REFLECTOR: Old Threade - Franklin oil pump spring

[Donald Royer]

As someone who spent considerable time fiddling with my oil pressure and
who has had the bottom end of my Franklin open. I know how the whole oil
bypass plate thing works and so maybe I can help.

First your statement that the stronger spring could replace either of the
springs in the bypass plate is NOT correct. The two springs control
different things. It would be easier to explain it if you you have the
Installation Manual (Plate 7) and Illustrated Parts List (Fig. 3 Oil pump
and bypass group) in front of you. The spring that should be replaced is
the one that faces the propeller end of the engine( Fig.3-21,22,23)(facing
left on Plate 7). This is essentially a plugged oil filter bypass. When it
opens the oil passes directly from the oil pump to the oil gallery of the
engine without going through the external circuit. In other words, the oil
is shunted from 7.1 to 7.2 of Plate7. In my case, the spring that came in
that position looked much like the stronger spring that was supposed to
replace it. The replacement spring is really not necessary, because the
same effect can be gotten simply by placing a couple of washers between the
nut and the spring. Clearly, too much back pressure in the oil cooler
curcuit will cause this bypass to open leading to overheating of the engine.

The other spring facing away from the propeller (Fig. 3-19,20) controls the
total oil pressure coming from the oil pump. I think of this as the gasket
saver. When this bypass opens, the excess oil is dumped back into the
crankcase. It normally opens at about 80-90 psi. If you want your oil
pressure to run a little higher you can put about one washer between the
spring and the nut. Be carefull with this, in an effort to force more oil
throught the cooler curcuit we boosted this too much and blew the core out
of the oil cooler radiator.

Hope that this helps.

Don Royer


> [Original Message]
> From: Jeff Clough <jclough at gci.net>
> To: reflector at awpi.com <reflector at awpi.com>
> Date: 12/26/2004 9:23:27 PM
> Subject: REFLECTOR: Old Threade - Franklin oil pump spring
>
> I hate to dredge this up again, but I could not find the info in the 
> archives......with the Franklin engine nstallation and an up front oil 
> cooler a stronger spring needed to be installed in the oil bypass area 
> to acheive greater oil pressure.   Supposedly the stronger spring could 
> replace either of the springs in the bypass pump.....Well for a few 
> years I have had the sronger spring and FINALLY went to install it..BUT 
> the two springs  in the bypass are different......one is a very light 
> spring and the other is the identical spring to the 'stronger ' one  I 
> was going to install.   The stronger spring when fully compressed is 
> still too long to fit in the space of the lighter spring.... I guess 
> what I need to know is this: is  the stronger spring which is already 
> installed is aqequate or if anyone who installed the stronger 
> replacement spring in place of the lighter spring had to cut the spring 
> length down.....Confused in AK....anyone else confused now?  THANX   
> Jeff Clough
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