[xk] What are spats?

Roar Sand wrote:

The force the valve spring exerts on the valve face / valve seat interface
is minimal compared to that of the combustion pressure on the valve head.
FWIW, Roar (672229)

Really… what is the differential??? Amazing… nice to have folks
that know what they are doing… Thanks>

John,
With an exhaust valve diameter of 1 and 7/16 inch ( standard XK ) the area
of the valve head is 1.623 in�.
Assuming a max combustion pressure of 600 psi, there will be 974 pounds of
gas pressure on the valve.
If you want to nitpick, there is a small overlap of the valve to the seat
that would cause a small reduction.
I have no pressure data on the engine in our cars, but 600 psi is
conservative. I have seen pressures above 900 psi in other gasoline
engines.
Obviously, the peak pressure depends on how hard you push on the gas pedal.
I do not know the specified valve closed spring load, however, a typical
number would be around 100 pounds, or less.
The spring load and gas pressure add up for total load of the valve on the
seat.
Does anyone care to figure out the impact load as the valve closes?
Roar

[Original Message]
From: John Shuck jshuck@optonline.net
To: xk@jag-lovers.org
Date: 15.01.2007 16:42:15
Subject: Re: [xk] Unleaded Fuel in XK’s

Roar Sand wrote:

The force the valve spring exerts on the valve face / valve seat
interface> >is minimal compared to that of the combustion pressure on the valve head.

FWIW, Roar (672229)

Really… what is the differential??? Amazing… nice to have folks
that know what they are doing… Thanks

In reply to a message from Roar Sand sent Mon 15 Jan 2007:

My assumption is that the spring is there primarily to keep
the tappet on the cam, and be strong enough to stop the
valve bouncing. I hadn’t thought about it before but Roars
comments would suggest that as long as the valves seal on
the seat long enough for the combustion pressure to finish
the job, all is well.

If you happened to see the movie the World’s Fastetst
Indian, a story about a fellow Kiwi, Burt Munroe and his
inaugural trip to the Salt Flats to race his modified Indian
motorcycle, I once saw at a quarter mile sprint event with a
modification to his ohv design. He had broken one of the
valve springs on the double spring setup. To make up for the
loss he used a big rubber band! Seemed to work. Perfect!

Regards

Keith–
The original message included these comments:

Assuming a max combustion pressure of 600 psi, there will be 974 pounds of
gas pressure on the valve.

The force the valve spring exerts on the valve face / valve seat
interface

is minimal compared to that of the combustion pressure on the valve head.


Keith Bertenshaw
Rockaway, NJ, United States
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Adolphe Menjou wore spats long before the Cats from Browns Lane:-)
Best
Klaus W. Nielsen-----Original Message-----
From: owner-xk@jag-lovers.org [mailto:owner-xk@jag-lovers.org] On Behalf Of
Jaginabox
Sent: Monday, January 15, 2007 12:59 PM
To: xk@jag-lovers.org
Subject: Re: [xk] What are spats?

In reply to a message from MELVIN SALTER sent Mon 15 Jan 2007:

I believe there were a few 150 cars made with wire wheels and a
special made spat. The spat had a coutout to accomodate the extra
space needed for the spinner. I remember seeing a pic somewhere, I
believe Jerry Oliver sent me a pic.
Frank

XK150 DHC, '66 Healey PhII,'03 Vette
Auburn, CA, United States
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Roar Sand wrote:

John,
With an exhaust valve diameter of 1 and 7/16 inch ( standard XK ) the area
of the valve head is 1.623 in�.
Assuming a max combustion pressure of 600 psi, there will be 974 pounds of
gas pressure on the valve.

interesting… the simple things we take for granted… wonder about
the pressures in a 3000 hp Supercharged Hemi with 40-50 lbs of boost…
Thanks for the info… john shuck who lacks adequate valve sealing
pressures at times…

In reply to a message from KeithB sent Mon 15 Jan 2007:

