adjusting cams was Re: [Shotimes] Help with engine stumble in 95 MTX

[Jim & Debbie Leyden]

Ian,

The correct sequence of a four stroke cycle engine is Intake, Compression,
Power (or expansion) and Exhaust, then start over.  So in reality, the
intake follows the exhaust.  Therefore, in order to increase overlap, you
would retard the exhaust cam (keeps it open later) and advance the intake
cam (opens it sooner).  Three degrees sounds close and it can be done
without the adjustable sprockets.

Jim



-----Original Message-----
From: shotimes-admin@autox.team.net [mailto:shotimes-admin@autox.team.net]
On Behalf Of Ian Fisher
Sent: Wednesday, August 10, 2005 3:28 PM
To: Zach Leahy; George Fourchy
Cc: shotimes@autox.team.net
Subject: adjusting cams was Re: [Shotimes] Help with engine stumble in 95
MTX

Interestingly enough, a lot of people I have spoken to
have (or plan on) retarding their exhaust cams 3
degrees to dial out overlap when using reground cams.

On the other hand, Lance Cheney has his exhaust cam
advanced 3 degrees to dial out overlap. Technically,
this seems to make more sense, right?

Intake valves open first followed by the exhaust. If
the exhaust cams are advanced 3 degrees, they'll close
sooner and spend less time open while the intake
valves are open. Does this make sense?

I am not going to install my +20's straight up. I plan
on either advancing or retarding them 3 degrees to
start with. I just need to figure out which way to go.
I know that at 0 degrees of adjustment, there is too
much overlap so I'm not even going to bother with that
setting.

Ian
--- Zach Leahy <leahyz@gmail.com> wrote:

> Yes George, that's what I did, in a couple
> positions.  What the
> previous post was saying is that you are retarding
> or advancing the
> entire valvetrain, intake and exhause when you move
> one tooth on the
> belt.
> 
> To actually be able to change just the intake, you
> need to move the
> intake one way nad then correspondingly move the
> exhaust (chains) the
> other way.  That would allow you to adavance the
> inake perhaps and
> retard the exhaust, decreasing overlap, or opposite
> to add overlap, or
> advande everything forward, or back.  Becasue the
> intake and exhaust
> cam are chaned together in order to change just the
> intake, one needs
> to adjust 4 sprockets.
> 
> Z
> 
> On 8/10/05, George Fourchy <krazgeo@comcast.net>
> wrote:
> > On Wed, 10 Aug 2005 08:58:39 -0700 (PDT), Ian
> Fisher wrote:
> > 
> > >On the SHO, the intake cams can only be adjusted
> > >independently using adjustable sprockets such as
> > >Josh's timing chain sprockets.
> > 
> > Theoretically, if someone wanted to spend a bunch
> of money to buy those sprockets, I
> > suppose one could.
> > 
> > But if you divide the number of teeth in the
> factory sprockets by 360, you'll get
> > the number of degrees either side of TDC one tooth
> will give.  I don't have any
> > right here...they are in storage, but if there
> were 90 teeth, each one would be 4
> > degrees.  If there were 60 (probably closer to
> correct), then each would be 6
> > degrees.  If the crank sprocket has 30, then each
> one would be 12, probably a bit
> > much for a slight valve timing exercise.
> > 
> > ...that sounds about right....30 teeth on the
> small sprocket, and twice as much for
> > half the speed...60 on the bigger sprocket.....
> > 
> > Count the teeth, then adjust the cam sprockets by
> as many degrees as you want to
> > try.
> > 
> > George
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> > Shotimes@autox.team.net
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