How did oil get to the pistons pre 1970?

RobFrost · 07-08-2024, 12:00 AM

How did oil get to the pistons pre 1970? I mean the to piston/cylinder wall interfaces, before piston squirters. I have an engine in which a couple of cylinders overheated and smeared their piston rings up the sides of the pistons. That may or may not have been due to an oiling problem, but I want to verify that mechanism is working. By what mechanism were they depending upon to get oiled anyway?

FWIW before you tell me to add oil squirters, I intend to notch the con rods to squirt oil under the poston crown, which will probably solve the problem anyway but the question stands...

Steam Driver · Steam Driver's Garage

Pre-1970 (actually I think it was after that) the cylinders were oiled in the way they had been from the beginning (more or less) of ICE’s. That was by oil slung from the rod bearings or in the case of non-pressure lubrication by the oil splashed on them by the crank from splash lubrication.

Piston squirters were added primarily to shoot oil on the back side of the piston crown for cooling purposes as engine output and bore diameter went up. Any cylinder wall lubrication was a secondary effect. Diesel engines had oil squirters for years before that for piston cooling.

Unless you intend to use the engine extremely hard the original arrangement should be adequate. A lot of us have run the early engines for miles that way with no issues.

RobFrost · 05:01 AM

Quote:

Originally Posted by Steam Driver

Pre-1970 (actually I think it was after that) the cylinders were oiled in the way they had been from the beginning (more or less) of ICE’s. That was by oil slung from the rod bearings or in the case of non-pressure lubrication by the oil splashed on them by the crank from splash lubrication.

Piston squirters were added primarily to shoot oil on the back side of the piston crown for cooling purposes as engine output and bore diameter went up. Any cylinder wall lubrication was a secondary effect. Diesel engines had oil squirters for years before that for piston cooling.

Unless you intend to use the engine extremely hard the original arrangement should be adequate. A lot of us have run the early engines for miles that way with no issues.

Thanks. How does oil get there? Is it fed from the nose bearing through the crank, or does it enter the crank at the main bearings? Trying to eliminate all possible causes of a couple of cylinders running dry.

I'm raising compression to 10.5, increasing bore to 86mm, increasing ports and intake stacks a few mm, switching to a hotter cam and upping the redline to 7,200 so a little extra cooling will protect me from some of the adverse effects of that.

I guess the damage must have been caused by the whole engine running short of oil. (Engine of unknown history).

Steam Driver · Steam Driver's Garage

Oil enters the crank via the main bearings and then exits the crank at the rod bearings lubricating them, then squirts out around them and is slung by the crank out onto the cylinder walls, pistons, and everywhere else.

Aside. On 911’s and practically every other engine oil is fed into the crank via the mains the oil pressure is high because the oil must fight the centrifugal force (from the spinning crank) opposing it. Some engines, like the 917, feed oil into the crank from the ends, so centrifugal force is actually assisting the oil pump. I think maximum pressure for the 917 was around 35psi. I may be incorrect about that; if I am I’m sure someone will correct me!

stownsen914 · 07-08-2024, 02:25 PM

Not to mention splash oiling from the crank and rods whipping through oil that collects in the sump, and slinging that around too.

As for the need for squirters in your engine, with your mods, naturally squirters would be a nice addition, but probably not technically necessary. Notching the rods is supposed to help a bit. My guess if you’re not doing extended high RPM like track use it’ll be fine.

Let’s see if any pro builders chime in.

Tyson Schmidt · 11:16 AM

Piston squirters were not installed for cylinder lubrication. It was for piston crown cooling.

By adding the squirters, the cooling effect allowed them to reduce the thickness of the top compression ring, since it no longer had to conduct as much heat away from the crown. This reduced friction and improved sealing.

RobFrost · 07-13-2024, 07:54 AM

Quote:

Originally Posted by Tyson Schmidt

Piston squirters were not installed for cylinder lubrication. It was for piston crown cooling.

By adding the squirters, the cooling effect allowed them to reduce the thickness of the top compression ring, since it no longer had to conduct as much heat away from the crown. This reduced friction and improved cooling.

I presume the oil cools the piston crown directly, too.

Sent from my SM-S918B using Tapatalk

Tyson Schmidt · 08-01-2024, 11:19 AM

Edited my previous post. The narrower top ring reduces friction and improves sealing, not cooling.

To answer your question, yes the oil directly cools the piston crown, Porsche claims by 50 deg. C which is significant.

CANPOLU · 12:44 PM

Before 1970, oil reached the pistons through a splash lubrication system, where oil was thrown onto the cylinder walls by the motion of the crankshaft. Some engines also used an oil pump to circulate oil through internal channels. Regular maintenance, such as checking oil levels and changing the oil filter, was essential to ensure proper lubrication and engine health.

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