Preparing Your Big Bore Machine Work

If you are doing a big bore project, and the bare sleeves have been sent to you for local installation, such as in the case of a Nemesis Racing Big Bore Kit, your machine shop must know what you want them to do. Based on your needs, prepare a To Do List for the machinist similar to the following:

1. Check and true up sleeves as needed.
2. Bore the cylinders for the sleeves to be press-fit into them.
3. Mill the cylinders to receive the inset of the sleeve collars (aka lips), but leave them 0.001" above cylinder the deck. See photos below.
4. Clear the sleeve-collars from around holes. If you are building an engine in excess of 108c.i, the machinist must make note of the encroachment the sleeve collar will have over the stud, oil, and alignment-dowel holes. The sleeve collar must have semi-circles bored at those locations. Pay special attention to the alignment dowel holes as these help properly align the head. See photos below.
5. Press-fit the sleeves into the cylinders. My machinist used a press-fit technique using heat rather than high pressure. The bored cylinders are heated to 400* for 45 minutes. Then the sleeves are dropped in, and a ten pound weight is placed on top while they cool. See results photos below.
6. Bore the sleeved cylinders. My machinist used a technique whereby the cylinders are fitted with a custom made 'torque plate' and placed under the same compression as when installed in the bike. This seemed like a great idea to me, but Nemesis assured me that, while the machinist's efforts are admirable, this technique is unnecessary, due to their high-tech metallurgy.
7. Finish with a 600-grit hone. My machinist used the 'torque plate' again.
8. If you are building a motor in excess of 110ci, the machinist must bore the crankcase cylinder holes to 0.020” over the sleeve OD. My machinist insisted on bolting the cases together with the same torques specified in assembling them--Nemesis again said it was fine, but unnecessary.
9. Grind a relief arc at bottom of the sleeves so they won't touch each other at center of engine 'V' when installed in to the case. Use the stock cylinder arcs as guideline models. See photos below.
10. Also grind another relief arc in the sleeves, 180* from the other ones, to make it easier to install piston rings. Again, use the stock cylinders as a reference. Note: My machinist skipped this step (with my approval), but I believe it made piston ring installation a little more difficult.
11. Grind a chamfer along the inside of the bottom ridge of the sleeves. This will also make it easier to install the piston rings. See photos below.
12. My heads got a Sun (aka SERDI) valve job. You may skip this if you are getting replacement heads, or are leaving your heads totally stock. As I understand, a SERDI type valve-grind cuts three, increasingly progressive angles to the valve and seat. This creates better air flow than a standard, single angle.

Note: If you can find someone to do a RADIUS type valve grind, do it. This method eliminates the angles altogether to make a more natural curve for air flow.