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| | | | Joined: Aug 2011 Posts: 60 Wrench Fetcher | | Wrench Fetcher Joined: Aug 2011 Posts: 60 | Does anyone know what cylinder pressure I should have on my 54 235? The mileage is unknown. anything to look for when I pressure test it?
Thanks!!
Bill Muse | | | | | Joined: Sep 2001 Posts: 29,269 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,269 | | | | | | Joined: Feb 2004 Posts: 29,771 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,771 | The problem is, no two compression gauges are likely to show the same pressure, even when testing the same cylinder. 100+ PSI is probably good, as long as all cylinders are within 5%-10% of each other. A better test than compression is probably a cylinder leakdown test, where a known air pressure is introduced into each cylinder with the crankshaft locked, and each one is measured for pressure loss. For instance, set a pressure regulator to 100 PSI with the air line blocked, then plug the air line into a spark plug hole. Listen for air leaking from the carburetor, tailpipe, and oil filler. If the pressure drops to 90 PSI, that cylinder has 10% leakage, and you can tell whether rings or valves are causing the leak. Bubbles in the radiator indicate a head gasket leak. Check all the cylinders and compare results.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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| | | | | Joined: Jan 2016 Posts: 631 'Bolter | | 'Bolter Joined: Jan 2016 Posts: 631 | Redneck compression gauge..........hold your thumb over the hole, crank the engine, thumb gets blown off the hole = adequate compression to start and run.
Last edited by showkey; 08/17/2016 3:02 AM.
| | | | | Joined: Dec 2008 Posts: 1,922 'Bolter | | 'Bolter Joined: Dec 2008 Posts: 1,922 | The quick rule-of-thumb (not science!) is static compression ratio X between 15 and 20, but it's going to be wrong with a hot cam.
8:1 = 120-160 psi, etc. | | | | | Joined: Mar 2010 Posts: 10,272 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,272 | Redneck compression gauge..........hold your thumb over the hole, crank the engine, thumb gets blown off the hole = adequate compression to start and run. Y'all can save you some time for beer drinking and carrying on and whatnot by multitasking and take ahold of the plug wire while your trying to keep your thumb from getting blowed off of the spark plug hole. A redneck man test, if you will.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Jan 2016 Posts: 631 'Bolter | | 'Bolter Joined: Jan 2016 Posts: 631 | ^^^^^^^^ That's not too far off .........summer college job in small engine repair.
You see 20 engines a day that need quick evaluation while the customer is waiting for an estimate in 10 minutes or less with 95% accuracy
Thumb ....blow off...OK........NO...sell engine work, stuck valve, or worse etc
Spark.......1/4" blue OK........NO...sell electrical work, points, coil, wiring, safety interlock switches, black box etc
Last FUEL....smells bad, ....yes...sell carb work with flush, wet vs dry plug sell carb clean and service.
Last edited by showkey; 08/18/2016 2:50 AM.
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