Keith
Kinda sorta. You want the valve to close rapidly to avoid the
overlap between the intake and exhaust valves, and to close them
before it’s time to open them again. When the engine reaches that
point, you get valve float and loss of compression. To achieve
higher RPMs, among other things, you need to increase the strength
of the valve springs. The purpose of the double spring (having an
inner and outer) is not only to increase the spring pressure, but
to offset the harmonics created when the springs are opened and
closed at such a rapid rate. There have been developments in valve
spring design which enable engines to reach much higher RPMs. One
design is a lever type spring. In time the coil spring may go the
way of the carburetor, push rods and distributor.
Joel–
The original message included these comments:

My assumption is that the spring is there primarily to keep
the tappet on the cam, and be strong enough to stop the
valve bouncing. I hadn’t thought about it before but Roars
comments would suggest that as long as the valves seal on
the seat long enough for the combustion pressure to finish
the job, all is well.
Keith


ex jag, '66 E-type S1 4.2, '56 XK140dhc
Denison, TX, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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In a message dated 1/15/2007 3:24:34 P.M. Eastern Standard Time,
roarsandnorge@earthlink.net writes:
Obviously, the peak pressure depends on how hard you push on the gas pedal.
I do not know the specified valve closed spring load, however, a typical
number would be around 100 pounds, or less.
The spring load and gas pressure add up for total load of the valve on the
seat.
Does anyone care to figure out the impact load as the valve closes?
Roar

Am I the only non-engineer on this list? Interesting reading though.

Regards, Otto M.

Am I the only non-engineer on this list? Interesting reading though.

Regards, Otto M.

Otto,
Us engineers have such a rotten reputation for being boring geeks, so to
get us back in good graces with the girls, only an XK would do!
Roar (672229)

No.
Bernard MD

Roar Sand a �crit :>

Am I the only non-engineer on this list? Interesting reading though.

Regards, Otto M.

Otto,
Us engineers have such a rotten reputation for being boring geeks, so to
get us back in good graces with the girls, only an XK would do!
Roar (672229)

In reply to a message from Ottman0401@aol.com sent Tue 16 Jan 2007:

Otto
I don’t think the impact load on the valve as it closes is that
significant. If you think about it, the valve is already closed by
the time combustion occurs, so the combustion pressure would not
affect the impact on the valve seat. Secondly, the cam lobe is
designed with somewhat of a ramp to set the valve down on the seat.
The cam lobe in the XK engine is designed with a very steep ramp,
so the valve would fully open and close at a much more rapid rate
then your basic automobile engine.
You know what, forget everything I’ve said. I’m not an engineer
either, so I don’t know what in the heck I’m talking about, but it
does make sense…Doesn’t it?
Joel–
The original message included these comments:

Obviously, the peak pressure depends on how hard you push on the gas pedal.
I do not know the specified valve closed spring load, however, a typical
number would be around 100 pounds, or less.
The spring load and gas pressure add up for total load of the valve on the
seat.
Does anyone care to figure out the impact load as the valve closes?
Am I the only non-engineer on this list? Interesting reading though.
Regards, Otto M.


ex jag, '66 E-type S1 4.2, '56 XK140dhc
Denison, TX, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

