-A while back I asked about how close you could run valve like in two valve wedge head engine where you are wanting to install the maximum oversize valves you can get in there.
-The other day I had VW crossflow head that the guy had installed oversize valves, where the valves showed they had obviously been hitting each other.
-The edges of all the valves had notches and one intake in particular had the entire circumference edge scraped downward from the chamber side, like the exhaust valve was pulling the metal of the margin towards the 45 seat.
-So I refaced the valve and machined the OD's to barely clean up the circumferences of the valve margins.
-Then I checked the clearance between'm with the valve installed and open about 1/2" and squeezed together by hand and they had about .014".
--------------------------------------
-So I showed the guy what had happened and let it go.
-He can see right down thru the sparkplug hole so he's going to check it and keep an eye on what happens.
-----------------------------------
-In the meantime I still have this other project here and I was starting to worry about it some so I decided to do a test.
-I took a pair of stainless steel 2.053" & 1.600 valves and clamped them side by side so they are touching in a vise and measured across them and got 3.653" with the valves at room temperature.
-Then I took a torch and heated both valves until they were visibly red and measured the distance across the valve and got 3.695".
-After letting the valves cool for a moment until the red color was gone, I measured the OD"s of each and I got the intake at 2.074" and the exhaust at 1.615".
--------------------------------------------------
-So the way I see it there needs to be about .021" on this size valves and that's if you open them to max lift and squeeze them towards each other.
---------------------------------------------
-This VW had been run two races on an oval track where one race the engine ran about 7800rpm and the next race it ran just a little over 9000rpm and finished 2nd and 4th.
-They found this original problem doing a leakdown test and a compression test, because they could tell that something wasn't right.
----------------------------------------------------
-The VW heads came off once again after I had increased the clearance to .014" and it had one more full race event on it.
-Reason for the heads to come off again was because of exhaust valve leakage, but this gave me a chance to look at the valve margins and there is NO EVIDENCE of contact with the .014" that I had between the valves.
-The problem this time was---they had used black silicone for the intake and exhaust gaskets and started the engine before the silicone had adequate time to dry.
-There was black silicone slimed in and under the exhaust valves near the shroud walls of two cylinders and that silicone showed no evidence that it was going to ever burn away.
-----------------------------------------------------
-I decided to also check a pair of titanium valves.
-I used a 2.100" and a 1.6", got them red hot and they expanded to 2.113" and to 1.610", so they expand a lot less than stainless steel.
-It looks to me like the Ti valves could maybe within about .015" of each other.
Want to know how close you can run the valves to each other?
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bill jones
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bill jones
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Ed-vancedEngines
Hi Bill,
In a way I like the way you think. That means going out of the box and doing the other than accepted. I am somewhat questioning your approah to heating the valves and getting them that hot. Although we all know that everything in the chamber does get hot, it is the exhaust valve that really gets hot. Camshaft design can play a large part in just how hot they do get.
I freaked whn I read about you heating Ti Valves with the torch though. You must have money to burn. Wow!
I am thinking that by your words you are heating the valves to a higher temp than they encounter in the engine. I am thinking this for several reasons. I have measured many vales after they have been run of differing materials including titanium and have not found so far instnces of them increasing in size to a permanent oversize, like in your example. Also if the intake valve were to be redhot there would be severe preignition leading to detonation. I would also not think that the exhuat valve would be getting a glowing hot or it would not cool enough during blow down to keep from igniting the incoming fuel mixture. That is jst thinking from me with no testing or facts.
I have read some rather interesting postings by you and I do really enjoy them.
Thx,
Ed
In a way I like the way you think. That means going out of the box and doing the other than accepted. I am somewhat questioning your approah to heating the valves and getting them that hot. Although we all know that everything in the chamber does get hot, it is the exhaust valve that really gets hot. Camshaft design can play a large part in just how hot they do get.
I freaked whn I read about you heating Ti Valves with the torch though. You must have money to burn. Wow!
I am thinking that by your words you are heating the valves to a higher temp than they encounter in the engine. I am thinking this for several reasons. I have measured many vales after they have been run of differing materials including titanium and have not found so far instnces of them increasing in size to a permanent oversize, like in your example. Also if the intake valve were to be redhot there would be severe preignition leading to detonation. I would also not think that the exhuat valve would be getting a glowing hot or it would not cool enough during blow down to keep from igniting the incoming fuel mixture. That is jst thinking from me with no testing or facts.
I have read some rather interesting postings by you and I do really enjoy them.
