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Old 05-04-2012, 09:04 AM   #1
enfielddnepr OP
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bmw r80 t0 r100 conversion

Dear folks, as an r80 is somehwqta cheaper then an r100, and the first will have less wear on the drive train as the r100 i have a quaestion about converting a 800 to 1000cc.
I know about the siebenrock kits.
quite expensive..The lower weight of the pistons is cool, will wear less on the bearings, but the higher compression i do not like.. want to keep octane 95 possible as fuel and don't like the extra wear..
So, i think the most basic is swapping the pistons and barrel;s from a r100?
but i guess the cylinder heads also need to be exchanged, the r100 head will have bigger valves? also carbs?
finally the final drive will need a diffenrent set of crown- and pignon wheels..
Does anyone here have experience with this?
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Old 05-04-2012, 09:26 AM   #2
Airhead Wrangler
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First off, which year and model bike are you starting with? R100s post '85 or so use the same size valves as R80 models. Same 32mm bings as well. You can have R80 heads machined to fit R100 pistons, but naturally you'll need to find someone who knows what they're doing and it won't be cheap. Good used R100 heads can be had for $250-300ish. Barrels and pistons in the $400-500 neighborhood. By the time you're all in, you're well within the price range of a siebenrock kit, but for used components. All that said, pricing for you in Europe is probably completely different. The 9.5:1 compression ratio they use is just on the edge of doable for regular pump gas. Mid grade and premium should be fine. 95 should be absolutely no prob for you.
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Old 05-04-2012, 09:32 AM   #3
enfielddnepr OP
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Quote:
Originally Posted by Airhead Wrangler View Post
First off, which year and model bike are you starting with? R100s post '85 or so use the same size valves as R80 models. Same 32mm bings as well. You can have R80 heads machined to fit R100 pistons, but naturally you'll need to find someone who knows what they're doing and it won't be cheap. Good used R100 heads can be had for $250-300ish. Barrels and pistons in the $400-500 neighborhood. By the time you're all in, you're well within the price range of a siebenrock kit, but for used components. All that said, pricing for you in Europe is probably completely different. The 9.5:1 compression ratio they use is just on the edge of doable for regular pump gas. Mid grade and premium should be fine. 95 should be absolutely no prob for you.
Hi, i was goning for the 1981-185 types.
'95 is the lowest octane of fuel you can get here..
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Old 05-04-2012, 09:33 AM   #4
Beater
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Quote:
Originally Posted by enfielddnepr View Post
Dear folks, as an r80 is somehwqta cheaper then an r100, and the first will have less wear on the drive train as the r100 i have a quaestion about converting a 800 to 1000cc.
I know about the siebenrock kits.
quite expensive..The lower weight of the pistons is cool, will wear less on the bearings, but the higher compression i do not like.. want to keep octane 95 possible as fuel and don't like the extra wear..
So, i think the most basic is swapping the pistons and barrel;s from a r100?
but i guess the cylinder heads also need to be exchanged, the r100 head will have bigger valves? also carbs?
finally the final drive will need a diffenrent set of crown- and pignon wheels..
Does anyone here have experience with this?
It depends on the years you're talking about.

A short list would include:
1. Pistons
2. Cyclinders
3. Heads: The heads are concave to the correct size of the cylinder ... so you need the right heads.

Optional (depending on the years):
4. Carbs: The 32mm Bings WILL WORK ... but the 40mm's will be better ... and Mikuni's (34's to 38's) are good too. If you go Mikuni call Rocky Point Cycle in MA, he can set you up with the right cables.
5. Exhaust: If the heads are 'big valve' ... from the 77-79 range, the output spigot might be 40mm and not the 38 that was stock for most.

Nice to have:
6. Final drive in the 32 to 34 / 11 range. You probably have a 37/11 ... and if you're setting up a dirt bike ... then it will be fine. But for road ... you'll have a whole lot of pickup, and the engine will be screaming at 80mph. But a 37/11 will work.
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Old 05-04-2012, 09:57 AM   #5
Airhead Wrangler
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Quote:
Originally Posted by enfielddnepr View Post
'95 is the lowest octane of fuel you can get here..
Which octane rating system do you use in Europe? RON?

