As discussed elsewhere, I've lost valve clearance again so will be pulling the head once I can get the garage cleared out.
Recap: I rebuilt this motor about 36,000 miles ago in 2015. The head got cleanup and new valve seals at that time, vac test showed valve seats in good condition. Due to electrolysis pitting the head lost .007" and the block lost .008", so when I reassembled it all I used a Cometic MLS head gasket that was .015" over thickness.
During the first part of 2021, around the time we did the Dixie Valley trip, I noticed uneven compression while the starter was spinning, but it would go away after the engine warmed up. Eventually I checked the valve clearance. Three intake valves were at effectively 0 clearance, and several more were under spec. Pulled the cams, measured the shims, did some swaps and new shims and brought everything back into spec. Compression test showed all 155-160 on all cylinders. Problem solved I thought.
Then I did about 6000 miles on hunt trips and all that. One mild overheat incident due to vegetation in the radiator, maybe 210-215 degrees for a few minutes, but no problems immediately after that. Some high winding here and there, mostly on ramps to I80.
Very recently I start noticing the uneven starter spin again. Compression test shows 140-155 all cylinders except #1 - down to 97. Borescope didn't show anything obvious though one exhaust valve may be a bit burnt. Pull the valve cover, recheck clearance, and discover the back intake valve on #1 is down to no clearance again - this was one of the 0-clearance valves that I re-shimmed, last measured at 0.229".
OK I've resigned myself to pulling the head again, not in a huge rush but would like my toy back on the trail again. I need to keep the garage usable until we're out of snow season anyway. So there's a bit of time to plan this out.
No matter what I do I'll need a new HG. After talking this through I think the .015" over HG may not be necessary. You engine builders can check my math on this. I measure the cam gear at 4.72" diameter, or 2.36" radius. That means the crank gear must be 1.18" radius. Losing .015" between the head and block means the cam timing is retarded by arctan(.015/1.18)=0.73 degrees. I don't think this is a problem. Any other complications here? If not I'll get stock HG and bolts on order.
Maybe I need to replace the head, maybe not. @lelandEOD and @justintpryor I think you both mentioned having unused motors lying about - let me know the details.
Maybe the smart play is for me to pull one of those heads and rebuild it and just count on doing a swap?
Recap: I rebuilt this motor about 36,000 miles ago in 2015. The head got cleanup and new valve seals at that time, vac test showed valve seats in good condition. Due to electrolysis pitting the head lost .007" and the block lost .008", so when I reassembled it all I used a Cometic MLS head gasket that was .015" over thickness.
During the first part of 2021, around the time we did the Dixie Valley trip, I noticed uneven compression while the starter was spinning, but it would go away after the engine warmed up. Eventually I checked the valve clearance. Three intake valves were at effectively 0 clearance, and several more were under spec. Pulled the cams, measured the shims, did some swaps and new shims and brought everything back into spec. Compression test showed all 155-160 on all cylinders. Problem solved I thought.
Then I did about 6000 miles on hunt trips and all that. One mild overheat incident due to vegetation in the radiator, maybe 210-215 degrees for a few minutes, but no problems immediately after that. Some high winding here and there, mostly on ramps to I80.
Very recently I start noticing the uneven starter spin again. Compression test shows 140-155 all cylinders except #1 - down to 97. Borescope didn't show anything obvious though one exhaust valve may be a bit burnt. Pull the valve cover, recheck clearance, and discover the back intake valve on #1 is down to no clearance again - this was one of the 0-clearance valves that I re-shimmed, last measured at 0.229".
OK I've resigned myself to pulling the head again, not in a huge rush but would like my toy back on the trail again. I need to keep the garage usable until we're out of snow season anyway. So there's a bit of time to plan this out.
No matter what I do I'll need a new HG. After talking this through I think the .015" over HG may not be necessary. You engine builders can check my math on this. I measure the cam gear at 4.72" diameter, or 2.36" radius. That means the crank gear must be 1.18" radius. Losing .015" between the head and block means the cam timing is retarded by arctan(.015/1.18)=0.73 degrees. I don't think this is a problem. Any other complications here? If not I'll get stock HG and bolts on order.
Maybe I need to replace the head, maybe not. @lelandEOD and @justintpryor I think you both mentioned having unused motors lying about - let me know the details.
Maybe the smart play is for me to pull one of those heads and rebuild it and just count on doing a swap?
