OK Guys, I need a little help here...ok, make that a lot! I've got a 390 in my '72 that is giving me fits. When I got the truck, the engine ran and had decent power, but the oil pressure was almost non-existent so while I was rebuilding the truck I decided to give the engine a complete rebuild. I took the block and heads to the same machine shop that has done every engine I have ever built and they tanked them and checked everything over and said that the block was not worn enough to need boring. The honed the cylinders and installed new cam bearings and that was it. They did a complete valve job on the heads as well. I also had them turn the crank. I built the engine using a mild RV style cam and an Edelbrock 4 barrel carb, but otherwise everything is stock. The truck ran good for a few months then the trouble started. With just over 5000 miles on the engine I was going down the road when it developed a knock in the bottom end and the oil pressure dropped to nearly zero. I shut it down and towed it home then pulled the engine and found that I had spun a cam bearing and apparently this caused the oil flow to the crank to be cut off which trashed the main bearings and scored the journals on the crank. Back to the machine shop to line bore the journals and buy a new crank. By this time I had read about the oil mods on this site so I gave this engine the full treatment. This time I installed the cam bearings myself and I put the engine back together and back in the truck. Another couple of thousand good miles then it developed a noticible miss. A compression check showed the #3 and #7 cylinders at about 90psi. I pulled the heads and the valve seats were badly recessed and the guides were shot. Off to the parts store for new heads! I installed the new heads and the truck ran good, but now it smokes considerably at idle and the exhaust smells like raw gas. I thought the carb might have picked up a little trash or the float stuck so I took it off, dismantled it and cleaned it completely. Put it back on and still it smokes. I know that the edelbrock carbs are picky about fuel pressure so I cranked it up, pinched the fuel line with a pair of pliers and it smoked until the carb ran dry. That ruled out flooding, so I e-mailed the edelbrock tech people who suggested going with different jets and metering rods to lean the mixture. I kept going leaner until the thing would barely run and it still smoked. I also adjusted the idle mixture screws until it wouldn't idle at all and it still smoked. The smoke is most noticible at idle or when you first let off the gas. At speeds above 2000 rpm there is no smoke noticible. The smoke looks white, which usually means water in the cylinder, so even though it smells like raw gas I figured I'd check the compression to see if I might have a head gasket leaking. The low cylinder was 132 psi and the high was 137, so that doesn't sound bad to me. At this point I am at a total loss. The engine runs smoothly and makes good power, but at low rpm's or when you let off the gas it looks like I'm fogging for mosquitoes. I'm hoping one of the FE guru's here can give me an idea of where to look next. This truck belonged to my wife's grandfather and it means a lot to her, but I've sunk a fortune in it already and can't afford to keep pumping money into it. I've built a lot of engines and never had one that I couldn't figure out, but this one has me completely stumped. If anyone has any ideas I'm willing to try just about anything at this point.

Thanks!

Clark

 

If it didn't smoke before the new heads and it does now and the heads are the only difference. Then guess what it may be the heads. If the intake runners on intake and head don't line up properly then it may cuase fuel to unatomize (is that a word?). This will allow alot of raw fuel to deposit in the cylinder. This maybe the cause of your problem.

The only way to be for sure of proper alignment is to use the same casting # heads that old heads were. If they are the same then you have other problems such as: valve guides could be bad allowing oil to seep through. A rich situation could be giving a false diagnosis of acctual problem. I am not sure were you got your heads, but I know that somemof the major chains carry reman heads for FE's. If you got it from one of them take it back. Get a new set hopefully closer to the casting # you had previously. If you can get a bare casting set have your machinist rework these heads so that they are right on. Install hardened seat and don't go over cam manufacturers specs for spring pressures. All of that should help, if not cure the problem.

Did you find out what cuased the valves to become recessed?? My guess is that still could be cuasing some kind of problem. Also post head casting #'s and that may help with the first possible problem I mentioned. I will try to reply ASAP with info on head #'s. By the way casting #'s are between center spark plugs on the heads.

Hope this info helps, and doesn't confuse. Good luck and keep the faith.

Scotty

 

[updated:LAST EDITED ON 05-Jan-03 AT 10:23 AM (EST)]Note on the recessed valve.

I had this problem in my original '72 heads. It's the soft seats on the new gas. Basically, without the lubrication in the gas, the seat ends up disintigrating during normal operation. Once this happenes, the valve will appear to be recessed into the head. It won't seal properly, and won't run properly, and will throw the rest of your valvetrain out of whack.

On mine, the engine had been rebuilt, and whoever worked the heads over just shimmed that one portion of the rocker shaft. After tearing things apart, I was really surprised the engine even ran. Good thing I didn't keep it going though, I had a broken piston skirt too, and would have had more problems. Three of my piston wrist pins had broken out of their keepers as well. Fun fun.

Anyways, hope that helps shine a little light on the valves becoming recessed.

As far as the white smoke... it does kind of sound like a problem with too much gas or the gas becoming too liquid on the way to be burned properly. I might suggest having someone do a port/gasket match on the heads and intake just to make sure it all lines up ok. But that's going to involve tearing your heads back off (and yes, I know what a pain that is)

Might see what other folks have to say though. I'm not 100% sure that that is causing your problem.
John

 

Heads matching is not the issue, I have a 61 head and a 72 head,
23 XXX miles so far, and it still purs like a kittin. As
long as the ports on the intake aren't too large for head ports
you should't have a problem.


Fe power

 

Clark! White smoke is coolant. Look at the plugs to see if one or two are nice and clean. I think that problem is with the new heads or the gaskets (intake and head). The rich mixture can be the carburetor, but I think you have eliminated that by changing the metering rods and the other tests you have made. Get the spec sheet for your camshaft. Is it ground 4 degrees retarded? Did you set the crank gear at o? Have you looked at the distributor, mechanical and vacuum advance mechanism? You know the old timing light and rev it up to see if the mark moves? Check the coil for a good spark and see if it passes the ohm test. Do you have anything going on with the plugs, like split fire, side gapped or anything?
William in Atlanta

 

Ok, the castting number on the heads is C8AE-H.

What John said is exactly what the machine shop told me about my old heads. They said the soft seats and unleaded gas were not a good combination. They said they could install hardened seats in my heads and fix them, but that it would be expensive. That is the reason I bought the neew heads, they already had hardened seats and new guides installed.

William, I don't think my problem is coolant. All the plugs look fine, there is no sign of coolant loss, no oil in the coolant, etc. and the smoke has a distinct gasoline smell. As for the other things you've mentioned, I'm running a pertronix ignition in the original distributor, but with a Crane advance kit and adjustable vacuum advance canistor. I'm running 10 degrees initial advance and 28 mechanical for 38 degrees total. The mechanical advance starts at just over 1000 rpm and is completely in by 2500 rpm. I have the wide cap, 8mm wires, and Bosch Platinum plugs. There is no pinging or anything else that makes me think it is ignition related. Just in case that was the problem I put new plug wires and new Autolite plugs in the truck today and it made no difference. As for the cam, the instructions that came with the cam said to install it straight up and that is what I did.

Clark

 

I thought about this a little bit more.

William is right. Most often white smoke is water of some kind. Black smoke would be too much gas. Bluish would be oil. I knew that...

You might have a leak somewhere in the system. Could be a gasket, could be a crack. I'd check the radiator, see if there's any oil in it (a good indication of a leak besides the smoke).

Might be worth it to tear things down and replace gaskets. And while you've got it apart see if there's any cracks in a cylinder wall or the heads.

I'd say there could be an off chance there's water being introduced somewhere else but if that was the case I'd expect it to burn off within a few minutes of running.

John