Engine builders help wanted
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
Engine builders help wanted
Dear all engine builders, would you be so kind and help me with my engine please?
After four years putting up with my smoky L48 in my 1980 I have finally decide to find out what is wrong with my engine.
I am going to do a compression test on Saturday; however I would like to know:
Is there a right way or wrong way?
What should the compression be?
Are there any other checks I should do to determine the condition of the engine?
Any input welcome
After four years putting up with my smoky L48 in my 1980 I have finally decide to find out what is wrong with my engine.
I am going to do a compression test on Saturday; however I would like to know:
Is there a right way or wrong way?
What should the compression be?
Are there any other checks I should do to determine the condition of the engine?
Any input welcome
Race Director
Joined: Mar 2008
Posts: 15,161
Likes: 17
From: coffee
a quick wikipedia search says 8.2:1 compression for the 1980 L48, I'm not sure what that would calculate out to on your compression guage, but it is a start, and you could do a search to convert the relative compression in whatever units that you have to ATM's.
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Dear all engine builders, would you be so kind and help me with my engine please?
After four years putting up with my smoky L48 in my 1980 I have finally decide to find out what is wrong with my engine.
I am going to do a compression test on Saturday; however I would like to know:
Is there a right way or wrong way?
What should the compression be?
Are there any other checks I should do to determine the condition of the engine?
Any input welcome
After four years putting up with my smoky L48 in my 1980 I have finally decide to find out what is wrong with my engine.
I am going to do a compression test on Saturday; however I would like to know:
Is there a right way or wrong way?
What should the compression be?
Are there any other checks I should do to determine the condition of the engine?
Any input welcome
** Crank engine through (4) compression strokes in each cylinder in turn, with the compression gauge in place.
** Record readings. Look for minimum of 125 in each cylinder
** Look for problems with adjacent cylinders having low compression
If they are all fairly low but even, it's OK. How many miles on car? A couple of shots of engine oil in each cylinder and a redo of the test will tell you if your rings are bad. If the oil increases the compression then it's rings. If the car smokes on DECELERATION, then it's valve guides and you won't see the increase in compression from oil.
Burning Brakes
Joined: Jan 2007
Posts: 1,057
Likes: 4
From: Concord Calif
** Disconnect power from the coil
** Crank engine through (4) compression strokes in each cylinder in turn, with the compression gauge in place.
** Record readings. Look for minimum of 125 in each cylinder
** Look for problems with adjacent cylinders having low compression
If they are all fairly low but even, it's OK. How many miles on car? A couple of shots of engine oil in each cylinder and a redo of the test will tell you if your rings are bad. If the oil increases the compression then it's rings. If the car smokes on DECELERATION, then it's valve guides and you won't see the increase in compression from oil.
** Crank engine through (4) compression strokes in each cylinder in turn, with the compression gauge in place.
** Record readings. Look for minimum of 125 in each cylinder
** Look for problems with adjacent cylinders having low compression
If they are all fairly low but even, it's OK. How many miles on car? A couple of shots of engine oil in each cylinder and a redo of the test will tell you if your rings are bad. If the oil increases the compression then it's rings. If the car smokes on DECELERATION, then it's valve guides and you won't see the increase in compression from oil.
He should also have all the spark plugs removed when cranking the engine over for this test. And don't forget to hold the carb wide open so the plates do not restrict the air flow. The total number that he gets is not that important as long as it is even, within about 6%. The oil check is a good one
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Last edited by SanDiegoPaul; Apr 9, 2008 at 06:37 PM.
Racer
Joined: Mar 2006
Posts: 291
Likes: 0
From: Guantanamo Bay, Cuba (home in Colorado Springs)
Pull the plugs, mark the plug wires.
Squirt a LITTLE oil in each cylinder through the sparkplug hole prior to the compression check. It's called a wet check.
Screw the guage/hose in the sparkplug hole securely.
Place a towel along the inside of each side of the engine bay to catch oil that gets squirted out when you turn the engine over.
