I have never experienced any camshaft breakage, but in a reprint of an
article from the English magazine Autocar from April 8, 1955 excessive
camshaft bending in the area of the oil pump drive gear is mentioned. And
this was with early light springs but continuous use over 5,000 rpm. to cure
the problems the front part only of the camshaft was increased in diameter
by 1/8". Remember, the span of support in the front of the engine is twice
as large as in the rear half. The drive gear has replaced the bearing that
would be expected in this location.
I believe that the shaft diameter should not be reduced below its
original as cast diameter for this reason. If a cam grind has so much lift
or duration that the shaft diameter has to be reduced to accommodate a small
base circle, then the lobes need to be welded up or a new cam blank with
large enough lobes should be used. The new cam blank should be checked to
make sure the front part of the shaft is 1/8" larger than the rear part. it
should also be the same minimum size as the original shaft.
In the original design, according the article in "The Autocar" at 6,000
rpm the camshaft was flexing .020" at the #1 exhaust lobe and only .008" at
the #3 exhaust lobe. Again, this was in the early development of the TR-2,
before the valve stems were uprated to 3/8" diameter and before the valve
springs were stiffened. The Tr engineers found increasing the diameter of
the whole length of the camshaft did not cure this uneven deflection, this
was only cured by enlarging the front part of the camshaft and leaving the
rear part untouched.
This uneven deflection could account for camshaft breakage in the area
around the oil pump drive gear.
The article with this information is in a "brooklands books" collection
"Triumph TR-2 & TR-3 1952 - 1960" The article is entitled "A Triumph of
Development The story of the TR-2" by John Rabson, A.M.I.Mech.E.
Regards,
Greg Solow
The Engine Room
Santa Cruz, Ca.
_______________________________________________
Support Team.Net http://www.team.net/donate.html
http://www.fot-racing.com
Fot@autox.team.net
http://autox.team.net/mailman/listinfo/fot
|