Re: Cams, John L.

[Bob Brooks <rbrooks@domain.elided>]

John A. Landry wrote:

> When he stopped taking his medication, strange voices in
> jmbrodsky@domain.elided's head said:
>
> >        Cam grinders can 'copy' cams just like Home Depot copies your house key.
> > The one side has the original cam and the other side has the 'blank' cam.  The
> >machine runs the grinders and pointers and voila, copied.  Not too much magic in
> >that one.  The question I have for you is why you would question the 'pull the
> >print' that the tech spoke about.  Each lift and all the angles have to be
> >stored somewhere.  Are drawings out of the question?
>
> No Joel... it's not that I'm questioning Federal-Mogul having a print.  I'm
> sure he actually pulled something because he put me on hold and cam back
> ruffling a piece of paper.  What surprised was the *lack* of information
> they had about the cam.  If you buy a cam from Crane or someone like that,
> you get this nice little card with the cam that tells you everything you
> ever wanted to know about it and then some.  This card is indispensable if
> you plan to degree the cam.
>
> The FM stock cam didn't have sort of specifications packed with it.  That's
> why I was forced to call them and then the tech pulled the print.  With the
> information he gave me from the print, it's not adequate to verify all the
> important manufacturing aspects of this cam.  In retrospect, it's clear now
> that all FM did was make a master cam for their production by copying a
> stock factory cam.  They probably took a few cursory measurements for
> verification purposes and made a print.  This is all fine with me as long
> as I have the detailed original factory specs to verify their work against
> (which I still lack).  I don't inherently trust anyone's work or quality...
> especially when it's going to get buried in my new engine!
>
> Failing someone coming up with specs for me, I'm planning on measuring the
> old cam directly or slipping it back into the block first and take full
> measurements on it there.  Obviously it has plenty of wear, but if I take
> that into consideration, I still should be able to get a pretty good idea
> of what to look for.  Then all I need to is see that the FM cam matches
> reasonably well.
>
> I know this all sound pretty ridiculous to many on the Digest, but I don't
> care.  I have plenty of time to spend on this rebuild project and I'm going
> to do what I feel is right.  There's no way I'm going to simply throw
> something that important into my new engine without checking its quality
> first.  When my block, crank and heads come back from the very reputable
> machine shop I'm using, I'll be checking every bit of work they did too.
>
> Shoot, just ask Mike Ryan about what he found when his engine cam back from
> the machine shop.  As I recall they installed a couple of pistons upside
> down on the connecting rods.  Assembling an engine with a mistake like that
> could destroy it in short order.  That's great attention to detail all
> right!  Maybe this affinity guys like Mike and I have for checking and
> double checking everything is because we were trained as pilots and had it
> drilled into our heads that one overlooked minor detail can result in
> untimely death?
>
> Take care,
>
> John L.
> --------------------------------------------------------------------------
> jlandry AT halcyon DOT com    |
> Conservative Libertarian      |
> Life Member of the NRA        |        All the GOOD things in life
> WA Arms Collectors            |              are DANGEROUS!
> Commercial Helicopter - Inst. |
> www.halcyon.com/jlandry/      |

John:

Chances are Federal- Mongul does not grind the cams themselves.  cam grinding takes
very specialized equipment.  My guess is that it is subcontracted out to a company
that specializes in cam grinding.

Not that that makes the job any better or worse, it's just the way things are done.
When I assemble any engine I always check everything that goes into it as well.
Including double checking the cam,  wether it's a factory replacement or supplied by
an aftermarket company like Crane .  Even if you get the card in the box, it does not
guarantee the cam is right.

You can check the cam on the bench, or in the engine.  Remember that the lift numbers
that are speced on the cam are actualy measurements of VALVE LIFT.  Not a measurement
of the lobe size on the cam.  You need to know the rocker arm ratio to figure out
what the actual lift measured directly on the cam is.

Not only do you have to look at lift and duration, but you should measure the lobe
centers.   Changes in the lobe centers will have a dramatic effect onh the way the
motor runs.

Just my 2 cents;

Back to Lurk Mode.

Bob
rbrooks@domain.elided

Micrel, Inc.
http://www.micrelinc.com