Turn the engine over 4 or 5 times.
Expect to see at least 90 psi.
Repeat process for all cylinders.
You SHOULD see about the same on all cylinders, give or take about 10%.
If you have a significant pressure reading discrepancy on a cylinder(s), then you may have; bad valves, worn rings, or a hole in a piston (worst case scenerio).
If you feel that the valves are bad, then you'll need to pull them and have a valve job done. Depending on if the engine is a "high-mileage" block, putting the heads back on, after a valve job, may damage the piston rings. If you have to replace valve guides, then you should have the valve seats reground. It adds up quickly.
Better yet, just pull the engine, rebuild it as a 383 stroker.
Squirt a LITTLE oil in each cylinder through the sparkplug hole prior to the compression check. It's called a wet check.
Screw the guage/hose in the sparkplug hole securely.
Place a towel along the inside of each side of the engine bay to catch oil that gets squirted out when you turn the engine over.
Turn the engine over 4 or 5 times.
Expect to see at least 90 psi.
Repeat process for all cylinders.
You SHOULD see about the same on all cylinders, give or take about 10%.
If you have a significant pressure reading discrepancy on a cylinder(s), then you may have; bad valves, worn rings, or a hole in a piston (worst case scenerio).
If you feel that the valves are bad, then you'll need to pull them and have a valve job done. Depending on if the engine is a "high-mileage" block, putting the heads back on, after a valve job, may damage the piston rings. If you have to replace valve guides, then you should have the valve seats reground. It adds up quickly.
Better yet, just pull the engine, rebuild it as a 383 stroker.
Instructor
Joined: Jun 2006
Posts: 146
Likes: 5
From: North Brunswick New Jersey
When my '79 L48 started smoking heavily at start-up and decelleration, I took off the heads, had them rebuilt, installed umbrella seals on the valve guides then reassembled. Now, I have no oil loss and the original engine has 120,000 miles to date. And, it still performs almost like new.
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Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
Hello All
The milometer is showing 69000? Mls. The condition of the car is very good and apart of the worn interior and Buba hacking the electric’s it is original.
Well, let me do the compressin test and take it from there.
Last edited by C3Paul; Apr 15, 2008 at 06:29 AM.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
I have done the compression check this morning while the engine was cold, all spark plugs removed, and throttle fully open and here are the results:
Dry check: 1:130, 2:130, 3:130, 4:140, 5:140, 6:140, 7:130, 8:130 PSI
Wet check: 1:150, 2:160, 3:155, 4:150, 5:140, 6:160, 7:145, 8:140 PSI
In a previous post I was told to look for 90PSI, but these numbers are a lot higher.
Also I took the picture of the spark plugs as I removed them and here are the pictures.
What do you think???
Dry check: 1:130, 2:130, 3:130, 4:140, 5:140, 6:140, 7:130, 8:130 PSI
Wet check: 1:150, 2:160, 3:155, 4:150, 5:140, 6:160, 7:145, 8:140 PSI
In a previous post I was told to look for 90PSI, but these numbers are a lot higher.
Also I took the picture of the spark plugs as I removed them and here are the pictures.
What do you think???
Racer
Joined: Mar 2006
Posts: 291
Likes: 0
From: Guantanamo Bay, Cuba (home in Colorado Springs)
Very good numbers on the compression checks. The right side plugs look as if there is some carbon & oil residue.
You may be able to get away with just a head job; regrind valves & seats, new oil seals on the valve stems. That'll also give you a chance to inspect the cylinder walls.
The 90psi I got was on a replacement GM motor that came in my project Vette. Probably swapped in because a previous owner killed the original engine. That engine is sitting in the corner of my garage awaiting it's fate.
You may be able to get away with just a head job; regrind valves & seats, new oil seals on the valve stems. That'll also give you a chance to inspect the cylinder walls.
