Old Piston + New Rings = Too Tight

[CP241]

Originally Posted by Cartmaster

Something needs to be locked up!!!!!

[sthreatt]

I'm thinking the same as Cartmaster. Carbon buildup in the ring grooves. Haven't done any in a lot of years but in a younger mans shoes I built a lot of motors. The ring groove cleaner was a standard necessity on every one for just the reason you describe. As the old rings wear they open an air gap inside that builds up carbon. With the new ring seating against a carbon deposit you get a tight piston.

[Lochlin]

Sorry about the delay with this one. I was away this weekend and, let's just say that my typing would have been very poor given my state for most of it. To answer everyone's questions:

The starter / gen, motor etc. are not locked up. The motor turns like a champ without the cylinder on it. It even turns without the head on it albeit slowly. It's almost like there is too much compression with the head on. The piton is definitely not hitting the head at TDC. The motor can be turned by hand, it's just tight.

The piston grooves are spotless. I cleaned them with a dremel tool equipped with a small brass brush. I have done this a number of times before and never had any issues like this. It's bizarre.

The rings are the right ones. I still have the old ones and they match up perfectly.

Really, the only other thing I did to this cylinder was hone it a bit. The cylinder is smooth and, in theory, should actually be less tight than it was before this work. Let me know if honing has ever caused anyone issues in the past, though.

All the same, a new piston rings arrived Saturday so I will try those out today. If that doesn't work (and I suspect it won't being that the new piston and rings look identical to old one) then I will just order up a new cylinder altogether.

[Lochlin]

I got this thing turning. It ending up being an electrical problem......the old bad ground.

After getting nothing on the engine I started tracing electricals. At some point, the solenoid started clicking wildly at which time I knew it wasn't getting enough juice to fully close. My issue was a hidden key switch ground behind the dash that I didn't know about. I replaced it and voila.

With regard the the motor being tight. It actually is. Compression is at 120 psi and factory is 90 - 100 on these low compression 2 cycles.

Thanks for all the suggestions. Here's hoping this post helps a future reader.