1915 cylinder barrel information.

[Dave@NZ]

Hi Guys,
New Member checking in, I am just starting to restore the engine of my cousins 1915 350cc Douglas twin, the frame assembly has been restored with some assembly to do the engine is mostly disassembled and requiring a full restoration.

My question to you is what diameter (o/size) can the cylinder barrels be rebored out to due scoring from the gudgeon pin with out any other problems.

Thanks in advance,
Dave.   

[Frank Lyn]

I was hoping someone would give you a definitive answer.... But here goes
JP Pistons (JP 0868 ) and the LDMCC supply pistons that are 0.040" oversize so that is a safe bet.

My TS24 had corrosion on the inside lower part of both cylinders and to clean up the pits completely, we would have had to go 0.060" over and bore it off center.  That was too scary so I had sleeves put in that converted the 350 cc to a 325 cc machine.  Now I am evaluating the piston problem and found a set of free used Honda CB550 to play with.  If I can bush the pin hole to get the proper compression height , that seems like a reasonable way to go.  But I will have to cut a bit into the meat of the piston to get the hole low enough to keep the compression up.  With only a c. 60 mm stroke? a little too-high piston pin means a lot of loss of compression.

[Dave@NZ]

Hi Frank,
Thanks for the information and good to hear .040" is the normal amount to remove.
Dave.