Joel,
You are on the right track.
Yes, cam lobes are designed with ramps at both ends of the lift curve.
The opening ramp is somewhat steeper than the closing ramp, and mechanical
lifter ramps are taller than hydraulic lifter ramps.
With mechanical lifters there has to be clearence in the system to allow
for temperature expansion of the parts involved, and to control the seating
velocity at all clearences, which constantly change during engine warm up
and at different engine loads ( read: exhaust gas temperatures), the ramp
has a "constant velocity section. That means that if you look at the lift
curve graphically, the constant velocity part is a straight line. At each
end of the ramp is a blend into the base circle at one end and into the
lift curve proper at the other end.
The seating velocity of the valves are controlled to a maximum of around
one meter per second to avoid noise and excessive wear.
If , for some reason, a valve seats off the ramp, there will be a clicking
noise from the valve hitting the seat too fast. This noise is often called
“tappet noise”, and happens either due to high clearence in the system, or
caused by a soft (airated) or collapsed hydraulic tappet.
Really hard seating, which is followed by a bounce back off the seat, will
happen at high speed when the spring is not capable of keeping the parts in
contact with each other during the lift cycle. The tappet can also leave
contact with the cam lobe, and when it comes crashing back into contact
again, bounce in the system can happen as the parts compress and relax.
To better understand what can happen, keep in mind that the load the spring
exerts on the valve train parts does not nicely follow the load
v.s.compression curve at high speeds.
When the valve starts to open at high speed, the coils closest to the
spring retainer get compressed first, and inertia causes a delay in the
force getting transferred to the rest of the coils.
This causes some of the coils to compress more than they would have at a
slower speed, and when that message gets transferred back, they relax
some. This sets up a “standing wave” in the spring and the coils “surge”.
It is sort of like an echo bouncing between two canyon walls.
This will cause a “wave” superimposed on the load v.s.lift curve.
At the low points in this “wave” the load of the spring is reduced, and
when this happens when the spring is trying to stop the opening motion and
reverse it to close the valve ( maximum negative acceleration), the load
may become insufficient, and there will be separation.
And, yes, with double springs the “standing wave” in the two will have
different frequencies, so it tends to keep the resultant combined load of
the two more even.

Sorry I went a little long with this, but there may be some out there that
will say: “Aha!”, and the rest can just hit “DELETE”!
Roar (672229)

[Original Message]
From: ex jag jcrprops@sbcglobal.net
To: xk@jag-lovers.org
Date: 16.01.2007 13:16:24
Subject: Re: [xk] Unleaded Fuel in XK’s

In reply to a message from Ottman0401@aol.com sent Tue 16 Jan 2007:

Otto
I don’t think the impact load on the valve as it closes is that
significant. If you think about it, the valve is already closed by
the time combustion occurs, so the combustion pressure would not
affect the impact on the valve seat. Secondly, the cam lobe is
designed with somewhat of a ramp to set the valve down on the seat.
The cam lobe in the XK engine is designed with a very steep ramp,
so the valve would fully open and close at a much more rapid rate
then your basic automobile engine.
You know what, forget everything I’ve said. I’m not an engineer
either, so I don’t know what in the heck I’m talking about, but it
does make sense…Doesn’t it?
Joel

The original message included these comments:

Obviously, the peak pressure depends on how hard you push on the gas
pedal.

I do not know the specified valve closed spring load, however, a
typical

number would be around 100 pounds, or less.
The spring load and gas pressure add up for total load of the valve on
the> > seat.

Does anyone care to figure out the impact load as the valve closes?
Am I the only non-engineer on this list? Interesting reading though.
Regards, Otto M.


ex jag, '66 E-type S1 4.2, '56 XK140dhc
Denison, TX, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

Oy!

What some of you are forgetting is that there are 4 strokes in this
scenario. You need closure to insure an efficient “intake suction then a
proper compression mix” well before you apply combustion pressure to the
valves. The springs or whatever is used to close off the chamber as
intake begins. If the valves don’t seal well at this point, besides the
mix being off, compression will be low and so will the results of the
burn.

The tappets don’t “ride” the cam lobes all the way around and the valve
springs don’t make them do this. You always need clearance to absolutely
assure that a valve is closed or mated to its seat! Oy!

Some of the “additives” beside slowing the fuel burn to a point where it
is controlable (efficient), ares proported to both aid in the transfer of
heat from the valve to the head ,“cushion and seal” their mating surfaces
and reduce friction between moving parts.

IMHO there is too much metallurgy in this arena and I’m not going there
as I still believe most valve and seat erosion is a result of improper
timing and fuel mix (aka: when it lights off and leaning)!

