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1970 AMC 390 oil smoke from RH bank

Printed From: TheAMCForum.com
Category: The Garage
Forum Name: AMC V8 Engine Repair and Modifications
Forum Description: AMC-made V8 engine mechanical, ignition and fuel from basic repair to high-perf modifications
URL: http://theamcforum.com/forum/forum_posts.asp?TID=104632
Printed Date: Jun/05/2020 at 12:30am


Topic: 1970 AMC 390 oil smoke from RH bank
Posted By: pinkta
Subject: 1970 AMC 390 oil smoke from RH bank
Date 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.



Replies:
Posted By: BDCVG
Date 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


Posted By: bvpotash1
Date 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. 


Posted By: Heavy 488
Date Posted: Mar/24/2020 at 2:41pm
While the cover is off, inspect the rear oil drain hole for blockage from crumbling seals.


Posted By: Ken_Parkman
Date 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.


Posted By: pinkta
Date 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


Posted By: pinkta
Date Posted: Mar/24/2020 at 3:39pm
Missed this question... intake is the factory OEM 5323C.

Sorry


Posted By: Sonic Silver
Date Posted: Mar/24/2020 at 3:45pm
Originally posted by pinkta pinkta wrote:

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

Sorry
5532


Posted By: pinkta
Date Posted: Mar/24/2020 at 3:49pm
yes I ended up with a 3 where it didn't belong. 532C manifold


Posted By: 401MATCOUPE
Date 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
68X,GoPac,343,AT,52A(1stCar)
68X,GoPac,390,4sp,52A
69X,GoPac,390,4sp,64A
70X,GoPac,390,4sp,87A,8
70X,GoPac,390,4sp,BBO,8
70 Jav SST,390,AT,BSO
74MatX,401,AT,Prototype
74MatX,401,AT


Posted By: PHAT69AMX
Date Posted: Mar/24/2020 at 3:55pm
Sympathetic to your dilemma, hopefully something not too involved.
A long shot, hope folks here aren't tired of hearing this...

While the intake is off the motor, screw all the intake bolts into the heads by hand until they bottom out and measure the distance beneath the heads. Also confirm the bolts are all the same length. Measure the intake flange thickness, washers if any, etc. Do the math, confirm actual clamping action is achieved by the manifold mounting bolts before they bottom out in all the blind tapped holes...

And just to point it out, anytime it is off the motor, always make sure the Intake Manifold does have in place the Sheet Metal PCV Baffle attached to the bottom of the Intake manifold with original 'Drive Screws' or other. There were 2 types, flat & domed, domed was later and on EGR type intakes.

Agree that stock AMC pistons were prone to be easily detonation damaged.


-------------


Link to a http://www.youtube.com/watch?v=MySiKQsmWxU" rel="nofollow - Short YouTube Burnout Video



Posted By: pinkta
Date Posted: Mar/24/2020 at 5:36pm
Sadly, I have no rebuild information. The lady said he had a box of papers and i would get it if she found it. I never. 

Anyway, I did see a .020 on one of the pistons when i used the camera. My head is telling he that I have broken ring lands on #6 cylinder and it is upsetting the engine with excess blowby, but I really have no idea of how accurate that may be. Is there a way to test something like that? 


Posted By: pinkta
Date Posted: Mar/24/2020 at 5:38pm
When I had the intake off there was a flat piece of metal(sort of fence like) that covered the area of the PCV on the inside of the intake. Should have taken a photo. 


Posted By: Heavy 488
Date Posted: Mar/24/2020 at 5:46pm
Ive had a broken ring land and it could easily be heard. Like a rattling rocker at part throttle.


Posted By: pinkta
Date Posted: Mar/24/2020 at 5:52pm
There is a couple of weird things at idle. I agree there is a sort of rapid light rattle if you are really listening. Also the engine seems to shudder at idle, very quick like and i cannot adjust it out with timing or carb adjustments. 

Make any sense? 


Posted By: Heavy 488
Date Posted: Mar/24/2020 at 6:04pm
With no papers in hand, no telling if a small cam update was done during a rebuild causing the small "shudder"  Unless it is opened up.


Posted By: ffltstn
Date Posted: Mar/24/2020 at 6:30pm
Years ago I have a bad oil smoke issue from my 401. I did not run a compression test, but the engine would run and rev fine.  It looked good in all cylinders till I took out the #8 piston. It came out in pieces.
No issues with the bore, no sign of a problem.  The fact that two cylinders have oily plugs makes me think that's not you issue, but anything is possible.



