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Old 11-22-2011, 07:05 AM   #61
Wirespokes
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You'll do just fine! Nice work on the speedo, by the way. Just keep water from going down the reset button!
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Old 11-23-2011, 12:53 AM   #62
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Originally Posted by davorallyfan View Post
My ODO went last weekend was doing crazy things looping the loop but my speedo remained the same - that being ever optimistic.

Bite the bullet, Dave and buy an Acewell unit.
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Old 11-23-2011, 12:59 AM   #63
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[Do you have the 1000cc and the longer 5th? Tell me more?[/QUOTE]

Yes.
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Old 11-23-2011, 01:03 AM   #64
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Originally Posted by GSD4ME View Post
Bite the bullet, Dave and buy an Acewell unit.

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.
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Old 11-23-2011, 01:25 AM   #65
_cy_
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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
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Old 11-23-2011, 03:31 AM   #66
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Great idea !!!

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 !!!
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Old 11-23-2011, 01:04 PM   #67
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Nice one from Spain
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Old 11-23-2011, 02:25 PM   #68
disston
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Originally Posted by _cy_ View Post
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
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...
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Old 11-23-2011, 02:29 PM   #69
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Anyone here also added the lower first gear?
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Old 11-25-2011, 10:27 PM   #70
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Originally Posted by Wirespokes View Post
You'll do just fine! Nice work on the speedo, by the way. Just keep water from going down the reset button!
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.
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Old 11-26-2011, 01:31 AM   #71
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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.
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Old 11-26-2011, 03:22 AM   #72
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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).
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Old 11-26-2011, 06:11 AM   #73
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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.

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Old 11-26-2011, 06:34 AM   #74
disston
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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.
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Old 11-26-2011, 06:43 AM   #75
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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?

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