Military Vehicles – October 2019

createdwhenthepistonsgodownontheirintakestrokes.There-

fore,anengine’sairmaybecleanedofdustandgritbypullingit

througha finescreenorfilterbeforeit goesdownthecarburetor

throat.

Oilfilters,ontheotherhand,wouldstillhavehadtowaitfor

a coupleofdecades.

Why?Becausemostearlyenginesdidnothaveoilpumps.

Instead,theywerelubricatedbya splashsystem.Therewasnoth-

ingexcepttheactionofthecrankshaftandconnectingrodsto

splashoilontopistonsandcylinderwalls.Thecrankshaftbear-

ingswerelubricatedbydippingintotheoilpanwitheveryrota-

tion.It’sdifficultto filteroilthat’ssimplybeingsplashedaround.

Witha splashlubricationsystem,abouttheonlywaytofil-

tertheoilis toputa screeninthefillerpipesotheoilgetsfil-

teredwhenyoufirstpourit in.Indeed,manyengineshadsuch

a screen...whichmayattesttothequalityofmotoroilduring

thosetimes.Evenupintothe1970s,manygasstationsstillsold

“bulkoil”ofa nastygray-greencolorfromglassquartjarswith

openfunnel-liketops,andtheseopenjarssatoutsideinracksno

matterwhattheweather.

Still,if oilis ofgoodquality.aswellaschangedoften(Ford

specified 500 milesfortheModelA),a splashsystemworkswell

enough onlow-RPMengineswithloose tolerancesandthick

babbitbearings.

Evenintothemid-1950s,theChevrolet 216 enginehadonly

a small oilpumpwhich provided lubricationto theoverhead

valverocker-arm assemblyaswell astotubes in theoilpan

whichwereaimedto shootoilat dipperspoonsonthecrankshaft

bearings, whileeverything elsewasstilllubricatedbysplash.

However,mostothercarandtruckenginesbythistimehadfull

pressure lubricationsystems.Nevertheless,many oftheseen-

ginesstilldidn’thaveoilfiltersorfilterswereofferedasoptions

oraftermarketitems.Theremustbea waytopushorpulltheoil

throughsomesortofscreenorfilterelement.Therefore,anoil

pumpis needed.

Aswithaircleaners(anotherarticle),therearemanykindsof

oilfilterswhichusemanykindsoffilteringmedia.Theserange

from simple wire mesh screens which keep out rocks and small

animals, to sophisticated canisters with replaceable paper or cot-

ton elements that catch particles of metal and grit too small to be

seen by the eye. However, there are actually only two basic types

of oil fi lters: the BYPASS and the FULL-FLOW.

THE BYPASS AND FULL-FLOW OIL FILTERS

The most common bypass oil fi lters historic military vehicle

(HMV) hobbyists will fi nd on their vehicles are the Military

Standard Junior and the Military Standard Senior. Later model

HMVs, such as the M151 MUTT, the Kaiser M715, and various

CUCVs such as the M880, and the HMMWV, have full-fl ow,

“spin-on” fi lters... a type with which many people are familiar

from changing the oil on their cars.

It’s easy to understand how both types work, because their

names describe their function. The BYPASS type does exactly

what its name implies: A portion of the engine oil bypasses the

main lubrication system and is routed through the fi lter, where

particles of metal and dirt are trapped in the fi lter element.

On the other hand, a FULL-FLOW type fi lters all of the en-

gine’soil,usuallyrightafterit leavestheoilpumpunderpres-

sure.Ona fewengines,though, thefilteris in thesuctionsideof

thesystembeforetheoilreachesthepump.

Thereareadvantagesanddisadvantagestobothtypes,so

MilitaryVehiclesMagazine • OCTOBER 2019 23

Full-fl ow “spin-on” oil fi lter on a Kaiser M715 engine.

After warming-up the engine — the oil pan should be hot to touch

— remove the oil pan plug and drain the oil into a suitable container.

While this is going on, open the oil fi lter’s case by unscrewing the

large bolt on top. On some fi lters this bolt is removable from the

cover, but on others it isn’t, so don’t try to pull it out if it doesn’t want

to come out. Then remove the cover. Oil shouldn’t pour out when you

do this, but it’s wise to be prepared. If the cover is stuck, tap it gently

upward with a wrench or small hammer. For a minimum of mess,

don’t remove the fi lter element yet. Instead, get a coffee can or other

container — one that’s obviously large enough to hold all the oil in

the fi lter — remove the drain plug from the bottom of the fi lter case,

and let the oil drain into the can. Wait awhile so most of the oil drains

out of the element. Five minutes is usually suffi cient.