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How to "loosen" a locked-up/seized 390 engine?...

October 15 2007 at 10:01 AM
Carlos  (Login bond007pr)

O.K. while I'm fairly used to work on old cars, I have practically no experience with locked-up engines.
I am in "the talks" with the current owner to buy a '63 Mercury Monterey Convertible (Only a bit over 1,000 made that year). The car is fairly complete sans the front bench seat(I'm assuming I can put a'63 Galaxie in), and a couple P/W switches, but what put "the brakes" on me was the fact that the owner told me and I quote: "The original 390 is there, but I couldn't get it to turn by hand". My first question is, can you actually get to move a big block with your hands? I've done this in VW engines before, but hey, this is a big block!!! Second, A good friend of mine told me to remove the plugs, pour some "Marvel Mystery Oil" into the cavities and let it "marinate" over a few days, then try to crank it, (still without the plugs) in order to loosen it up. Does this sound feasible?

Any ideas/opinions/feedback?


This message has been edited by bond007pr on Oct 15, 2007 10:01 AM

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(Login milner351)

Re: How to "loosen" a locked-up/seized 390 engine?...

October 15 2007, 10:06 AM 

your friend beat me to the suggestion.

I know it sounds like snake oil, but marvel mystery oil is some amazing stuff.
I've seen it loosen up many things I thought were lost causes.

I'm assuming you'd be planning on rebuilding the 390 anyhow, or at least going through it to check what's there and putting in new gaskets.

Might as well give the mystery oil a try... if the car is not far from you, all that's lost is time, gas money and a can of marvel.


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Tom P
(Login tomposthuma)

often not

October 15 2007, 10:08 AM 

It depends how tight the fan belt is if you are trying to turn the fan. You should be able to turn it with a 15/16" socket and 18" long breaker bar.
It depends why it's stuck but you can do more harm by trying if there is rust in the bores and turning it breaks the rings and scuffs the bores. If it won't turn with a breaker bar you are better off beheading it and taking a look.

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(Login pmw)

freed up a 390 once

October 15 2007, 10:12 AM 

It had not been running for only 2 years and was stuck hard , I soaked the cyls first with penetrating fluid for 2 days then trans fluid for a day or 2 , I was able to get the engine to start turning with a pipe wrench ( I know it pretty brutal )on the crank snout apacer . gently back and forth until it would turn 360 degrees smoothly . The fan and rad were removed for access . I put each cyl to bottom center and used an air nozzle to clean out the dust and crust from the cyls . The engine started right up after reassembling the front end , but had a miss , I ended up pulling the heads due to stuck valves . I cleaned the bores with a scotchbrite pad after the heads were removed and they had very little rust on them , but you could see the marks were the rings were starting to bond to the # 2 cyl wall . I dont think I would free one up that way again . I would pull the heads at the very least and see what awaits inside . The car your talking about could have been parked when the engine seized due to a bearing or rod failure , who knows ? expect the worst and then any surprises you get will be good ones

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(Login milner351)

Re: freed up a 390 once

October 15 2007, 10:16 AM 

""The car your talking about could have been parked when the engine seized due to a bearing or rod failure , who knows ? expect the worst and then any surprises you get will be good ones""


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(Login gear_head_62)

I agree - you need to find out why it's locked

October 15 2007, 10:39 AM 

If it won't free up with a little penetrant down the spark plug holes (I use PB Blaster in situations such as this) and a breaker bar, I would stop trying and pull the heads and pan if possible.

Steve Photo Sharing and Video Hosting at Photobucket

-1965 Custom, police 390/4v, 4speed
-1962 Galaxie 500 Town sedan, FE/8v, C6
-various other junk

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(Login milner351)

Re: I agree - you need to find out why it's locked

October 15 2007, 10:45 AM 

this is a great time to rent buy or borrow a bore scope, they are coming down in price, but are still up there.

pulling the plugs and having a peak into each cylinder would tell a lot.

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(Login hardwy)

Run away Carlos..