The 90psi I got was on a replacement GM motor that came in my project Vette. Probably swapped in because a previous owner killed the original engine. That engine is sitting in the corner of my garage awaiting it's fate.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
[QUOTE=VIPERBARON;1564984839]Very good numbers on the compression checks. The right side plugs look as if there is some carbon & oil residue.
You may be able to get away with just a head job; regrind valves & seats, new oil seals on the valve stems. That'll also give you a chance to inspect the cylinder walls.
By registering higher compression while there is some oil injected in the cylinders, does not that mean that the rings are worn, rather then the valves?
You may be able to get away with just a head job; regrind valves & seats, new oil seals on the valve stems. That'll also give you a chance to inspect the cylinder walls.
By registering higher compression while there is some oil injected in the cylinders, does not that mean that the rings are worn, rather then the valves?
Racer
Joined: Mar 2006
Posts: 291
Likes: 0
From: Guantanamo Bay, Cuba (home in Colorado Springs)
The "wet" check seals the rings. You should get a higher number when wet. If not, then I'd suspect valves. Blown rings are obvious due to the smoke when running the engine.
Valve guides can be reconditioned or replaced. If you got a similar reading when wet, then I'd suspect deteriated valve seats & faces.
Valve guides can be reconditioned or replaced. If you got a similar reading when wet, then I'd suspect deteriated valve seats & faces.
Le Mans Master
Joined: Mar 2004
Posts: 7,493
Likes: 1,502
From: Little Rock AR
The least you could do is replace the valve seals. With this much age they are bound to be shot regardless of the miles. The valve guides will be worn as well but you could probably get away with a set of umbrella seals for a while longer.
The ring seal isn't all that bad. I would be inclined to do the valve seals first and see if the results are acceptable to you. This is cheap and fairly easy vs the time/money/challenge of an overhaul.
The plugs might need one step up in heat range.
-Mark.
The ring seal isn't all that bad. I would be inclined to do the valve seals first and see if the results are acceptable to you. This is cheap and fairly easy vs the time/money/challenge of an overhaul.
The plugs might need one step up in heat range.
-Mark.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
Thank you all for your reply
What I am confused about is, everyone is talking about head job which is the easy job, however if the compression increased in wet check does not that mean that the rings are worn rather than the head?
What I am confused about is, everyone is talking about head job which is the easy job, however if the compression increased in wet check does not that mean that the rings are worn rather than the head?
Intermediate
Joined: Jun 2006
Posts: 41
Likes: 0
From: hooksett nh
I am sorry if I have contributed to any of your confusion, I looked at my previous reply and realized I was wrong and edited it:o , with a squirt of oil and any increase in a reading this indicates worn rings, look into a "leak down check" this will give you the most accurate diagnosis
Le Mans Master
Joined: Mar 2004
Posts: 7,493
Likes: 1,502
From: Little Rock AR
A valve job required much more work with the removal of the cylinder heads and reconditioning the valves and guides along with replacement of the seals.
The ring replacement requires a complete engine removal, dissasembly and overhaul. It might end up needing to be bored out oversize and then the cost goes much higher. A full rebuild is in order at that point.
Your test results indicate more than 0 miles (not brand new) but are not bad enough by themselves to positively warrant a full overhaul in my opinion. Any engine will show some improvement when you put oil in the cylinders and do a compression check. Your pressure increase was not that large with the oil added so the ring seal is still serviceable in my opinion.
Other opinions are available and welcome.
-Mark.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
Your test results indicate more than 0 miles (not brand new) but are not bad enough by themselves to positively warrant a full overhaul in my opinion.
What do you mean by this statment
/Your test results indicate more than 0 miles (not brand new)/
If this was your engine and your money, what would you do?
a; do the head job- top end?
b; do the rings-bottom end?
What do you mean by this statment
/Your test results indicate more than 0 miles (not brand new)/
If this was your engine and your money, what would you do?
a; do the head job- top end?
b; do the rings-bottom end?
Last edited by C3Paul; Apr 15, 2008 at 02:47 PM.
