- crossed posts, now you've added pictures, I'm going to check out my spare parts) I haven't done it myself yet but there is a bit of top end work in the bikes recent history from previous owner(s). I'll be investigating the top end on the 90/6 soon as I need to do the pushrod seals, so we'll see about that donut then. You might be right. Before I got the G/S I was going to build my pile of spare parts into a twin shock G/S type thing- spare 90/6 engine, early 100RS frame, choice of gearboxes and final drives and much more.... would have been fun. I keep trying to bring myself to part out all my parts... but I just can't seem to do it. Maybe I should just hang on to it all and keep a nice project in the bank...
interesting, here is some more photos of some 90/6 top end spares, forgive the jaundice, my super bright garage light doesn't photograph too well, the piston and head squish band/shelf just slot right in to each otherand hold the piston firmly would this be a donut looser Lornce? (that stuff is like baked on sand) The two out of four spare pistons I checked both have spots of that beaten up rim/edge.
interesting that an R90/6 head are that efficient... what about an R90S head? back on topic: couldn't one achieve same effect by switching to a higher ratio final drive? then installing a lower first gear?
First off, the piston never enters the head, at least not the side. Pistons normally stop flush with the top of the cylinder. The squish band is something like .060" or more (don't recall exactly) wide - and that's the distance between the piston and head. The 90S head is essentially the same - only difference is the intake spigot and the area directly around it.
Always an option. I think the advantage of the higher gear in the trans is that the standard 4th to 5th gear ratios are considered close, even too close. So the gear modification opens the ratios up a little. Changing the final drive might get you the higher final ratio you want but the 4th gear is raised too and it's still close to 5th. What I want is a gear set, final drive, whatever, that makes my speedometer accurate. Charlie