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Process overview
So what does case blueprinting involve?
The objectives in blueprinting any engine case are always the same:
• Machine the bearing bores in line
Doing all the above as close to perfection as possible is what I have been doing for 33+ years and thousands of cases.
On this page, you'll find a brief overview of this process from start to finish. The description and photos are of
a Yamaha KT100 case, however the procedure is virtually identical regardless of engine make/model. The complete
process is actually quite a bit more involved than can be covered in this simple overview, but this should give you the
general idea.
This is the preferred method for a customer to ship a case to me:
• Case halves bolted together with all screws and alignment pins
After the case arrives, the serial number is recorded along with the customer's name (and later; the date that the machine
work is completed, along with any information I feel might need to be noted for that particular case).
All sharp edges on the outside of the case are deburred/chamfered before anything else is done. The cases are then
disassembled and the area directly under each of the case screws is spotfaced flat and square. Then each of the case
screw holes are chamfered on both sides of that case half. Finally, the center (sealing) surfaces of
each case half are lapped flat.
Each case half is then bored to a specific size for accepting an aluminum sleeve. If the case is a KT100, the back face
of the bearing bore is "stepped" for clearance for a double-row self aligning bearing. (I do this on all KT100 cases even
if the customer is running standard single-row bearings).
Each case half is then heated (in an oven) to a specific temperature, and the correct sleeve is installed. The case half
is then allowed to cool slowly to room temperature.
The case halves for a given engine are then assembled (with alignment pins, and case screws torqued). The assembled case
is attached to a dedicated fixture and "indicated in" until the best possible location for the bearing
bores is determined. Then the bearing bores are machined to their final size and the back faces of the bearing bores are
skimmed to insure they are absolutely parallel. The end result: bearing bores that are perfectly in line, back faces
that are perfectly parallel, and bearing interference that is correct for the case and bearing type.
A finished bearing bore looks like this:
Now the case halves go back into the oven so the main bearings can be installed. The case halves are then allowed
to cool to room temperature.
Next, the case halves are assembled and case screws torqued. The complete case is then picked up and bottom is machined
flat.
Finally, the case is picked back up by its base (or fixture) and the crank centerline is indicated in to within .0001, and then the top
surface is machined.
Here is the finished product: much better than new in every way.
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