What the ....?

[rob w]

On a KTM engine there's a blank pocket hole cast into the cylinder. It's at the rear, above the intake, towards the top, angling from the R.H. side towards the center.
I've often wondered what it's intended for. Then on a spare 400 cylinder I saw that this one was drilled through into the bore with a 5mm hole, then tapped from the outside and plugged with a 12 x 1.75mm bolt. It's done very well. (factory-like)
The only thing I can think of is that it's for a compression release, but 12mm is the wrong size..is'nt it? Inquiring minds what to know, thanks.

 

[Rocket]

Rob
I'm sure it was for a compression release to aid starting.  I have never seen one installed, but KTM must have been thinking ahead.  The mid-70's Yamaha 500's had a compression release that was connected to the kicker that automatically opened when the bike was kicked over.
If you look in a parts manual for the 75+ bikes, it will show a picture of the compression release but the part numbers are not there.
Rocket

 

[Larry Perkins]

It used a Magura compression release.  I have an NOS one somewhere.  It has a lever like the older Magura chokes in plastic.