It's not the kit unless there is a defect that you did not catch. That's why I said to start from scratch.
You might have put the rings in upside down, the end gap could be wrong, the piston could be too loose in the cylinder, the chain tensioner for the cam could be jammed, the head gasket could be leaking, valves could be bent or have damaged seats.
there are too many things to list. One step at a time.
Get a feeler gauge, and start with the piston fit in the bore with no rings installed. It should bee between .002, and .0035" everywhere in the bore. End gap should be no larger than .004" anywhere in the bore.
I have seen brand new cylinders that have a reverse hourglass effect in the middle of the bore. Use the piston to square the rings to measure this.
It's easier to speculate, and type all day than it is to do this right, and that says alot because putting one of these together is about the easiest of all engines. One cylinder/piston to measure.
I am in the middle of building three engines right now.
One, '69 Triumph
Two, QMB 139
Three, 350 Chevy marine HP
I always measure everything, and plasti-gauge all the bearings. That process takes longer than assembly. As a matter of fact I am weighing/balancing all the moving parts in the Triumph because that one is mine, and I want a bad ass engine that will last at least ten more years before another rebuild. It's already 45 years old.
Set your mind to doing this right, and you can get it done. You wasted more time already than it would have taken to dig up the ore/forge the parts/build the engine. I'm busting your balls because I know how easy it is to build this engine. You don't see it that way, YET.
