Engine dies and cannot crank when hot

Ok, first off I am a mechanic with over 35 years in the trade. Started off in my youth working on small engines (had a thriving lawn and garden business with employees at age 13 and did all my own rebuilding and repairs) So small engines of all types are not a problem. So what you are about to read is more of a statement of facts surrounding a recent purchase I made and the fun working with the seller trying to resolve the problem (which is not yet resolved btw) and a few discoveries along the way. There is a spin off from this thread concerning ignition timing and timing curves that I would love to put together more information on.

I picked up a BGF kit and during installation discovered the engine was stuck. A little PB and gently rocking of the engine back and forth using the included spark-plug socket I got it freed up after an hour. I know some of you are thinking out loud "I would have stopped right there and contacted the seller" well it was about midnight when I made this discovery and since I have plenty of tools and equipment handy I grabbed my little boroscope took a look inside and decided all was well at this time. So I finished up the install and hit the hay. The next morning I mixed up a fresh batch of oil and gas and tried it out...................

Now I have had an ongoing problem from the moment I first started the engine. It will run for about 1/4 of a block while steadily loosing power then dies. It will only slip the clutch trying to start till it cools down. It has no power and in fact will barely pull the bike for the first 1/8 block and the final 1/8+ you'll have to pedal to keep it going. Once this happens the engine will barely turn over with the plug out until it cools. Now of course I immediately checked for the usual problems like fuel, spark, engine temp and compression. After about 20 blocks of riding and testing (at 1/4 block at a time) I made my initial diagnosis. The engine was trying seize, it is time to contact the seller.

I am going to make this next part short, very short.

Seller first claimed the clutch was out of adjustment and therefore was the reason the clutch would slip when trying to restart the engine after it died. Of course I reaffirmed that the clutch was in adjustment, free from grease and would still slip with the engine hot and plug removed (albeit not as bad) Then the seller claimed the compression was too high and I needed to install an extra head gasket and base gasket (it had 2 head gaskets and 2 base gaskets already) What I wanted to know from him was how can it be an excessive compression problem with the spark-plug removed?? Well his explanation was due to excessive compression it over heats and was causing the problem. This was Friday at this point and on Monday I had the extra gaskets in my hands (fast service I'll give him that) Anyway, I installed 1 each head and base gasket at a time. First the head gasket (total of 3) and retest, still the same problem. Then the base gasket with the additional head gasket, still the same problem. then just for the fun of it I removed the extra head gasket, hmmmm still no change, go figure! And now I am starting to hear a squeaking coming from inside the engine. So once again I contact the seller and now have remove it, pack it and ship it back, oh joy of joys!

During all of this I ran some tests to establish some base line information on this particular engine and had some questions that I have spent the last week on here searching for answers to. I could not find the answers I was looking for (at least not the complete answer, just bits and pieces)

So in my next couple of posts I am going to delve into the ignition timing curve and port timing on the 66cc 2 strokes and see what we come up with.

The nice thing about hard chrome cylinders is they are rather forgiving, up to a point. You can see where it was getting tight in the cylinder but thankfully running a rich oil/fuel mixture saves the cylinder......for now. It only runs for 1/4 a block which is about 15 seconds. I gets just hot enough to prevent the engine from running because drag exceeded power available. And since the rotary weight of the internal flywheels and rotor are so light and it just barely runs it never gets enough rpm to make enough power to force damage from seizing under power. The max rpm it has got to was roughly 2000 rpm (a tiny tach is a wonderful piece of equipment to have) You can tell that most of the problem is in the cylinder since you can rock the crank if it happens to stop with the piston at TDC with little effort and then it gets tight (except for allowed movement from the wrist pin and crank pin tolerances) one you come off of TDC. It cools off after about 10 minutes then your good for another 1/4 block. As for scuffing ,none on the piston when I had it out. Only on the chrome bore was there any discoloration in spots where you could see the rings were tightening up on the high spots in the cylinder. I did find a nice 1 1/2" long steel swarf in the lower end but thankfully it was shaped so as to stick to the side of the crankcase where the rotor is. Magnetism kept it in check and away from the rotating assembly. The problem I am running into is now I have developed a squeal right before it dies and that was the final straw. It is going back to BGF and we will see what happens next.