I just rebuilt my Super M with a Redpower major overhaul kit with 4 1/8 bore domed pistons with the large wrist pins.
Everything was rebuilt/replaced: new rod & main bearings, crank ground, new wrist pin bushings, 8060 head was resurfaced with new valves and guides, block was NOT surfaced, & copper coated the Felpro head gasket. Bearings were all plastigaged and piston and ring gaps were checked. I retorqued the head after first bringing it up to full operating temp and set valves to 0.017" I then took it on an extended tractor drive varying throttle along the way. I noticed a slight knocking sound when the engine was fully warmed up and rpm's were above 3/4. So I drove it at a lesser RPM where it didn't, thinking the valves may need adjustment. After reaching our destination and letting the tractor cool down, I started the tractor up and it no longer knocked at high RPMs, but again as the tractor reached normal operating temp the high RPM knock came back.
I proceeded to adjust the valves, varied the timing, changed to a colder spark plug, looked inside at the pistons, compression was all 130lbs. Nothing seemed unusual. I could turn the engine over easily by hand. Drive it around for 5 minutes and the knock would come back. I researched the web and determined the piston must be hitting the head. Thoughts were the dome is contacting the head chamber since I had it planed.
Upon tear down I found the pistons were contacting the head. (photos) Not the dome, but the word "front" was easily seen in the head on 3 of the 4 cylinders. The "front" and arrow extend above the flat portion of the piston by 0.015 to 0.020". Two of the three marks easily wiped off when cleaning off the carbon. #1 cylinder actually left a slight mark in the head. I filed the "front" and arrow from atop the pistons and ordered a new head gasket kit today.
I know aluminum piston expand when hot, which explains why it knocked only at operating temp. Also the Felpro head gasket is metal on one side and fiber on the other. A metal/fiber/metal may have provided just enough clearance.
Has anyone else experienced this issue? How much deck height clearance do I need?
Everything was rebuilt/replaced: new rod & main bearings, crank ground, new wrist pin bushings, 8060 head was resurfaced with new valves and guides, block was NOT surfaced, & copper coated the Felpro head gasket. Bearings were all plastigaged and piston and ring gaps were checked. I retorqued the head after first bringing it up to full operating temp and set valves to 0.017" I then took it on an extended tractor drive varying throttle along the way. I noticed a slight knocking sound when the engine was fully warmed up and rpm's were above 3/4. So I drove it at a lesser RPM where it didn't, thinking the valves may need adjustment. After reaching our destination and letting the tractor cool down, I started the tractor up and it no longer knocked at high RPMs, but again as the tractor reached normal operating temp the high RPM knock came back.
I proceeded to adjust the valves, varied the timing, changed to a colder spark plug, looked inside at the pistons, compression was all 130lbs. Nothing seemed unusual. I could turn the engine over easily by hand. Drive it around for 5 minutes and the knock would come back. I researched the web and determined the piston must be hitting the head. Thoughts were the dome is contacting the head chamber since I had it planed.
Upon tear down I found the pistons were contacting the head. (photos) Not the dome, but the word "front" was easily seen in the head on 3 of the 4 cylinders. The "front" and arrow extend above the flat portion of the piston by 0.015 to 0.020". Two of the three marks easily wiped off when cleaning off the carbon. #1 cylinder actually left a slight mark in the head. I filed the "front" and arrow from atop the pistons and ordered a new head gasket kit today.
I know aluminum piston expand when hot, which explains why it knocked only at operating temp. Also the Felpro head gasket is metal on one side and fiber on the other. A metal/fiber/metal may have provided just enough clearance.
Has anyone else experienced this issue? How much deck height clearance do I need?