Munched piston

[Vintagewannabe]

I am tearing down my 73 RD350 to rebuild, and pulled the heads to measure squish. Right cylinder looks pretty good, but the left... well I guess I figured out why it had such low compression.
My guess on the cause of this only happening in one cylinder is ignition timing. When I got the bike I put in new points and condenser and set timing 1.8mm btdc.
When I got the bike, one side was not firing, and I don't know what it looked like inside before I got it running.
So either it had some issue before I got it, or I messed up the timing on that cylinder somehow
Points are new old stock daichi

Right
And left

[m in sc]

thats usually from late ignition timing. very retarded.  not lean or oil. man that sucks

[Vintagewannabe]

thats usually from late ignition timing. very retarded.  not lean or oil. man that sucks

So that sounds like either it happened before I got the bike, or I just got the timing horrifyingly off.

[m in sc]

that looks like older damage that somebody sold you. bummer. my supposedly rebuilt meticulous t500 motor had similar old damage. it was still holding compression but this is from lean/airleak detonation.  note the central location vs your exhaust side damage. yes i rebuilt it

[Vintagewannabe]

I started looking bad at my notes and things on this bike, and I think you could tell how bad it was the moment I put the chambers on. When I would watch the exhaust and listen, you could tell that the left cylinder just didn't "pop" like the right did as the exhaust came out. Which if it was like that since I got it, that would mean I have been running it like this for over a year. It always amazes me what these old two strokes can get away with.