Thx,
Ed
Thanks Bill- answers my question (and problem)
Ed- I expect Bill will answer himself, but knowing him, I am sure he was not suggesting INTAKES get that hot at all- was just a test to see what happened and get some measurements. He does think outside the box and gives us (as you do) some great info, insight, and tips.
Ed- I expect Bill will answer himself, but knowing him, I am sure he was not suggesting INTAKES get that hot at all- was just a test to see what happened and get some measurements. He does think outside the box and gives us (as you do) some great info, insight, and tips.
This is something I'll be looking at if I ever get my 495 Cam Am BB back together. It has 2.30" in. & 1.94" ex. in late sixties aluminum heads. ~ 0.010" valve to valve clearance at 0.220" lift at the moment. Guess it depends on what durations and LCA I settle on.. (I wonder if the distance between the guides will increase faster with temperature than the valve diameters?) Don't think I'm brave enough to test it Bill's way! 
Felix, qui potuit rerum cognscere causas.
Happy is he who can discover the cause of things.
Happy is he who can discover the cause of things.
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bill jones
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-I also had done some tests on what happened to the lengths of the valves but I don't know if I posted that anywhere and I didn't save that information---but that was sort of a revelation---especially between the SS and Ti valves-----where the ss valves get seriously longer with heat.
--------------------------------------------------
-It doesn't worry me to do certain things like heat up a component like that because I have developed my own perceptions of what happens inside a running engine.
-------------------------------------------------
-Stuff that bothers me is like I have BBF engine with "C" heads (sort of like big chief heads)---where I have to set the valve lash at .004" cold and when the engine temp is nice and toasty the valve adjustment comes right in to .024 and .026"---what's really happening there?
---------------------------------------------------
-I also feel that a lot of people way under estimate the intake valve temperature and just how cold the intake charge is when it is wetted with fuel---especially methanol.
-One of the problems is we tend to work on the engine after it has cooled-----can't ever get in there to measure stuff while it smoking hot.
-sort of like tire temperatures-----by time we get a temp gun on'm after a drag strip run they have dissipated so much of the heat I seriously doubt that we get a true idea of what happened during the run.
--------------------------------------------------------
-Regarding the BBC aluminum heads of madbills----I found that you seriously need to test EVERY chamber at the overlap valve clash points because the guides all seem to have slight differences within each head to where you might be able to open one pair of valves something like .050" further before they clash than the closest pair that may clash way before your comfort zone.
-And on BBC where you are concerned about the clash point being too close you might also want to machine the valve margins slightly on those same angles so the valves pass each other with grace.
-Need to get a magnifying glass down in there at the clash point and you'll see what I mean.
--------------------------------------------------
-It doesn't worry me to do certain things like heat up a component like that because I have developed my own perceptions of what happens inside a running engine.
-------------------------------------------------
-Stuff that bothers me is like I have BBF engine with "C" heads (sort of like big chief heads)---where I have to set the valve lash at .004" cold and when the engine temp is nice and toasty the valve adjustment comes right in to .024 and .026"---what's really happening there?
---------------------------------------------------
-I also feel that a lot of people way under estimate the intake valve temperature and just how cold the intake charge is when it is wetted with fuel---especially methanol.
-One of the problems is we tend to work on the engine after it has cooled-----can't ever get in there to measure stuff while it smoking hot.
-sort of like tire temperatures-----by time we get a temp gun on'm after a drag strip run they have dissipated so much of the heat I seriously doubt that we get a true idea of what happened during the run.
--------------------------------------------------------
-Regarding the BBC aluminum heads of madbills----I found that you seriously need to test EVERY chamber at the overlap valve clash points because the guides all seem to have slight differences within each head to where you might be able to open one pair of valves something like .050" further before they clash than the closest pair that may clash way before your comfort zone.
-And on BBC where you are concerned about the clash point being too close you might also want to machine the valve margins slightly on those same angles so the valves pass each other with grace.
-Need to get a magnifying glass down in there at the clash point and you'll see what I mean.
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Cobra
Bill Jones- I try to stay away from posting anything that requires in depth knowledge of themodynamics or computational mathematics, but will post this link anyway. This is research into the combustion process. Researchers have found that combustion chamber parts run far hotter than previously thought. http://www.eng.warwick.ac.uk/oel/papers ... 1-0747.pdf
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SchmidtMotorWorks
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I just saw a presentation about some CAE analysis that was done to determine the source of a power dip at certian speeds on an F1 engine. It was discovered that the valve heads flop around a considerable amount when certain vibrations peak and the valves weren't sealing well. The source was the buckets rocking in their bores and side loading the valves. Tightening-up the conventional clearances (they did't say which but I assume it was valve guide and bucket bore) provided some improvment.
