Engine filling with oil?

Robert59095 · 06:04 AM

I have been reading Wayne's wonderful book on engine rebuilding - great ideas and tips. I'm not sure I extracted an answer on this topic from the book, so I thought I would post here and see what people say, maybe Wayne can chime in.

Before I took my 8K-after-getting-rebuilt engine apart, one thing had been bothering me. I would spend 5 minutes warming the car up, and it totally burned off oil the entire time, smoking heavily. When I took the engine apart, there was evidence that the lower part of the pistons were sitting in oil, maybe the lowest 1/2" of the piston. Also when I pulled the cylinders, it was also clear there that the lowest part of the spigots were also immersed in oil (the car sat for a while before being disassembled.)

So, here's the question: it this normal, or should the crankcase always be drained to the level of the suction pipe of the oil pump even after sitting for a while? Does oil drain by gravity from the oil tank to the crankcase? When doing a fresh build, how quickly does the oil pump build pressure, sucking oil from the tank?

I was also suspect of the heads, and have had them rebuilt, so, hoping for no smoke!

- Rob

Flat6pac · 12-31-2018, 07:57 AM

The oil will balance levels between the tank and motor sump.
There is nothing in the system to hold the oil in the tank.
When you start the engine oil is supplied by the tank.
Sump oil is sent to the filter by the scavenge pump section of the oil pump
Between the rings and the exhaust valves some oil seepage into the cylinders
Is possible.
The longer I let my 85 set the more smoke I have on startup
Bruce

Steve@Rennsport · 12-31-2018, 03:28 PM

The fix for this is Rothsport's one-way valve installed in the "S" hose connected the tank to the engine.

Works perfectly.

Trackrash · Trackrash's Garage

Some things to consider. How much oil did you keep in your tank? Very full may make a difference.

Do you park on a slope?

I had a motor smoke a lot on start-up and it turned out the rings in one of the cylinders had all the gaps on the bottom. I thought I had broken rings.

Steve@Rennsport · 01-02-2019, 07:51 AM

Quote:

Originally Posted by Trackrash

Some things to consider. How much oil did you keep in your tank? Very full may make a difference.

Not really, fluids seek their own level, Aristotle articulated it and wrote it down.

Leakage through the oil pump plays a role here as thats where the oil flows from the tank to the case.

Walt Fricke · 01-02-2019, 04:43 PM

How the oil, under only a rather small head of gravity pressure, is able to get through the oil pump and into the sump has always seemed like a mystery. The bottom line is that it does, though, so how doesn't matter much.

Oil is slippery stuff, and hot oil slipperier, so I guess it can flow out along the shafts in the oil pump, which are not sealed, and directly into the sump and indirectly into the scavenge side and then out the pickup tube. The pump shaft and gear tooth and end clearance are fairly tight, but larger than oil molecules I suppose. The leakage in these ways isn't significant for the running engine, but given time stopped it adds up.

It is hard to see how it could rise high enough through the passages after the pressure pump outlet to get to any bearings, though - it has to rise pretty high relative to the tank level to do that, as that all starts up toward the top of the engine case.

Robert59095 · 01-02-2019, 06:36 PM

Trackrash -
Thanks for the tip. My pistons were only wet on the bottom 1/2-3/4", so lowering the oil tank level is a great idea. When my new engine is up and running, I will monitor this. If the static level barely came up to the cylinder bottoms, I'm sure it would smoke less. Also, note to self: be sure to clock my ring gaps at 90 and 270 if I don't like burning oil on startup, thanks!

Rennsport Steve -
You know, I just had Glen Yee go through my SC oil pump. I am going to hit him up with this question. I know he checked all the clearances

Walt -
I haven't run into you or your lovely wife around town in a long time. We may have to fix this somehow. See note to Trackrash about getting my oil pump reworked at Yee Motorsports. I'm sure he made all the clearances in the pump right on the money. I will contact him and post his response here, thanks, Walt!

- Rob

stownsen914 · 05:32 AM

It's possible address the issue of slow seepage into the motor by jacking the car when stored to change the level of the oil tank relative to the motor. Unfortunately this isn't easy to do when you have the stock oil tank. I guess you could jack up the left side of the car - not very convenient. When I store my racecar with a front mounted oil tank, I jack the back up or roll the rear tires up on blocks. Voila, no smoke on startup after long storage.

[Edit] Proximity of the stock oil tank to the motor makes this method a little harder, but I wonder if driving the left side of the car up on some boards would make a difference?

VFR750 · 01-06-2019, 09:54 AM

I rebuilt the top end of my engine 4 times in 4000 miles. At least one set of rings had the gap at bottom every time. One time all 3 on one side were at bottom.

Yes, installed them correctly.

They move. Fairly quickly too.

During the summers I very rarely had smoke on start.

Last week, after sitting for 5 weeks. Big cloud out the pipe that took about 5 seconds to clear out.

May be time to try the check valve.

Robert59095 · 01-08-2019, 04:01 AM

Stownsen914, VFR750 -

It appears that the culprit is a couple of things. Worn out pressure relief pistons allow oil by and wide tolerances in the oil pump both let the oil find its own level when the car is sitting. The check valve may work, but clearly is a band-aid.

- Rob

stownsen914 · 01-08-2019, 05:14 AM

Agreed that there are probably several ways oil can seep its way from the tank to the sump over time until the oil levels in the two are equalized. You can alter the equilibrium by jacking the car when stored to raise the engine relative to the tank. This is easier with a front mounted tank of course like in a racecar. I've been doing it for years, and no more smoky startups. I'm just not sure I it's possible with the tank in the stock location.

Scott

Robert59095 · 01-16-2019, 10:50 AM

Here are a few things I have learned.

Oil leaks into the engine past for oil bypass piston, especially if it is worn. My case will have a fresh 11mm oil bypass mod, so I should be better there. It also leaks through the oil pump. Mine was just rebuilt, and at closer tolerances than factory (thank you Glen Yee). That should help as well.

Third tip. I was always of the head that the more oil in the tank the better, since it is an air- and oil-cooled car. Bad idea. Put minimum in your tank, so that the static level of the oil in the case, once your car has rested sufficiently, will not cover the bottom of the pistons, leading to major oil burning on start up.

- Rob

Steam Driver · Steam Driver's Garage

An interesting thread. When I acquired my long-parked (at least 12 years) SC and drained the oil I expected to find about all of it in the engine, and little in the tank. Not so; it was about 50-50.

Another surprise was that when pulled out of its garage there were zero oil drips under it. Absolutely none; no seepage after all those years. And that was even with a pair of broken head studs.