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Old 01-05-2012, 04:11 PM   #16
puncar thogoole
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Don't forget the pre 81 /7s had heavier flywheels, it's often stated the later lighter flywheel bikes had more vibes (& faster acceleration).
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Old 01-05-2012, 04:22 PM   #17
bikecat OP
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Hi,

Thanks for the feedback. I was prompted to ask after reading this on UKGSR:

http://www.ukgser.com/forums/showthr...t=88688&page=4

"I learned that only the most experienced mechanics worked on the Basic production line, indeed many of them wanted to be a part of the final limited run... I met few of them later over a couple of beers and it was great to hear them still talk with a very real fondness about that last air-cooled motor, the simple elegance of the steel frame and the racing heritage that final basic represents.

I asked why the decision had been made to make it an 800 and not a 1000 motor and the unanimous answer I got was its the smoothest air-cooled boxer they ever made - any power advantage was negligible - I've ridden a couple of GS 1000's over the years and would have to personally agree. Anyone who's ridden one knows it would be hard to accuse even a 1000cc air-head of being a quick bike by todays standards. .."

It piqued my interest in how the 800 is smoother than the 1000 boxer. I agree that the K75 is really smooth.

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Old 01-05-2012, 04:50 PM   #18
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I've owned the 600, 750, 900 and 980 Airheads, so heres my $.02.

The R60s are OK. I never paid attention to the vibes because I was usually wringing it's neck, trying to get it out of it's own way. The R75 is tons smoother than an R90 and the R90 is smoother than an R100. I also remember that out on the highway, riding the R75 I had to plan my passes, downshift and let the bike spool up before pulling out. With the R90 I could just roll-on and go.

Of all of em, my all-time favorite engine is the R90. When BMW built that one, they really got it right. Smooth enough, powerful, great mileage... For me, that engine just has a majick to it and I could happily own one as my only bike.

R100s are kind of in a class of their own. They vibrate, run hot and suck gas but they also generate significantly more HP and torque than the smaller engines. When I had to decide which engine to put into my latest bike I went for the big one and I'd do it again. It's the same choice you have when you're building a Hot Rod car. "Do I build a 283, a 327 or a 350?" Well, you're almost certainly going to build a 350 because it turns out more HP and torque for the same $$$$.

I remember riding a San Jose'd 1050 77-S Airhead and it was smooth but it wasn't as smooth as an R75. The difference? On the built-up R100, you could feel those big slugs going up and down and the cylinders firing !! Talk about good vibrations!

I'm almost 100% sure that magick surrounding the R80 GS is that the engine has the right power output and smooth power delivery thats right for it's gearbox, frame, suspension and weight. Add in it's inherent smoothness and it's the perfect little Airhead!
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Hawk Medicine screwed with this post 01-06-2012 at 05:30 PM
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Old 01-05-2012, 04:59 PM   #19
Grayghost66
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Quote:
Originally Posted by supershaft View Post
800's have around 9mm smaller bores and 2mm smaller exhaust valves. Some say they are smoother for their smaller pistons but I never hear that about 750's, 650's, 600's, 500's, and 450's. Maybe the R80 pistons work out right with the crank weights at the speed most cruise at? I have test ridden tons back to back. I can't tell that much difference in vibration compared to the difference in power but I suspect I cruise at a higher rpm than most. There is a big diff in power. Overall I guess they are a tad smoother but I miss the power of the liter bikes too much to care. The engines are the exact same size on the outside so I want the biggest bore that works well and I think that is 94mm and 980cc. I like R65's but the cylinders and heads are much smaller externally making for a much smaller feeling engine. There are hogged out 450's to the exact bore to stroke ratio of a R100: 1.33:1 which are what I call a hogged out 900. A R80 is 1.2:1.

The Siebenrock pistons I put in my R100 are barely lighter than the stock pistons. Most of the advertised weight savings is in the shorter wrist pins and then they take that not very impressive figure and add both sides together. You can go a LOT lighter than the Siebenrock setup with Venolia's and wrist pins like Luftmeister use to sell.
I have to ask (not trying to hijack the thread)....I have always been interested/curious about the R100 Siebenrock pistons and big bore kit. Can you comment on the difference in power, any difference in vibration, and in your opinion....worth the investment?
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Old 01-05-2012, 06:26 PM   #20
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Mine already was a 1000. The rings look different but it will take some years to know how they hold up. I hate the finish they put on the cylinders. It looks like silver paint. I hate engines painted silver. I thought the inside of my wrist pins were crudely machined and the chrome wasn't as good as BMW's but BMW has damn good chrome. Robtg balanced my rods so I won't be able to compare vibrations.
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Old 01-05-2012, 08:39 PM   #21
Hawk Medicine
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Quote:
Originally Posted by Grayghost66 View Post
I have to ask (not trying to hijack the thread)....I have always been interested/curious about the R100 Siebenrock pistons and big bore kit. Can you comment on the difference in power, any difference in vibration, and in your opinion....worth the investment?
If you do a search you'll find that the Siebenrock kits have a very good reputation. Matter of fact, I can't recall ever reading or hearing a complaint about Siebenrock's quality. Cost, yes. Quality, no.
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Old 01-06-2012, 07:27 AM   #22
fishkens
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Originally Posted by bgoodsoil View Post
I've heard the 980cc Siebenrock kits are super smooth since the pistons weigh so much less than stock.
I installed Siebenrock pistons and the engine runs quite a bit smoother. But I also balanced the rods and did quite a bit of other work so Siebenrock can't take all the credit.

Bottom line: a properly tuned, freshened and balanced airhead will run much better than a tired one. Not a lot of science there.
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Old 01-06-2012, 08:53 AM   #23
Rob Farmer
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I have a R100 Bitsa that Richie Moore did the heads on. It's running 9:1 pistons and his one piece valves running in F1 technology valve guides all setup with Groks Harmonizer. It has to be one of the smoothest airheads I've ridden and pulls like a train. Lovely!

I've got to admit I'm not a big fan of the 80 motor and prefer the extra grunt you get from the 100.
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Old 01-06-2012, 02:52 PM   #24
Caddy82rats
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What I can compre :
R80 G/S best engine for smooth
Just after my ex 77 RS, my ex 79 RS not so good
and my 90S not so smmooth a litel rough... but so sexy !
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Old 01-06-2012, 03:02 PM   #25
wmax351
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I personally really like the large flywheel. Smooths things out a lot, for any bike. My R75/5 is very smooth, even without any additional balance blueprinting. My uncle's EV11 Guzzi California was also very smooth, with 1100 cc's in a 90* vtwin. The cali has a ~35 pound flywheel, iirc.
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Old 01-06-2012, 05:36 PM   #26
Hawk Medicine
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Originally Posted by wmax351 View Post
I personally really like the large flywheel. Smooths things out a lot, for any bike. My R75/5 is very smooth, even without any additional balance blueprinting. My uncle's EV11 Guzzi California was also very smooth, with 1100 cc's in a 90* vtwin. The cali has a ~35 pound flywheel, iirc.
Yeah, the heavy flywheel tends to mask the vibrations but not only are the vibes still there somewhere but the engine won't wind up as quickly and the transmission won't shift as well.

I've always lightened my flywheels and these days I'm happy not to have one at all.

Horses for courses I suppose.
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