newer engine burns oil?

[grumpyvette]

grumpy I recently had a local guy rebuild my engine and I think its burning excessive oil, as it goes thru about a quart every 200 miles, where do I look for the cause, and yes i verified its not leaking oil and the spark plugs do show some oil being burnt.

there are chances of pre-ignition and knocking, if temperature of the inlet air is higher than normal. As the temperature of the air will be higher, the temperature of air-fuel charge will also be higher (petrol engine) which means there are chances of ignition of air-fuel mixture even before the piston reaches its precise point during normal combustion.

The above picture gives a general idea about how knocking occurs.

theres several areas and Ill point out a few Ive seen. one of the first things ID suggest,is an old time test, have a buddy follow you in his car while you rapidly accelerate your car thru the first three gears then leave it in gear and pull your foot off the throttle and let the engine brake or drag the car to a lower speed. much more oil smoke on acceleration is generally related to high cylinder pressure and oil getting past the ring seal, much more oil smoke on engine braking generally related to high port vacuum levels and bad valve seals or valve guides, being worn, the next test,is to pull the intake and inspect carefully, you should easily see indications of a leaking intake gasket or bad valve guides under close visual inspection, thus you may find and determine if the oils entering the cylinders thru the heads or past the rings,it helps to know if the route the oil takes into the cylinders is thru the heads or past the rings,thus related to the heads or the rings

(1) rings need to seat to the cylinder walls this normally happens in the first 15 minutes of run time on a properly set up set of piston rings and a correctly honed cylinder wall. use of the wrong rings, or the wrong tension rings can increase oil burning
viewtopic.php?f=53&t=3897&p=26602&hilit=hone+plate#p26602

(2) FAILURE TO USE A TORQUE PLATE BEFORE HONING THE CYLINDER WALLS TENDS TO REDUCE THE CYLINDER WALL SEAL.
viewtopic.php?f=53&t=509&p=28226&hilit=hone+plate#p28226


(3)Ive seen guys who installed, new piston rings in the piston grooves either upside down in the ring grooves or installed the rings in the wrong grooves or in the pistons with more, or less than the ideal side clearance to the bore walls. if you install the rings incorrectly with the wrong side facing the top of the piston it results in an engine that basically pumps excess oil into the cylinders , you could burn 3 -4 quarts an hour if the compression rings are all upside down
Ive also seen piston grooves that were damaged or had the wrong back clearance or end gap cause problems.
viewtopic.php?f=53&t=1797&p=36469&hilit=piston+grooves#p36469
viewtopic.php?f=53&t=9490&p=34913&hilit=piston+grooves#p34913

(4) a defective p.v.c. valve or incorrectly installed valve cover baffles can cause excessive oil consumption.
viewtopic.php?f=52&t=2005&p=5328&hilit=positive+crank+case#p5328

(5)milled heads and intake surfaces must match, its common for guys to mill heads during a valve job but fail to have the intake machined to match., failure to do the machine work correctly frequently results in the intended to be mated, sealing gasket surfaces not seating and sealing correctly
viewtopic.php?f=51&t=5460&p=16311&hilit=mill+angle#p16311

viewtopic.php?f=50&t=2988&p=9055&hilit=mill+angle#p9055


(6) intake gaskets can be and frequently are sized to math intake ports on an engine, failure to match the port size to the gasket can cause leaks
viewtopic.php?f=52&t=5537&p=16750&hilit=1206+1207#p16750

(7) valve seals can be incorrectly installed, the wrong size or damaged due to use of the wrong valve train clearances
viewtopic.php?f=52&t=5306&hilit=valve+seals

(8) valve guides can be installed wrong, damaged or worn.
viewtopic.php?f=55&t=5081&p=14463&hilit=mill+angle#p14463

(9)the rocker stud threads can be a path into the intake port allowing oil to enter the intake port from the valve spring area in some heads

viewtopic.php?f=52&t=7979&p=27511&hilit=valve+guides#p27511

(10)excessively high oil levels in the crank case can cause excessive oil thrown on the cylinder walls to cause excessive oil burning
viewtopic.php?f=54&t=64
(11) in rare cases excessively high exhaust scavenging can cause you to burn a bit more oil

