Cam position sensors

[Chris Wilson]

If I turn a 8mm thick dural ring to mount in front of the cam pulley, and then screw a single steel tab on the periphery as the single tooth, how big do I need to make the tooth? At half engine speed i doubt such a tooth will seriously affect balance, but being anal, would having a bigger dural "bump" opposite it, at 180 degrees, as a balance mass be seen by the sensor?

Now, hiding in shame, as i should know this, but got to ask I'm afraid. If I buy a pre laser cut crank trigger wheel for the crank nose, (solid to the hub of the damper... ), from one of the vendors of generic timing wheels, they all appear to have been pre cut with a missing tooth. Is that what I need, or does sequential injection, coil on plug set up need all crank teeth present? Thanks, I need to be clear as I read crank and cam triggering issues are one of the commonest problems people new to installing EFI suffer.

I have gone ahead and bought a commercially laser cut crank trigger wheel with 2 missing teeth. I can mount this to the hub part of the crank damper, so it's solidly mounted to the crank, no rubber!

Before I mount it and drill /tap the holes, can someone just tell me if, and how, I need to orientate the two missing teeth relative to the crank position, or doesn't it matter? Similarly, how should I orientate the tooth on the cam pulley wheel relative to the crank / cam position. Thanks

[IDP]

From M800 Help file.

MODE 7 : TWO MISSING TEETH TWICE PER CYCLE

Requires both the REF and SYNC Signals.

This mode is not normally used on two stroke engines.

REF SIGNAL :

The REF Signal must have two adjacent missing teeth twice per
engine cycle (two adjacent missing teeth per engine rev - for 4
stroke engine).

All teeth including the imaginary missing teeth must be evenly spaced
(including odd fire engines).

The number of active edges (Teeth) per engine rev should be set
in the Setup Parameter "Crank Reference Teeth". Counting the
missing teeth.

The minimum number of teeth is dependant on the cranking RPM of the
engine. The minimum cranking RPM for 60 teeth per rev is 100 RPM,
below this RPM the engine will not start. 60 teeth per engine rev
is the recommended minimum for general use.

It is best if the missing teeth are not in the normal range of timing
as they may reduce the timing accuracy.

It is also best if the missing teeth are not placed too close to a TDC
point as this is where the engine RPM is changing the most which can
cause false interpretation of the missing teeth. See the help on the
Tooth Ratio parameter for more detail.

The Setup Parameter "Tooth Ratio" should be set to 50.


SYNC SIGNAL :

The SYNC Signal must provide one active edge for every engine cycle
(720 degrees of crank rotation on a 4 stroke engine). This edge must
be positioned to happen 180 +/- 70 degrees of crank rotation before
the Index Tooth for TDC cylinder 1 compression stroke.

This method allows easy alignment of the SYNC Signal due to the large
tolerance on its alignment.

CRIP :

The Setup Parameter "Crank Index Position (CRIP)" must be set to
indicate the position of the REF Index Tooth relative to TDC cylinder
No 1. The Index tooth is the tooth immediately following the missing
teeth that follow the Sync signal. The Crank Index Position may be
set any where between -10 and 720 degrees.

Edge Directions :

The edge directions are configured in the Sensor Setup screens.
The sensor edge direction may be either "rise" or "fall". This refers
to the signal direction at the active edges of the pickup wheel.
Refer to the data on the sensor to establish if the active edge is
rise or fall.

[Martin]

Have the cam sensor read the tooth on the cam when the 2 missing teeth is furthest away from the crank sensor. That should give you a "relative sync postition" of about 50% which is ideal. The thing is...the closer you go to 100% or 0% the closer the cam tooth comes to the gap which. If this is very bad, lets say right at 0% or 100%, you could be a cycle out on your timing if the cam signal occurs just before and then just after the missing teeth. This can happen is the cam chain has a little bit of slack....in other words the cam signal will jump back and forth over the 2 missing teeth causing the reference tooth (1st after the gap) to be seen one cycle later, changing all the timing by 360deg.

If this was a multitooth setup (12 evenly spaced) the timing would jump by 30 deg (360/12) which would cause havoc. I Prefer 2 missing per cycle over multitooth for this reason. 2 missing gives you almost a whole rotation of space to have the sync occur. Multi tooth only gives you the space between the 2 consecutive ref pulses since the ECU just use the pulse after sync for the reference tooth.

Martin

[MarkMc]

Start with the engine at TDC compression number 1. Wind it BACKWARDS 60 degrees, have the missing teeth line up with their sensor at this point. Spin the engine BACKWARDS a further 180 degrees from there (total of 240 BTDC Comp) and have your cam sensor line up with its tooth there. The CRIP will be about 60, give or take a few degrees.

[Chris Wilson]

Great info, hopefully I am clear on this, as i have started machining the bits Thanks again.