See some of you guys soon!

Regards,
Rick

Aha!

No delete about it, this one’s a keeper. Went in the CIF (Critical
Intelligence File).

Thanks, Roar

Peter Hill
677087>Joel,

You are on the right track.
Yes, cam lobes are designed with ramps at both ends of the lift curve.
The opening ramp is somewhat steeper than the closing ramp, and mechanical
lifter ramps are taller than hydraulic lifter ramps.
With mechanical lifters there has to be clearence in the system to allow
for temperature expansion of the parts involved, and to control the seating
velocity at all clearences, which constantly change during engine warm up
and at different engine loads ( read: exhaust gas temperatures), the ramp
has a "constant velocity section. That means that if you look at the lift
curve graphically, the constant velocity part is a straight line. At each
end of the ramp is a blend into the base circle at one end and into the
lift curve proper at the other end.
The seating velocity of the valves are controlled to a maximum of around
one meter per second to avoid noise and excessive wear.
If , for some reason, a valve seats off the ramp, there will be a clicking
noise from the valve hitting the seat too fast. This noise is often called
“tappet noise”, and happens either due to high clearence in the system, or
caused by a soft (airated) or collapsed hydraulic tappet.
Really hard seating, which is followed by a bounce back off the seat, will
happen at high speed when the spring is not capable of keeping the parts in
contact with each other during the lift cycle. The tappet can also leave
contact with the cam lobe, and when it comes crashing back into contact
again, bounce in the system can happen as the parts compress and relax.
To better understand what can happen, keep in mind that the load the spring
exerts on the valve train parts does not nicely follow the load
v.s.compression curve at high speeds.
When the valve starts to open at high speed, the coils closest to the
spring retainer get compressed first, and inertia causes a delay in the
force getting transferred to the rest of the coils.
This causes some of the coils to compress more than they would have at a
slower speed, and when that message gets transferred back, they relax
some. This sets up a “standing wave” in the spring and the coils “surge”.
It is sort of like an echo bouncing between two canyon walls.
This will cause a “wave” superimposed on the load v.s.lift curve.
At the low points in this “wave” the load of the spring is reduced, and
when this happens when the spring is trying to stop the opening motion and
reverse it to close the valve ( maximum negative acceleration), the load
may become insufficient, and there will be separation.
And, yes, with double springs the “standing wave” in the two will have
different frequencies, so it tends to keep the resultant combined load of
the two more even.

Sorry I went a little long with this, but there may be some out there that
will say: “Aha!”, and the rest can just hit “DELETE”!
Roar (672229)

[Original Message]
From: ex jag jcrprops@sbcglobal.net
To: xk@jag-lovers.org
Date: 16.01.2007 13:16:24
Subject: Re: [xk] Unleaded Fuel in XK’s

In reply to a message from Ottman0401@aol.com sent Tue 16 Jan 2007:

Otto
I don’t think the impact load on the valve as it closes is that
significant. If you think about it, the valve is already closed by
the time combustion occurs, so the combustion pressure would not
affect the impact on the valve seat. Secondly, the cam lobe is
designed with somewhat of a ramp to set the valve down on the seat.
The cam lobe in the XK engine is designed with a very steep ramp,
so the valve would fully open and close at a much more rapid rate
then your basic automobile engine.
You know what, forget everything I’ve said. I’m not an engineer
either, so I don’t know what in the heck I’m talking about, but it
does make sense…Doesn’t it?
Joel

The original message included these comments:

Obviously, the peak pressure depends on how hard you push on the gas
pedal.

I do not know the specified valve closed spring load, however, a
typical

number would be around 100 pounds, or less.
The spring load and gas pressure add up for total load of the valve on
the

seat.
Does anyone care to figure out the impact load as the valve closes?
Am I the only non-engineer on this list? Interesting reading though.
Regards, Otto M.


ex jag, '66 E-type S1 4.2, '56 XK140dhc
Denison, TX, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php