Jim's Cushman Scooter Site
How to Repair a Cracked Cylinder
By Bill Turner
In this article Bill tells how he repaired his cracked cylinder. He also offers an explanation of why it cracked.
The cylinder wall of this 2-7/8 inch M8 Cushman engine cracked in the fin area on the flywheel side. I did not want to discard the block so I decided to repair it. Here is the solution. You may have to modify this procedure depending on just how and where your block is cracked.
Refer to the pictures and drill holes down through the top of the block with the proper bit for a 5/16-24 tap. In this case I drilled five holes spaced as shown in the photos. The holes are located just outside the gasket area and go down on the outside of the cylinder wall. Drill through the top of the block and continue down through all of the fins as shown in the picture. Enlarge the top part of each hole for the shaft of the bolt with a 5/16 inch bit. Then tap the rest of the way down through the fins. An extra long tap will be required.
Thread bolts into the holes as tight as possible, being careful not to
break any fins. Then turn the block upside down and weld the underside of
the top two fins (they will be on the bottom now) to each 5/16” bolt
(depending upon where the crack is). Use special rods made for welding
cast iron. Do not attempt to weld up the crack because doing so could warp
or heat stress the block or burn through the cylinder. After the block
cools turn it back right side up and mill the heads of the bolts down
flush with the block so that they will not interfere with the head or the
A sleeve that can be used for the M8 block is an L A Sleeve Company part number LA-214. Its outside diameter is 3.0625 and allows a standard 2.875 inch finished bore. This sleeve is longer than necessary and must be cut to size.