Can an engine really be too tight?

timwinters

timwinters

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@Ted DuPuis

I've always thought that the theory "if it doesn't burn any oil at all then it's too tight and won't last as long" is an OWT (or more aptly put, complete BS).

But I'm curious as to your opinion.

Apologies in advance if you've already discussed this here.
 
I personally haven't seen anything that indicates "too low" oil consumption results in a reduced service life. My opinion is that it's BS that's written by people who think it sounds good in theory but have no evidence to back it up.

On the other side of it, high oil consumption usually isn't a problem until you get into operational issues (i.e. I'm going to run out of oil on my flight), but at a certain point people just decide they "need" to do something about it. I haven't seen high oil consumption engines fail at any dramatically higher rate, either. The concern is if the high oil consumption is coming from a cracked case or the like.

Basically, do your best to fix oil leaks when you can, track oil consumption, if it changes, try to figure out why. Also look at what your engine likes for an oil level. I find the older an engine gets, the lower oil level it's happy with. Again, I've not seen anything that indicates this is a problem, just that it's a side effect of age and looser clearances.
 
I have an engine,,,
An old Motto Guzzi, the over sized Porsche pistons in overbored Guzzi cylinder jugs are loose as a goose.
The Rings,,, they are ,, just right.
Runs great, doesnt burn any oil.
Creeping along, for miles leaving the Oyster Run in Anacortas in the HOT sun,
We crept passed hundreds of "right engines" that had to pull off and Wait to cool off due to Heat Seizure!

I drove on...
 
Yes an engine can be too tight. Engine designers take thermal expansion into account when setting min and max dimensions of parts. If parts are used that are out of spec parts can seize,slap, scuff and a whole lot of other bad things.

Bob
 
robert lomax said:
I have an engine,,,
An old Motto Guzzi, the over sized Porsche pistons in overbored Guzzi cylinder jugs are loose as a goose.
The Rings,,, they are ,, just right.
Runs great, doesnt burn any oil.
Creeping along, for miles leaving the Oyster Run in Anacortas in the HOT sun,
We crept passed hundreds of "right engines" that had to pull off and Wait to cool off due to Heat Seizure!

I drove on...
Click to expand...
Damn this traffic jam...
 
robert lomax said:
I have an engine,,,
An old Motto Guzzi, the over sized Porsche pistons in overbored Guzzi cylinder jugs are loose as a goose.
The Rings,,, they are ,, just right.
Runs great, doesnt burn any oil.
Creeping along, for miles leaving the Oyster Run in Anacortas in the HOT sun,
We crept passed hundreds of "right engines" that had to pull off and Wait to cool off due to Heat Seizure!

I drove on...
Click to expand...

I'm talking about 4 and 6 cylinder horizontally opposed aircraft engines using only the finest technology from the 1930's and '40's..like those found in the typical single engine Piper and Cessna. :)

unsafervguy said:
Yes an engine can be too tight. Engine designers take thermal expansion into account when setting min and max dimensions of parts. If parts are used that are out of spec parts can seize,slap, scuff and a whole lot of other bad things.

Bob
Click to expand...

I'm talking specifically about burning oil, not clearances. Assuming you were also talking about burning oil then exactly what credentials do you have that would allow you to make such a definitive statement?
 
robert lomax said:
I have an engine,,,
An old Motto Guzzi, the over sized Porsche pistons in overbored Guzzi cylinder jugs are loose as a goose.
The Rings,,, they are ,, just right.
Runs great, doesnt burn any oil.
Creeping along, for miles leaving the Oyster Run in Anacortas in the HOT sun,
We crept passed hundreds of "right engines" that had to pull off and Wait to cool off due to Heat Seizure!

I drove on...
Click to expand...

I think "Robert" is definitely wrapped too tight! :goofy: :loco:
 
You may be right,,,
I may be crazy...
But I may just be the Lunatic you're lookin for.....

I may be wrapped tight,, but
I am wound loose...

hope this helps
 
Remember how I found you there
Alone in your electric chair

yup
 
there are only two ways an engine can burn oil. 1. It gets buy the oil control ring.
2 it gets through the valve guides. So how do you "tighten" it up without reducing clearances of those parts?

Bob
 
timwinters said:
@Ted DuPuis

I've always thought that the theory "if it doesn't burn any oil at all then it's too tight and won't last as long" is an OWT (or more aptly put, complete BS).

