oil stained intake runners?

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
Grumpy I pulled my intake manifold on my recently rebuilt engine, to do a cam change, and found that the runners and plenum areas both look like they have been lightly oil stained, the engine runs fine, its not smoking at idle or when I run it hard and I've triple checked the intake gaskets and the engines sure not sucking oil from the lifter gallery area, I've done a compression test ans I've got an almost perfect 160-167 low to high, cylinder too cylinder compression test consistency , so where is the minimal oil coming from.

this is not at all rare, especially on newer engines that have mild performance cams.
in most cases the cause is a small amount of oil leaking past the rings or valve seals, especially if the heads you installed were not equipped with new valve seals.
But
theres a good chance reversion pulses are causing a fine oil mist, from oil getting past the valve seals, valve guides or rings, during the cams low speed operation (idle) too be sucked back into the intake plenum
keep in mind REVERSION PULSES in the intake can spread oil over the runner and plenum in some cases.
at high rpms the intake charge of fuel air has the inertia , to continue to pack air into the intake valve even as the piston passes bottom dead center and starts upward compressing the air in the cylinder, intake runner port speeds can exceed 200 fps,at lower engine speeds theres enough time for the flow to reverse temporarily as the piston rises thus oil mist drawn from the rings and intake valve guides get forced back into the plenum.
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many guys see this if they install older heads , on an engine that are basically in good shape but may have minor wear on the valve guides and valve seals, or before the piston rings fully seat and seal.on a new short block , especially , if the engines PCV valve and breather are not functioning at peak efficiency.
often installing a breather catch can significantly reduces this, but if your cars engine "LOPES" and "RUMBLES" at idle one of the strong indications that the engine sees some intake charge reversion, at low speeds , its almost a given that their will be minor reversion, and as a result minor oil film on the intake runners.
if youve ever installed a longer duration cam in a tuned port engine design, your very likely to find the intake runners show a light oil discoloration as the engines allowing those long runners to draw oil up out of the cylinders at lower idle speeds during the cams over lap timing.
you might want to pull a spark plug and use a flex micro cam to inspect inside the cylinder
http://www.getlizardcam.com/index.jsp

http://www.getlizardcam.com/index.jsp#product_selection

https://www.walmart.com/ip/6LED-Wat...0812&wl11=online&wl12=623029814&wl13=&veh=sem

this is also a good inspection tool
http://www.thetoolwarehouse.net/p-6283- ... pv618.aspx
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heres a cheaper version that works with a lap top computer

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a common cause of oil in intake ports is having the heads machined without matched changes to the intake, manifold, and gasket surfaces, but reversion pulses in the intake runners can and do transfer oil from the valve guides and oil mist,getting past piston rings into the intake runners due to reversion pulses

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If the valve springs are to be removed with the heads still on the car,

the last thing you want is too remove a valve spring and have the valve to drop into the cylinder,
if you use air the crank tends to want to spin the crank to BDC, youll want to verify TDC ,
and make sure the flywheels temporarily prevented from turning from that the TDC position,
Ive used both methods both work,you can put 6 ft of rope in the cylinder while its in BDC then turn it to TDC, Ive used both with zero issues,
If you use the compressor youll want to keep it at 120 psi and constantly feeding pressurized air to keep the valves held in place,
and theres a small chance the compressor pushes enough moisture to allow water to accumulate in the cylinders,
so be sure you spin the engine with the starter with the spark plugs removed several times before you re-install plugs.
if you use the rope, theres a very low chance that the rope will tangle and form a knot that makes removal difficult,
in either case be sure the pistons locked at tdc,
before removing the valve springs, on each cylinder.
read through these links

https://www.hotrod.com/articles/ctrp-0302-performance-intake-configuration/

http://garage.grumpysperformance.co...n-cylinder-head-intake-ports.5081/#post-14463

http://garage.grumpysperformance.com/index.php?threads/port-speeds-and-area.333/

http://garage.grumpysperformance.com/index.php?threads/catch-can-related-info.4636/#post-12610

http://garage.grumpysperformance.co...reather-hole-in-valve-covers.2005/#post-35665

http://garage.grumpysperformance.co...gine-oil-fowling-spark-plugs.7692/#post-53056

http://garage.grumpysperformance.com/index.php?threads/intake-sucking-oil.4891/#post-24722

http://garage.grumpysperformance.com/index.php?threads/detonation-damage.2883/#post-7484

http://garage.grumpysperformance.co...-you-failed-emmision-testing.3522/#post-18430
 
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