Race Engine Built Question
11-15-2007, 12:55 AM
#31
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Mark---
no offense intended, just horrified at the suggestion of using a dremel on something as critical as piston notching.
it's kind of like using a piece of sandpaper by hand to overbore a cylinder......
---Russ
no offense intended, just horrified at the suggestion of using a dremel on something as critical as piston notching.
it's kind of like using a piece of sandpaper by hand to overbore a cylinder......
---Russ
11-15-2007, 01:11 AM
#33
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again, none taken.
I dont think the piston notches are that critical, well, how you make them, anyway. to do them from scratch would be ugly, but just triming 1mm or .5mm off the outer edge, you can see from the picture, its not a big deal. AND thats on the relatively deep cuts of the 2 valve pistons. on the S4 pistons or S3 pistons, you can see, they are barely cut. since the modification will never be seen after the engine is assembled, and totally functionable, why would it matter? now, sand paper to the bore???? hardly the same, dont you agree.
as i mentioned, the valves go pretty far down, and as you may know, our engines are interference engines. so, since you can cut .175 deep cuts for the 2 valve 5 liter mods, i would think that S4 rebuilds should use the 85 pistons and cut some deep valve reliefs so that it might become a non-interference engine. Just a thought.
anyway, the bottomline, especially with S4 or S3 4 valve pistons, the valve cuts are so small, they really dont do anything during normal operation. you certainly cant rotate the engine with a valve fully depressed by even the stock cams. However, the 1-2mm deep valve pocket might help when rotating the engine with a slipped belt, or rotating the cams with the piston near TDC. the valve pocket also has an angle so when it hits, it puts a axial force on the valve, not a radial one, that could bend it, even slightly.
Mk
I dont think the piston notches are that critical, well, how you make them, anyway. to do them from scratch would be ugly, but just triming 1mm or .5mm off the outer edge, you can see from the picture, its not a big deal. AND thats on the relatively deep cuts of the 2 valve pistons. on the S4 pistons or S3 pistons, you can see, they are barely cut. since the modification will never be seen after the engine is assembled, and totally functionable, why would it matter? now, sand paper to the bore???? hardly the same, dont you agree.
as i mentioned, the valves go pretty far down, and as you may know, our engines are interference engines. so, since you can cut .175 deep cuts for the 2 valve 5 liter mods, i would think that S4 rebuilds should use the 85 pistons and cut some deep valve reliefs so that it might become a non-interference engine. Just a thought.
anyway, the bottomline, especially with S4 or S3 4 valve pistons, the valve cuts are so small, they really dont do anything during normal operation. you certainly cant rotate the engine with a valve fully depressed by even the stock cams. However, the 1-2mm deep valve pocket might help when rotating the engine with a slipped belt, or rotating the cams with the piston near TDC. the valve pocket also has an angle so when it hits, it puts a axial force on the valve, not a radial one, that could bend it, even slightly.
Mk
11-15-2007, 01:13 AM
#34
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yeah, i have lots of pictures. the euro 2 valver pistons are flat, the 85 have a slight dish as i have shown on the picture, the S4 are really dished out.
are you sure you made a 5 liter ?
mk
are you sure you made a 5 liter ?
mk
11-15-2007, 07:03 AM
#35
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11-15-2007, 08:58 AM
#36
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$224 is hardly breaking the bank.
Don't forget the rest of it. New head gaskets and labor to install the valves etc.
11-15-2007, 10:42 AM
#37
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And then dr nick got me into "needing" to buy a boat
On a serious note - I think at $14 each - they are cheaper than anything out there and about 1/2 price when compared to a custom job from ferea or anyone else. But it would be a shame to pull your engine just for a valve job. I am lucky that the GTS lump is sitting on an engine stand and there is no real time pressure yet...
11-15-2007, 12:01 PM
#39
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and all these years, i still cant get over the design. I make those valve cuts on the 5 liter pistons for the 2 valver, and i lever down the valve and it hits at .3", (total lift is .45" or something) . this means the valve pocket only needs to be .15" more for a non interference. Ill have to check my euro '82 pistons, but i think those deep pockets are at least,2x as deep as the 85 euro pistons and it might mean non interference. Also, it kind of indicates if the 4 valve pistons only need a little knotches, why cant they be deepened so that the 4 valve is non interferene. heck, we are only talking about 6ccs here. you could shave the head that much, to make up the compression with out any issues.
Just thinking out loud.
mk
Just thinking out loud.
mk
11-15-2007, 08:01 PM
#40
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Mark if you shave the heads the valves move closer to the piston....and you might want to rethink this one too.."the valve pocket also has an angle so when it hits, it puts a axial force on the valve, not a radial one, that could bend it, even slightly."
11-15-2007, 08:33 PM
#41
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why cant they be deepened so that the 4 valve is non interferene.
Broke the belt, bent the valves.
11-15-2007, 08:37 PM
#42
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Thats a good point. 1mm of that 4.5 mm valve depth cut would be taken up by shaving of the head. ahh, what am i even talking about this for! I am no expert here. Beware, my only experience is building 5 liter 2 valve motors with cookie cutter valve cuts! 
However, i think it makes sense if you can cut the valve reliefs as deep as we do with the euro cuts on the 4 valve pistons, why not make them deeper by 4.5mm and make up for it with a one mm shaving of the heads. you might end up with a non interference engine! did you notice the valve cuts on the 85 4v pistons only being 1mm or so deep?
I see what you mean about that statement below. kind of a stretch to think that the force on the valve would be right down the axis with a pocket vs a flat top pison. I think what you are pointing to is that the force is radial either way, and the valves will bend unless you are lightly hand cranking .
mk
However, i think it makes sense if you can cut the valve reliefs as deep as we do with the euro cuts on the 4 valve pistons, why not make them deeper by 4.5mm and make up for it with a one mm shaving of the heads. you might end up with a non interference engine! did you notice the valve cuts on the 85 4v pistons only being 1mm or so deep?
I see what you mean about that statement below. kind of a stretch to think that the force on the valve would be right down the axis with a pocket vs a flat top pison. I think what you are pointing to is that the force is radial either way, and the valves will bend unless you are lightly hand cranking .
mk
Mark if you shave the heads the valves move closer to the piston....and you might want to rethink this one too.."the valve pocket also has an angle so when it hits, it puts a axial force on the valve, not a radial one, that could bend it, even slightly."
11-15-2007, 08:53 PM
#43
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Correct the valves are angled , the piston moves straight up an down so even with the pocket angled so the head of the valve hits at about the same time it still wants to bend the valve.
11-15-2007, 10:35 PM
#45
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wonder how many laps/miles was on it......?
https://rennlist.com/forums/928-forum/384089-unusual-water-pump-failure.html