But I'm curious as to your opinion.

Apologies in advance if you've already discussed this here.
Click to expand...
I don't know how it can be too tight if all the clearances are within tolerance. if so, it will turn freely, and not burn oil.
 
unsafervguy said:
Yes an engine can be too tight. Engine designers take thermal expansion into account when setting min and max dimensions of parts. If parts are used that are out of spec parts can seize,slap, scuff and a whole lot of other bad things.

Bob
Click to expand...
How can you assemble any aircraft engine with out using the proper parts and checking each part for proper fit?
I once had Lycoming send me a set of .002" under rod bearings for a standard crank. It was very apparent right away that they were the wrong fit. Each step in the assembly procedure has a quality control check. you can't make these engines too tight when you follow the book.
 
Cpt_Kirk said:
Come again?
Click to expand...
Pistons are slightly oval, normally having a slightly larger diameter perpendicular to the piston pin. The part of the piston that's in line with the pin has more mass, which is required for strength. When heated, the area with more mass expands more than the part that's perpendicular to the pin, which is larger to begin with, causing the piston to become more round.
 
GlennAB1 said:
Pistons are slightly oval, normally having a slightly larger diameter perpendicular to the piston pin. The part of the piston that's in line with the pin has more mass, which is required for strength. When heated, the area with more mass expands more than the part that's perpendicular to the pin, which is larger to begin with, causing the piston to become more round.
Click to expand...

While a few engines are manufactured with cam ground (a better description than "oval") pistons, by no means are all pistons constructed in this manner as you assert.
 
If you want to be pedantic about it, ok. But for air cooled engines, yes, they're oval.

And yes, all engines are air cooled. Some are helped out by water, oil... :)
 
GlennAB1 said:
Pistons are slightly oval, normally having a slightly larger diameter perpendicular to the piston pin. The part of the piston that's in line with the pin has more mass, which is required for strength. When heated, the area with more mass expands more than the part that's perpendicular to the pin, which is larger to begin with, causing the piston to become more round.
Click to expand...
Good to know. Thanks
 
Tom-D said:
How can you assemble any aircraft engine with out using the proper parts and checking each part for proper fit?
I once had Lycoming send me a set of .002" under rod bearings for a standard crank. It was very apparent right away that they were the wrong fit. Each step in the assembly procedure has a quality control check. you can't make these engines too tight when you follow the book.
Click to expand...

i know you and I can't because we use the book and the proper parts and tools. but I am sure you have seen even more crazy stuff than I have in an airplane.

bob
 
unsafervguy said:
i know you and I can't because we use the book and the proper parts and tools. but I am sure you have seen even more crazy stuff than I have in an airplane.

bob
Click to expand...
that's why I use approved methods and practices as required by FAR 43.
 
This is not an engine thread. It's an oil thread. I want my money back.
 
I'd put a wager in the "no" category. If an engine is too tight in the fact that it does not have the correct ring end gap clearances, it will burn oil like crazy within a couple hours of use. But if the engine is running correctly and not using oil, I wouldn't be concerned. It doesn't need to burn oil to run right.

Out clunky air cooled engines just have a serious tendency to burn oil slowly. They aren't necessarily designed to do so.
 
All engines burn oil, period. Some just burn more than others, and some do not burn a really detectable amount. But they still burn oil.

I'd bet many people would be amazed at how much money is spent by OEMs on oil consumption tests and how to control it. Maybe not so much on aircraft engines but it definitely happens on new on and off road engines.
 
Ted DuPuis said:
On the other side of it, high oil consumption usually isn't a problem until you get into operational issues (i.e. I'm going to run out of oil on my flight).
Click to expand...

We ran an R-2600 which was burning, blowing, throwing, slinging 5 GALLONS per hour for a bit on a B-25. Oil would drip off the vertical tail on that side after a flight. With 30 gallon capacity, we didn't worry about running out, but we got tired of the mess and expense of the oil consumption.
 
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Checkout_my_Six said:
burn?....or consume?

Ahem....mine consumes it doesn't burn. :D
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Mine sips oil. Somewhat daintily, I might add. :D

On an I0-320, all the Van's guys (and most others?) run it right at the 6-quart level...any more than that, and the excess ends up on the belly through the breather tube.
 
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