-------------
Ken In Orlando Fl.
'73 Javelin AMX
'73 Javelin


Posted By: Sonic Silver
Date Posted: Mar/24/2020 at 6:55pm
Originally posted by PHAT69AMX PHAT69AMX wrote:

Sympathetic to your dilemma, hopefully something not too involved.
A long shot, hope folks here aren't tired of hearing this...

While the intake is off the motor, screw all the intake bolts into the heads by hand until they bottom out and measure the distance beneath the heads. Also confirm the bolts are all the same length. Measure the intake flange thickness, washers if any, etc. Do the math, confirm actual clamping action is achieved by the manifold mounting bolts before they bottom out in all the blind tapped holes...

And just to point it out, anytime it is off the motor, always make sure the Intake Manifold does have in place the Sheet Metal PCV Baffle attached to the bottom of the Intake manifold with original 'Drive Screws' or other. There were 2 types, flat & domed, domed was later and on EGR type intakes.

Agree that stock AMC pistons were prone to be easily detonation damaged.






Is it okay to use a domed baffle on a non EGR intake? I assume that the flat one won't clear the bottom of an EGR intake. Is that correct?


Posted By: pinkta
Date Posted: Mar/24/2020 at 7:24pm
On the matter of a cam issue and the small shudder at idle. The car came with a brand new cam and lifters. No idea why? Could this be someone(now deceased) knew what was going on? can a cam issue cause this smoking on one side? 


Posted By: Trader
Date Posted: Mar/24/2020 at 7:52pm
The cam will not cause oil into a cylinder. As for the baffle, either flat or dome will be fine as long as you use one on the stock manifold. It was common practice to have steel mesh in the baffle to slow flow and allow oil a path to collect to the bottom of the baffle. That may have even been factory.
Some have put scotch brite pads in here - lots of debate on that one (I would not)!

Take Ken's and Phat's advisement's first and if no problem is found, time to pull the right head to have a good look.
Another possibility that I would not wish on anyone, is that the person that did the rebuild did not use the AMC torque sequence. This can cause the block to crack from the intake side of the block  to the cylinder - especially if it has been over bored. When taking the head bolts out, if one on the intake side of #6 is wet with oil, mag flux the cylinder. 


Posted By: billd
Date Posted: Mar/24/2020 at 7:54pm
Originally posted by Ken_Parkman Ken_Parkman wrote:

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.


I used plastigage and dry-fit an intake on the 390 I had and found the upper part smashed out flat and the bottom ends of the plastigage was hardly touched. Bingo - there was the issue. Angle was off, the intake hit at the top and hardly at the bottom of the ports. 
I had everything clean, put the plastigage along the ports top to bottom. 

-------------


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http://antique-engines.com" rel="nofollow - http://antique-engines.com


Posted By: pinkta
Date Posted: Mar/24/2020 at 8:35pm
Thank you to all who have participated in this query. I have a lot of new direction and will be on this as soon as I can. 

When looking at the old intake gasket there is no obvious area around 6/8 ports the is not compressed to the eye. before i go all the way on this, i will plastigage the manifold fit and see what I get. 

I was going to pull the engine, but i agree, pulling the RH head is a lot easier step to take as far as learning what is going on. that will be step 2 of the "next to happen" sequence. 

Thank you again, i fell I am going in the right direction with guidance from those who know. I was a GM dealer for 30 years, but not a whole lot of engine work, especially on AMC's. My first car was a 70 AMX, the passion has not left town. 

Thank you all one more time, I will keep this thread posted. If there are more relative ideas, i will be happy to act on them.

Glenn


Posted By: gmonde
Date Posted: Mar/25/2020 at 6:03pm
Originally posted by 401MATCOUPE 401MATCOUPE wrote:

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. 

yep my thoughts exactly, most off the shelf pistons for 390 where cast,, if its a actual 70 390
532 intake
529 block
291c heads

the compression is over 10.5-1 and pump gas is not is friends with this engine,, i broke a few sets of cast piston ring lands 


-------------
Gmonde

www.gmondeperformance.com

1970 rebel machine G/SA

11.23 @ 116.00

1970 amx 390 E/S
10.96 @ 120.96


Posted By: ccowx
Date Posted: Mar/25/2020 at 10:29pm
I am also one that has broken a piston or two in my day in a 1970 390. Not tolerant of detonation! In your case I am inclined to think that you are looking at broken ring lands. I am a bit puzzled by your even compression but you are losing oil for sure on that cylinder and there is lots of blow by, so I would expect you to have one or two pistons with something broken. 