October 15 2007, 11:36 AM 

You don't want to waste your time with that Ol' Junker.. Give my the guys name and number and I'll save you all that work..
Galaxie seats are the same frame and basics, but the fabric and patterns are completly different. A good interior guy can replicate it though..
We just freed a 390 in a donor car. Soaked the cylinders with sea foam and/or marvel mystery oil and let sit about a week. Work it back and forth with a breaker bar then slap 24 volts to the starter.
Chances are it's still junk.. Seriously though, if you decide to pass on the car let me know.

1963 Maurader S55
428 4spd

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(Login hastyb1)

Many times its just a valve

October 15 2007, 1:14 PM 

pull the push rods. or remove the rocker and smack eack valve with a dead blow hammer to see if one is stuck.

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Ray Hillebrand
(Login Rhillebrand)

Re: How to "loosen" a locked-up/seized 390 engine?...

October 15 2007, 1:19 PM 

I've dealt with a few rusted stuck 428s. Even if you break it loose it still is going to need to be pulled apart and refreshed. Chances are the oil rings will be rusted tight against the piston, rust will also jam the compression rings. I have pulled them out and could have reinstalled them without a ring compressor. If the cylinders are rusted so will be the crankshaft. Believe it or not, even with oil on the bearings they still rust. Condensation is usually the cause. In most cases the valves will be rusted to the heads and wont open or close properly.
Whether stuck or not it sounds like you can get a nice car. Don't take any chances that could permanently kill the motor...

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1960 Town Vic
(Login 1960townvic)

What do you mean by locked?

October 15 2007, 1:26 PM 

All the advice above is good for pistons stuck in the bore by rust. But it the engine is intact, and the hood was on the car, that is unlikely. If I did not see anything obvious up front, I would like to crawl under and look at the flywheel.

Sometimes locked means that the neutral safety switch is misaligned, and no power gets to the starter. I would want to hear the starter engage before I jumped to the conclusion that the motor was frozen.

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(Premier Login reman)

What everyone else said, plus...........................

October 15 2007, 1:51 PM 

use the "stuck" factor as a major bargaining tool. If it has been kept dry, hood closed, it will likely turn with the 15/16" and breaker bar on the damper/front pulley bolt. If that does not turn it, but it has been kept dry, it will most likely be stuck valves. RonW

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(Login cammerfe)

Forty years ago I bought....

October 15 2007, 1:58 PM 

a '59 Austin Healy. It had been setting in a garage for a year with the trans out and the front suspension in pieces. I put it all back together but in order to get the engine to turn, I primed it and then had a friend push me up to about thirty MPH. I had it in second gear and dumped the clutch. the first try just dragged the tires. With the second try it came loose and on the third try it started to run. I drove it back and forth to school (Livonia to downtown Detroit) for a year and then used it occasionally for another year before selling it. It used a quart of oil about every 1500 miles.

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(Login FalconStng)

freeing up locked engines.

October 15 2007, 2:08 PM 

I've freed up many an engine back in the day when I was young with no money. (Now I'm older with no money...lol). At any rate, I fill the crankcase up with diesel fuel, pull the plugs and fill all the cylinders with diesel fuel, and pour diesel, and fill the intake with diesel fuel. Now comes the hard part...patience. It's good to wait a week or so. The longer you wait the better off you are. I've freed VW's, assorted car engines including flathead v8's and tractors this way. Many of them I ran for a long time afterward without the need to overhaul. One word of caution....I did burn one down like this once....a VW....enough diesel got out into the muffler....I had the engine running....then poof....ignited the diesel and burned the car to the ground...I called the guy I was doing the work for....I've got some good news and some bad news....the good news is I got your car running.....LOL.

Good Luck,


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Barry R
(Login Barry_R)

Been there, Done that

October 15 2007, 3:53 PM 

This has just a bit of an off-topic touch - but it should spark some memories for the Detroit based crowd here.

Several years ago a buddy and I went to look at a 64.5 Mustang convertible that had been sitting alongside a Birmingham garage for several years. We found the car to be in reasonable shape and were curious as to the "J-J" letters pasted on the door.

The older gent selling the car told us that it belonged to his daughter - Jo-Jo Shutty McGregor - the helicopter flying weather girl for CKLW - the "big 8" - one of the most famous radio stations in the midwest during the 60's. Kinda cool....

Anyhow - the 289 was locked solid. We filled it through the plug holes and the carb with CRC-56. After a couple days we were able to rotate it about 15 degrees using a breaker bar and a three foot hunk of pipe. A few more days, and more CRC and we got 45 degrees. After about a week of this the darn thing broke completely free and fired right up. Smoked like all heck for a day or two and then cleared out & ran fine. Amazing.

Barry Rabotnick

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doug smith
(Login cjshaker)


October 16 2007, 5:12 AM 

I remember that station VERY well. Grew up listening to all the hits on that station........before FM was popular. I can still hear the jingle as they sang C..K..L..Wwww.


69 Mach 1 R-code - 427MR 4-spd
68 F-250 4wd - 390HP 4-spd
58 2dr Del Rio Wagon - 390 4-spd
63 Mercury Comet 4dr 170ci 3-spd. (24mpg)
65 Galaxie 500 2dr hrdtp - 352 automatic ( )

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(Login cammerfe)


October 16 2007, 6:34 AM 

was actually a Canadian station (note the 'C' instead of our 'W' or the western states 'K') from Windsor. And Byron McGregor---who married Jo-Jo---had to be the most belligerent sounding talker there ever was. He made a cloudy day sound like the end of the world. Those were the days!

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(Login MT63AFX)

Did the owner have the plugs out when trying to turn by hand? Simple question.........n/m

October 15 2007, 4:42 PM 


Mickey Thompson's 63 1/2 AFX Hi-Rise 427 Lgt/Wgt Galaxie,
1957 C-600 Cab-over carhauler w/390-4V, 2-speed rear-end
FGCofA member #4908
MCGC member #75

"There will ALWAYS be an FE in my LiFE"

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(Login tejarboc)


October 15 2007, 5:00 PM 

Be sure and check for the obvious. Be sure that the motor is not stuck due to some "mechanic" doing something silly. For example, I had a bro-in-law who replaced the clutch on his Austin. (Yetch!) The car sat for a year or so while he messed around with it. When he tried to fire it, the engine was "seized". He dragged it out of the garage and pulled it around the block with a friend's truck trying to free the engine by popping the clutch to no avail. I eventually got involved, thanks to the nagging of my ex-wife and found that the idiot had replaced the flywheel bolts with ones that were longer and they had threaded through the crank and embedded into the back of the block. My clue was when I pulled the trans and saw that the flywheel was loose and that the bolts were bottomed out against the block! LOL

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John Bednorz
(Login 68RCodeConv)

Had a 68 Torino with a locked up 390.....

October 16 2007, 7:27 AM 

turned out that mice were living in the intake and peed down past an open valve. Huge pits in the cylinder walls.

That motor wasn't going to spin no matter how big a breaker bar you got.

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(Login dablack)

just be careful

October 17 2007, 6:06 AM 

I was loosening a stuck 360 from a 72 F250 w/ 24,000 original miles. I stripped the front end to where there was just the frame and the motor. Had my 15" ratchet on the crank bolt. Yep, I thought I was making progress, but I was actually ripping the head off of the bolt. Strong like bull!

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(Login 65custom)

I have done 2 of them with Marvel's

October 18 2007, 12:37 AM 

..the first worked out nicly... the second marinated for a few weeks - I would go out every day and lean on the breaker bar a bit - never freed up. I gave up - poured the cylinders, lifter valley, rocker area's etc full of Marvels - wrapped it in a tarp - and stuck it in a corner. It has been about 6 months - I guess I should go out there and give it a try tomorrow.

If it dosn't work I'll be disassembling it and trying to break cylinders free one at a time - if that does not work I'll be haivng it vatted...

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