The only way you can know when you have reached the limit as regards tuning is when your next development step fails to work.
Cadwell was just such a time. I had built an engine with a slightly bigger bore, bigger ports and a slightly higher compression.
I took it to the Morini club track day the week before and it seized.
I had noticed it getting hotter than usual.
I stripped it and saw the fuel height in the remote float chamber was a bit low, so took pains to measure and mark everything so I could get the fuel height spot on
I then rebuilt it all in the bike and ran it up. It was still getting hotter than I liked and it sounded harsher than normal.
It was midday Thursday and I needed to go Friday pm, but I stripped out the engine again and checked all the matching of the water passages between head / gasket and block.
I used air tools to match everything up and had the engine rebuilt by 2 am Friday. I got a few hours sleep and got up at 6.30 to built it all into the bike again and load the trailer.
At Cadwell it was hard to start and was getting hot. I went to the line and it stalled before the sighting lap and we could not start it. You can understand that this was an exhausting, expensive and very disappointing experience. To be honest, with all the late nights and rushing and pushing, all on my own, I did start to feel my 70 years a bit.
I have the block and pistons I used last year and will rebuild the motor with these components. Of course, I should note that as far as I know, I am the only competitor still using unleaded petrol rather than alcohol or avgas. Even the difference in inlet port size and timing will permit more gas to be transferred and this effects the pressure of the charge at the point of ignition and thus the speed of flame propagation. I feel sure that I had just gone too far and I was getting detonation. The next step is to measure carefully the head volume. I know the piston to head clearance was about as before so I suspect the effect of the bigger inlet ports and larger port areas pushed it over the edge. When it is rebuilt with last years block and pistons, which were nearer road spec, I will measure everything to get a good comparison. Any man can stand success, but you need to be realistic when things go wrong. It is an opportunity to learn. The racer is used to try out how much I can get out of Alfred’s design. Road engines for customers benefit from this experience but are always well within the known safe zone. I never pretended to be a genius, but do my best with what I was born with.
Rotten luck Roger, I feel for you, the nearest I ever came to such angst and frustration was running out of tyres due to a series of punctures, at least we were spared getting as far as the line! That was years and years ago but I still remember the feelings.
I’m equally confident that given your reputation and energy you’ll solve the problem and like Arnie, “You’ll be back!”
Sorry to hear you had problems at Cadwell, the trials and tribulations of improving two stroke performance.
I had a similar experience, but stopped before it siezed. The cause was too much back pressure caused by too small a restrictor bore in the tail pipe.My engine ran harshly and got extreemly hot. Removing the restrictor fixed the problem.