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Valve Seating
https://www.ausmini.com/forums/viewtopic.php?f=2&t=74924		 Page 1 of 2
Author:  MG Rocket [ Mon Jan 09, 2012 2:00 pm ]
Post subject:  Valve Seating
First I want to thank the Mokesta and GR for their pictures.
I've placed them one above the other and as you can see there is a very different approach to valve seating.
On the first picture you can see how the closed inlet would interfere with the expelling of the exhaust gasses. As GR explained and can be seen in the second picture, the flat valve does not interfere with the flow of exhaust gasses across the roof of the chamber.
However in the flow bench of my mind, the intake in the first picture would flow earlier and with less restriction except for the proud exhaust valve, which in this case would give disturbance to the flow as this is the primary direction of the inflow........but then again, both valves are momentary open so it might not be a concern at all.
Somehow it would seem a better idea to bury the exhaust valve so it was flush with the roof and again in my flowbench I cannot see how this would have an impact on performance because of the pressures that the exhaust is pushed/drawn out.
On the other hand combustion would be cleaner in the second pic because I imagine bits of fuel would be hiding in the crevices of the proud valves.
Anyway, I'm just throwing this out to get opinions and explanations.


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Author:  VulcanBB18 [ Mon Jan 09, 2012 2:50 pm ]
Post subject: 
I've found it really hard to "mind flowbench" a lot of this stuff, as just one little missed factor can really throw your predictions off.

for example it's easy to forget about how close the cylinder walls are, especially to the exhaust valve. Another one is that the flow is heavily influenced by the "direction" of the port.

I would say that both types of valve setup could be make to work equally well, it's more about the overall package & knowing what you want and need, and making it all work together to achieve that goal. Only folks with extensive hands-on experience (eg. miniman & GR) are going to be able to give more detailed information....

cheers,
Author:  TheMiniMan [ Mon Jan 09, 2012 3:55 pm ]
Post subject: 
well,, for starters , i find it hard to believe that (if it were for a race car) that GR would leave the sharp edges around his valves,,, i`m expecting that he has just meant that pic to show his seats & how proud the valves sit off the chamber roof,,, but i also expect that he would normally give the chamber/roof a decent grind/polish to at least remover the sharp burrs/edges so they don`t become super red/white hot spots,,, i also suspect he would de-shroud & shape his chambers too

so hence i don`t see his pic being a final of what his optimum chamber looks like, of this i have no doubt (unless the customer was really scabby & didn`t want to pay so much,,, & even then i`d suspect that if that was the case that GR would say go away :-)

so it`s a bit unfair to compare OK???

so,,, in actual fact, i`d be betting that GR would show some sort of lift in the final roof height & with those sharp edges removed , the "proudness of the valves may not seem so different to Marks.

but i do think (in my opinion) that marks are sitting QUITE proud, probably a little more proud than i would have them, but if he`s got a good, thin, seat , with a decent leading angle before it, then cool...

Mine (generally) are about in-between both pics.

& yet again,,, i run 2 different systems,,,--> one for road & one for race,,,so (for me) there is another issue there to
Author:  Mokesta [ Mon Jan 09, 2012 4:19 pm ]
Post subject: 
Interesting topic. On my head the unleaded valve seat inserts are quite deep and it appears that ther person who put them in wanted plenty of meat underneath them so their surface sits close to the combustion chamber. The inserts are more cylindrical than rings with a depth larger than their thickness.

In terms of output my engine is no fire breather. I am sure I have posted the dyno charts for it. It has done two dyno dynamics "shoot out" mode runs on different days and been within 1hp.

I have noticed that while the valve seats are in perfect condition, the exhaust valve seating area is a bit eroded and needs lapping.

M
Author:  TheMiniMan [ Mon Jan 09, 2012 5:51 pm ]
Post subject: 
yeah the exhaust seat insert is visible in the pic & they`re generally all like yours now days & are set-up with quite a solid "interference" fit, something like 5 or 6 thou from memory

& you can see the "lead-in" angle cut into GRs head (maybe 20deg? --> the angle-cut just around the outside of the valve heads) but can hardly see any lead-in on Marks head
Author:  GR [ Mon Jan 09, 2012 7:01 pm ]
Post subject: 
Hi Matt
The head i used is a throw away i just cut the seats on it to show people, so i did not blend the chambers in or lay the chambers back
Graham
Author:  MG Rocket [ Mon Jan 09, 2012 7:25 pm ]
Post subject: 
GR wrote:
Hi Matt
The head i used is a throw away i just cut the seats on it to show people, so i did not blend the chambers in or lay the chambers back
Graham

Ah! I see now! That would make quite a difference. 8)
Author:  Mokesta [ Mon Jan 09, 2012 8:28 pm ]
Post subject: 
The head on my car has no real lead in or out of the valve seat. It's just a road car and a moke running a stock bottom end. I also didn't (still don't) have very much disposible income when I put the car together 13 years ago.

M

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Author:  MG Rocket [ Mon Jan 09, 2012 9:12 pm ]
Post subject: 
I'm getting a better picture now. I see that Graham uses a very narrow valve seat in comparison to standard. By fading the seat back into the port and smoothing it out into the chamber he gets the best of both... recessed valve for better exhaust flow and still get a nice response on lift off.
Graham how do you find seat/valve wear on the narrow seat?
By the way, I hope none of my posts come across critical. I know it's a bit weird and all, but I often lay in bed visualizing this sort of stuff. :oops:


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Author:  TheMiniMan [ Mon Jan 09, 2012 11:41 pm ]
Post subject: 
the thinner seat is the better seat (In my opinion) they tend to seal better & last longer

But that`s not to say that a 1/4 of a mm seat width is any good :-) that`s a bit too thin
Author:  TheMiniMan [ Mon Jan 09, 2012 11:43 pm ]
Post subject: 
hey GR, can you K-line mini guides? seems like the ones in your pic are K-lined yeah???
Author:  graham in aus [ Tue Jan 10, 2012 8:26 am ]
Post subject: 
Hey Matt, I can answer that one, Graham K lined some guides in a Moke head for me, was a while ago, but I'm fairly sure he still does them.
:P
Author:  drmini in aust [ Tue Jan 10, 2012 9:58 am ]
Post subject: 
Graham doesn't do K-liners in house, he sends the heads out. :wink:

[edit] syntax
Author:  TheMiniMan [ Tue Jan 10, 2012 11:56 am ]
Post subject: 
Hhhmmm hardly anyone up here can do the small guides (apparently) i been having trouble finding someone to do them these days
Author:  GR [ Tue Jan 10, 2012 5:33 pm ]
Post subject: 
HI Matt
Yes i can get them k lined my mate does them for me, there are two liners you can use a cheap one and a more expencive one, the good ones have a spiral around them to hold oil.
when we were playing on the dyno with the clearance in the guide we could get them down to .0005 and they still did not lock up, so we try to run them at around .0007 clearance on NEW valves, worn valves are a bit harder because you can not get the tip of the valve through the guide i only use the expencive ones.
Graham
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