Horizons Unlimited - The HUBB

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-   -   Downsizing? (https://www.horizonsunlimited.com/hubb/bmw-tech/downsizing-7890)

DaveO 25 Jul 2003 08:22

Downsizing?
 
After 2 R75s and 2 R80s I find the 1000 (95 model) is very rough. That low-down torque is usable, but it's not pleasant.
What would it take to drop the size back to 800?
One complication seems to be that whereas US-market bikes had the same 32mm Bings, the European & Aus 1000s had 40mm carbs.
Shold I even contemplate this?

Grant Johnson 25 Jul 2003 08:34

You need everything from the crankcase out - that's carbs, heads, barrels and pistons. Rocker assemblies are identical on same year bikes. Pipes should be the same that year.

You SHOULD be able to find someone gagging to go the other way, and make a profit on the deal!

I recently did that myself - converted my 86 R80G/S to a 1000. Very straightforward - just replace it all!

A possible cure for the roughness is to use lighter pistons available from Touratech. The only real reason for the difference in smoothness is the greater weight of the 1000cc pistons. If you could get the pistons down to the weight of the 800 pistons you'd have the same balance, and it would feel just like a strong 800.

The best but most expensive way is to get the lighter pistons and also rebalance it. That means taking out the crank.

------------------
Grant Johnson

Seek, and ye shall find.

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One world, Two wheels.
www.HorizonsUnlimited.com

Timo 25 Jul 2003 12:00

I'm thinking of going the way Grant did. I have a low milage 800cc setup currently. Let me know if you are serious about the swap.

I had an 88' R100GS last so I know what you mean about rough running. the 800 is much smoother. On the other hand, I miss the power of the larger cylinders. If I were to do it all again, I'd probably spend the time and money trying to smooth out the 1000. It's a tough call. I find the 800 fine for everything except hard excelleration for passing with a load and passenger. Can't beat the tractability of the 800 for slower running or more relaxed hwy cruising tho'.

dc lindberg 25 Sep 2008 18:05

How did it go ?
What did you chose to do ?

My reply - YES!
I have now run Siebenrock 1000cc dual-plugged for about two years. TOO much power at winter! I sort of regrett the up-grading, but faced with the cost of renewing heads, pistons and barrels I opted for 1000cc due to the shear cost of redoing my 800cc high compression conversion.

My recommendation on the 800cc system depends on what your demands are (where and how to drive).


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