Re: [OMC-Boats] Dwell/tach

From: Lee Shuster (lib1) <lib1@...>
Date: Fri, 11 Sep 2009 22:03:33 -0600

NO, you're describing a SECONDARY HV INDUCTIVE pickup designed to
sense pulse firing off No.1 cylinder. I'm not surprised that's what
you are more familiar with. These induction pickups are also commonly
used on timing lights as well.

NOTE: I"M Pretty sure that's NOT what you have with the RAC If it
has the common red and black alligator clips.

This RAC tach/dwell PROBABLY hooks up to one of (two) the small
threaded terminals on the COIL. The coil has THREE CONNECTIONS.

1) HV SECONDARY which sends high voltage spark to the center
distributor terminal. IGNORE

2) + IGN (PRIMARY) Voltage from the ballast resistor (small threaded
terminal) IGNORE

3) - (PRIMARY) voltage small lead to distributor and lead to tach
(Small threaded terminal) HOOK UP THE RED TACH LEAD HERE. Connect the
BLACK TACH lead to any common ground.

THERE"S NO Timing "port" like you're used to viewing on motorcycles.
Instead there will be timing "marks" on the rotating damper which is
connected to the front crankshaft. There will be a static pointer.
Point your timing light at the pointer when the engine is running
(follow the manual instructions to adjust timing). The distributor
will mechanically advance the timing over 20 degrees as you increase
the RPMs up to roughly 2750 to 3000 RPM. It's not recommended you
alter ign timing, until you checked compression, gapped the plugs,
checked spark plug HT wire resistance/HV, set the points & dwell.

Have fun. BTW, I researched the Buick V8 faimly a little more. The 300
shares pretty much everything with the 340 and would be a no-brainer
bolt in. The 350 Buick shares very little, I'm not sure exhaust
manifolds would swap over.

On Sep 11, 2009, at 8:00 PM, Justin DeSantis wrote:

> Cool, I'm looking forward to hooking it up and comparing it's accuracy
> to my other 2 tachs. Hopefully it's correct. You just clipping it on
> to the outside of the plug wire like a modern tach, or does it require
> some special hook-up procedure. One more question where is the port to
> inspect timing? (I ordered a service manual. Not here yet.)
> On Fri, Sep 11, 2009 at 8:47 PM, Lee Shuster <lks@...> wrote:
>> I've got one of those old-school RAC's too. Pretty common back in the
>> sixties.
>> Simple to hook it:
>> 1) You connect the Red side to the (-) coil primary (same terminal
>> which has
>> the lead to your distributor points.
>> 2) Then the other side is connected to a good engine ground.
>> Should have a switch to change from 6 to 8 cyl. (4 cyl used 1/2 the
>> 8 cyl
>> reading).
>> On Sep 11, 2009, at 5:45 PM, Justin DeSantis wrote:
>>> Hey gang. I borrowed a dwell meter and tach combo from a friend. I
>>> can't for the life of me figure out how to use it as a tach though.
>>> It's an old RAC dwell/tach. all it has is red and black alligator
>>> clips. Other tachs I've used just go to the spark plug cable, one
>>> wire. How does this thing hook up for use as a tach? One lead to the
>>> spark plug, one to the battery negative? I know how to use it as
>>> dwell, but not as tach. Anyone use one of these old beasts?
>>> _______________________________________________
>>> OMC-Boats mailing list
>>> OMC-Boats@...
>> _______________________________________________
>> OMC-Boats mailing list
>> OMC-Boats@...
> _______________________________________________
> OMC-Boats mailing list
> OMC-Boats@...
Received on Saturday, 12 September 2009

This archive was generated by hypermail 2.2.0 : Tuesday, 29 July 2014 EDT