I guess this valveguide clearance issue might even be more important on push-rod engines because I guess they are subject to higher side loading.
I guess this valveguide clearance issue might even be more important on push-rod engines because I guess they are subject to higher side loading.
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bill jones
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-I'd sure like to see all the effort of that single cylinder engine applied to one cylinder of a modern race gasoline engine-----and then do the same thing like on a methanol sprint car engine-----and again on a top fuel engine.
-Then maybe could derive some real satisfaction that the tests were valid towards our way of thinking.
-Then maybe could derive some real satisfaction that the tests were valid towards our way of thinking.
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SchmidtMotorWorks
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Cobra
Optical engineering is currently being used in racing. Here is another site to check: http://www.soue.org.uk/souenews/issue2/icengine.html
You can build something similar with a common B&S engine!
You can build something similar with a common B&S engine!
I changed valve size in a pair of 360 darts and with the engine and the actual valve train ect,ect. all together..... I was able to go thru the spark plug hole and at overlap I had a tight .030 . It was Ti intakes and SS exh valves and never did clash.
On Kawasaki motorcycle 4 valve heads I would have to grind an angle on the margins at appropiate angles as Bill Jones stated when changing valve size and camshafts to prevent diasasters. Brent
On Kawasaki motorcycle 4 valve heads I would have to grind an angle on the margins at appropiate angles as Bill Jones stated when changing valve size and camshafts to prevent diasasters. Brent
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maxracesoftware
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Re: Want to know how close you can run the valves to each ot
Great Info Billbill jones wrote:-A while back I asked about how close you could run valve like in two valve wedge head engine where you are wanting to install the maximum oversize valves you can get in there.
-The other day I had VW crossflow head that the guy had installed oversize valves, where the valves showed they had obviously been hitting each other.
-The edges of all the valves had notches and one intake in particular had the entire circumference edge scraped downward from the chamber side, like the exhaust valve was pulling the metal of the margin towards the 45 seat.
-So I refaced the valve and machined the OD's to barely clean up the circumferences of the valve margins.
-Then I checked the clearance between'm with the valve installed and open about 1/2" and squeezed together by hand and they had about .014".
--------------------------------------
-So I showed the guy what had happened and let it go.
-He can see right down thru the sparkplug hole so he's going to check it and keep an eye on what happens.
-----------------------------------
-In the meantime I still have this other project here and I was starting to worry about it some so I decided to do a test.
-I took a pair of stainless steel 2.053" & 1.600 valves and clamped them side by side so they are touching in a vise and measured across them and got 3.653" with the valves at room temperature.
-Then I took a torch and heated both valves until they were visibly red and measured the distance across the valve and got 3.695".
-After letting the valves cool for a moment until the red color was gone, I measured the OD"s of each and I got the intake at 2.074" and the exhaust at 1.615".
--------------------------------------------------
-So the way I see it there needs to be about .021" on this size valves and that's if you open them to max lift and squeeze them towards each other.
---------------------------------------------
-This VW had been run two races on an oval track where one race the engine ran about 7800rpm and the next race it ran just a little over 9000rpm and finished 2nd and 4th.
-They found this original problem doing a leakdown test and a compression test, because they could tell that something wasn't right.
----------------------------------------------------
-The VW heads came off once again after I had increased the clearance to .014" and it had one more full race event on it.
-Reason for the heads to come off again was because of exhaust valve leakage, but this gave me a chance to look at the valve margins and there is NO EVIDENCE of contact with the .014" that I had between the valves.
-The problem this time was---they had used black silicone for the intake and exhaust gaskets and started the engine before the silicone had adequate time to dry.
-There was black silicone slimed in and under the exhaust valves near the shroud walls of two cylinders and that silicone showed no evidence that it was going to ever burn away.
-----------------------------------------------------
-I decided to also check a pair of titanium valves.
-I used a 2.100" and a 1.6", got them red hot and they expanded to 2.113" and to 1.610", so they expand a lot less than stainless steel.
-It looks to me like the Ti valves could maybe within about .015" of each other.
on a True Wedge,
i viewed .020" as the tightest
and .025" or more plenty enough
my .020" as "the least" thru experiences with good Guides
came out really close to your .021"