Finishing the Girdle Machining

This blog post is dedicated to Chris Hodgson from San Jose BMW. I saw Chris and his crew at the BUB Bonneville motorcycle speed trial event last week while helping wrench for Scott Kolb on his 125cc partial streamliner. Scott set a new 2 way record of 146.7mph on the last day of the event after lots of tweaking. There's an article over at Hell For Leather on the effort. The trip was lots of fun, especially when a record is set. Every speed lover needs to go to Bonneville. It's only 2 hrs outside of Salt Lake City and besides having no speed limit also presents an awesome vista in any direction.



Back to the topic at hand, I had the short block with me for display purposes and Chris Hodgson was like 'when did you do that machining, the blog is not up to date, what are you waiting for!!!!!' Being chastised by an internet follower compelled me to get my ass back in gear. That fact that it was a person who is a world renowned BMW tuner made it go into high gear! Chris and crew also took a record with their BMW HP2 so it was a happy pit area all around.

Chris, this update is for you and hopefully I will be able to work on the project and update the blog regularly.

Now on to our regular programming...........

After the last post, which was machining the girdle split surface, we are up to the balance of machining on the girdle part. We were up to this point on the part:

Oil gasket and split surface machined:


The next step is to machine the girdle subplate then complete the part machining. The subplate screws to the oil pan surface and is accurately aligned to the trunnion table with dowel pins.



The first set of features to be machined is the crankshaft main bearing split surface:

Facing:


Drilling/tapping.......


Then the 4th axis is indexed 90 degrees and the clutch side is machined. there is a bunch of profiling for the cassette transmission side plate, trans and oil shaft bearing bores, gear clearance, and misc threaded holes.

Cassette mounting flange:

Gear clearance:


Roughing the bearing bores:


Once these deep bores and pockets are done the 4th gets rotated -180 degrees to machine the output sprocket side. The features on this side are the generator cover surface, oil filter mount, oil pump drive and pressure chambers, and starter bore. Yes, a starter motor! No rollers, no bumping, just press the magic button.


Facing gasket surfaces:

Some operations are pushing the limit of tool stability, like this 1" dia x 8" long insert end mill:


Starter motor mounting hole:

Gerotor porting:

The oil pump is a gerotor supplied by Melling, a high quality OEM/aftermarket automotive parts manufacturer. This style pump is highly efficient and compact when properly packaged. A lot of design assistance for the entire oil pump circuit was provided by Marc Goulet of Melling. Marc is also a motorcyclist and was kind enough to donate his time and put up with my unending questions on the subtle details of high performance oil system design. Marc has been involved in the design of some top level F1 engine oiling systems so he is definitely the person to ask in this field.

Inner and outer oil pump gerotor:


These parts fit into dual eccentric pockets that have CNC porting designed to allow high flow with minimal power losses.

Those 3 machining positions contain all of the high tolerance operations. Now on to some less critical ones:

Oil drain hole:


The position of the subplate is then indexed 90 degrees on the trunnion table and we machine the:

Upper engine mount:


Lower engine mount:


Starter mount:


That covers the majority of the machining on the girdle. Bearing bores will be finish machined as part of a complete crankcase assembly.

It ends up being one sweet looking part:




Stay tuned for more soon!