Engine top end rebuild?

[three8six]

Well it appears that my cam has thrown a lobe as I have bought a rebuilt quadrajet. Bought a new fuel pump. Bought new plugs, new wires. Set timing to 0 degrees, and my truck still runs awful. It stumbles shuts off and dumps big clouds of black smoke out of the exhaust. The motor is only a 4.3 v6(it's an 1986 SWB Chevrolet auto trans). So I am curious as to what kind of money am I looking at in parts? I know I would need a cam, lifters, timing chain/gear, and all associated gaskets/seals? Really from what I've seen for cost, I just need to abandon this ship and go a different route honestly...thanks for all suggestions and help ahead of time.

[Psycho71]

If it has flattened a lobe on the cam, you need to rebuild the whole thing. All that metal from the lobe has circulated throughout the oil system now.

But all in all, the 4.3 V-6 is about the best V-6 engine I've ever owned. I had one in a 1/2 ton long bed and it was a great little engine as long as I didn't try to run like it was a v-8. If it was doing a good job before, I'd spend the money to fix what ya got. It'll likely cost more to swap to something else when you factor in the added parts to do a swap of some sort.

[jaredts]

What troubleshooting have you done?  I'm not sure I would jump to conclusions yet.  Don't know what you mean by set timing to 0 degrees, as that's not where it goes if you're talking ignition timing.  You could plull plugs one at a time while its running to see if one cylinder is causing all your problems.  You could also borrow a compression tester and figure that out.  You could remove your valve covers and start it up, then run out quickly before there's an oil mess and look to see if all of your rocker arms are moving the same amount.  That will tell you if your cam is o.k.  You put on a newly rebuilt carb.?  Did you tune it, set the idle mixture, choke, anything on it?  Have you verified that the carb. isn't just flooding from a stuck float valve?  Are you using a stock type mechanical fuel pump?  Are these the same symptoms you had before you changed all those parts?

[topp]

If it has flattened a lobe on the cam, you need to rebuild the whole thing. All that metal from the lobe has circulated throughout the oil system now.

But all in all, the 4.3 V-6 is about the best V-6 engine I've ever owned. I had one in a 1/2 ton long bed and it was a great little engine as long as I didn't try to run like it was a v-8. If it was doing a good job before, I'd spend the money to fix what ya got. It'll likely cost more to swap to something else when you factor in the added parts to do a swap of some sort.

I'd say the I-6 used in late model trailblazers are better.  They make almost the same numbers as the 350's that were put in these trucks, and I think the torque is a little higher.
Here are the specs- 291 hp, 277 lb·ft , all-aluminum 4.2 L "Atlas" LL8 inline-six engine

[three8six]

Carb was tuned after being installed. It's not the problem. Also what do you think my timing should be set at? I'm talking 0 degrees without vacuum advance. I do not know what it is with the hose connected. We have timed it a couple of other ways just hoping the balancer was wrong. Also I do have spark at every cylinder. I have new coil, new distributor. All installed. I have not done a compression test. But if I have lost a lobe you are saying the entire motor needs to come apart?

[three8six]

Also as far as looking at my rocker arms while it is running? No I have not tried that, probably won't as my truck has a pretty recent paint job on it and I have recently cleaned the motor. I have no doubts in its effectiveness though.

[jaredts]

With the vacuum disconnected your timing should be in the neighborhood of 8 to 12 degrees before tdc, could be more.  You won't hurt your paint job running it for a few seconds with the valve covers off, at worst you'll drizzle a little oil down the sides of the block and maybe on the exhaust manifolds.  If you've lost a cam lobe you'll see one rocker arm not moving or barely moving.  A compression test or cylinder leakdown test would tell you a lot.  I don't doubt there's some truth to the shavings in your oil thing, but people replace just cam and lifters all the time.  The lobe wear should have been gradual enough to be washed out over several oil changes.  Pulling one plug wire off at a time while its running is a quick test.  You look for one wire that makes little to no difference when you pull it.  If the rpm's don't drop then that cylinder's not doing its share of the work.  It could be a bad valve, cam lobe, rings, plug, wire, it just tells you there's something wrong with that cylinder.

[three8six]

8-12 degrees before(retarded?)? hmmmmm.....That is a different take on it than what Ive been told. Not in anyway saying you are wrong. I have done the spark plug test(removing one wire at a time) and all of them seem to make a different equally. Also you just made it seem like a lot of oil was going to come pouring out. I have yet to do a compression test. Though I will post results when done. I will say the truck idles fine, and idles good but under load is when all these problems(see above) occur. Thanks very much for your suggestions keep them coming please.

[Grim 82]

IF the 4.3 follows the same rules as a sbc V8, set it at 8-12 degrees before top dead center. If you are at zero now, turn the distributor CCW.

[zieg85]

The sticker on my core support of my 1986 C10 4.3L V6 says 0 degrees BTD at 600 rpm, vacuum line off the distributor and plugged all at normal operating temp....

[three8six]

BTD? You mean TDC right?

[zieg85]

BTC is what it says actually

[three8six]

Please guys I think I did something really stupid...don't be too rough on me. Anyways well what if the vacuum on the side of the distributor is hitting the tube(with vacuum coming from it) when I spin it that far CCW? So I need to do what to correct this if it's the problem? Also shouldn't the #1 terminal on the distributor be close to being lined up with the center of the motor?(I'm sorry I just don't trust a lot of the off this boards advice?)

[HAULIN IT]

8-12 degrees before(retarded?)? hmmmmm.....That is a different take on it than what Ive been told. I have done the spark plug test(removing one wire at a time) and all of them seem to make a different equally. I will say the truck idles fine, and idles good but under load is when all these problems(see above) occur.

The 8-10* BTC would be ADVANCED from 0, not retarded. It doesn't sound like a cam lobe problem by your description...It would either be shaking badly & making a dum, dum sound (exhaust valve) or be popping back through the carb every revolution (intake valve).   

what if the vacuum on the side of the distributor is hitting the tube(with vacuum coming from it) when I spin it that far CCW? So I need to do what to correct this if it's the problem? Also shouldn't the #1 terminal on the distributor be close to being lined up with the center of the motor?

I don't understand what is hitting, the vacuum advance canister hitting the intake runner or something? Sounds to me you need to pull the distributor & align the rotor better to #1 on the cap. Not sure what you are referring to by "lined up with the center of the motor?" It doesn't matter where you call #1 as long as you have the firing order correct, however I like to make it "correct" per original...It also helps with sparkplug wire lengths since they were likely figured for the original placement.
Sounds to me that you have some ignition timing concerns, but the basis of the engine seems sound by your description. Lorne   

[three8six]

It does sometimes pop through the carb but then it shuts off, but certainly not on every revolution. My timing is set at about 8 degrees advanced. I guess I'll just keep playing with it. It's not hitting the intake runner but it is hitting something that sticks out of the intake with 3 vacuum lines coming from it. I am sorry I am feeling dumber by the moment. Thanks for all suggestions.