Something tells me we've covered this territory before--but it's not my
memory. At this point I can start reading a book over the moment I
finished it and still be surprised by plot twists. My clue is that Google
knew what I was going to search for--as soon as I typed "Cam flat" it
added lifter and rotation
>From the Crane cam site:
Lifter rotation is created by a taper ground on the cam lobe and the
convex shape of the face of the flat tappet lifter. Also in some cases,
the lobe is slightly offset from the center of the lifter bore in the
block. If the linear spacing of the lifter bores in the block is not to
the correct factory specifications, or the angle of the lifter bore is not
90 degrees to the centerline of the cam, the lifter may not rotate.
Even if the engine you're rebuilding had 100,000 miles on it and the cam
you removed had no badly worn lobes, this still doesn't mean that your
block is made correctly. It just means that the break in procedure caused
everything to work correctly. Be careful to watch the pushrods during
break in to verify lifter rotation. Don't assume everything will work
correctly the second time.
(b) Note: Always use new lifters on a new flat tappet cam. If you are
removing a good used flat tappet cam and lifters and are planning to use
them again in the same (or another) engine, you must keep the lifters in
order as to what lobe of the cam they were on. The lifter breaks-in to
the specific lobe it is mated with and it can't be changed. If the used
lifters get mixed up, you should discard them and install a new set of
lifters and break the cam in again as you would on a new cam and lifters.
You can use new lifters on a good used cam, but never try to use used
lifters on a new cam.
(c) Note: Roller tappet cams don't require any break-in. You can use
roller lifters over again on a new cam if they are in good condition.
There will be, of course, no lifter or pushrod rotation with the use of a
roller tappet cam.
http://www.cranecams.com/instructions/valvetrain/camfail.htm
-----Original Message-----
From: Larry Young [mailto:cartravel@pobox.com]
Sent: Thursday, December 19, 2002 5:52 AM
To: Wes Dayton
Cc: Friends of Triumph
Subject: Re: TR Cam Lobes
Wes,
This is the way I understand it. For proper operation you need two
conditions:
(1) the lobe of the cam must be tappered so that it will contact the
lifter off center and cause it to turn and (2) the lifter has a slight
crown so that the point of contact is not at the edge of the cam lobe.
Larry Young Forever Young Racing
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