Monday, 6 June 2011

Stroker Breathing advice from Performance Indian

"Hi Steve, Jim Mosher here.
I too have had a ton of breather trouble from
my 57" Scout. My friend Matt Blake also had alot of oil loss issues. Once, I
had oil coming out my distributor hole where my magneto is installed. In
general a good breather system requires a quick acting check valve like the
"Krank-Vents" that I sell. The next thing is that the Krank-Vent has to be
mounted above the connection to the motor, and not running down hill. The
motor needs a generous hole for the air to escape. I am using the normal
Scout breather hole at the rear/top of the pump with a 3/8" 45 degree hose
fitting going upward about 7"-8" into the Krank-Vent. Lately, I have been
tapping a 1/4" pipe thread hole for a fitting on the flat surface of the
right case just behind the distributor mount for more air to escape from the
cam chest. I will tie the (2) fittings together into a "Y" fitting made of
thin walled 1/2" tubing that will connect to the 1/2" inlet of the larger
Krank-Vent. Then run a 1/2" hose back to the rear of the bike. I like
everything going uphill with large tubing to slow the air speed, reduce
drag, and to work against gravity. Some oil will collect in the tube, and
then run downhill back to the cam chest. On my Twin 57" Scout Bonneville
racer, I took it one more step. I found that oil can get into the oil pump
cavities, and not drain off well, so I found a spot on the cam cover where I
drilled a 1/4" hole to let oil get back to the cam chest. I will try to find
a pic of this hole for you. Please note the picture shows how to modify a
cam cover so you can use an aluminum pump like a 648!
   One of the things that make me wonder alot is the fact that crank-case
pressure can work for you as well as work against you. The pressure is handy
for forcing oil mist into small places like into the cam chest (that's why
it is a good idea to drill a series of 1/8" holes in the cam chest of the
right case just under the intersection of the lifter arched pad, and the
push rods for better oiling like they did on Chiefs in '52-'53). The
pressure will also force oil through a small hole into the pump to oil the
rear cam gear that drives the distributor. It also pushes oil up the push
rod guides, and the valve guides. Please note that it is a good thing to get
this oil into the intake guide, but not beyond the valve guide into the
combustion chamber, and that is why I am a firm believer in intake valve
guide seals! The pressure can also aid in forcing oil into the drive side
bearings. Indian installed the baffles in the cases, so that this pressure
would be somewhat blocked preventing too much oil from getting on the
cylinder walls. Today with better honing, and rings, we no longer need these
baffles. On the other hand, it is better to get the crank-case into a vacuum
state by using a quick acting check valve to let air out, but not back in.
This allows the pistons to come down without having to pump air out of the
motor. And when the check valve closes, the motor will not have to pull air
back into the motor. This process actually causes the rings to seal better,
hence increasing manifold vacuum, and saving the horsepower needed to move
air both in, and out of the cases. I have been running Krank-Vents for years
on HOT bikes without any oiling issues, so I guess they get enough oil
everywhere they need it. Maybe todays oil is better as well.
   Back to the oil spewing of a 57"er. You want alot of breather outlet area
in places where there is not alot of churning oil mist, and as of yet, I
haven't come up with the perfect solution. I will though, because I have to
make my Twin-Scout perform without loosing oil. My 57"er has Duff's original
prototype vent on the left case timing hole, and it picks up some oil mist
from the spinning flywheels. I don't recommend this hole for venting. I like
the cam chest area the most for venting, because it is less turbulent. There
needs to be more holes between the cam area, and the flywheel area, so the
air can freely pass through (look at a Norton cam chest!). There may need to
be some small sheet metal baffles inside the cam chest near the outlet holes
to discourage oil splash from exiting. I will be working on this in the
future, and I'd like to see you post this E-mail, so others will also "get
on board" to find a good 57" breathing solution.
   As for the Twin-Scout, it won't run at Bonneville untill next year,
because I am feverishly working on (2) Bonneville bikes for this year's
Speed-Week at Bonneville. One is a Norton that we ran last year that
actually beat the worlds record by .002 MPH, but they didn't give us the
record, because it was too close. (The Bastards)! The other is a HOT 45"
Scout that already holds the record. Two years ago, he set the record, and
last year he added my cams, and lifters, which made the bike go 30 MPH
faster! This year with a completely new motor, he should go faster yet. I
just got my sheet metal finished for the Twin-Scout, and soon it will get
fully disassembled, painted, and put back together. I am getting it titled,
and liscenced, so I can develope it on the back roads of New Mexico before
running it on the salt. Here's a pic of it with the sheet metal models in
   I hope all this helps. See Ya; Jim Mosher"

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