(12) verify your piston to valve clearance and valve train geometry,are correct and if you pull a cylinder head look carefully for detonation damage you won,t be the first guy to find a barely bent valve. or partly melted piston is the cause of excessive oil burning
viewtopic.php?f=52&t=399

http://garage.grumpysperformance.com/index.php?threads/oily-crud-on-intake-valves.12083/#post-57903

viewtopic.php?f=53&t=110&p=33300&hilit=detonation#p33300

viewtopic.php?f=50&t=2883&p=31942&hilit=detonation#p31942

viewtopic.php?f=50&t=8744&p=30912&hilit=detonation#p30912

viewtopic.php?f=87&t=332&p=30684&hilit=detonation#p30684

viewtopic.php?f=50&t=609&p=26934&hilit=detonation#p26934

viewtopic.php?f=44&t=1758&p=26252&hilit=detonation#p26252

 

[87vette81big]

Grumpy can You Elaborate more on excessive oil consumption with High scavenge exhaust systems ?
Like on a Race Car ?
Dual 3", 4", & 5" systems ?
Big primary tube headers 2" & up ?

 

[grumpyvette]

the simple way to explain that is that on many cars the exhaust valve naturally runs a great deal hotter than the intake valve on the cylinder heads for the simple reason its rapidly, and constantly being blasted with hot exhaust gases exiting the cylinder and unlike the intake valve its not being constantly cooled to a small degree by the flow of far cooler intake and fuel charges of air/fuel mix entering the cylinder.
not that temperature difference is HUNDREDS of degrees hotter during the engines operation, which forces the exhaust valve guides and exhaust valve stem to be operated with a significantly greater clearance between the valve guide and valve stem.
some guys even leave the valve seals off the exhaust valves because they believe the exhaust port never sees a negative pressure condition, forgetting that the whole concept of headers is related to cylinder scavenging where the fast moving exhaust gases tend to drag in the next intake charge as they exit the cylinder
a properly tuned set of headers with the correct cam timing can have 4 to 5 times longer and stronger negative pressure sucking oil thru the valve stem to valve guide clearance than the intake port experiences, then consider that the higher heat levels tend to reduce valve seal durability and youll quickly realize the race engines potential to have some oil lost thru that exhaust valve guide

A CORRECTLY TUNED SET OF HEADERS , MATCHED TO A CORRECTLY DESIGNED CAM TIMING HAS A SIGNIFICANT EFFECT ON INTAKE FLOW AND CYLINDER SCAVENGING EFFICIENCY, EXHAUST SCAVENGING CAN BE 5 TIMES STRONGER THAN THE PISTON, MOVEMENT INDUCED NEGATIVE PRESSURE (VACUUM) IN THE INTAKE RUNNERS
ANY significant BACK PRESSURE HURTS the effective scavenging, the header scavenging was supposed to provide. HEADERS are supposed to be designed to increase cylinder scavenging ,thus increasing the next cylinders volumetric fill efficiency,back pressure is always bad, but if you increased the header size too much you reduced the exhaust gas velocity thus reducing the cylinder scavenging, this has zero to do with back pressure, but a good deal to do with effectively using the velocity of the gases flowing out of the cylinder to draw in the next fuel fuel air charge.
in many cases adding an extended collector to the headers will get you back the previous headers efficiency,The exhaust system on a well-tuned race engine can exert a partial vacuum as high as 6-7 psi at the exhaust valve at and around TDC. Because this occurs during the overlap period, as much as 4-5 psi of this partial vacuum is communicated via the open intake valve to the intake port. Given these numbers you can see the exhaust system draws on the intake port as much as 500 percent harder than the piston going down the bore. The only conclusion we can draw from this is that the exhaust is the principal means of induction, not the piston moving down the bore.
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