OT: Oil burning engine

[rhoward]

I just bought a well used Ford F450 Super Duty flatbed with a 460 engine. I know the motor has a couple of burnt valves as when idling I it drops a cylinder or maybe two and on acceleration chugs up to speed. So I am certain the heads need to be rebuilt. The second issue is that it burns oil and smokes. I am hoping that this is because of loose valve guides and/or bad seals. But it could be rings and that worries me. Don't want to do a head job just to find the rings are shot. So here are the symptoms: on cold start-up no smoke, no smoke at idle, no smoke on acceleration, lots of blue smoke on decelleration as when going down a hill. If I give it even a tiny bit of throttle the smoke stops immediately and I mean immediately.

So what is the consensus? Heads, rings, both? Bty the engine has 137K miles on it and runs fine other wise. No weird noises, no overheating, good oil pressure.

Randy

 

[bjorn toulouse]

.........lots of blue smoke on decelleration as when going down a hill. If I give it even a tiny bit of throttle the smoke stops immediately and I mean immediately.

The description you give indicates valve seals/guides.
In a coast situation you have very high manifold vacuum which sucks oil through the guides.


Rex

 

[Carl Darnell]

Normally when the engine smokes on start up and then does not smoke much after that it is the valve guides and/or valve guide seals. When the engine smokes all the time it is the rings.

I think your looking at a valve job and new rings. The problem is if the cylinders are worn over .005" to maybe .010" being the max you may not have much luck.

.005" would be a safe bet for it working. On a truck that size it is not that much harder with the heads off to pop the pistons and replace the rings.

EDIT: of course it should go without saying that the rod and main bearings should be replaced as other have stated and please don't knurl the guides, it's a waste of money.

 

[moonlight machine]

There are just as many miles on the bottom end as the top end Just do the whole job and be done with it. If you seal the top with worn rings you will end up with a oil burner for sure. make sure you check the rod bearing clearance. if you fix the top end and the bearings are not up to snuff the next thing that will happen is you will end up with a rod knocking.

 

[Mud]

lots of blue smoke on decelleration as when going down a hill. If I give it even a tiny bit of throttle the smoke stops immediately and I mean immediately.

Worn rings.

 

[Hemiracer]

Do a leakdown test. It will reveal the extent and location of your cylinder leakage.

Roger

 

[KIMFAB]

Pull the plugs and do a compression check then shoot some heavy oil in the cylinder and another compression check. If the second reading is reasonably higher than the first it shows the rings are also bad.

 

[willbird]

I do not claim to be the worlds foremost expert on internal combustion engines, but I have never seen a person cure oil USAGE with repairs in the top end of the engine, nuisance smoke on startup yes, but actual oil usage beyond a pint in 1000 miles nope.

It used to be back in the 60's 70's and even into the 80's that GM engines were often worn enough on the cyl that they needed to be bored, but my brother in law has had one from the 80's that the cyl were very nice at 150k and just needed honed.

Bill

 

[loggerhogger]

I had a Mazda pickup that smoked like a freight train at startup. didn't use hardly any oil between oil changes, and a friend told me to have the valve guides knurled, and replace the seals. I had a mechanic friend do just that thinking that it would fix the problem when in fact, it made it worse. i would start the engine and the whole parking lot at work would be filled with blue oil smoke. I consulted with another mechanic, and he said that fixing the valve guides and seals without doing a ring job put more stress on the already worn rings causing them to allow more oil to pass by. It still didn't make a lot of difference on the dip stick between oil changes but that initial blue cloud on startup was embarassing to say the least. I finally traded the truck in and moved on.

 

[Alpacca Fortyfive]

I'm with Mud and Carl,

leaking valve guides drip oil onto the valve or into the cylinder which then blows out on start up, after that, there generally isn't enough coming through to give visible smoke or excessive consumption.
With worn rings, especially on engines with a throttle valve in the intake, when you decelerate, there is a vacuum in the cylinders during induction stroke, so oil spray gets sucked out of the crank case into the cylinder, hence the smoke. opening the throttle valve again stops the suction and so the smoke stops.

If there is that much wear with relatively low miles (unless the miles are incorrect or previous owners flogged the poor thing - high pressure in cylinders = lot of bearing pressure for rings on bores = increased rate of wear), something else may well be wrong, for example it has gone too long between oil changes, or had the wrong grade of oil, so it would be as well to check the big end, main and thrust shells.

We've got a 30 ton volvo dumper in pieces at work, it was smoking really badly on start up, but, ammong the problems we've found are seriously worn shells on the big ends and mains, and the guys fished the thrust shells out of the sump. The guys who we use for re cons say that the block and crank are beyond repair now. a strip down at an earlier stage may well have saved these.

 

[gbent]

A compression test does nothing to tell you the condition of the oil control rings. I know very little about Fords, so I don't know if the oil rings and the compression rings wear at the same time. There are some engines with ring packages where the oil rings wear out first, others where the compression rings go first, and others are well balanced. But do not assume loss of compression means poor oil control and vice versa.

Oil control was always an issue with big bore engines. That is the reason both Ford and Chrysler went with V-10 engines. Oil control is easier on 10 smaller pistons than 8 big ones. Poor oil control was causing problems with getting the engines to pass emissions.

My opinion is the entire engines needs rebuilt. Do not knurl the guides, that is a poor fix good only for brooming the vehicle to some unspecting sucker. And I'll agree with Willbird about a redone top end rarely curing an oil burning problem.

 

[split tenth]

Could be a ruptured diaphram on transmission vacuum modulator if so equipped.Check modulator with hand held vacuum device.

 

[J-Head]

If it were me I would keep running that engine the way it is because once the Cap and Trade bill passes you won't be running that big block gas guzzler much and you will never get your money back. If it is an operational problem and you can not get your job done the way it is look for a truck like the one I have in my driveway (1988 F-250 with 351 V8) with a rotted out body and a mechanically perfect engine and swap it.

 

[J. Randall]

Randy, I am going to be a little different than everyone else. If you definitely have burnt valves, then pull the heads first, bring each piston up to the top and inspect. If they all have a light even coat of carbon on the top, then it is most probably just valve guides and seals. If you are washing much oil up past the rings the tops will be washed clean of carbon and shiny around the edges. If this is the engine that had been setting for quite a while, you could also have some stuck rings, a little good quality penetrating oil will some times unstick them.
James

 

[lazarus]

Check Fords recall list, 1991 or 2 460's had a recall on the rings-they rebuilt our work truck for free. Don't know what year yours is, but it might be listed.

 

[flutedchamber]

If you are interested, I have a pair of 460 heads. They are cooked, surfaced, magnafluxed, NEW guides, valves, springs, keepers, retainers and seals.

It would be best if you used springs that match the cam you are running.

Roy

 

[Sean in CT]

I had a 460 powered box truck (van style front) with a c6 trans (ie no overdrive) and 4.10 gears.
If i used a multigrade oil such as 20w50 the oil pressure would start dropping after 500 miles so i got lifter tick at idle, esp coming off the highway. PRobably didnt help the bearing, rings etc either.

I switched to straight 40 weight which solved the problem. I think these engines get really hot in the valley area and cook the viscosity enhancers in multigrade oil, esp in the van style with low gearing.
What i learned is that 20w 50 is really 20 weight with viscosity enhancers (polymerizers is whet the chemists call them) which break down in Fords.../
just a tip for the future when its all fixed...

 

[jim rozen]

Some of the full synthetic oils use no VI enhancers at all, notably the mobil one
20W50. As such it does an excellent job in high temperature applications.
For a long time I ran that exclusively on air cooled motorbike engines. I've since
mostly switched to shell rotella synthetic.

Jim