 Stumped, Low Compression |
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| AKJammer |
 Sep 7 2016, 09:04 PM
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#1
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Newbie  Group: Members Posts: 6 Joined: 19-July 15 From: Alaska Member No.: 18,971 Region Association: Pacific Northwest  |
Engine: 1.8 1974.
I tore down the engine to replace Dead gaskets and seals. Purchased new jugs and pistons reassembled the engine. Fired it up and have 90 lbs of compression on 3-4 125 on 1-2. Completed a leak down test and all is good as it is holding what compression there is... Tore the engine down again and measured the cc of the heads and they are all the same. Part number 021.101.371S on both heads. Measured the deck height of the pistons at TDC and they are all the same.... Head gasket shims are all the same. What am I missing??? Thanks Jammer! |
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| rgalla9146 |
Sep 7 2016, 09:14 PM
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#2
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Advanced Member Group: Members Posts: 4,743 Joined: 23-November 05 From: Paramus NJ Member No.: 5,176 Region Association: None 
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Fuel injection or carbs ?
If carbs, were the carbs open on both sides ? |
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| AKJammer |
Sep 7 2016, 09:19 PM
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#3
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Newbie Group: Members Posts: 6 Joined: 19-July 15 From: Alaska Member No.: 18,971 Region Association: Pacific Northwest |
QUOTE(rgalla9146 @ Sep 7 2016, 07:14 PM)  Fuel injection or carbs ? If carbs, were the carbs open on both sides ? Dual 40's and just rebuilt. They were opening. Thanks |
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| injunmort |
Sep 7 2016, 10:29 PM
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#4
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Senior Member Group: Members Posts: 1,024 Joined: 12-April 10 From: sugarloaf ny Member No.: 11,604 Region Association: North East States |
ring gap, ring stagger, valve seats, valve clearance, piston to wall clearance, your missing a lot.
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| AKJammer |
Sep 7 2016, 10:46 PM
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#5
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Newbie Group: Members Posts: 6 Joined: 19-July 15 From: Alaska Member No.: 18,971 Region Association: Pacific Northwest |
QUOTE(injunmort @ Sep 7 2016, 08:29 PM) ring gap, ring stagger, valve seats, valve clearance, piston to wall clearance, your missing a lot. Thanks! But do Brand new Pistons and cylinders leak? If they were bad would that not show up on the pressure test? Also Would the valve seats held pressure during the pressure test if they were a problem? Valves adjusted by myself and rechecked by another person, and they were good. |
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| wndsrfr |
Sep 8 2016, 05:27 AM
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#6
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Senior Member Group: Members Posts: 1,449 Joined: 30-April 09 From: Rescue, Virginia Member No.: 10,318 Region Association: MidAtlantic Region
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QUOTE(AKJammer @ Sep 7 2016, 08:46 PM) QUOTE(injunmort @ Sep 7 2016, 08:29 PM) ring gap, ring stagger, valve seats, valve clearance, piston to wall clearance, your missing a lot. Thanks! But do Brand new Pistons and cylinders leak? If they were bad would that not show up on the pressure test? Also Would the valve seats held pressure during the pressure test if they were a problem? Valves adjusted by myself and rechecked by another person, and they were good. Rings haven't seated.....drive it like you stole it a couple days & check again.... |
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| rgalla9146 |
Sep 8 2016, 05:42 AM
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#7
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Advanced Member Group: Members Posts: 4,743 Joined: 23-November 05 From: Paramus NJ Member No.: 5,176 Region Association: None
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QUOTE(AKJammer @ Sep 7 2016, 11:19 PM) QUOTE(rgalla9146 @ Sep 7 2016, 07:14 PM) Fuel injection or carbs ? If carbs, were the carbs open on both sides ? Dual 40's and just rebuilt. They were opening. Thanks When doing a compression test the carbs must be propped open. "they were opening" doesn't sound right. |
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| stugray |
Sep 8 2016, 05:49 AM
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#8
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Advanced Member Group: Members Posts: 3,825 Joined: 17-September 09 From: Longmont, CO Member No.: 10,819 Region Association: None |
QUOTE(wndsrfr @ Sep 8 2016, 05:27 AM) Rings haven't seated.....drive it like you stole it a couple days & check again.... (IMG:style_emoticons/default/agree.gif) And the engine is supposed to be warmed up as well. |
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| TheCabinetmaker |
Sep 8 2016, 06:00 AM
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#9
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I drive my car everyday Group: Members Posts: 8,336 Joined: 8-May 03 From: Tulsa, Ok. Member No.: 666 |
Sounds like an aka problem
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| VaccaRabite |
Sep 8 2016, 07:57 AM
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#10
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En Garde! Group: Admin Posts: 13,729 Joined: 15-December 03 From: Dallastown, PA Member No.: 1,435 Region Association: MidAtlantic Region
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Compression on a fresh top end-er builds as the rings seat.
