K100 vs k1100 cooling questions

[sooprvylyn]

Recently I've been in a discussion w another bricker about the cooling systems of the k100 and k1100 and I am hoping for some clarity and history.  He claims, and backs up with pictures, that both the radiator and the water pump on k100 is different and more efficient than those of the k1100.  Looking at the parts fiches for both bikes I note that the part number of the radiator is the same, as is the impeller shaft for the water pump.  He claims the k100 radiator was 2-3 core where the k1100 one was a single core. He also showed me pics of a k100 water pump next to a k1100 one. The gear ratio, and toothing, appears totally different, blowing same part number out of the water. I know there was a old version of the impeller, but whats up w a totally different impeller shaft? What's going on here?  I assume bmw 1st gen k100 may have had some different parts that were then upgraded and standardized for later 4 cylinder bikes? I was under the impression that k100 and k1100 had the same cooling system, save the cast vs stamped impelllers.

[Scott_]

I can't say as I know all the details, but there were some K100 years that had 3-core radiators. All K1100's only came with 2-core.
They aren't necessarily 100% interchangeable though.
To fit a 3-core on a 1100 you have to modify the stock fan/mount to get it to fit as the thicker core places the fan closer to the engine, and the lower mount hits on the block.
Another other option is to replace the stock fan with the lower profile spal fan as many others have done here on the forum(you can do a search for them).

[Laitch]

I was under the impression that k100 and k1100 had the same cooling system, save the cast vs stamped impelllers.

According to MaxBMW's fiche, the pump drive shaft and the oil drive gear changed at 1/90, so their part numbers changed. The oil drive gear tooth count changed from 17 to 32 which would be likely to increase oil pressure. The stamped water impeller probably would be lighter. Did you ask your fellow Bricker to explain exactly why the earlier pumps were more efficient? Please let us know.

[Kaos]

According to MaxBMW's fiche, the pump drive shaft and the oil drive gear changed at 1/90, so their part numbers changed. The oil drive gear tooth count changed from 17 to 32 which would be likely to increase oil pressure. The stamped water impeller probably would be lighter. Did you ask your fellow Bricker to explain exactly why the earlier pumps were more efficient? Please let us know.

I thought it was the other way around. That the 32 tooth system with newer impeller provided better coolant flow, so this indeed makes me curious.
And they do indeed have different partnumbers but are interchangeable, provided you use both gears.
And i do believe i had to switch the cover to run the newer impeller on my 2v

[Laitch]

Recently I've been in a discussion w another bricker about the cooling systems of the k100 and k1100 and I am hoping for some clarity and history.  He claims, and backs up with pictures, that both the radiator and the water pump on k100 is different and more efficient than those of the k1100.  I was under the impression that k100 and k1100 had the same cooling system, save the cast vs stamped impelllers.

The answer to this query is contained in this thread. I've linked to the comments of Inge K—an experienced Brick technician and major contributor to knowledge of Classic Bricks—to whom the Motobrick Workshop is dedicated. I've started with his comments but the whole thread is interesting and includes how one Bricker adapted his Brick's engine to operate a K1200 water pump.