 Compression Check Acceptable Numbers?, Compression Check |
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| 91422.7 |
 Apr 25 2015, 05:20 PM
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#1
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Newbie  Group: Members Posts: 36 Joined: 8-October 14 From: Eugene, Oregon Member No.: 17,991 Region Association: Upper MidWest  |
I'm working on a friends car and we checked the compression with it cold. We retrieved the following readings: #1 cyl 70 lbs, #2-80 lbs., #3-80 lbs., #4-100 lbs., Engine has been running for about 6 months. Based on these readings what do you suggest? Is it ok to go ahead and get the engine running and drive it like it is or are you taking a chance of doing further damage? Run some diesel or ATF through the carbs and see if that would loosen the valves up some, then recheck Compression after a few hundred miles or is it time to tear it down and do a Valve job? Thanks for any suggestions.
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| 91422.7 |
Apr 25 2015, 05:21 PM
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#2
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Newbie Group: Members Posts: 36 Joined: 8-October 14 From: Eugene, Oregon Member No.: 17,991 Region Association: Upper MidWest |
I forgot to mention the engine is a 2.0L out of a 1975 Porsche 914.
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| VaccaRabite |
Apr 25 2015, 06:15 PM
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#3
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En Garde! Group: Admin Posts: 13,419 Joined: 15-December 03 From: Dallastown, PA Member No.: 1,435 Region Association: MidAtlantic Region |
Those are shit numbers.
Was the engine hot, and the throttle wide open? You want to see 100 psi in each cylinder, engine hot and throttle open. If you can't get that it's time to start saving for a top end rebuild. Zach |
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| 91422.7 |
Apr 25 2015, 06:26 PM
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#4
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Newbie Group: Members Posts: 36 Joined: 8-October 14 From: Eugene, Oregon Member No.: 17,991 Region Association: Upper MidWest |
Engine was cold, throttles (dual Weber 40s) were closed!
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| somd914 |
Apr 25 2015, 06:33 PM
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#5
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Member Group: Members Posts: 1,171 Joined: 21-February 11 From: Southern Maryland Member No.: 12,741 Region Association: MidAtlantic Region |
Agree numbers are bad, and agree it has to be done on a hot engine with throttle wide open. However, I thought 120-130 was on the lower end, but I can't seem to find any definitive numbers right now.
You also don't like to see a spread of more than 10% or so. Valve adjustment can affect numbers also. |
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| 91422.7 |
Apr 25 2015, 06:44 PM
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#6
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Newbie Group: Members Posts: 36 Joined: 8-October 14 From: Eugene, Oregon Member No.: 17,991 Region Association: Upper MidWest |
Sounds good, we will get the engine running, let it warm up then recheck compression! Thanks
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| euro911 |
Apr 25 2015, 09:02 PM
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#7
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Retired & living the dream. God help me if I wake up! Group: Members Posts: 8,845 Joined: 2-December 06 From: So.Cal. & No.AZ (USA) Member No.: 7,300 Region Association: Southern California 
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Don't be too quick to judge. The #s didn't real look good on my wife's 1.7 when we first tested it, but decided to let it be for the time being. One day I decided WTH and adjusted the valves - found #3 & 4 were tight (#3 was way too tight).
Interestingly, those were the low reading cylinders. The engine was really peppy after adjusting all the valves. |
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| Mike Bellis |
Apr 25 2015, 10:00 PM
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#8
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Resident Electrician Group: Members Posts: 8,345 Joined: 22-June 09 From: Midlothian TX Member No.: 10,496 Region Association: None 
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Make sure the valves are adjusted properly first.
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| Dave_Darling |
Apr 25 2015, 10:34 PM
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#9
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914 Idiot Group: Members Posts: 14,980 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California
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Adjust the valves and get it running. If those are the cold numbers, the warm numbers will probably be just fine.
--DD |
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| VaccaRabite |
Apr 26 2015, 06:39 AM
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#10
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En Garde! Group: Admin Posts: 13,419 Joined: 15-December 03 From: Dallastown, PA Member No.: 1,435 Region Association: MidAtlantic Region |
Check the valves for sure.
Engine needs to be hot so everything is expanded. Throttle needs to be open so the cylinders are getting air. Valves need to be right so you are not leaking air out of a partially opened valve (valve too tight). After that, you can try a thick oil to bring up compression as you said. But at that point, you are ordering parts and saving money for the head rebuild. As DD said, just getting the engine adjusted and hot will bring your numbers up considerably. Zach |
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| rgalla9146 |
Apr 26 2015, 08:03 AM
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#11
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Advanced Member Group: Members Posts: 4,544 Joined: 23-November 05 From: Paramus NJ Member No.: 5,176 Region Association: None
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The fault with those numbers is mostly the closed throttle. |
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| TheCabinetmaker |
Apr 26 2015, 08:39 AM
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#12
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I drive my car everyday Group: Members Posts: 8,300 Joined: 8-May 03 From: Tulsa, Ok. Member No.: 666 |
Do like the others have said with all plugs removed
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