Use and re-use of a modified cam decision

[Scott Fisher]

--- passat TS <passat_ts at hotmail.com> wrote:
>
> Should I remove the 272 brand new cam from the new
> engine (NF), install it on
> the current engine (KX), and later put it back in
> the new engine?

I can think of two issues you'd need to clarify first:

1 - Piston/valve clearance with the new cam.  If the
new cam increases valve lift and duration
substantially (and if it doesn't, why are you using
it? :-), you will want to make sure the valves don't
hit the pistons.  This will be particularly crucial
with the old valve springs in the current motor (tired
springs may not close the valves as quickly, and if
they're open farther and longer, you can get
interference).  Be on the lookout for valve float --
if you have anything like an adjustable rev limiter,
you might consider setting it a few hundred RPM lower
for this one event.

2 - Lifter/follower wear on the cam lobes.  The
biggest problem with changing cams is wear due to
improper breaking in -- follow the manufacturer's
instructions to the letter.  Usually this is something
like using lots of special cam lubricant (Redline
synthetic is preferred by most of the SCCA racers I
hang around with), and then most importantly running
the engine at 2500 RPM for 20-30 minutes.  This
ensures a good wear pattern between the cam and the
followers/lifters.

To be absolutely safe, I'd then treat the
reinstallation in your NF motor as if it were a new
cam (I'm assuming you're using new lifters in the NF,
right?).  Slather it with tons of lube again and break
it in as if it were new, because the lifters are new.


Can anybody think of any other precautions?  If the
lifters interchange between an NF and a KX, you might
consider using the new lifters with the new cam in
your KX for this one event, then move the cam and
lifters back into the NF when you prepare it.  That
would eliminate the need for a second break-in
procedure -- though you'd still be wise to use lots of
good preassembly lubricant on your brand-new motor.

Best,

--Scott Fisher
  Tualatin, Oregon



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