1150 RT P&C's in R11S?

Jozef Schumann · Jozef Schumann's Garage

Hello Folks -
I've searched and see posts referring to SJBMW's (1150) 12:1 pistons - Question is: are the O.E.M. (mahle/kolbenschmidt?) 1150 barrels and slugs just a simple R&R or do the 1150 barrels require spigot O.D. machining.... or?

I don't want to go high compression and prefer to stay OE on the slugs.

As always - thank you for your expertise.

J.S.

BadToTheBown · BadToTheBown's Garage

Assuming you have R1100 engine cases, to fit R1150 cylinders, you will need to have 1mm machined off the skirts that go into the engine cases. Your machinist needs to use soft chuck jaws to avoid ruining the Nikasil the rings ride on and seal against.

On the pistons, IF you are running stock valves, you can run stock R1150 pistons or aftermarket (i.e. SJBMW pistons). IF you are running larger valves, do NOT use stock pistons, go with the aftermarket pistons. I don't know if Chris (SJBMW) has anymore of these pistons but they are nice looking Venolias and his service has been excellent. I have a set but I'm using mine. I didn't cc them but they look to be 12:1 to 12.5:1 range. I don't know what RT pistons are but I doubt they are more than 11:1. Perhaps someone else on the forum will know what's available from stock pistons.

Good luck.

Chris Canning · 03-20-2015, 03:30 PM

From what I can remember their were two different kits one for the early bikes and another I think was post 04??

There were several kits in Germany but could never work out if they came from BBP or were a different supplier.

BadToTheBown · BadToTheBown's Garage

I can't say for sure on post '04 but I can say you can machine '04 cylinders to fit an R1100S. The big difference I ran into was where the dowel pins were in heads and cylinders, and as you would expect, the head gaskets. I focus on '04 dual spark engines and parts now to keep my interchangeability high as practical. I also like the Rockster engines because they are black but now I'm off topic.

Jozef Schumann · Jozef Schumann's Garage

I see Gent's - I was hoping for a less involved refit. My son spotted a low mileage 1150 P&C set on eBay which piqued my curiosity, but with 20k miles on my '03 prep and given the fact it runs so well - I reckon I'll pass until some point in the future when I might revisit the issue come refresh time.

Thank you for the insight.

J.S.