MGB & GT Forum
Compression test results!!!
Posted by dbd74mgb
Topic Creator (OP)
Oct 25, 2014 12:25 PM
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mgbanthony
Anthony Henderson
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Oct 25, 2014 12:30 PM
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Your test indicates potential ring problems in a couple of cylinders, as well as perhaps general wear and tear in the valve train as well.
A cylinder leak down test would give you more data.
If engine is running OK with decent oil pressure, not burning large amounts of oil and has fair power I would likely continue to drive it.
Your results sound like those of an average tired low compression engine, which may well run a while yet.
A cylinder leak down test would give you more data.
If engine is running OK with decent oil pressure, not burning large amounts of oil and has fair power I would likely continue to drive it.
Your results sound like those of an average tired low compression engine, which may well run a while yet.
Oct 25, 2014 12:49 PM
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If I get questionable compression readings I put the plugs back in, check the valve clearances, warm the engine up, then retest. Often the readings improve greatly. Assuming the engine runs fine and has good oil pressure, don't necessarily think rebuild yet.
OTOH, if your readings don't improve and/or oil pressure and running are also issues, start thinking about a new engine.
Friends talking around a fire is the history of mankind.
Edited 1 time(s). Last edit at 2014-10-25 12:53 PM by Rod H..
OTOH, if your readings don't improve and/or oil pressure and running are also issues, start thinking about a new engine.
Friends talking around a fire is the history of mankind.
Edited 1 time(s). Last edit at 2014-10-25 12:53 PM by Rod H..
Oct 25, 2014 12:59 PM
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HiPowerShooter
James Booker
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Oct 25, 2014 01:08 PM
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Why the aggressive posture for starting your engine Douglas??
I would Definitely start and warm it...and leave the contempt issue for another day!lol!
Sorry...it's Saturday.
But yes, start and warm it for a few minutes. Doesn't have to be operating temp but just warm to the touch. Also...how do your plugs look? You can get an overall idea of individual cylinder health by reading them.
"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.
"Who do you think you are? I am."...Pete Weber
73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...
Edited 1 time(s). Last edit at 2014-10-25 01:09 PM by HiPowerShooter.
I would Definitely start and warm it...and leave the contempt issue for another day!lol!
Sorry...it's Saturday.
But yes, start and warm it for a few minutes. Doesn't have to be operating temp but just warm to the touch. Also...how do your plugs look? You can get an overall idea of individual cylinder health by reading them.
In reply to # 2833633 by tourtelot
Defiantly a warm engine for a compression test.
D.
D.
"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.
"Who do you think you are? I am."...Pete Weber
73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...
Edited 1 time(s). Last edit at 2014-10-25 01:09 PM by HiPowerShooter.
Oct 25, 2014 03:11 PM
Joined 12 years ago
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In reply to # 2833640 by HiPowerShooter
Why the aggressive posture for starting your engine Douglas??
Because 1) it's Saturday, 2) it's raining and 3) I have a bad clutch master cylinder. And because I have trouble spelling "definitely" (and the computer doesn't REALLY help.)
D.
Douglas Tourtelot
Seattle, WA
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Oct 25, 2014 03:47 PM
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In reply to # 2833711 by tourtelot
it's raining
You're in Seattle...
Eric Russell ~ Mebane, NC
1961 MGA #61, 1981 Alfa Romeo GTV6, 1984 Alfa Romeo Spider, 1991 Honda ST1100
Donthuis
Don van Riet
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Oct 25, 2014 04:00 PM
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As usual cylinder #3 is the weakest, both on dry as well as wet it is more than 10% below the others. Still for a LC engine the overall level is OK.
Strange that cylinder #4 is so high when wet, maybe too much oil added? Anyhow you may contine driving if the crank is not rumbling in its gears
Maybe cylinder #4 has slightly more carbon buildup inside the head, LC is normally 130psi max, not 150
PS Sometimes cylinder #3 is lower because of headgasket problems, so if the bearings are OK, a new headgasket may be a gamble worth taking
Once the head is off checking the valves with petroleum, see JT video is easy enough. When new ones are necessary going to a leadfree head is the most logical step
Edited 1 time(s). Last edit at 2014-10-26 06:52 AM by Donthuis.
Strange that cylinder #4 is so high when wet, maybe too much oil added? Anyhow you may contine driving if the crank is not rumbling in its gears
Maybe cylinder #4 has slightly more carbon buildup inside the head, LC is normally 130psi max, not 150
PS Sometimes cylinder #3 is lower because of headgasket problems, so if the bearings are OK, a new headgasket may be a gamble worth taking
Once the head is off checking the valves with petroleum, see JT video is easy enough. When new ones are necessary going to a leadfree head is the most logical step
Edited 1 time(s). Last edit at 2014-10-26 06:52 AM by Donthuis.
ohlord
Rob C
A tiny Island off the coast of Washington State, N.W., USA
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Oct 25, 2014 05:02 PM
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Do a proper leakdown test by cylinder it will tell you way more than a wet or dry compression test.
If that is what you want to know about your engine.
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If that is what you want to know about your engine.
LNDRVR4X4.COM
Home of Project "INCARN8'
1957 Series 1 Land Rover electric VEHICLE CONVERSION
FIXITUPCHAP.COM
FIXITUPCHAP INCORPORATED
RD3 Radar/ Electronic Warfare Technician
VIETNAM 1969-1972
Oct 25, 2014 07:11 PM
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As Anthony said, if its running OK, just drive it! If you are looking for something more than a 'fun' occasional drive, then by all means consider rebuilding to bring back to 'original' or 'MORE'. If each of mine idles nice and 'seem' like they are moving 'fast' especially on twisty roads, I'm happy.
Oct 26, 2014 12:05 AM
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Oct 26, 2014 02:16 AM
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Don't do anything yet. There is nothing diagnostic about a compression test or even a leakdown test if the engine is dirty. You may want to Seafoam it and then adjust the valves and test again. Or spend an afternoon and pull the head, lap the valves and re-install and test again. Compression numbers like that are probably valve leakage, not rings. You may be a candidate for a minor rebuild - lap valves and change the rings and rod bearings but that's the worst I can imagine with those initial compression numbers. Holler if I can help. Basil 707.762.0974 basiladams@yahoo.com
Basil C. Adams
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Basil C. Adams
1956 MGA Coupe (Show Car)
1957 MGA Roadster (Driver)
1958 MGA Coupe (Racecar)
1959 MGA Coupe (unrestored)
1960 MGA Coupe (unrestored)
1960 MGA Roadster (Driver)
MKIII Elva Courier (E1056)
1967 427 Cobra
1972 Alfa Romeo Montreal
A coupla late MGBs
1960 Austin Healy BN7
More Cars than Brains
Topic Creator (OP)
Oct 26, 2014 11:55 AM
Joined 17 years ago
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OK there were a lot of answers and a few questions, so here goes -
- I did on a warm/hot engine,
- oil pressure is about 60 pounds driven, falls to about 45-50 at idle,
- car runs fine, just seems to lose power on steep hills,
- not burning oil but it does tend to leak, about a cup after a long run 150+ miles,
- the plugs look great, here are pics, they are a light grey, and this was after town driving.
- I did on a warm/hot engine,
- oil pressure is about 60 pounds driven, falls to about 45-50 at idle,
- car runs fine, just seems to lose power on steep hills,
- not burning oil but it does tend to leak, about a cup after a long run 150+ miles,
- the plugs look great, here are pics, they are a light grey, and this was after town driving.
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Oct 26, 2014 12:24 PM
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Oct 26, 2014 12:36 PM
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