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08-20-2004, 10:53 PM
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#1 |
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madcow
Join Date: May 2004
Location: Glendale, Arizona
Posts: 86
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Compression PSI
I checked the compression on my 1970 1/2 ton SWB 350-4 bolt today and every cylinder was between 120-130 psi. The manual states it should be 150 psi. My question is, should I rebuild or get a new long block, or leave it as is? The motor is a bit tired, and I'm getting ready to repaint it, so I'm debating if I should change it out before painting.
Any suggestions? |
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08-20-2004, 10:59 PM
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#2 |
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Registered User
Join Date: Jul 2003
Location: north of Phx AZ about 30 miles
Posts: 698
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That is not really bad compression numbers. Mkae sure you have a freshly charged battery, no sparkies in the block. Also do a oil squirt in the cylinder test to compare the numbers, it will also tell you if the rings are worn or the valves are shot. A little more work here will pay off in saving you money for work that you did'nt need to do.
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Andy,Phx AZ '67 C-10 (Ahhh, done at last. Well there is that disk front end I want to put in and...) "23 C-Cab-sold '48 Ford 8N tractor(still working) '67 Scout(Now on the road) '70 MG B.-sold |
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08-20-2004, 11:02 PM
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#3 |
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Registered User
Join Date: Jun 2004
Location: Gainesville, Fl
Posts: 382
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yeah I would definetly not re-build if the numbers are that high, of course I have no clue what you are going to use it for, daily driver? street/strip?
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Man I need another 67-72!!! 
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08-20-2004, 11:05 PM
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#4 |
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Saving 1 truck at a time!
Join Date: Aug 2001
Location: Kent, WA
Posts: 6,465
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Did you test with the throtte wide open...it makes a big difference! Also crank about 3-5 compression strokes...I know you probably know this but I forget sometimes so I am only providing you a reminder here...LOL!
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'68 C20 Longhorn 50th Anniversary 400/TH400 '68 C20 Longhorn 50th Anniversary 468/TH400w/buckets '72 C20 Halfhorn (Longhorn w/o cab and front clip) '69 Flxible Cruiser (look up ugly in the dictionary) |
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08-20-2004, 11:05 PM
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#5 |
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Fabricate till you "puke"
Join Date: Jun 2002
Location: Ill
Posts: 9,402
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one of the biggest factors in comp(cranking pressure), is that all cyls are within 10 % highest to lowest. it doesnt sound too bad from that standpoint. you could also have a loose timing chain, retarding the cam timing & also causing slightly lower cranking #, or if the eng was not warmed up, & throttle proped open during the test, the # will read a little low....just fruit for thought. Best of luck,crazyL
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69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears.... |
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08-21-2004, 06:00 PM
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#6 |
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madcow
Join Date: May 2004
Location: Glendale, Arizona
Posts: 86
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Thanks for the information.
The engine was cold when I did the test, and the throttle was not wide open. Do you have any idea what percentage difference +/- these two things make on average.? I assume that the PSI would go down, but by how much? 5-10% maybe? Its not a daily driver.....I use it to go to Home Depot, kids baseball practice, etc. I can live with it this way if I can get away with it. Thanks for the help. |
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