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how air-tight are auto combustion chambers 3
- Thread starter markhutch
- Start date
GregLocock
Automotive
what about the valve seats?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376
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- #4
patprimmer
New member
There is a test called a leak down test that measures exactly how much leaks past under test condition. In a running engine the amount varies greatly with test conditions and the condition of the engine. Oil and temperature, rpm and especially wear all play a part.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
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- #5
markhutch,
There is no such thing as a 100% air-tight recip piston engine cylinder. As others noted there are two areas where gas leakage occurs in the cylinder working space- past the valve seats and past the rings. Leakage past the rings accounts for the largest percentage, while leakage past the valve seats is usually fairly small under normal conditions. Of the leakage past the rings, some leakage is between the ring face and bore surface, some goes past the piston ring land and lower ring face, and some goes through the ring gap space.
The typical static leakdown test and motoring compression pressure test will give a qualitative indication of the cylinder's sealing ability versus an established benchmark. But what really matters is the cylinder sealing ability under dynamic firing conditions. The high temperatures, high pressures, and significant dynamic forces that exist in a firing engine at high rpm can all affect the sealing function of rings and valves.
Here's a good technical reference on piston ring conformability:
Hope that helps.
Terry
There is no such thing as a 100% air-tight recip piston engine cylinder. As others noted there are two areas where gas leakage occurs in the cylinder working space- past the valve seats and past the rings. Leakage past the rings accounts for the largest percentage, while leakage past the valve seats is usually fairly small under normal conditions. Of the leakage past the rings, some leakage is between the ring face and bore surface, some goes past the piston ring land and lower ring face, and some goes through the ring gap space.
The typical static leakdown test and motoring compression pressure test will give a qualitative indication of the cylinder's sealing ability versus an established benchmark. But what really matters is the cylinder sealing ability under dynamic firing conditions. The high temperatures, high pressures, and significant dynamic forces that exist in a firing engine at high rpm can all affect the sealing function of rings and valves.
Here's a good technical reference on piston ring conformability:
Hope that helps.
Terry
- Thread starter
- #6
patprimmer
New member
I would have thought an auto combustion chamber is one in an engine for an automobile.
Zero leak down means the rings are butted out. 17% means rings or valve seats or gasket is real bad.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
Zero leak down means the rings are butted out. 17% means rings or valve seats or gasket is real bad.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
- Thread starter
- #9
winfieldblue
Automotive
Zero leak down means the rings are butted out unquote
I haven't used "total seal 2 piece rings" but would assume that Dicer is running them in his j.d.m.
I haven't used "total seal 2 piece rings" but would assume that Dicer is running them in his j.d.m.
patprimmer
New member
A JDM engine is Japanese Domestic Market. It is a term used in the second hand engine industry to identify engines sold OEM in Japan as JDM spect are often higher power output than engines for other markets. Once it is rebuilt to non OEM spec it is no longer truly JDM.
The odds of one being retrofitted with gapless rings is about ten zillion to one, but I suppose it is possible but it's no longer JDM.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
The odds of one being retrofitted with gapless rings is about ten zillion to one, but I suppose it is possible but it's no longer JDM.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
Even so-called (1 or 2 piece) "gapless" ring designs still have leak paths. It's just that the cross section area is reduced and the length of the leak path is greatly increased and more convoluted. This combination reduces the leakage flow rate by increasing the flow resistance.
Due to the high peak combustion pressures and small compressed gas volume at TDC conditions, even an extremely small piston ring leak path can impact engine efficiency.
Due to the high peak combustion pressures and small compressed gas volume at TDC conditions, even an extremely small piston ring leak path can impact engine efficiency.
pontiacjack
Electrical
FYI- The "percentage" read by a leakdown tester is not conveniently translated into more precise terms (such as a flow rate of the "leak")- except at 0% and 50% and 100%. 0% and 100% are obvious. At 50% the "leak" flows indentically to the tester's internal orifice. The industry standard orifice is .040" diameter. So... although 50% leakdown is generally thought of as a trashed cylinder, the "leak" is equivalent to a .040" hole; as you ponder this, keep in mind the typical dimensions of ring end gaps.
Also consider how slowly a gas can pass through a "leak" in relation to a piston's cycle time of a running engine. An illustration is the old Falcon (170 c.i., about 8:1 C.R.) that I drove (on all six cylinders) for many tens of thousands of miles with a "dead" cylinder (tester showed over 99% leakdown). Yet the only way to make that cylinder misfire was to pull the plug wire! Of course the cumulative result of the blowby was a noticeable volume of crankcase fumes out the vent (no PCV).
Also consider how slowly a gas can pass through a "leak" in relation to a piston's cycle time of a running engine. An illustration is the old Falcon (170 c.i., about 8:1 C.R.) that I drove (on all six cylinders) for many tens of thousands of miles with a "dead" cylinder (tester showed over 99% leakdown). Yet the only way to make that cylinder misfire was to pull the plug wire! Of course the cumulative result of the blowby was a noticeable volume of crankcase fumes out the vent (no PCV).
thruthefence
Aerospace
"Of course the cumulative result of the blowby was a noticeable volume of crankcase fumes out the vent (no PCV)"
I had a similar run out engine (in an econoline van) that I simply vented the crankcase vent (disconnecting the road draft tube) to a 1 gallon clorox jug, loosely filled with teflon plumbers tape. The tape attracted the oil mist, which eventually formed droplets settled to the bottom of the jug, to be dispensed back into the sump at next oil check interval. In this way, I was able to extend my oil usage from 1 qt/ 50 miles, to 1 qt/ 150 miles.
I had a similar run out engine (in an econoline van) that I simply vented the crankcase vent (disconnecting the road draft tube) to a 1 gallon clorox jug, loosely filled with teflon plumbers tape. The tape attracted the oil mist, which eventually formed droplets settled to the bottom of the jug, to be dispensed back into the sump at next oil check interval. In this way, I was able to extend my oil usage from 1 qt/ 50 miles, to 1 qt/ 150 miles.
JayMaechtlen
Industrial
I had a Plymouth 170 cid slant six- if I didn't clean number five spark plug often enough it would pack up solid. (catch it soon enough, could just scrape the crud out and keep running it.) As long as it had a serviceable plug in that cyl, it ran fine.
After I replaced it with a fresh 225, I tore it apart for inspection. The 3-piece oil ring in that bore was worn to where the central expander was riding on the cylinder bore.
Jay Maechtlen
After I replaced it with a fresh 225, I tore it apart for inspection. The 3-piece oil ring in that bore was worn to where the central expander was riding on the cylinder bore.
Jay Maechtlen
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