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For years, actually almost from the time when I first bought my car in =
1965,
I used a rev limit of 6800 rpm which I arrived at by doing some =
corrected
piston speed, inertia calculations based on a formula in a book on =
Sports
Car Engines by Phillip H. Smith, a well known English author of the 60s.
Using stock rods, Hepolite pistons, both Su and Weber carbs, Kastner =
"D"
and "F" cams and a basically stock crank with a lightened ( 18 lbs..) =
stock
flywheel and a C/R from 11:1 to 12 1/2:1, I went through 3 cranks like
clockwork at 7,000 miles intervals. I would put an engine together, it
would be nice and smooth, no vibrations at all from 1,000 to 6800 rpm .
Then at 7000 miles, this was hard street driving, autocrossing, drag =
racing,
and some street"drag racing," a vibration would appear at about 2800 to =
2900
rpm. When this would happen it was a very obvious change in the engine.
There was no doubt that something had changed. So I would pull the pan, =
the
#4 rod cap and inspect the rear radius of the #4 crank throw. sure =
enough
there would be a crack beginning there. Just a small hairline, but it =
was
visible non the less. I would pull the engine and the crank and have =
the
crank magnafluxed just to be sure. But the answer was always the same.
A crack it was. I tried shot peening , it did not help, no difference =
in
crank life at all. The rods always passed mag, and as I went through
various different stages of tune, I eventually lightened the rods from =
the
original 2 lbs.. each to 1 1/2 lbs.. each, most of the material being =
removed
from the big ends. The pistons were also lightened as were the pins.
Finally I found a crank preparer who suggested welding up the rear
radius of the #4 journal where the cracks always appeared so a larger
radius could be ground so as to spread the area where the loads were
concentrating over a larger area. The crank was stress relieved and d
DEEP CASE nitrided.
THIS CRANK WAS IN MY ENGINE OVER A PERIOD OF 10 years, 30,000 MILES AND =
3O
ODD VINTAGE RACE EVENTS. It was in my engine when a rod broke at 6000 =
rpm
at Sears Point. Fortunately it was not damaged in the ensuing blow up. =
That
crank is still good and it going to go back into my engine when it I go
through it again. In many customer engines that we have built over the
last 20 years, I have never seen a deep case nitrided crank crack or =
break
if the engines were kept under 6800 rpm.
I HAVE SEEN 2 ENGINES BREAK STOCK, RACE PREPARED CONNECTING RODS. In =
both
cases the engines were being reved over 6,000 rpm.
My conclusion is that if you have a well built properly =
clearanced
bottom end with a deep case nitrided crank and stock rods, the safe rev
limit is 6, 000 rpm.
With good quality forged steel con rods(carillo, crower, etc.) =
the
safe rev limit is 7,000 rpm.
By the way, maybe if there is a metallurgist out there he can =
address
this, I would NOT recommend "shot peening" stock rods. I believe =
that
shot peening a stock British rod of EN 16 steel, which is what TR-4 rods =
are
made of, "work hardens" the surface skin of the rod and makes it so that =
the
surface cannot stretch or flex. At high rpm the inertia loads on the =
rod
are such that the core of the rod is not strong or hard enough to =
prevent
the rod stretching. So it stretches and the hard outer skin cracks! =
Then
the rod breaks. Shot peening may work to strengthen stock rods, but =
only if they are first heat treated to the appropriate hardness. Maybe =
something like Rockwell C scale 35 or so. This is just a guess on my =
part.=20
By the way, I have never run any kind of a damper. I do now =
run an aluminum alloy flywheel which weights about 12 lbs. with a =
stock ring gear on it.=20
-----Original Message-----
From: Bill Babcock <BillB@bnj.com>
To: Friends of Triumph <fot@autox.team.net>
Date: Thursday, January 21, 1999 2:27 PM
Subject: Rev Poll
>I'm seeing a big discrepancy in redlines and other crankshaft-related
>issues. I suggest a poll to get a little clearer picture of what's =
going
>on. I suggest everyone send replies directly to me rather than
>cluttering the list, and I'll consolidate the information into a table.
>The final tabulation will not include names, so you can feel free to
>list your four liter TR3 motor. I'll just list the basic info in
>spreadsheet form. Here's what I have in mind for information to be
>gathered:
>
>Engine type: (TR3/4; TR6, etc.)
