Small but important
At the bottom of each of our 4 cylinder bores, mounted on the crankcase is a little pipe.
These 4 items are piston oil spray pipes, they squirt oil on the underside of the pistons.
These are piston cooling nozzles, they spray a controlled pressure and amount of engine oil on to the underside of the pistons. The nozzles squirt into a particular area under the piston crown which allows the oil to quickly circulate around the piston underside, conducting the piston's heat to the sprayed engine oil which then falls back to the sump, and circulates with the engine oil through the oil cooler and filter and back around again.
Modern engines run at high temperatures, a turbocharged Delta engine can get very hot in the combustion chamber. The cooling oil jets are important, an overheated piston can try to seize up in its bore and cause serious bore scouring and piston ring damage.
The picture on the left is from the Mahle piston website, it shows the damage done to an overheated Ferrotherm piston (steel piston crown and aluminum skirt) showing seizing marks, with cylinder liner heat damage,
caused by a cooling nozzle failure.
This is a new Integrale piston cooling nozzle
Diesel compression ignition engines run at even higher temperaures, cooling oil on diesel pistons is essential, these pistons have a channel around the underside
which circulates the oil allowing even cooling of the piston crown.
The picture on the right from the Mahle site shows a cooling nozzle broken by a piston skirt. Clearances can be tight, and a misaligned nozzle fitment will cause trouble.
The cooling nozzles are quite delicate, and can easily be bent or broken if they are not removed before working on the pistons or bores, they can be easily damaged by withdrawing the connecting rods.
If the jet pipe is bent it won't spray in the right place,
if broken it will just spray uselessly into the crankcase area.
There is a little ball and spring in the inner end of the spray nozzle base which controls the flow of oil, not letting it dribble out at low oil pressure, and governing the nozzle oil pressure assuring a jet of oil in the right place.
This little orifice can block up and not allow oil through, dirty engine oil and low usage can allow a build up of sediment in the valve and block it.
From Mahle..Failure to observe the oil change interval may result in damage to the cooling oil nozzle. In this case, there’s a risk of polymerization of the engine oil, particularly with biofuels such as rapeseed and soybean oil, which can cause clogging of the cooling oil nozzles.
Click on the Mahle boxes to visit their site
These are my own nozzles, I've been keeping them for a special occasion. The time has come to use them now,
they are old but in good condition with all the ball valves moving freely
Above is a nozzle from an Alfa Romeo engine, the owner found it in his sump. It's on an Alfa forum, and the owner discovered it when changing his sump gasket.
The nozzle has had an impact of some kind, or perhaps many impacts, and broken off.
With my Evo1 engine rebuild being done a second time, I'm making sure all lubrication passageways are cleaned properly, there are many in a Delta block, small diameter oil feeds to these nozzles and the balancer shaft bushes needing attention.
Steve at ERS says 2 of my existing nozzles might be a bit constricted, so I have a used spare set which I've taken to a fuel injection specialist for a good cleaning. The whole engine block has been sent away for ultrasonic cleaning.
New valves are available at the usual outlets, at various prices. I have learned the importance of these little nozzles, and cleanliness in general.
Shown above is one of the pistons used in my
engine's first rebuild,
a .40 thou oversize item from Tanc.
These survived well and can be used again.
Never make any assumptions on an engine rebuild,
check your own work, and anybody else's
who is working on your engine.