THE MOMENT OF TRUE.

WHAT NOW?

I had the cylinder head revised and ready to mount with its valves and seals changed.
I clean the cylinder block, mostly to remove dust and some impurities with a cloth.
I give a turn to the crankshaft to clean the piston heads and inspect the liners for any scratches.
At one point I notice that piston number 5 does not reach its top peak, there is a gap between the edge of the piston and the end of the liner, not the same with its twin piston number two.

Pistons number 1 and 6.
 
 

Pistons number 3 and 4.
 
 
Piston number 2.
 

Piston number 5.
 

The piston number is 1.8 millimeters short of the upper maximum point.

 

My balls have fallen to the ground, another fucking breakdown added.

Maybe a bent connecting rod?

Whatever it is, I'm going to have to completely disassemble the fucking engine again.

 

That's heart breaking, but at least you caught it before more trouble.

I went back to the garage.
After a long time racking my brain as to how I could do to test if the piston or the connecting rod is loose, using without success the suction cups from the valve seat sanding stick and some other suction cup from my children's toy arrows or even a big suction cup I found from a towel hook in the bathroom, nothing.
I thought of an unorthodox method, I fixed the piston head with masking tape, turned the crankshaft little by little until I got its tension and voila!
I recorded this video.

Youtube video

(It is impossible for me to insert the youtube video, in the previous version of the forum I had no problem with the videos).


From what can be seen in the video, it appears that the crankshaft connecting rod bearing support has loosened.

Any other suggestions?
 

The piston ring tension on the cylinder would hold the piston in place. If you rocked the crankshaft back and forth and #2 moved up and down and #5 stayed still then you have your answer.

Makes sense. You're still removing the engine to fix the problem. Maybe you left a conrod not torqued to spec?? I have a rule. NEVER install a nut or a bolt without torquing to spec OR mark the bolt or nut to remind you to FINISH torquing to spec. A lesson I learned from working in the nuclear plant for 29 years.

There is one thing I am not clear about, when I disassembled the engine I changed the connecting rod bearings on this cylinder, took out some worn out non-original ones and installed new ones from Z1300.de.

There is so much clearance that it looks like I lost the rod bearings.

If the top of the connecting rod bearing remained in place the piston would reach its upper maximum point, even if the bolts were loose.

I don't understand this.

Any possibility that crank journal has been ground down to smaller diameter for the bushings you found in place?

Then replaced with OEM, leaving too much clearance?

Just thinking back to my r69/s crank that someone had done that too..

Fortunately, my smart engine builder caught it..