AMC 360 Burning oil, but where? - Off-Road Forums & Discussion Groups
Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

 
LinkBack Thread Tools Display Modes
post #1 of (permalink) Old 03-04-2012, 04:17 PM Thread Starter
I Might Just Know What I'm Talking About
 
Join Date: Oct 2000
Location: C-ville, VA
Posts: 1,586
Thanks: 0
Thanked 0 Times in 0 Posts
 
AMC 360 Burning oil, but where?

So I'm spooling up to get back to work on my CJ project. I fired up the donor 360 today to move the donor CJ closer to the garage for removal of some parts.

The PO mentioned that it burns oil. At first, it showed slight oil burning (very faint blue smoke, barely visible. At operating temp, the blue smoke increased a lot.

It runs and sounds great. As I understand it, the two most likely sources of oil are bad rings and bad valve seals.

If the engine burns more oil at operating temp than when cool, would that point to the valve seals more so than rings? I have a second 360 that would desperately need a rebuild (won't spin by hand). Could I rebuild those heads with new valve seals and swap them on the running motor?

Jeep...need I say more?
ExtinctJeep is offline  
Sponsored Links
Advertisement
 
post #2 of (permalink) Old 03-04-2012, 11:04 PM
Enthusiast
 
Join Date: Sep 2006
Location: Vancouver USA
Posts: 282
Thanks: 0
Thanked 0 Times in 0 Posts
 
I understand your reasoning however Iím not sure you can guess based on the symptoms. The age of your 360 may have something to do with everything too as during the 1970s some vehicles ran on leaded gas and others required unleaded gas. The deciding factor on having to use cats and unleaded was based on the GVW of the vehicle, a compromised to appease business who complained about having to use a more costly unleaded gas. The GVW limits allowed pickup trucks to be exempt; I donít remember the exact number but it was fairly low. The net effect was that cars now needed to have cats and run unleaded fuel while pickup trucks and other heavier vehicles such as the (FSJ) Cherokee and Wagoner escaped the clutches of the new requirements; at first anyway. Within a year or two the GVW was raised again to catch Ĺ ton and low GVW ĺ ton pickups then finally unleaded became the law of the land for all. The CJ unfortunately was considered a ľ ton truck out of the gate and was saddled with a cat by 1973. (maybe 1972) The purpose of this bit of history is that as long as an engine ran leaded gas the valve stem seats did not need to be hardened as the lead in the gas provided engine component lubrication that unleaded gas of course doesnít have so depending upon the age of your 360 it may or may not have hardened seats which may have a bearing on where/how the oil is getting into the cylinder to be burned. The other the factor is expansion. If seats, or rings for that matter, are warn and expand when heated up the oil could be coming from either seats or cylinders or both.

1978 CJ5, AMC 401, CJ T18, Scout D300, 2 1/2" Lift, Locked Front/Back
Saddle Tramp is offline  
post #3 of (permalink) Old 03-05-2012, 05:22 AM
Moderator
 
Jim_Lou's Avatar
 
Join Date: Dec 2001
Location: Belleville, Illinois
Posts: 11,482
Thanks: 15
Thanked 18 Times in 13 Posts
         
Extinct was asking abut seals, not seats. The problem with the valve seats is that unleaded gas can, in theory, cause rapid wear of non-hardened valve seats, allowing combustion gas to leak past the valve. Unleaded gasoline doesn't cause any problem for valve seals, as far as I have ever heard, so is unrelated to oil leaking down the valve stems and being burned.

Were I doing this project, I would run a dry & wet compression test. That will definitively quantify the condition of the compression rings, and that will pretty accurately tell you the condition of the oil control rings. If dry compression is close to wet compression, the rings are in good condition and your oil burning is coming from somewhere else, and not necessarily valve seals. A bad PCV valve can suck oil from the top of the engine into the intake manifold, for example. With a full complement of emission controls there are probably other possible causes. You should eliminate all other possibilities before opening up the engine.

EVERYTHING's easy for the guy who doesn't have to do it.
B. Dash Fabrication
Jim_Lou is offline  
Sponsored Links
Advertisement
 
post #4 of (permalink) Old 03-05-2012, 08:10 AM
Official Curmudgeon
 
CJ7Taz's Avatar
 
Join Date: Nov 2001
Location: Kansas
Posts: 4,701
Thanks: 2
Thanked 1 Time in 1 Post
 
Quote:
Originally Posted by ExtinctJeep View Post
So I'm spooling up to get back to work on my CJ project. I fired up the donor 360 today ...
So, how long has it been since the donor 360 has been run? If itís been a while, itís pretty normal for it to burn oil. The rings, especially the oil wiper rings get stuck in the grooves due to the oil, mixed with sludge, thickening up.

Higher mileage engines get tapered cylinder walls, flaring toward the bottom, and out of round bores from wear. If the rings arenít free to follow the distortion, they can allow oil to get into the combustion chamber. Run it for several hours before you do anything drastic.

