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High consumption of oil due to Piston ring end gap 4
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BrianPetersen
Mechanical
It is important for the piston ring ends to be (a) parallel, and (b) not have too large a gap - but of course, not too little a gap either. Too big, and the engine has high leakdown and burns oil. Too little, and the ring may seize when the engine gets hot.
End gaps that are not parallel represents a leakage path that is not absolutely necessary.
I learned that ring gaps need to be absolutely parallel the hard way.
End gaps that are not parallel represents a leakage path that is not absolutely necessary.
I learned that ring gaps need to be absolutely parallel the hard way.
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patprimmer
New member
Wider at the bore is worse.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
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Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
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- #6
A tapered compression ring gap would be low on my list, but substituting a better
What is the minimum and maximum gap of the tapered ring? What is your specification for ring gap? What is the oil consumption rate? Is the excessive consumption under load, or high vacuum conditions? what style oil ring are you using? Is the piston ring set bought from a name brand manufacturer? Did this problem just arise with a previously acceptable design? What's the crankcse ventilation design like?
The 1955 SAE paper describing the Chevy V8 development includes a section about high oil use at high vacuum conditions being related to axial oil ring clearance, and improved dramatically when the oil ring was changed to the modern 3 piece axially loaded design. A very similar story, reportedly by a participating factory engineer, is on the internet about the Dodge slant six engine was being developed.
What is the minimum and maximum gap of the tapered ring? What is your specification for ring gap? What is the oil consumption rate? Is the excessive consumption under load, or high vacuum conditions? what style oil ring are you using? Is the piston ring set bought from a name brand manufacturer? Did this problem just arise with a previously acceptable design? What's the crankcse ventilation design like?
The 1955 SAE paper describing the Chevy V8 development includes a section about high oil use at high vacuum conditions being related to axial oil ring clearance, and improved dramatically when the oil ring was changed to the modern 3 piece axially loaded design. A very similar story, reportedly by a participating factory engineer, is on the internet about the Dodge slant six engine was being developed.
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- #7
BrianPetersen
Mechanical
No; that will seize the engine if the tolerance stack-up is not in your favour. What does the piston ring manufacturer specify for ring gap? What does whoever originally designed the engine specify for ring gap? Failing that, look at other comparable engine designs, and see what they specify for ring gap.
patprimmer
New member
The normal method when developing a race engine is to run tighter and tighter gaps until you lose power or scuff up a bore, then add 0.002". This presumes you have a disposable block for testing or you are running at a size where you can still do an overbore to repair.
Of course care is taken to keep them square and parallel.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
Of course care is taken to keep them square and parallel.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
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- #10
JORGEVW,
The reason modern recip piston engines work as well as they do and have low oil consumption is due to the highly developed state of the modern oil control ring. The oil control ring, when working properly, creates a perfectly micro-thin layer of oil on the cylinder liner surface for the compression rings to slide over. This layer of oil is thick enough for the compression rings to achieve partial hydrodynamic contact conditions, thus preventing wear and friction. Yet it is also thin enough to keep the oil film from overheating and flashing-off.
If your engine has excessive oil consumption, it's likely due to the fact that your oil control rings are not working properly. This may be due to oil ring groove fits, piston-to-liner fits (rocking at TDC or BDC), or excessive crankcase pressures.
Good luck,
Terry
The reason modern recip piston engines work as well as they do and have low oil consumption is due to the highly developed state of the modern oil control ring. The oil control ring, when working properly, creates a perfectly micro-thin layer of oil on the cylinder liner surface for the compression rings to slide over. This layer of oil is thick enough for the compression rings to achieve partial hydrodynamic contact conditions, thus preventing wear and friction. Yet it is also thin enough to keep the oil film from overheating and flashing-off.
If your engine has excessive oil consumption, it's likely due to the fact that your oil control rings are not working properly. This may be due to oil ring groove fits, piston-to-liner fits (rocking at TDC or BDC), or excessive crankcase pressures.
Good luck,
Terry
re zero compression ring end gap vs blowby - wh
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