So assuming you cut your ring gaps correctly... Here is how I was taught to break in a fresh motor. Warm it up. When at operating temp, on your favorite quiet road, put the car in second gear and STOMP ON IT. All the way up the rev range. Then foot off and let the car engine brake back down (keeping the car in second gear). Do that two more times. Your rings should now be seated, and compression should be around 140-160 or so. Zach |
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| injunmort |
Sep 8 2016, 07:58 AM
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#11
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Senior Member Group: Members Posts: 1,024 Joined: 12-April 10 From: sugarloaf ny Member No.: 11,604 Region Association: North East States |
if it were mine and it is out and apart. i would do a light hone on the cylinders (break the glaze), check my ring gaps again, stagger the gaps at 60 degrees and reassemble the cylinders. on the heads, fill each combustion chamber with lighter fluid with spark plugs in the holes and check for leakage past the seats. the chambers should hold the fluid. if they don't, lap the valves into the seats and try again until it seals. reassemble.
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| AKJammer |
Sep 8 2016, 12:10 PM
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#12
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Newbie Group: Members Posts: 6 Joined: 19-July 15 From: Alaska Member No.: 18,971 Region Association: Pacific Northwest |
Thanks All! I have some Ideas of what to do now! See if I can get this up and running before snowfall!
BTW what is an AKA problem? if your referring to Knowledge then yes... I am a noob. (IMG:style_emoticons/default/piratenanner.gif) |
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| Root_Werks |
Sep 8 2016, 12:15 PM
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#13
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Village Idiot Group: Members Posts: 8,668 Joined: 25-May 04 From: About 5NM from Canada Member No.: 2,105 Region Association: Pacific Northwest
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QUOTE(rgalla9146 @ Sep 8 2016, 04:42 AM) QUOTE(AKJammer @ Sep 7 2016, 11:19 PM) QUOTE(rgalla9146 @ Sep 7 2016, 07:14 PM) Fuel injection or carbs ? If carbs, were the carbs open on both sides ? Dual 40's and just rebuilt. They were opening. Thanks When doing a compression test the carbs must be propped open. "they were opening" doesn't sound right. I agree, it might be why a leakdown will show something like 80/79, but a compression will show 90psig. You need to allow air into the intake system. Prop the throttle to stay open and re-run the test. |
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| AKJammer |
Sep 8 2016, 01:07 PM
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#14
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Newbie Group: Members Posts: 6 Joined: 19-July 15 From: Alaska Member No.: 18,971 Region Association: Pacific Northwest |
QUOTE(Root_Werks @ Sep 8 2016, 10:15 AM) QUOTE(rgalla9146 @ Sep 8 2016, 04:42 AM) QUOTE(AKJammer @ Sep 7 2016, 11:19 PM) QUOTE(rgalla9146 @ Sep 7 2016, 07:14 PM) Fuel injection or carbs ? If carbs, were the carbs open on both sides ? Dual 40's and just rebuilt. They were opening. Thanks When doing a compression test the carbs must be propped open. "they were opening" doesn't sound right. I agree, it might be why a leakdown will show something like 80/79, but a compression will show 90psig. You need to allow air into the intake system. Prop the throttle to stay open and re-run the test. Yep will do! But either way the plugs were not firing on 3-4 side unless I had the rpms up. I installed new cap rotor pertonics points coil wire and plugs..... |
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| r_towle |
Sep 8 2016, 07:05 PM
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#15
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Custom Member Group: Members Posts: 24,705 Joined: 9-January 03 From: Taxachusetts Member No.: 124 Region Association: North East States
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You may want to check to make sure the case is flat where the cylinders set.
Older cases have been known to sink in the middle and that makes sealing the heads nearly impossible |
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| Root_Werks |
Sep 9 2016, 10:18 AM
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#16
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Village Idiot Group: Members Posts: 8,668 Joined: 25-May 04 From: About 5NM from Canada Member No.: 2,105 Region Association: Pacific Northwest
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Also noting you stated 3-4 "side" doesn't fire until the rpm's are up. Sounds like an idle circuit adjustment/issue/vac leak etc. more than compression.
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| old dog |
Sep 9 2016, 08:54 PM
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#17
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Member Group: Members Posts: 63 Joined: 14-December 12 From: Oxnard,CA. Member No.: 15,257 Region Association: Central California |
Just a thought.... Is the cam timing correct ? Good leakdown, different compression side to side.... Cams not timed properly
Again, just a thought. |
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| rgalla9146 |
Sep 10 2016, 04:03 AM
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#18
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Advanced Member Group: Members Posts: 4,743 Joined: 23-November 05 From: Paramus NJ Member No.: 5,176 Region Association: None
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QUOTE(old dog @ Sep 9 2016, 10:54 PM) Just a thought.... Is the cam timing correct ? Good leakdown, different compression side to side.... Cams not timed properly Again, just a thought. ......that would require a Very special cam |
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