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I lapped my valves and got good results testing both off the engine (pouring alcohol in intake/exhaust chambers and waiting to see level unchanged) and on (cylinder leakdown test). However, as soon as I reinstalled the cams and turned them a few cycles to open and shut the valves, I lost the seal and they were leaking again, which could be confirmed by placing a hand on the intake opening. Most leakage was on intake.

I am trying to explain this. Could it be that there was some lapping residue (lapping paste) inside the valve shaft that got into the seal/seat area after opening? Or could it be that the springs got disrupted from the initial position by moving and now they won't close shut? Or the rotation of the valve out of seal? Should I expect that all of these deviations are normal reassembly occurrence and will go away by by breaking the engine in?

UPDATE: The same effect occurs when I go through about a dozen open-shut cycles of valves manually, not with cams installed but by pushing the valve tappet with the rubber end of a hammer handle while holding the hammer by the head. After I do that, I disassemble the valve and put it back together -- without re-lapping it !! -- and it sits fine again while they remain unopened. This makes me suspect it happens because the springs/plates/stems are stiff and unbroken in and it may fix itself by breaking the engine in.

amphibient
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  • You turned the cams independently of the crankshaft while the head was on the engine? If that's the case then you may have bent some valves. – jwh20 Nov 02 '22 at 17:53
  • @jwh20 -- NO -- I was particularly mindful of that. my engine is non-inteference and the valves don't get in the way of pistons under any position. even with that in mind, I made sure no piston was in TDC when i was turning the cams – amphibient Nov 02 '22 at 18:02
  • Ok, thanks for clarifying. I would be sure to find the cause of the leak before going further. If there is a problem with the valve seating you want to know now rather than later. – jwh20 Nov 02 '22 at 18:08
  • How would I know it's the springs and how would I know it will or will not be fixed by breaking in? – amphibient Nov 02 '22 at 18:11
  • Springs? Are they broken or bent? I said what I would do. You, of course, are free to proceed as you see fit. But to me it sounds like you have a problem that should be corrected before you complete the engine reassembly. – jwh20 Nov 02 '22 at 18:30
  • Did you adjust the cam clearances after installing the cams? Have you re-checked them after detecting the leak? – HandyHowie Nov 03 '22 at 07:32
  • @HandyHowie that is irrelevant because it happens even when I open each valve several times manually, by pushing the rubber handle of a hammer against the lifter a dozen times. The spring seems to retract fine – amphibient Nov 03 '22 at 15:12
  • check the update guys – amphibient Nov 03 '22 at 15:59
  • Is there play between the valve stems and valve guides? – HandyHowie Nov 03 '22 at 16:54
  • @HandyHowie absolutely, positively not. very tight – amphibient Nov 03 '22 at 17:31
  • When you lapped the valves, did you see a continuous polished ring on both the valve and seat, not covering the whole face? – HandyHowie Nov 03 '22 at 18:21
  • @HandyHowie -- yes, I will take a picture and post it in the chat – amphibient Nov 03 '22 at 19:15
  • Let us continue this discussion in chat. – amphibient Nov 03 '22 at 19:25

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