Old Britts, MK3 Crank Case Puller

MK3 Crank Case Puller

If you have ever tried to split a set of cases using mallets and screw drivers, you know how hard it is to split the cases without damaging them. I had made a crank case puller for pre-MK3 motors some years back and needing to separate a set of MK3 cases. Not wanting to try it the hard way I worked up this easy and safe (for the cases) solution. Having lots of threaded bars and lots of 6061 T6 aluminum 2" x 1" bar stock the logical solution is pictured above. If you have a way of turning down the ends of threaded bars and threading the end to 5/16 x 24 you could easily make this puller. If you don't have a lathe you can find some 5/16 x 24 threaded rod or you could use a 5/16 x 24 bolt around 8" long, cut off the head and thread the end.

I cut two 8" pieces from some 12 x 1.75 metric threaded rod that I received by mistake (I have around 30' and am always looking for some use for it), but you could use 1/2" threaded rod. I turned down 1/2" of the end and threaded it to 5/16 x 24.

I then cut a 7" piece of the aluminum -- or you could use a steel bar thick enough to not bend when you apply the pressure required to split the cases. The nice thing about aluminum is that it acts like soft jaws on a vise and will not bung up the end of the crank shaft. Two of the four holes in the left crank case are almost directly opposite each other, as pictured above. The holes are 5 1/2" inches apart. I milled two slots 1/2" wide and 1" long, the centers of which are 5 1/2" apart. I also milled a circular indent in the center .1" deep with a diameter of .63" (not pictured) to steady the bar over the crank shaft that sticks out the left case. You probably don't need the center hole unless you get a real stubborn case, which in this case I did.

Having a CNC mill, I tend to get carried away and engraved the name of the tool on the face of the puller. This is obviously of zero importance in splitting the cases.

As I stated, the cases I wanted to split were very difficult and without a puller could not have split the cases. The front dowel was rusted and would not let go. The back separated right away, but the front would not budge. I ended up tightening both nuts, creating a gap in the rear of around an 1/8", putting a bolt through one of the back engine mounts and applying pressure to pivot up the front. No go so then I applied heat to the front and more pressure on the front puller nut, and finally it slowly came loose.
Puller

This is a picture of all the parts that make up this puller. Since I still have lots of the material required to make more pullers and the CNC program, you can order this puller.

The current price for the puller (part # OB-70601) is $50.00.
The rental price for the puller (part # OB-70601/R) is $20.00, with a $30 deposit.
Prices are current as of 12/28/08.

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