[xk-engine] D type cams

Hi
Just finishing a 3.4. The question has cropped up as to the
benefits of D type cams.
Would love to hear of your experiences with these.
Regards Roger–
spitzstick
hobart, Australia
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In reply to a message from spitzstick sent Sat 12 Nov 2011:

Think of Camshafts as trade offs…
Gain power at higher RPM in exchange for loss of power at
lower RPM…
I love camshafts but then I build my cars to race not for
the street…
Mind you the use of ‘‘D’’ type camshafts without the racing
wide angle head, unmuffled exhaust, Webers/ fuel injection
will cost you power.–
MGuar
Wayzata Minnesota, United States
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In reply to a message from spitzstick sent Sat 12 Nov 2011:

Hi
I had hoped for a more technical response.
Any body out there who can be infomative.
For example, do you get full benefit by changing the grind
on existing cams and using thicker shims,or is it better to
use new billits.
Roger–
spitzstick
hobart, Australia
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In reply to a message from spitzstick sent Fri 18 Nov 2011:

Hi Roger

It’s not possible to give a full technical answer to a non-
technical question. You made a vague request for ‘experience’
without any reference to the vehicle or its intended use. How long
is a piece of string? Besides which, who even knows what a D-type
cam is? One thing is for sure, it’s not radical…

The XK engine started out with lift of 0.3125’’ and timing of 15,
57, 57, 15 which is what the timing stayed for the life of the XK
engine, give or take. The lift did increase pretty early to 0.375’’
but that too stayed the de facto lift for every XK engine. The
later parabolic cams changed very marginally but were developed
primarily to boost refinement.

My original D-type workshop manual describes the D-type cam as
having 0.375’’ lift and timing of 30, 60, 60, 30. That’s all it
says. So standard lift and a tiny bit more duration. Just for
comparison, the same manual gives nine headings of data for the oil
pressure relief valve spring…

So we’re not talking wild extremes here, we’re talking basically a
road cam that was a fraction better than the production version
when coupled with race inlet/exhaust systems to make use of the
timing change, with no requirement to idle as smoothly or be as
docile in traffic as a road car, even though the D-type generally
was a complete pussycat compared to contemporary race cars. You did
not say what your car is or where/how you propose to drive it so
this may or may not be relevant.

Remember the objective was endurance above everything, not outright
performance. Is that your aim? If your aim is not to survive 24 hrs
non-stop, why use the settings for those who did want that?

Doubtless by the time fuel injection was tried , followed by the
3.8 engine for the Ecurie Ecosse ‘semi-works’ entry, they
experimented with more lumpy profiles, but that was after the
manual was written and those cams were never fitted to production D-
types. I haven’t seen those cam specs written down anywhere and
would be interested to know what evidence any seller uses to
justify the label ‘D-type’ on any cam different from 3/8’’ and
30/60/60/30.

I haven’t researched it for Jags, but I can’t see any cam grinder
selling a so-called performance cam with identical lift and almost
identical timing to the cam in every production slush-box smog-
regulated sedan. Would you pay serious money for one? So I doubt
you can even buy true D-type cams unless you go out of your way to
commission a set.

Your second question about regrinds versus billets is nothing to do
with D-types and is a matter of personal preference and cost.
There’s no ‘right’ answer, although technically at the ultimate
limit it would be better to have well made billet cams and normal
shims for reasons of reciprocating mass, and possibly eventual
durability depending how much they ground off the base circle. But
the reason people grind the bases circle is primarily to gain lift,
and D-type cams are standard lift. So…

Pete–
1E75339 66 D, 1E33100 66 FHC, 1R7977 69 OTS, 65 Mk2 3.8 MOD
Cambridge, United Kingdom
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In reply to a message from PeterCrespin sent Sat 19 Nov 2011:

Thank you Pete, just the response I was hoping for.
The cam guy I have been talking to will grind from a billet
an original D type cam though as he has said it wont make
much difference; Which you confim.
There is 3.4 here that has all the goodies on. The owner
says that the biggest improvement came from having the
needles tweeked on a dyno.
Regards Roger–
spitzstick
hobart, Australia
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In reply to a message from spitzstick sent Sat 12 Nov 2011:

spitzstick;
If you want I can run my computer program and tell you
exactly what sort of power and what power curve your engine
will make (assuming proper tuning) with any camshaft.
I’m a racer, This is a lesson I learned the hard way… I
have nearly a dozen camshafts of various grinds… (I sure
wish I’d had access to this program when I was buying all
those camshafts back in the 60-90’s .
On the street please do yourself a favor and use stock.
While I’d love to unload some of these camshafts on the
unsuspecting public I just can’t. I have to look at this
face every time I shave…
Please note that stock does not mean old one… while the
old ones might be OK they need to be carefully measured to
confirm…
There is ever so much slight taper of the lobe. The reason
for that and a slight crown in the lifter, is that helps the
lifter rotate and not wear out one side of the lifter.
I can no longer see well enough to measure the tiny
amounts we’re talking about (.0001 or so). Instead I simply
measure the lifters… If they are all round, (I can detect
it more than measure it using the micrometer as a go-no go
gauge)
Then I’ll reuse the camshaft… If there is more than .001
wear on one side of the lifter. Or there are faint rings on
top of the lifter I know the camshaft is history…(as are
the lifters)–
MGuar
Wayzata Minnesota, United States
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In reply to a message from MGuar sent Tue 22 Nov 2011:

The reason that followers rotate is that the cam is ofset by
about 2mm from the centre of the follower the followers are
ground dead flat and the cams are ground dead flat also.
Any high spot would soon wear through. What you are saying
about things being out of round by 1 thou or a tenth of a
thou makes no sense.
Roger–
spitzstick
hobart, Australia
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In reply to a message from spitzstick sent Sat 3 Dec 2011:

The taper/radius is the normal method used by manufactures
to ensure rotation of the lifter…If the lifter doesn’t
rotate then the thrust side wears quickly.
If the camshaft is offset from the lifter then when the
guide comes up (as they do when racing if not pinned or the
engine severely overheated) the cam would leave offset
grooves in the guide. They don’t.
I used to get ever so slight a rocking when I laid a
straight edge across the lifter. Lately none of the
replacement lifters have had that radius on them… so it’s
not unusual to see those telltail rings showing at 40,000
miles…–
The original message included these comments:

In reply to a message from MGuar sent Tue 22 Nov 2011:
The reason that followers rotate is that the cam is ofset by
about 2mm from the centre of the follower the followers are
ground dead flat and the cams are ground dead flat also.
Any high spot would soon wear through. What you are saying
about things being out of round by 1 thou or a tenth of a
thou makes no sense.


MGuar
Wayzata Minnesota, United States
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In reply to a message from MGuar sent Sat 3 Dec 2011:

Sorry mate what you are saying is wrong.
Tell me what engine you are looking at.
Roger–
spitzstick
hobart, Australia
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In reply to a message from spitzstick sent Sun 4 Dec 2011:

Roger;
All camshafts have a taper to them (every so slight) and
all lifters have a slight (ever so slight) radius to
them…That causes the lifter to rotate and prevents one
sided wear…
I can’t begin to tell you how many V8 engines I’ve had to
replace camshafts that are worn out. (it’s much worse on
V8’s due to the extra weight of pushrods and resistance of
rocker arms) Notice the cam lobes start to wear on one side
and the lifter gets concave in the center… Most recently on
a buddies MGTF with pushrods and rockers.
It’s not so serious on the Jag because no pushrods or
rocker arms. Yet you will notice it by the lifters wearing
concave… You can usually spot that even without a straight
edge across the lifter by slight rings if the top of the
lifter is the correct angle to the light…
You can confirm it on a Jaguar XK engine if the lifter
guide has come up from either high revs or overheating and
causing contact with the cam lobe…If the lifter was offset
then when the lobe comes down and strikes the guide it would
leave a deep gouge and a shallow gouge. The lifter guides
I’ve had to replace have all had equally deep gouges. (or
been totally destroyed as in one case)
Now to be fair I’ll try to figure out a way to measure
the center of the lobe in relationship to the lifter… I
suspect that is filled with inaccuracies since the potential
to miss measure is great…
I know all engines are called flat tappets. However if
you look at Offenhuaser’s book you will see how Miller put
a radius in his tappets and Fred Offenhauser carried it to
an extreme level before reversing it to nearly imperceptible
by the time his engines were turbo’d.
I can imagine that the latest F1 engines have lifter
rotation as a very small priority compared to our old slow
revving Jaguar XK engines…–
The original message included these comments:

Tell me what engine you are looking at.
Roger


MGuar
Wayzata Minnesota, United States
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In reply to a message from MGuar sent Thu 8 Dec 2011:

Roger;
All camshafts have a taper to them (every so slight) and
all lifters have a slight (ever so slight) radius to
them

MG

This is not true in the XK Engine and not true for about every
production twin cam engine with Morin type bucket tappets.