One thing I wondered in looking over this thread, the static compression in this engine seems to be a bit low. 155 seems to be quite low all round, I would expect that from an 8:1 smog motor, not a high compression engine from the 60's. Mine has around 25 pounds more than that. It is stock oem cast pistons other than being .030 over. Compression is around 10.4:1. 

Do you think you have a ring issue all round, perhaps wrong rings or some other problem with the rebuild? The low compression and excessive blow by might be explained by this. I wonder if you might have a broken, mis installed or even missing oil control ring on #6 also?

Chris 


Posted By: Boris Badanov
Date Posted: Mar/26/2020 at 3:52am
1970 390 pistons are at best good paperweigts.
I broke a few dozen.

My guess is broken pistons
or a botched back yard overhaul.

Poorly fitted rings or especially the oil rings
missing or sticking will do this.

Either way you have at least one broken piston.
AMC pistons aint bad but the 1970 390 was
an exception, they were really not up to the task.


-------------
Gremlin Dreams


Posted By: 303Y03
Date Posted: Mar/26/2020 at 10:10am
There were some very poor 1970 390 cast piston made by Badger 20-30 years ago.
They were known to break from the top ring up from detonation.
Have some here.


Posted By: pinkta
Date Posted: Mar/29/2020 at 3:59pm
Hello to those following this thread....I have decided to go right through the engine this fall (hopefully)and ensure it is done right at least once. This new reality of life has made it so i better not start as God knows when i can finish with all the shops shut down. 

I am in complete agreement that at least one piston is broken. i also suggest the compression is low for a 10.5/1 engine. as someone stated, a lot of things tell me folks that were not sure what they were doing are involved in this rebuild 5 years ago. I will not go that route.

   Can I ask what pistons would be recommended to put in when i do get to this?? I am a fan of forged but? I am also thinking lowering compression might be the way to go? I'll also be going through the heads, anything to ensure I do there? 

Thanks again everyone, I truly appreciate the knowledge on the forum and plan to work with you folks come rebuild time. 


Posted By: ccowx
Date Posted: Mar/29/2020 at 6:07pm
I would not neccesarily do the forged thing, unless you are seriously interested in performance. Cast are generally lighter. They should be fine and will save some money. I would not worry too much about the comments on cracking pistons, just make sure the timing is good. I have run a set of stock cast oem types for a decade now, with numerous trips to the drag strip and no problems. 

As for compression, bear in mind that the camshaft will make a big difference here too. I am running a Group 19 cam which has lots of overlap and may help a bit. All that being said, you might consider getting a set of later large chamber heads and use that to lower compression. It is a lot easier to swap heads than pistons and they flow slightly better out of the box anyway. 

Further thoughts on the compression thing, I have 10.4 to one compression, calculated on the overbore and all that and I have no problems. You can limit the total advance and how long it takes to come in. Many people want to have it all in very fast and as much as possible. AMC v8's like anything from 34-38 total at WOT typically. I run 91 octane no ethanol and I have a total of 36 degrees. I could probably do 38 but I prefer to err on the side of caution. Timing is similarly a bit slow to come in by some standards. I still can turn a 13 second quarter on stock tires like that. Lots of inital and a fast advance curve generally help when it comes to low end and off the line, which is less important for most of us since we are just incinerating tires for the first 50' anyway! Ease off on the timing and buy yourself a margin of error. 

Another thing to consider is that you may not have as much work to do as you think. The bores sound like they are good and the bearings may well be also. If they are not damaged then really all you need to do is pull it apart, check all the clearances, put in new pistons and reasemble it correctly. Balancing is also obviously a good idea but overall you are pretty much able to do much of it yourself at home. 

It really depends on what you want, but if a stock rebuild is the goal, you are probably most of the way there and could still make cruising season, assuming you don't have any more ugly surprises! Now, let's just hope there is a cruising season...

Chris 


Posted By: pinkta
Date Posted: Mar/30/2020 at 11:35am
Hi Chris
That is exactly the stuff i need to know. Really appreciate the time taken. I am not a hot rodder and have every intention of going back to stock as the engine is original and all the part numbers line up. My summers are fairly booked up for a retired guy, so I am likely going to make this a fall project. I know the shop i would take it to is closed right now. 

Because I really do not know what I have, I am going to do it completely over again. 

I agree, social distance and cruising are not compatible....

Thank you
Glenn


Posted By: Boris Badanov
Date Posted: Mar/30/2020 at 5:41pm
Sucking on a Corona BEER and thinking that cars cant get the dang virus.
So why stop? Just nail it and hang on.

-------------
Gremlin Dreams



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