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| | | | Joined: Jun 2012 Posts: 258 Shop Shark | | Shop Shark Joined: Jun 2012 Posts: 258 | Hey all
what should the stock compression numbers be on a 1955 261? (cold).
mine has a 848 head on it, and I did a compression test this morning, I just wanted to know how the numbers compare.
best regards
jay | | | | | Joined: Feb 2002 Posts: 12,029 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Feb 2002 Posts: 12,029 | what's most important is that all cylinders be close to the same, if there's a wide variation highest to lowest you should consider an overhaul
Bill | | | | | Joined: Dec 2000 Posts: 3,399 Gas Pumper | | Gas Pumper Joined: Dec 2000 Posts: 3,399 | My numbers, recently tested on a 1958 261 with the 848 head are as follows:
138, 139, 138, 140, 139, 138
Hope this helps!
| | | | | Joined: Aug 2013 Posts: 568 Shop Shark | | Shop Shark Joined: Aug 2013 Posts: 568 | At least they're all similar. I don't know what the exact recommended numbers are.
I can explain it to you, I can't understand it for you.
| | | | | Joined: Aug 2013 Posts: 568 Shop Shark | | Shop Shark Joined: Aug 2013 Posts: 568 | Everything I've researched shows your in range. The sites i looked at said between 130-150 your in the middle with a 2psi difference. That's good I believe.
I can explain it to you, I can't understand it for you.
| | | | | Joined: Sep 2001 Posts: 29,269 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,269 |
1955 2nd series 6 cylinder (Shop Manual) - on a truck engine that has been run for ". . several minutes and allowed to warm up and lubricate the valve mechanism", with all spark plus removed : 130 pounds or better with all 6 readings within 5-10 pounds of each other.
| | | | | Joined: Mar 2010 Posts: 10,275 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,275 | The things that effect compression checks are, your gauge may not be calibrated the same as the guys gauge to which you are comparing your numbers, and the barometric pressure on a given day affects the reading. This means that you could have different readings on different days with the same gauge if a high or low pressure weather front should role through on day two. Don't get hung up on the value of the actual number as long as the difference between cylinders is not significant. Could all cylinders/valves be worn exactly equal and give low readings within 2% of each other? Possible I suppose, but extremely unlikely.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Aug 2013 Posts: 568 Shop Shark | | Shop Shark Joined: Aug 2013 Posts: 568 | I just check for normalcy. A digital thermometer is a great tool to check for proper combustion. Shoot each cylinder and exhaust port. By far the most accurate i think. Plus you don't have to remove the plug. I'm lazy...
Last edited by Hollow65; 09/03/2013 10:22 PM.
I can explain it to you, I can't understand it for you.
| | | | | Joined: Jun 2012 Posts: 258 Shop Shark | | Shop Shark Joined: Jun 2012 Posts: 258 | I was wanting to know what a cold 261 stock engine would read.
the 130 number seems to be on a warmed up 261.
thanks everybody | | | | | Joined: Mar 2010 Posts: 10,275 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,275 | A cold check will only tell you if you have a dead cylinder(no compression to speak of). You really need to do it on a fully warmed up and normalized engine to get usable data for comparing the individual cylinder pressure readings.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Oct 2007 Posts: 91 'Bolter | | 'Bolter Joined: Oct 2007 Posts: 91 | I did a cold check on my 261 with an 848 head and they were all in the 150 -155 range. | | |
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