>What you use as a redline:
>Crank mods:
>Rod mods:
>Harmonic balancer (yes/no/sort of)
>Flywheel mods:
>Bore:
>Reliability (low/medium/high)
>Comments:
>
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<DIV> </DIV>
<DIV>For years, actually almost from the time when I first bought my car =
in=20
1965,<BR>I used a rev limit of 6800 rpm which I arrived at by doing some =
corrected<BR>piston speed, inertia calculations based on a formula in a =
book on=20
Sports<BR>Car Engines by Phillip H. Smith, a well known English author =
of the=20
60s.<BR>Using stock rods, Hepolite pistons, both Su and Weber =
carbs,=20
Kastner "D"<BR>and "F" cams and a basically stock =
crank with=20
a lightened ( 18 lbs..) stock<BR>flywheel<FONT color=3D#000000 size=3D2> =
</FONT>and=20
a C/R from 11:1 to 12 1/2:1, I went through 3 cranks like<BR>clockwork =
at 7,000=20
miles intervals. I would put an engine together, it<BR>would be =
nice and=20
smooth, no vibrations at all from 1,000 to 6800 rpm .<BR>Then at 7000 =
miles,=20
this was hard street driving, autocrossing, drag racing,<BR>and some=20
street"drag racing<FONT color=3D#000000 size=3D2>,</FONT>" a =
vibration=20
would appear at about 2800 to 2900<BR>rpm. When this would happen =
it was a=20
very obvious change in the engine.<BR>There was no doubt that something =
had=20
changed. So I would pull the pan, the<BR>#4 rod cap and inspect =
the rear=20
radius of the #4 crank throw. sure enough<BR>the<FONT =
color=3D#000000=20
size=3D2>re</FONT> would be a crack beginning there. Just a small =
hairline,=20
but it was<BR>visible non the less. I would pull the engine and =
the crank=20
and have the<BR>crank magnafluxed just to be sure. But the answer =
was=20
always the same.<BR>A<FONT color=3D#000000 size=3D2> </FONT>crack it =
was. I=20
tried shot peening , it did not help, no difference in<BR>crank life at=20
all. The rods always passed mag, and as I went =
through<BR>various=20
different stages of tune, I eventually lightened the rods from =
the<BR>original 2=20
lbs.. each to 1 1/2 lbs.. each, most of the material being =
removed<BR>from=20
the big ends. The pistons were also lightened as were the=20
pins.<BR> Finally I found a crank preparer who =
suggested=20
welding up the rear<BR>radius of the #4 journal where the cracks always =
appeared=20
so a larger<BR>radius could be ground so as to spread the area where the =
loads=20
were<BR>concentrating over a larger area. The crank was stress =
relieved=20
and d<BR>DEEP CASE nitrided.<BR>THIS CRANK WAS IN MY ENGINE OVER A =
PERIOD OF 10=20
years, 30,000 MILES AND 3O<BR>ODD VINTAGE RACE EVENTS. It was in =
my engine=20
when a rod broke at 6000 rpm<BR>at Sears Point. Fortunately it was =
not=20
damaged in the ensuing blow up. That<BR>crank is still good and it =
going=20
to go back into my engine when it <FONT color=3D#000000 size=3D2> I =
</FONT>go<BR>through it again. In many customer engines that =
we have=20
built over the<BR>last 20 years, I have never seen a deep case nitrided =
crank=20
crack or break<BR>if the engines were kept under <FONT color=3D#000000=20
size=3D2>6800</FONT> rpm.<BR>I HAVE SEEN 2 ENGINES BREAK STOCK, RACE =
PREPARED=20
CONNECTING RODS. In both<BR>cases the engines were being reved =
over 6,000=20
rpm.<BR> My =
conclusion is=20
that if you have a well built properly clearanced<BR>bottom end with a =
deep case=20
nitrided crank and stock rods, the safe rev<BR>limit is 6<FONT =
color=3D#000000=20
size=3D2>, 0</FONT>00 rpm.<BR> =
With good=20
quality forged steel con rods(carillo, crower, etc.) the<BR>safe =
rev limit=20
is 7,000 rpm.<BR> By the way, =
maybe if=20
there is a metallurgist out there he can address<BR>this, I=20
would NOT recommend "shot peening" stock =
rods. I=20
believe that<BR>shot peening a stock British rod of EN 16 steel, which =
is what=20
TR-4 rods are<BR>made of, "work hardens" the surface skin of =
the rod=20
and makes it so that the<BR>surface cannot stretch or flex<FONT =
color=3D#000000=20
size=3D2>. At</FONT> high rpm the inertia loads on the rod<BR>are =
such that=20
the core of the rod is not strong or hard enough to prevent<BR>the rod=20
stretching. So it stretches and the hard outer skin cracks! =
Then<BR>the=20
rod breaks.<FONT color=3D#000000 size=3D2> Shot peening may work =
to strengthen=20
stock rods, but only if they are first heat treated to the appropriate=20
hardness. Maybe something like Rockwell C scale 35 or so. =
This is=20
just a guess on my part. </FONT></DIV>
<DIV><FONT color=3D#000000=20
size=3D2></FONT> <FONT =
size=3D2>By the=20
way, I have never run any kind of a damper. I do now run an=20
aluminum alloy flywheel which weights about 12 lbs. with a =
stock=20
ring gear on it. </FONT><BR>-----Original Message-----<BR>From: Bill =
Babcock=20
<<A href=3D"mailto:BillB@bnj.com";>BillB@bnj.com</A>><BR>To: =
Friends of=20
Triumph <<A=20
href=3D"mailto:fot@autox.team.net";>fot@autox.team.net</A>><BR>Date: =
Thursday,=20
January 21, 1999 2:27 PM<BR>Subject: Rev Poll<BR><BR><BR>>I'm seeing =
a big=20
discrepancy in redlines and other crankshaft-related<BR>>issues. I =
suggest a=20
poll to get a little clearer picture of what's going<BR>>on. I =
suggest=20
everyone send replies directly to me rather than<BR>>cluttering the =
list, and=20
I'll consolidate the information into a table.<BR>>The final =
tabulation will=20
not include names, so you can feel free to<BR>>list your four liter =
TR3=20
motor. I'll just list the basic info in<BR>>spreadsheet form. Here's =
what I=20
have in mind for information to =
be<BR>>gathered:<BR>><BR>>Engine type:=20
(TR3/4; TR6, etc.)<BR>>What you use as a redline:<BR>>Crank=20
mods:<BR>>Rod mods:<BR>>Harmonic balancer (yes/no/sort =
of)<BR>>Flywheel=20
mods:<BR>>Bore:<BR>>Reliability=20
(low/medium/high)<BR>>Comments:<BR>><BR></DIV></BODY></HTML>
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