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Compression test results |
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Smitty52 
AMC Apprentice 
Joined: Aug/05/2008 Location: Bolton Landing Status: Offline Points: 227 |
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 Topic: Compression test resultsPosted: Jan/16/2017 at 1:07pm |
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The 304 in my 74 Jav just had not seemed to run right before I put it away for the winter. I warmed it up today and did a compression test. Seems #1 is lower than the rest. These numbers are with the throttle closed
Cyl # Dry Wet 1 95 122 2 120 125 3 140 152 4 120 130 5 140 170 6 125 150 7 130 160 8 125 165 I did a retest on #1 and it was 110 dry. May have been some left over oil in there from the wet test although I redid the dry test after doing all the other cylinders. Seems to be a lot of variance between cylinders. AFAIK the engine is original and the odo read 73K. It does not run or drive like a 173K car though. Thinking it may be time to find a rebuilt 360 long block. What do you all think?
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AMO#8454, AMCRC# 8066
69 Ambo coupe, 401, M12, 66 Ambo 990 Wagon, 327,PW,PB,PS,posi,AM/FM,AC 74 Jav 360 auto ac 2003 FLHTCI, 1977 Yamaha XS750 2015 Chry 200, 2006 Pacifica |
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purple72Gremlin
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Charter Member Joined: Jul/01/2007 Location: Illinois Status: Offline Points: 16611 |
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Posted: Jan/16/2017 at 3:39pm |
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throttle should be open................. Just me, but Id do a leakdown test.......that will tell you more IMHO.
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Smitty52
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Joined: Aug/05/2008 Location: Bolton Landing Status: Offline Points: 227 |
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Posted: Jan/16/2017 at 6:20pm |
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Yep, I had always been taught to do the test with an open throttle. Not sure why but I went and redid it
Closed throttle Open throttle Cyl dry wet dry wet 1 110 122 105 118 2 120 125 140 145 3 140 152 150 170 4 120 130 152 160 5 140 170 153 173 6 125 150 135 147 7 130 160 153 175 8 125 165 170 180 Am going to order a leak down tester.
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AMO#8454, AMCRC# 8066
69 Ambo coupe, 401, M12, 66 Ambo 990 Wagon, 327,PW,PB,PS,posi,AM/FM,AC 74 Jav 360 auto ac 2003 FLHTCI, 1977 Yamaha XS750 2015 Chry 200, 2006 Pacifica |
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ccowx
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Joined: Nov/03/2010 Location: Yukon Status: Offline Points: 3510 |
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Posted: Jan/16/2017 at 9:46pm |
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The ideal is to have about 10% or less variation between cylinders. You are definitely a bit wider than that, but in a higher mileage engine, probably not a big deal. In a running engine dynamic sealing will probably mean that everything is staying fairly tight, though you would have a bit of blowby.
Chris
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maximus7001
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Joined: Jun/27/2011 Location: Winnipeg,Canada Status: Offline Points: 1086 |
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Posted: Jan/17/2017 at 12:59am |
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A repeat compression test cannot be considered dry after a wet rest. It would need to be started and run for a bit again before an accurate dry test can be done again.
Edited by maximus7001 - Jan/17/2017 at 1:11am |
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1968 Javelin SST
1997 GMC Safari AWD 2001 Daewoo Nubira SX (Winnipeg only model) 1997 Honda Accord EX (Canadian Model) Winnipeg, home of the Jets. |
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farna
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Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19676 |
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Posted: Jan/17/2017 at 6:04am |
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Not real bad considering high mileage (for a 1970s engine), though there is a good bit of difference between lowest and highest (about 40%). Being in a Javelin it has probably been run pretty hard at some point in it's life also. A leak down test will show more. I'd just do the lowest and highest cylinders, compare the two again. The good thing is there is no big difference between adjacent cylinders, so head gaskets are good. Probably cylinder wear, but could be valves not sealing very well. If you don't have time/funds to do a rebuild, you might want to rebuild the heads this year and the bottom end later. Many don't like that, but head gaskets aren't that costly. You end up spending a little more, but spread the costs out, which helps sometimes. Gotta eat and pay rent first! I remember having to do things like that...
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Frank Swygert
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maximus7001
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Posted: Jan/17/2017 at 6:20am |
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Yes, another fresh compression test with open throttle will tell. As it is looks like valves but retest and post it to be sure. What oil and how much is going in the cylinders for the wet? Is it a proper screw in guage? How long did it warm up for?I really would not worry about it at this point. If it's not blowing oil everywhere I would just drive it and have fun.
Edited by maximus7001 - Jan/17/2017 at 6:28am |
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1968 Javelin SST
1997 GMC Safari AWD 2001 Daewoo Nubira SX (Winnipeg only model) 1997 Honda Accord EX (Canadian Model) Winnipeg, home of the Jets. |
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Smitty52
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Joined: Aug/05/2008 Location: Bolton Landing Status: Offline Points: 227 |
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Posted: Jan/21/2017 at 1:18pm |
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OK I did a leak down test and figure I might just live with it for now. The good news is that there was hardly any leaks past the rings as the oil fill tube was quiet for each cylinder. Cyl #! had the highest leakage as might be expected. The rear main seal leaks a quart every 150 miles so my plan was to replace that. If I can find a way to do that without pulling the engine then I will leave the heads alone for now. However, if the engine has to come out then the head work is easy when it is on a stand. On Cyl 8 I do not think I had it at TDC. I pulled the valve covers off (and it looks super super clean) and rotated the engine until both rocker arms were free of tension before I tested a cylinder but 8 may have been a little off. I will recheck just for my own peace of mind.
So, any tricks to replacing the rear seal without pulling the engine??? Closed throttle Open throttle Leak rate area Cyl dry wet dry wet 1 110 122 105 118 25% E 2 120 125 140 145 15% 3 140 152 150 170 17% I 4 120 130 152 160 17% I 5 140 170 153 173 10% 6 125 150 135 147 15% I 7 130 160 153 175 18% I 8 125 165 170 180 20% E |
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AMO#8454, AMCRC# 8066
69 Ambo coupe, 401, M12, 66 Ambo 990 Wagon, 327,PW,PB,PS,posi,AM/FM,AC 74 Jav 360 auto ac 2003 FLHTCI, 1977 Yamaha XS750 2015 Chry 200, 2006 Pacifica |
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Boris Badanov
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Posted: Jan/21/2017 at 4:19pm |
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It's obviously wasted Exhaust valve seats.
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Gremlin Dreams
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6PakBee
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Posted: Jan/21/2017 at 4:29pm |
Looking at all the results I think that it is very probable that a valve job is in order. |
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Roger Gazur
1969 'B' Scheme SC/Rambler 1970 RWB 4-spd Machine 1970 Sonic Silver auto AMX All project cars. Forum Cockroach |
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Boris Badanov wrote: