The Knowledge - Velocette Owners Club

pressure gauge that reads in 1 lb increments to 20 or 30 psi? I have some extra bolts threaded 1/8"
BSP, so I should be able to make up an adaptor ok.
# VOCNA 206 I have a fuel pressure gauge on mine (a cool old Moon Equip. one), 0-15 lb. seems to
work fine.
# VOCNA 207 I wonder what the application is (was) with a 0-15 scale, I doubt it is an automotive
gauge. That is the sort of thing I am looking for, but I googled Moon Equip. and the only have 0-80 and
0-100 gauges now and there is nothing on eBay.
# VOCNA 208 Back in the good ole days, when cars had carburetors and you could tell what was
what once you opened the hood, 6-8 pounds was normal fuel pressure as I recall.
# VOCNA 209 I do not know much about these gauges and was focusing on oil pressure gauges - I
assume adapting a fuel pressure gauge is not hard - I guess I will find out. Do they have a capillary
tube like a "good ole" oil pressure gauge? I am not sure I want to go the route of a sender unit that
converts pressure into an electrical signal.
# VOCNA 210 Mine has the same compression fitting affair as a mechanical oil pressure gauge.
While we're on the subject, I also have a gauge on a push rod Velo but it's next to useless. The
peculiar thing is that on start up it will have upwards of 10 psi, then within 4-5 minutes (way before the
oil gets hot) it will drop to 1-2. Not that they need a bunch of pressure, I just have never understood the
reason for the big drop. The things it feeds, crank, cam, followers and rockers all have fixed size
orifices. Tried it on a couple engines with same result.
# VOCNA 221 What you describe is very common. It is one of the reasons why a cold automatic
transmission has such a harsh shift for the first few accelerations but diminishes before the engine and
trans warms up. It is caused by three things: pump leakage, viscosity of the oil, and a little to the
amount (mass) of the oil to be pumped. Mostly it is the viscosity of the oil. Our Velos are old engines
with rather large clearances compared to modern engines so we have to use high viscosity oil. Oil
viscosity is not linear to temperature. Most viscosities are given at 100 degrees C. Viscosity increases
rapidly below 50 degrees C and usually triples around 20 degrees C (room temperature). Hopefully it is
apparent that the oil viscosity is high when the engine is started which causes the high pressure. As the
oil warms it reaches a much lower viscosity long before the engine reaches operating temperature. The
Velo oiling system is a flood system not a pressure system. Even so 1-2 psi is too low. With o-rings
between the timing cover gear oil jets a new pump will deliver 5 - 6 psi a pump with normal wear will
deliver 3-4 psi. Pump wear occurs mostly on the gear and body faces. A new pump has .001" to .0015"
gear end play. If more than .003" clearance is present the pump should be rebuilt or replaced. You can
check the pressure side of the pump gear end play be pulling on the worm gear shaft in the timing
cover.
# VOCNA 213 You're right in your understanding that the 0-15 or 0-30 PSI gauge is likely to be more
accurate than those with bigger numbers on the dial. A Bourden Gauge is operated by a flat tube coiled
up in the casing, with the central, closed end of the tube connected to the spindle through a gear
reduction. As fluid (or gas) is admitted into the open (threaded) end of the gauge, the tube is
pressurized, causing it to uncoil, or attempt to straighten, thereby rotating the spindle with it's attached
needle.
# VOCNA 216 Lots of cheap gauges are available. McMaster Carr has them on their website:
www.mcmaster.com/ Do a quick search for pressure gauges. The catalog page 512 has a tutorial on
gauge types. Page 513 has several gauges with 0-15 psi ranges for $8-$9US each. They have 1/8NPT
fittings. Page 515 has some 0-15psi gauges with metal frames for $7.24 and $13. Grainger has similiar
items. www.grainger.com Page 1198 has liquid filled 15 psi gauges for $16. part # 4ZG16 is 15 psi for
$8.55 You can also try MSC. You may need to open an account with some of these guys to order from
them, but it will be worth the hassle.
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