Fishrider wrote:I finally, got my pistons together. Required a little honing of damaged cylinder. Unfortunately, I did end up purchasing two new pistons. Not the one I had an issue with. Apparently, while fitting the cylinder head the outside tubes came down on both outside cylinders damaging the tops. I decided it was best to replace them. Just some more dumb tax added to the list.
For anyone who has never put pistons back in an inline 4 remember three things. 1. Take your time 2. Don't force anything. They should go smoothly once the rings are properly seated. 3. Nothing is easy.
I have moved on to other issues. Namely I am having a problem with cams and valves. I bonered numbering my valve caps and shims. I had them lined up, but I really had no idea where they went. So I I just put them all back in, set the cam chain and then proceeded to measure valve clearances. I figure I will just move them around until I get the proper clearances, and if nothing lines up then I will get some new shims. HOWEVER, after rotating the pistons into place for each set of lobes I noticed I have zero valve clearance on any of the valves. Is it possible that my valves are seated that much lower after cleaning and lapping? Is this common with a rebuild? Do I just get thinner shims and start over?
Edit:
I went ahead and took all the shims out and took measurements with just the buckets on. I am getting no more than about .5mm clearance. The shim sits in the valve about 1.82mm. Since clearance should be between .08-.18mm the math would be (clearance without shim + valve seat hole - (.1mm evenly between .08 and .18) = Shim Size
If I get .5mm clearance with no shim:
(.5 +1.82 -.1) = 2.22mm
so 2.15mm or 2.20mm shim with a clearance of .17 or .12 respectively. I would do this calculation for each valve obviously, and of course re-check once I get the new shims and hope I don't need different shims. Is it better to get closer to the smaller clearance or larger? I would assume the larger clearance as wear on the valve causes clearance to get tighter. Correct?
If I get measurements that give me shim sizes under 2mm do I then have to get the stems ground?
All current shims are 2.25 - 2.35 with one that is noticeably bigger with no markings on it. Which I thought was strange.
Top End Cam Shafts.jpg
Its hard to see from the angle, but there is no day light there. Its the same with all the lobes.
Cam Lobe 1.jpg
Had to scratch my head a bit on the explanation of how the piston tops got damaged e.g 'by the tubes'. After a bit of thinking, my guess is the engine was turned over with the head and camshafts fitted but without the cam chain fitted. Turn it over with no cam chain on and the pistons at TDC will strike any valve that is being held near fully open by the camshafts, and there will certainly be one or more.
I'm taking it you checked the offending valves to make sure they didn't get bent. If enough force was applied to damage the piston tops, then that's enough to possibly have bent the valve. Rechecking the valve face to set fit with bearing blue would be probably the simplest and most accurate way to check, no way would the seal be correct if the valve had been bent.
Would lapping the valves (if the valves had not been refaced and the seats cut) materially alter the valve clearances, no. It would make a small difference, but nothing major, well not unless you lapped for days and wore a great big groove in the valves. The difference it would make should have been easily accounted for within the normal factory shim range (2 to 3.20mm) . I've had the seats cut on my head, and in a previous rebuild the valves refaced (valves were replaced last rebuild) and yes thinner shims were required but nothing radical and it was still well within the factory shim range.
If you would need to go below a 2mm shim, is grinding the valve stems a solution? IMO,no, its a backyard hack. The correct fix would be to replace the offending valves, and if still a problem have new valve inserts fitted to the head (or alternatively replace the cylinder head). The reason you can't get a correct valve clearance in the factory shim range is (a) the valve stems are stretched, (b) the valves have previously been refaced past their serviceable limit, or (c) the valve seats have been heavily cut. Or obviously a combination of these factors.
Sinking valves into a cylinder head due to resurfacing or cutting the seats increases the combustion chamber area, decreasing compression, so hurts engine performance (the reason I replaced all 12 valves last rebuild rather than reface them a second time).
Valve clearances, if you have the option work towards the .08mm size or the inlets, and 0.18mm for the exhausts. The inlet clearances won't change over time, but the exhausts may tighten up a bit. The reason they tighten up is not valve cap wear but rather the valve face sinking into the seat on the punishingly hot exhaust valve.
Aim for your theoretical shim size, but definitely get a few extras either side. The chances of it working out 100% spot on based on calculations is in my experience next to zero. It should in theory, but for some reason it just doesn't. It always takes a bit of trial and error to get some right.