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1970 AMC 390 oil smoke from RH bank

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pinkta View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pinkta Quote  Post ReplyReply Direct Link To This Post Topic: 1970 AMC 390 oil smoke from RH bank
    Posted: Mar/24/2020 at 2:26pm
Good day all. I have a real good one for the wizards on this forum. About 8 months ago I bought a one owner, original paint,1970 BBB AMX with only 47K miles on it. The fellow that bought it new had recently passed and I got it from his widow.

The engine had been overhauled 5000 miles ago and I was fairly sure it was good to go. Not so....When you start the car cold it will be good for a minute then slowly start pouring blue smoke(oil) out of the RH exhaust. I found in the previous owners notes he was adding about a quart to 100 miles or less. So I do know it was an existing issue. I cant even bring myself to drive it on the street it is so bad.

Anyway once I got over getting paying all the money for a car with this issue, I started to look into what may be going on. Compression is good all around, about 155 average. the number 6 and 8 spark plugs were very oil fouled, esp #6. My gut feeling told me it could be an intake gasket issue so I recently changed it as I found the rear seal on the block to the manifold was out of place. After changing the gasket the front seal on the block proceeded to blow out. So I am fairly sure I have extreme internal pressures at work. The PCV and grommet are new, I used the FelPro aluminum valley pan gasket as one should. The motor is stock and original to the car. I do not however, know what parts were used to overhaul the engine.

Now to today, I used a cheap inspection camera to look into 6 and 8 cylinders. It appears that number six piston has had some cylinder detonation as the surface is not smooth as the others are. It is also black with what I would think is oil residue. The cylinder walls that I can look at are all good the cross hatch is still evident.

Well after all that my question is whether or not to pull the engine now or is there something I have not checked that I should do first? Please ask whatever questions you feel may assist in your evaluation of this mess.

Thank you in advance for anything you can offer, the car is gorgeous and I really want to be able to use it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BDCVG Quote  Post ReplyReply Direct Link To This Post Posted: Mar/24/2020 at 2:33pm
Remove the valve cover and eyeball the umbrella stem seals.
1965 Austin-Healey 3000

1970 AMX 390 5 spd, Control Freak IFS and rear coil overs,4 wheel disc brakes

2008 Subaru OBXT 5MT
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bvpotash1 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/24/2020 at 2:40pm
Try removing the PCV, plugging PCV hose and manifold grommet. Might help you eliminate that as the source of the problem. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Heavy 488 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/24/2020 at 2:41pm
While the cover is off, inspect the rear oil drain hole for blockage from crumbling seals.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Ken_Parkman Quote  Post ReplyReply Direct Link To This Post Posted: Mar/24/2020 at 3:28pm
What intake is on it?

The good compression would indicate there is not a gross cylinder wall problem. I have seen intakes binding and not sealing correctly, and a consumption problem specifically on adjacent cylinders 6 and 8 may mean some kind of a gasket sealing problem in that corner of the intake, and then the vacuum at idle or other higher vacuum condition is sucking oil from the lifter valley.

If you still have the old intake gasket look for signs of incorrect sealing at 6 and 8 intake runner pair. Maybe the sheet metal is not correctly crushed? Look for the intake binding on the valve cover shoulder and not seating right.
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pinkta View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pinkta Quote  Post ReplyReply Direct Link To This Post Posted: Mar/24/2020 at 3:37pm
Well, I covered off a few matters. The valve stem seals are the nylon spring wound ones and look very good as best I can tell through the springs. The heads are very clean under the valve covers and the drain hole is wide open.

I ran the car with the PCV out and the carb inlet plugged and there was no change n the oil/smoke out the back. Lots of vacuum at the plate below the carb. I looked in the RH tailpipe and it is wet with oil. The LH looks normal to me.

In looking at the old gasket, I cannot see anything obvious telling me it was a misfit.

I believe it is safe to say the #6 cylinder is relative here but I sure don't understand why.

Thank you for the replies to date, please keep them coming if something comes to mind. I will try most anything to be sure what the next step is for this dilemma. .

Glenn
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pinkta View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pinkta Quote  Post ReplyReply Direct Link To This Post Posted: Mar/24/2020 at 3:39pm
Missed this question... intake is the factory OEM 5323C.

Sorry
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic Silver Quote  Post ReplyReply Direct Link To This Post Posted: Mar/24/2020 at 3:45pm
Originally posted by pinkta pinkta wrote:

Missed this question... intake is the factory OEM 5323C.

Sorry
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pinkta View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pinkta Quote  Post ReplyReply Direct Link To This Post Posted: Mar/24/2020 at 3:49pm
yes I ended up with a 3 where it didn't belong. 532C manifold
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 401MATCOUPE Quote  Post ReplyReply Direct Link To This Post Posted: Mar/24/2020 at 3:55pm
Do you have records on rebuild???  1970 390 had huge piston breakage problems from AMC, my 70 AMX broke a piston at 14,000 miles.  you could have great compression with a broken oil control ring.....Was the rebuild with pistons and overbore?  or maybe original pistons with new rings????   I had buying cars with "rebuild" engines, 90% of the time I have to pull it back apart to fix common errors.......patiently trouble shoot this, alot of good folks on here to help you look at a lot of angles.  Do you have the receipts from the previous work????  That would be a great place to start. 
Ross K. Peterson
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