The XK is not a pushrod V-8 engine.

You can simply take two new XK tappets out of the box and press
them together to prove there is no radius. If you are unfamiliar
with DOHC engines take look at the Lampredi designed FIAT 124 twin
cam. They made about +2 million of these and unfortunately they
all run contrary to your claim that ‘‘all’’ lifters have a slight
radius and all ‘‘cams’’ have a taper. The FIAT cam followers have
the shims on the top of the buckets for easier adjustment, a
version of the Salmson/Petit patent. The shims are flat on both
sides and the cams, which also have no taper, ride directly on the
flat shims. And the same shims are used by Ferrari and others
UNDER their tappets. This would not work very well if there was
any radius.

Tappet rotation is not caused by any taper or radius. R. Bywater
describes it this way:

‘‘Although some manufacturers have used expedients like grinding
minute taper on the cam lobes to promote tappet rotation, engineers
at Jaguar reasoned logically that there would always be slight
misalignments from manufacture that would create offset forces
sufficient to provoke rotation naturally.’’

If you have White’s Offenhauser book, you can read how Leo, not
Fred or Harry, added radiused tops to Henri’s tappets when he
copied the flat tappets on the 1919 Ballot. Outside of a few
Bugatti’s that copied Leo, I can’t find a single production twin
cam with radiused tappets. Can you name one ?

Paul–
The original message included these comments:

Roger;
All camshafts have a taper to them (every so slight) and
all lifters have a slight (ever so slight) radius to
them…That causes the lifter to rotate and prevents one
sided wear…


PS
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In reply to a message from PS sent Sat 10 Dec 2011:

Don’t forget all the twin cam bike engines, where DOHC
became the norm before it did on cars (with honourable
exceptions). Under or over the bucket - I’d like Frenchy to
name a tapered version from Messrs Yamaha, Honda, suzuki,
Kawasaki et al.

Frenchy is in one of his periodic holes where his vast
experience in some areas seemingly imbues him with
infallibility in others. The same competitive tenacity
which has served him well in certain circumstances means he
is unlikely to put his shovel down any time soon. It isn’t
as if it’s the first time Frenchy has vowed black is white.

Pete–
The original message included these comments:

Bugatti’s that copied Leo, I can’t find a single production twin
cam with radiused tappets. Can you name one ?
Paul


1E75339 66 D, 1E33100 66 FHC, 1R7977 69 OTS, 65 Mk2 3.8 MOD
Cambridge, United Kingdom
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In reply to a message from PeterCrespin sent Sun 11 Dec 2011:

Who is Frenchy please?–
christopher storey
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In reply to a message from christopher storey sent Sun 11 Dec 2011:

Mr MG Jaguar / MGuar was asked for his name when he first
joined eighteen months or so ago. His surname is Dampier as
per the email I believe and although he has never given his
name he said he was called Frenchy at School.

It is a weakness of mine that as an adult I strugle with
schoolboy nicknames or avatars when corresponding with
people. I feel that addressing people by their surnames is
too brusque, yet using aliases or joke names is annoying
and off-putting but he is quite within his rights of
course. However, having said he used to be called Frenchy
I’d sooner call him that than Mr Dampier.

Pete–
1E75339 66 D, 1E33100 66 FHC, 1R7977 69 OTS, 65 Mk2 3.8 MOD
Cambridge, United Kingdom
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In reply to a message from PeterCrespin sent Sun 11 Dec 2011:

Ah, all explained thank you Peter . A Happy Christmas to you by the
way–
christopher storey
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In reply to a message from PeterCrespin sent Sun 11 Dec 2011:

Thank you Pete;
Frenchy is the nickname I was tagged with in the US Navy…
It would have likely died out except for flight school where
we are all assigned call signs and Frenchy worked for me…
after 9 years of service Frenchy became indelible. I’ve
lived with that name now for over 40 years. It’s on about
1/2 my official paperwork and I usually get checks made out
to Frenchy…
William is a nice honorable name… The British have had a
few Kings and now a Prince with that name. I have no
objection to it… I suspect the difference lies in the
informality we Yankee’s have against the more
structured/formal approach the British have…I realize that
may be a irritation in England. For that I do apologize. Out
of deference I try to take care using proper tittles etc.
until given permission to use less formal whenever
addressing British subjects…
One final comment…I am not of french ancestry. I believe
I was named after William Dampier the famous British
Buccaneer.–
MGuar
Wayzata Minnesota, United States
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