EDIT: wikipedia to the rescue. It looks like you guys use RON. We use AKI. Our regular fuel which some people use in 9.5:1 engines without report of problems is 87 octane on our AKI rating which is equivalent to about 91-92 on the RON rating system. Therefore if your "regular" is 95 RON then it's better than our "regular."
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Airhead Wrangler screwed with this post 05-04-2012 at 10:02 AM
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Old 05-04-2012, 10:38 AM   #6
BeemerShop
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If you don't like the 9.5:1 compression ratio of the Seibenrock kit, install one low test base gasket per side part number 11111335650 and that will drop compression to 8.8:1. The Seibenrock kit is the ticket.

Seibenrock has a kit designed for the R80 with pistons machined to fit the heads so no head modifications necessary, makes it a bolt on kit. We sell and install a lot of them with great results.

Ted Porter
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Old 05-04-2012, 11:00 AM   #7
bmweuro
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Last time I was looking for used post 81 pistons and cylinders it seems like they were all around $500.00. Then you have to clean them up buy rings($140.00) and more than likely replace the rusting pushrod tubes($120.00). So $720.00 vs $890.00 for new Siebenrock.
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Old 05-04-2012, 11:06 AM   #8
BeemerShop
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Quote:
Originally Posted by bmweuro View Post
Last time I was looking for used post 81 pistons and cylinders it seems like they were all around $500.00. Then you have to clean them up buy rings($140.00) and more than likely replace the rusting pushrod tubes($120.00). So $720.00 vs $890.00 for new Siebenrock.
Hey there stranger. Yeah, and they're becoming harder to find. Congrats on Boxer Metal, cool shop.

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Old 05-04-2012, 11:10 AM   #9
wirewrkr
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All right you two, get a room!
All we need now is for Bud P to pop in and we could have an old farts party!
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Old 05-04-2012, 11:13 AM   #10
BeemerShop
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All right you two, get a room!
All we need now is for Bud P to pop in and we could have an old farts party!
He'll be along any minute the old fart.
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Old 05-04-2012, 11:48 AM   #11
outfit
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So this was a real bargain
http://www.ebay.co.uk/itm/BMW-R100RT...item2a1c8cd2da

Previous week I got a pair for 120 inc pistons. Thought I'd button it all up and see what the result was. I'm pleased to say the result was perfect. Just put on the usual new gasket's and rubber's.
So I'd say keep an eye open on ebay and be as good a judge of what you see as is possible and then go for it.

outfit screwed with this post 05-04-2012 at 11:54 AM
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Old 05-04-2012, 12:04 PM   #12
Beater
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Quote:
Originally Posted by outfit View Post
So this was a real bargain
http://www.ebay.co.uk/itm/BMW-R100RT...item2a1c8cd2da

Previous week I got a pair for 120 inc pistons. Thought I'd button it all up and see what the result was. I'm pleased to say the result was perfect. Just put on the usual new gasket's and rubber's.
So I'd say keep an eye open on ebay and be as good a judge of what you see as is possible and then go for it.

That would have been a real bargan in the US ... I have no idea of the market in Europe ...
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Old 05-04-2012, 03:53 PM   #13
lkchris
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You're really better off just finding an R100.

Because you really should match your "new" R100 engine with the same rear drive ratio that BMW typically fits. R100 won't be as smooth as an R80 and won't be so comfortable always spinning at R80 rpms.
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Old 05-04-2012, 04:12 PM   #14
Airhead Wrangler
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Quote:
Originally Posted by lkchris View Post
You're really better off just finding an R100.

Because you really should match your "new" R100 engine with the same rear drive ratio that BMW typically fits. R100 won't be as smooth as an R80 and won't be so comfortable always spinning at R80 rpms.
Yeah, I got ahead of myself there. Since you don't even yet have this bike, I'd say you'd be better off just starting with an R100 to get a suitable final drive ratio. Just be patient. The right one will come along.
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Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.
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Old 05-04-2012, 08:02 PM   #15
bmwrench
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Originally Posted by BeemerShop View Post
He'll be along any minute the old fart.
Will not!
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