What Are You Doing To/With Your Car Today?
Today I removed the rocker shafts, and the failed keepers on #4 and #7. The displaced half actually fractured into two pieces in my fingers. Both of those valves feel as though they were seating properly. BUT as I lifted the left shaft off, I could see that #3 intake wasn't even attached to its keeper any more! That keeper had a rocker arm pad-shaped wear mark on the top, further confirming that it had failed to hold up the valve. Luckily, my new valve seals helped prevent it from falling into the cylinder. That would have been fun.
But worst of all, with a straightedge along all the tips, that valve would not come up closer than about .080 to the perfect straight line of the others, and of course the cylinder would not hold air, all coming out the carb. So that one, at least, is bent. Explains the clank noises all right.
So at least the left head has to come off... and #3 intake valve replaced. Hope there is no damage to the KB280 pistons' valve reliefs or tops.
The big question, of course, is WHY did this happen?
I felt sure that the keepers were properly seated when I assembled the springs on the bench, because I know what happens when a valve falls into the cylinder.
I have not over-revved the engine.
My calculations showed that there should be plenty of p/v clearance. There was with the same short block and cam on my iron heads! Once I repair the damage I think I'll clay it for a direct measurement.
I'm going to replace all 32 keeper halves after finding this third injured valve. Over on Moparts, some think a 3/8 keeper or two could have found its way into the bag of 11/32 keepers... hard to tell now when they are chewed up or fractured or both!
A couple of snaps of the carnage so far:
Today I removed the rocker shafts, and the failed keepers on #4 and #7. The displaced half actually fractured into two pieces in my fingers. Both of those valves feel as though they were seating properly. BUT as I lifted the left shaft off, I could see that #3 intake wasn't even attached to its keeper any more! That keeper had a rocker arm pad-shaped wear mark on the top, further confirming that it had failed to hold up the valve. Luckily, my new valve seals helped prevent it from falling into the cylinder. That would have been fun.
But worst of all, with a straightedge along all the tips, that valve would not come up closer than about .080 to the perfect straight line of the others, and of course the cylinder would not hold air, all coming out the carb. So that one, at least, is bent. Explains the clank noises all right.
So at least the left head has to come off... and #3 intake valve replaced. Hope there is no damage to the KB280 pistons' valve reliefs or tops.
The big question, of course, is WHY did this happen?
I felt sure that the keepers were properly seated when I assembled the springs on the bench, because I know what happens when a valve falls into the cylinder.
I have not over-revved the engine.
My calculations showed that there should be plenty of p/v clearance. There was with the same short block and cam on my iron heads! Once I repair the damage I think I'll clay it for a direct measurement.
I'm going to replace all 32 keeper halves after finding this third injured valve. Over on Moparts, some think a 3/8 keeper or two could have found its way into the bag of 11/32 keepers... hard to tell now when they are chewed up or fractured or both!
A couple of snaps of the carnage so far:
