Inline Twin Engine Ep. 7

The progress on the engine continues. In this episode I’ll be making the cylinder sleeves and pistons.

The cylinder sleeves are turned from cast iron bar stock. The first side is turned to finish size on the outside and inside diameters. This ensures concentricity.

Inline Twin 101 (800x450)

After parting off, the sleeves are finished on the second side. The small shoulder will create a groove in the cylinder block for an O-ring.

Inline Twin 102 (800x450)

Finish turned sleeves:

Inline Twin 103 (800x450)

…and that’s how they look installed in the cylinder block:

Inline Twin 104 (800x450)

The surface finish in the bore turned out very nice and was cylindrical within less than 0.01 mm. I contemplated to just leave it as is, just turned. But I decided to finish lap the bore. Since the surface finish was already really good, and the bore straight, the lapping took mere minutes to complete (note the cling film on the lathe bed, to protect it from any lapping compound drips).

Inline Twin 105 (800x450)


The next parts are the pistons.

I started with turning a boss to hold the blank in a collet for the subsequent operations. The piston diameter is 32mm, too large to go directly into a 5C collet.

Inline Twin 106 (800x450)

Chucked in a collet, the OD is turned to finish size and the grooves for the rings are cut:

Inline Twin 107 (800x450)

Using a collet block, it is over to the mill to cut the recess for the connecting rod:

Inline Twin 108 (800x450)Inline Twin 109 (800x450)Inline Twin 110 (800x450)

Without removing the piston blank from the collet block, the wrist pin bore is drilled and reamed. This ensures the hole is perfectly perpendicular to the milled recess.

Inline Twin 111 (800x450)Inline Twin 112 (800x450)

The last operation is to face off the chucking boss. The piston is clamped very gently in the 3 jaw chuck with some paper to protect the surface from getting marked up.

Inline Twin 113 (800x450)Inline Twin 114 (800x450)

The finished Pistons:

Inline Twin 115 (800x450)


Thank you for visiting my shop.

If you have any questions about the engine or any of the other projects, please leave a comment below, or email at yogisworkshop(at)

For other projects from the shop, please check out the Projects Page in the top menu.


One comment

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s