I have built a Kubota L175 tractor from two salvaged tractors. The engine is from the Serial No. 14034 tractor with 2443 hours on the clock. The head is from Serial No. 10623, 1187 hours.
I got it running with a new aftermarket head gasket and no head shim. The compression cold was 340 psi in cylinder #1 and 260 psi in #2.
I removed the head and found impressions on top of both pistons of the head glow plug cover and channel. (See attached photos) The head gasket at the copper reinforcement around the piston bore measured .063. At TDC, the pistons are .015 above the block deck.
The cylinder walls do not show any wear. I had the valves ground and reinstalled the head with a new Kubota factory head gasket (.050 thick after disassembly), and a .008 thick head gasket shim. The compression cold then measured 320 psi in #1 and 300 psi in #2. With a squirt of oil the compression increased to 340 and 330.
I removed the .008 shim and reassembled the head with three 1/2” lengths of .060 solder on the tops of each piston. After rotating past TDC, #1 piston solder strips measured between .032 and .041 and #2 piston was .036 to .042.
My questions are:
The pistons should have never hit the head since the gasket used was .063, compared to the .050 gasket used when measuring piston - head clearance. The first time I started the motor, while bleeding the air out of the injector lines, I could have injected enough fuel in the cylinders to almost hydro lock them before it started. Could the fuel have hydro formed the impressions on top of the pistons?
The compression cold is just above what I understand is the recommended minimum. At operating temperature and now without the .008 shim, should I expect the compression to be closer to 400+ psi?
I am hesitant to start it before knowing what caused the impressions on top of the pistons. Any help would be greatly appreciated.
I got it running with a new aftermarket head gasket and no head shim. The compression cold was 340 psi in cylinder #1 and 260 psi in #2.
I removed the head and found impressions on top of both pistons of the head glow plug cover and channel. (See attached photos) The head gasket at the copper reinforcement around the piston bore measured .063. At TDC, the pistons are .015 above the block deck.
The cylinder walls do not show any wear. I had the valves ground and reinstalled the head with a new Kubota factory head gasket (.050 thick after disassembly), and a .008 thick head gasket shim. The compression cold then measured 320 psi in #1 and 300 psi in #2. With a squirt of oil the compression increased to 340 and 330.
I removed the .008 shim and reassembled the head with three 1/2” lengths of .060 solder on the tops of each piston. After rotating past TDC, #1 piston solder strips measured between .032 and .041 and #2 piston was .036 to .042.
My questions are:
The pistons should have never hit the head since the gasket used was .063, compared to the .050 gasket used when measuring piston - head clearance. The first time I started the motor, while bleeding the air out of the injector lines, I could have injected enough fuel in the cylinders to almost hydro lock them before it started. Could the fuel have hydro formed the impressions on top of the pistons?
The compression cold is just above what I understand is the recommended minimum. At operating temperature and now without the .008 shim, should I expect the compression to be closer to 400+ psi?
I am hesitant to start it before knowing what caused the impressions on top of the pistons. Any help would be greatly appreciated.
