New engines don't blow oil past the rings. Why not?

VFR750 · 08-31-2015, 03:50 PM

Question: why do rebuilt air cooled engines need so long for rings to seat?

What are they doing to new engines that are different? They don't burn oil. They don't need a break in. They have the same rpm range. They make far more hp per liter.

It can't solely be because air cooled cylinders are different. Round cylinders are round. Rings are round. They do not bend to fit non round cylinders and they don't wear-in with oblong shapes to fit non round cylinders.

It can't be because the engines are flat. Some engine seal very well. Others don't. (Mine). Flat six is not a hindrance to good sealing.

What is it about a well broken in engine? What does it look like and can we build it like that from the get go?

The Surface finish on my Nikasil plated Alusil cylinders seemed amazingly rough brand new. And after 900 miles they had barely smoothed out. After "deglazing" they looked a little smoother. And I went very gently on the red scotchbrite! Don't say that I scrubbed off all of the Nikasil. Didn't happen.

Is there a better way? Can't we replicate modern cylinder surfaces and rings and get non leaking rings upon the first start?

Thoughts?

Tippy · 08-31-2015, 04:00 PM

My engine sealed real quick after I rebuilt it. Maybe I'm missing something here?

VFR750 · 08-31-2015, 04:52 PM

Not all seal quickly. Basically you missed a whole lot of fun...

What cylinders and prep did you do? Which rings?

Tippy · 08-31-2015, 05:05 PM

Total Seal conventional rings, Nikasils, and very light oil?

Was going to go fully dry. I think this is where you guys get into trouble.

mreid · 08-31-2015, 05:35 PM

VFR, it's the Goetze rings you used. The factory matches the ring and cylinder materials carefully to promote an appropriate balance of break in vs longevity.

RedCoupe · 08-31-2015, 07:49 PM

Agree with mreid totally. My dad is a retired engineer who worked for both GM and Ford prior to moving to aerospace. He has talked to me about the extensive testing that was done on new engines to make sure that they had just the right surface on the cylinders, rings that had been tested over and over for quick seating together with the absolute correct initial oil. Everything was designed so that, regardless of who the first driver of the new car was, there would be zero problems seating the rings. On the other hand, when we as enthusiasts overhaul engines, we have to use the "best practices" that we have gained through our own experience along with what we have read in technical books and from folks on forums like this one. There is no way that we can equal the engineering and extensive testing on break in that is done by the manufacturers. A family friend bought a brand new 912 along with two new 911's in the 60's and 70's, and IIRC there was no big deal about breaking in the brand new Porsche engines. Just had to vary speeds and loads over the frirst couple thousand miles and all was good!

VFR750 · 09-01-2015, 07:35 AM

My post was to have the conversation about moving away from the "best practices" which currently causes mixed results.

Maybe I'm trespassing on the professional engine builders proprietary information. I'm ok with keeping that private. They earned it. So telling us what they do differently might not happen. I'm ok if they don't comment on that.

But for the rest of us, can the old best practices be modified knowing today's engines are virtually fool proof?

Can I just inspect a bunch of corvette engines and copy what they do? Seems a pretty stout engine to copy. Esp for my little 3.0.

Henry Schmidt had a great bit of input in a 2004 thread where he stated the standard honing was too coarse. He was saying a surface finish of 3-6 Ra was best. Sounds smoother than my cylinder walls were when new.

The experts recommend deglazing used cylinders. And they seem to reseal well. But the deglazing process in no way is capable of recutting the surface like a home would. So to me, that supports smoother is ok.

So is the new honed surface just rougher than it needs to be, but we stick with it because it's the best practice?

Are the Goetze rings just a little too imprecise, and then require a lot of wear to be seated?

Just asking.....

304065 · 09-01-2015, 08:38 AM

New engines are broken in on propane in a dyno test cell.

An aircooled cylinder distorts like a banana under operating load.

After 2 hours running at widely varying RPM on an engine stand my 901/05 motor had virtually no blowby coming from the oil tank breather. It can be done.