If it turns out to be valve stem seal problems, the seals can be changed without removing the heads. A piece of SOFT rope is fed into the cylinder through the spark plug hole (Make sure there is enough left to pull it out later). Run the piston up by hand until it holds the valves in place. Now, the valve springs can be removed, the seals replaced and the springs and keepers replaced.

There are 10 kinds of people in the world.
Those who understand binary and those who don't.
CJ7Taz is offline  
post #5 of (permalink) Old 03-05-2012, 10:09 AM
Mud in my Veins
 
Caver Dave's Avatar
 
Join Date: Apr 2000
Location: Winston-Salem, NC
Posts: 5,512
Thanks: 0
Thanked 0 Times in 0 Posts
 
Quote:
Originally Posted by ExtinctJeep View Post
The PO mentioned that it burns oil. At first, it showed slight oil burning (very faint blue smoke, barely visible. At operating temp, the blue smoke increased a lot.

It runs and sounds great. As I understand it, the two most likely sources of oil are bad rings and bad valve seals.

If the engine burns more oil at operating temp than when cool, would that point to the valve seals more so than rings?
I think this is NOT correct... IOW, oil smoke on startup is usually attributed to valve stem seals as it leaks down into the chambers while off & is usually burned off shortly after startup.
Where as worn rings/bores (as Taz mentioned) usually bring on the constant oil smoke... as the oil warms up, it flows better and more easily pushed past the rings into the chambers.

Quote:
Originally Posted by Jim_Lou View Post
The problem with the valve seats is that unleaded gas can, in theory, cause rapid wear of non-hardened valve seats, allowing combustion gas to leak past the valve.
While I'm unsure if they ever changed their methods on "hardening" valve seats... I was told they were "induction hardened" by electric element just around the seat area, rather than hardened seats being pressed in, typical in most Chevy/Ford(?) heads.

I have seen these seats first hand when the "sheetmetal" intake gasket got crinkled slightly on #2 cyl (supposed pro rebuild), creating a vacuum leak/leaning on that cyl... completely burning the exhaust side seat area away to the point of NO compression

A used & recently rebuilt set of heads from a local bud was cheaper than having mine repaired...

Quote:
Originally Posted by Jim_Lou View Post
Were I doing this project, I would run a dry & wet compression test. That will definitively quantify the condition of the compression rings, and that will pretty accurately tell you the condition of the oil control rings. If dry compression is close to wet compression, the rings are in good condition and your oil burning is coming from somewhere else, and not necessarily valve seals.
Ditto, but add a leakdown test after dry/wet tests

Quote:
Originally Posted by CJ7Taz View Post
So, how long has it been since the donor 360 has been run? If itís been a while, itís pretty normal for it to burn oil. The rings, especially the oil wiper rings get stuck in the grooves due to the oil, mixed with sludge, thickening up.
Ditto, if it's been sitting for months expect some smoke initially, but after 15-20 should be gone. If the rings *ARE* stuck, the backyardigan method is ATF or MarvelMO dribbled into the cylinders and left to work for a few days. it can even be added to the crankcase to de-sludge the block, but be sure to not run it too long and expect to replace all the now weeping seals

Caver Dave
'72 "Mossy Edition" Commando
the Trail Forge
Caver Dave is offline  
post #6 of (permalink) Old 03-05-2012, 12:31 PM
Official Curmudgeon
 
CJ7Taz's Avatar
 
Join Date: Nov 2001
Location: Kansas
Posts: 4,701
Thanks: 2
Thanked 1 Time in 1 Post
 
I forgot to mention, CHANGE THE OIL.

There are 10 kinds of people in the world.
Those who understand binary and those who don't.
CJ7Taz is offline  
post #7 of (permalink) Old 03-06-2012, 10:37 AM
Mud in my Veins
 
Caver Dave's Avatar
 
Join Date: Apr 2000
Location: Winston-Salem, NC
Posts: 5,512
Thanks: 0
Thanked 0 Times in 0 Posts
 
Quote:
Originally Posted by CJ7Taz View Post
I forgot to mention, CHANGE THE OIL.
Definitely, as "some" products (STP/Motor Honey/Restore) have additives that make the oil "cling" better and WILL cause smoking from an otherwise healthy engine!

Caver Dave
'72 "Mossy Edition" Commando
the Trail Forge
Caver Dave is offline  
post #8 of (permalink) Old 03-17-2012, 07:30 PM Thread Starter
I Might Just Know What I'm Talking About
 
Join Date: Oct 2000
Location: C-ville, VA
Posts: 1,586
Thanks: 0
Thanked 0 Times in 0 Posts
 
Thanks folks. I'm planning to pull the engine over the next month and move it into it's permanent home (my other CJ). I'll do some of these tests after it is in the new frame.

Jeep...need I say more?
ExtinctJeep is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Off-Road Forums & Discussion Groups forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome