Hello all, I've got few questions about my truck's engine.. Its a 390 v8 with c6 automatic transmission. Its the truck's second engine, and this motor was freshly re-built when it was dropped in in 1984 or 85. The problem is now it smokes. I've tried thickening the oil and all that, and it worked for a while, but now it smokes worse than ever. So, I'm thinking of either re-building it or replacing it. Which would be the way to go? I've never done a rebuild before, and I've been told that it's either the piston rings or the valve guides that are causing the problem. So, what should I do? How hard would it be to re-build an engine? How much would it cost? I know the smart thing to do would probably be just replace the whole truck, but, I'm attached to this one, and I don't want to just junk it. So, what would be your advise?

Sam

 

Before getting drastic on it, try a couple things, and give it a physical. Check the intake manifold bolts for tightness- a loose intake will suck a lot of oil from the valley. Also you can pull the valve covers to see if the oil return holes are clogged with sludge- the valve covers will fill up with oil and it'll get stinky. Shafts & rockers still tight? Sloppy clearances will also put too much oil in the covers. Are the drainback tins in place? PCV system working right? If nothing simple, try a compression test, all cylinders close together? Do they get better if you squirt a little oil in the cylinders? How do the plugs look, do they foul?

 

I should have mentioned this in my first post, I did a compression test and I had about 110 psi in 6 cylinders and 80 in one, I think the last one was about 60 psi, and its plug was gummed up with oil. When I get the chance I'll have to pull the valve covers and take a look.

Sam


p.s. In the mean time, would there be any harm in adding a second bottle of oil thickener?

 

It's like drinking a pint of Whiskey at night for a head cold. It won't help the cold, but you might feel differently about it.



John

 

as far as a rebuild goes generally i prefer to replace old with new parts if pratical and with in my price range.

last time i went through lmc and totalled up the cost of replacing the internals on my engine i came up with a price tag of about 3k plus shiping and handleing.
new
cam, shafts, valves springs pistons rings etc same heads intakes exhaust block distributor and a new rebuild carb.
i think prices have gone up but i don't think by much. i am still gonna do the rebuild but money says do it a little latter. hope it helps

 

ps i am with you i should by logic and price tag scrap it and move on but i like the truck so i will do it get my money's worth in the long haul

 

I've got another question, which is more likely to be causing the problem: My piston rings or my valves? I took the truck and drove around the block a couple times and let the engine warm up, and it seems like it smokes bad at idle, not so bad with slight throttle, and pretty bad when I give it more gas. I also pulled all the plugs this morning and one was really gummed up with oil, so I cleaned it off and started the truck, I got some smoke, and I ran the motor for about 3 minutes or so, then pulled the plug again, and it had already gathered some more oil. I'll have to check that manifold though, maybe that could help.

And jowilker, the reason I'd like to do it is so I can drive the thing home, without making life too miserable for the poor guy trapped behind me on the road!

Sam

 

I'd quit using the oil thickener (STP?), check for gunk in the valve covers, and change the oil, adding a can of Seafoam to the oil, and another to the gas tank with 1/2 tank of gas- the oil will probably get dirty real quick, if it does, change it again quick to get the crap out- the filter will only catch so much crap before it clogs 'n bypasses. Worth a try to see if the rings are sticking, and the valves 'n seats may clean up a bunch- having some compression left instead of dead holes makes it worth taking a chance on bringing it back. Keep changing plugs if they foul, keep the cylinders firing and hot, give it a chance- that oil thickener may have made things worse instead of better. The 428 in my '66 T-Bird had good compression on 7 and only 50 on the 8th, rough idle but smoothed out at speed- a couple detergent oil/ Seafoam changes and a couple cans in the tank, and the cylinder is up to 90, and getting better the more I drive it.
Bought a sweet little Ford 8N tractor last weekend, nice shape one-family ranch tractor from Calistoga, they hadn't worked it hard in years, as it was missing and smoking, and they had a 9N and an NAA there, never tried to fix it. Got it started, good oil pressure, barely had enough power to get on the trailer- and stinky. Had a plug wire that was missing the end- wire was just stuck in the boot New plugs and a wire robbed off a 390 core in the shop, fresh Delo 400 with Seafoam, and Seafoam in 10 gal of gas, ran it for 1 hr, big smoke cloud for a while, it's purring like a kitten now, smoking less all the time, hasn't even fouled a plug- needs to pull a disc or run a mower for a while, build a little heat in there

 

Sam, Don't fret over that, mash the gas and make him run to keep up. You will be home before he knows what is going on.

These guys may be headed in a little different direction that you are aware of.

Let's see if we can't get you straightened out without spending a lot of money.

Whattyasay?




John

 

I like that idea! This is my first vehicle and money is rather tight for me.

Sam

 

Another question, what oil should I use? I'm thinking something along the lines of just straight 30 weight, I think this whole mess was uncovered when my grandpa had the oil changed at the shop and the window sticker says they put in some C1030 oil. I'll admit I'm a little nervous about putting some more cleaner in the engine, I'm worried the gunk in there is the only thing keeping everything sealed up... Would this be anything to worry about?

Sam

 

Sometimes several oil changes in a row and some driving can free up stuck oil control rings and clear up most of the smoking just like a few others have said. detergent additives are ok, just follow the directions and don't use them all at once. I'm a fan of BG MOA. You that the rings are the problem in you cyl with low compression by doing a "wet" compression test, or doing a leakage test. the wet test is simply putting some clean motor oil down the spark plug hole and retesting compression- if the compression improves, your rings are leaking/stuck. A leakage test involves putting the suspect cyl at TDC compression and applying compressed air through the spark plug hole. noise in the intake manifold indicates leaky intake valve, noise from ex pipes indicates leaky exhaust valve, noise in crank case indicates rings. I"m pretty sure from what you've said here, that your problem is with the rings.

The cheap way out is a few 500 mile oil changes in a row. If this doesn't work, then you'll have to decide if its worth it to you to tear it down, locate the problem and fix it. If the motor's in good condition otherwise, there is nothing wrong with just doing a ring job, gaskets and driving it. If it comes to a rebuild, just do a good job inspecting and measuring everything, and replace the stuff that needs replacing.

15w40 diesel oil has more of the good stuff for flat tappet cams and more detergents- its great in these old motors. 10w30 or 10w40 is also just fine. Don't worry about oil leaks- if an old ford ain't leakin' oil, its out!

 

Did you check the vacuum modulator line for tranny oil ? A modulator leaking will cause a lot of smoke, same for clogged head drainbacks or intake gasket sucked out.


Good Luck-----------Hotwrench

 

vacuum modulator would lead to oil fouling in all holes, and he has low compression in the hole with the oil fouling- an intake gasket or oil drainback problem wouldn't cause a loss of compression.

 

Ok, thanks guys. I got the truck home, my grandpa drove it over (it was his rig since 73) and he gave a real good workout on the freeway for several miles, it smoked for a while but it cleared up after about a mile. Now it only smokes when I start it, only for a few seconds and not real bad. I think I'll change the oil and then take it from there. I'd like to enjoy it for a while before I do much to it!

Sam