How airtight is a cylinder?

That is because they don't start very well. There are a LOT of starting/ignition methods for engines. Hot tube, hot bulb, preheated dome, glow plug, preheated chamber, gas start (switching to diesel when warm) flame licker, wick start, high and low tension ignitors, spark plugs are just a few off the top of my head. I've had at least one of each.

Genius.

No, Delco became Delco way way back.

I'm not sure of the history of Dayton (the motor company,) but I think they're more than a Grainger "house" brand.

I own a Dayton Speedaire light weight portable air compressor.It is an oiless rotary valve air compressor driven by an electric motor.I bought it second hand from a guy about thirty years ago.I only used it to air up the tires on my vehicles.I think the graphite vanes (I think they are made of graphite) have worn down because now it will only pump up tires to about thirty pounds air pressure.There is a slide lever valve thingy on the air hose, but set wide open,it will only pump up to about thirty pounds air pressure I wonder where I can buy some new vanes? cuhulin

I don't think those vanes are graphite, but some other hard material, not entirely easy to come by. I knew a guy who rebuilds those rotary-type compressors, used for the compressed air in commercial #6 boilers, to atomize the spray of oil through intricate nozzles. I used to know the name of this compressor--it's very common in the oil burner industry, used by the company Industrial Combustion on their "DE" burner. Makes a helluva racket. Most boiler houses have a rebuild place for these compressors--they might be able to hook you up with a rebuilder who can supply you with this material.

Didn't know SpeedAire was Dayton. Their small horizontal piston/oil compressors are very good, cast iron heads, surprisingly quiet. Campbell Hausfield told me they make those heads for Speedaire, as well as for the HD/Husky brand. Iffin you want to go piston/oil. :)

I have seen articles in old magazines before about converting lawn mower engines into jig saws, old style tredle sewing machines too.Look in the June 2007 Popular Science or Popular Mechanics magazine and you will see an article about a guy who converted a small one cylinder horizontal shaft gas engine into a six stroke steam engine.The article says the exhaust from the engine is so powerful it was blowing the paint off of the ceiling. cuhulin

I bet it is graphite. The vacuum pumps on our aircraft have graphite vanes in them.

Dan

Well, it's an awfully hard/tough graphite, then. Hard to imagine it being graphite. But whatever it is, Industrial Combustion should be able to tell you who makes those rotary (rebuildable) compressors.

The leakage of a cylinder will depend on how carefully it is built, meaning how close are the clearances and tolerances of the cylinder, piston, ring land clearances, valve seat sealing and sometimes, sparkplug thread seal.

A properly prepared racing engine will show a leakdown value of about

2%. That is, when 100 psi is applied to the chamber, about 2 psi gets away due to leakage. In a well worn production engine, the leakage value could easily be in the range of 20-25%. A junk engine will show 40-50% leakage. A blown piston will show 100% leakage.

If a gas pressure of 100 lbs were applied to a 4 in piston, the downward force would be about 1256 lbs. The applied force is simply multiplied by the area of the piston. In a real engine, combustion pressure can be much higher, perhaps as high as 300-400psi. But these combustion pressures only last for about 20 crankshaft degrees and then fall as the piston moves downward.

A high performance engine would have a BMEP of about 10-12 BAR, or about 145-175 psi average for the entire cycle. Some race engines will run a BMEP 0f 15-16 BAR, a turbocharged diesel about 24-28 BAR, and a top fuel drag engine ???

Since the combustion pressure is generated very quickly, even a leaky piston will still run (albiet poorly) because the gas does not have time to get past the rings and piston skirt.

The race car mechanics I am familiar with set up a racing engine very LOOSE. The rationale is that it will be running hotter than a production engine, so if you set it to production clearances it may seize up when it gets to operating temperatures, so you need to set it loose. Thus, pressure measurements on a cold engine will be less than (or, more leakdown) a stock, new, engine, and more like a well worn stock engine.

The common description of the old Offy engines as sounding like a threshing machine were very apt. It was set up with large clearances and the cam tower used straight spur gears. Once warmed up and on the track under competition it sounded fantastic, though.

That whole paragraph makes absolutely NO sense. If you put 100 PSI of air pressure into ANY piston engine cylinder, it will leak back to zero over a few seconds of time. The difference between a well-sealed cylinder and a worn out one will be in how LONG the pressure takes to drop, not in how many PSI it drops!

Steve wrote in news:eradnYwMcKGxnx3bnZ2dnUVZ snipped-for-privacy@texas.net:

There is, after all, an air gap at the ends of each piston ring...

I used to own an old one lunger cast iron engine that I bought at a junk yard many years ago.The piston was froze up when I bought the engine.I brought the engine home and I removed the spark plug and I poured some motor oil in the engine and I waited a few weeks.The crankshaft still wouldn't turn.Then I removed the cylinder head and I used a 2 x 4 and my sledge hammer.That piston wouldn't budge at all.The next time I hauled some junk to the junk yard, that engine went back to the junk yard too. cuhulin

He is writing about using a leakdown gauge.

After how many seconds?

--scott