When BMW introduced the Nikasil cylinders in the US in the 1981 model year, they came with the 8.2:1 low compression pistons to help meet EPA requirements. So, my 1983 R100RS has low compression pistons. But, in Europe, BMW provided 9.5:1 pistons and rings for use in the Nikasil cylinders and they are still available.
The higher compression makes a useful difference in torque and horsepower:
The 8.2:1 compression pistons produce 53-Ft-Lb and the 9.5:1 compression produces 56 Ft-Lb and, or about +5% for the higher compression.
The 8.2:1 compression pistons produce 66 Hp and the 9.5:1 compression produces 70 Hp and or about +6% for the higher compression.
I intend to use this bike for two up touring and it has over 80,000 miles on it. So I am going to install 9.5:1 pistons sized for the “B” sized cylinders I have (part# 11 25 1 337 175) to get a useful boost in torque and horsepower.
New 9.5:1 “B” Size Piston Kit For “B” Size Cylinder
New Piston Kit Contents-“B” Size, 9.5:1 Piston (93.97 mm)
For the best fit and an oil tight motor, the recommendation from Tom Cutter at Rubber Chicken Racing Garage is to replate the Nikasil inside the cylinders and then hone it to get the proper clearance that matches the actual pistons. There is some variability in the pistons and this approach mates the cylinder dimensions to the piston dimensions for a tight seal.
Here is the link to the write-up of the procedure.
I recently renamed this site “Brook’s Airhead Garage” in recognition that over the almost 10 years since I started it, 95% of the content is about how to rebuild, restore and care for BMW airhead motorcycles. So what happens? A friend, Rohn, talked me into doing a 72,000 mile service on his 2004 R1150RS.
I too own a 2004 R1150, but mine is an RS. Generally I’ve had a dealer do most of the routine maintenance on it. Although, I have told myself that I ought to broaden my horizons mechanically and become more knowledgeable about it’s maintenance. Rohn’s request pushed me over the edge.
In researching the work required for this service and the history of work done on Rohn’s bike, I noted that his fuel pump is original. Mine died at about 75,000 miles in Des Moines, IA at the intersection of I-35 and I-80 in a construction zone on my way to Michigan. Unlike an airhead, there wasn’t a thing I could do to coax it back to life. I told Rohn he might consider his fuel pump and the internal hoses a “preventative maintenance” item and he agreed to have me replace it.
In looking around for information on the internet, and YouTube, to prepare me for this work, I wasn’t able to find good instructions for replacing the fuel pump. There are several resources that show how to replace the filter, but the fuel pump seemed to be left out.
So, I put this material together to fill that gap.
I started this blog back in 2009 as a general blog space with the original name “Motorcycles and Other Musings” to cover the expected content. As is often the case with an idea, it takes it’s own course and becomes what it is meant to be.
This blog is 90% about BMW Airhead motorcycles I’ve worked on in Brook’s Garage which I had built in 2012. SO ….
I changed the name of the blog to better reflect what it has become over the past 10 years.
Same content, same author, same passion for helping amateurs keep their classic BMW airhead motorcycle(s) running smoothly.
I also updated my YouTube channel to use the same name.
I have created over 50 short videos that are used in the documentation of the various rebuilds I have done. The number of subscribers for my YouTube channel is just about the same size as for this blog.
And, I’m starting to plan for another restore/rebuild project soon. The bike is a 1983 R100RS. I may do a “resto-mod” on this bike, or I may not. I’m still thinking about the direction I want to take.