engine troubles

[Michael Nielsen]

I've got 2 problems that i cant seem to figure out. Ive got a rebuilt 350 about 1000 miles ago ( guy i bought it from got it from a builder.) attached to a th350 that was rebuilt at the same time as the engine swap with a NP205 on the back of that.

1. I have this sound like a marble in a can when accelerating at about 1700 RPM then above that it goes away and its not there at lower RPMs. I've done lots of research and cannot figure it out. it only makes the sound under load at that RPM if i put it in neutral while im moving it doesnt make the noise. I have an edelbrock 600 cfm 1405 carb on it that I replaced the metering rod springs to the heaviest one they have. Ive retuned it and still cannot get it to go away. I have played with the timing but no luck. I might add that when i got the engine i pulled the valve covers and noticed that one of the heads was from a 305 ( i asked a neighbor who is a car builder) and i was told it was fine so i didnt bother with it. So any Ideas on what the sound is and how to fix it?
2. I also have this weird white smoke that only comes out of the passenger side bank ( ive got true duals) but the smoke isnt an all the time thing its occasionally at start up but its more common after i stop driving. Ill get home and put it in park and let it idle for a minute or 2 and then it starts to smoke only from the passenger side. the oil is clear and the radiator fluid as far as i can tell is clear aswell. any idea what this could be?

Please help i've got a 300mile road trip coming up and i need to have it fixed

 

[Frankenchevy]

The rattling could be the way your exhaust is routed. Have you looked to see if it’s close to anything, like your transfer case? Are you sure everything is clearing in the head? You should do an Internet search on a squish test.

One of the heads from a 305? So do you have two different types of heads on your motor?

White smoke is usually coolant in the combustion chamber.

 

[1987 GMC Jimmy]

Expanding it a little, exhaust rattles can also be caused by an EFE valve that’s falling apart if you still have the factory manifolds. The honeycomb inside your catalytic converter could also be breaking up if you still have that. I wouldn’t describe detonation as a marble in a can sound, but it’s in the neighborhood depending on how you interpret sounds. So you’re running two different heads, huh? I would say that’s a no-no even if the valves and chambers are the same size. I don’t see a way that both banks of the engine can agree with each other and work together that way, especially when one side probably has higher compression than the other. White smoke at start up is normal, but if it doesn’t clear up when the vehicle’s warm, there’s a problem. I acknowledge that I’m reiterating some of what was already mentioned. I’d start by doing something about those heads. I’m so anal retentive that I don’t think I would have driven it more than once before doing something about that.

 

[Michael Nielsen]

The rattling could be the way your exhaust is routed. Have you looked to see if it’s close to anything, like your transfer case? Are you sure everything is clearing in the head? You should do an Internet search on a squish test.

One of the heads from a 305? So do you have two different types of heads on your motor?

White smoke is usually coolant in the combustion chamber.

I'll check the exhaust later today and get back. But I put the exhaust in and it looked like it was clearing everything. I've never heard of a squish test but I'll look into it. Yea it's got 2 different heads on it but a guy I know who has built several cars said it was okay. I should also add that it only makes the noise after it gets warmed up. Before it gets warm it's fine.
I'll look more into it as soon as I can.

Expanding it a little, exhaust rattles can also be caused by an EFE valve that’s falling apart if you still have the factory manifolds. The honeycomb inside your catalytic converter could also be breaking up if you still have that. I wouldn’t describe detonation as a marble in a can sound, but it’s in the neighborhood depending on how you interpret sounds. So you’re running two different heads, huh? I would say that’s a no-no even if the valves and chambers are the same size. I don’t see a way that both banks of the engine can agree with each other and work together that way, especially when one side probably has higher compression than the other. White smoke at start up is normal, but if it doesn’t clear up when the vehicle’s warm, there’s a problem. I acknowledge that I’m reiterating some of what was already mentioned. I’d start by doing something about those heads. I’m so anal retentive that I don’t think I would have driven it more than once before doing something about that.

The exhaust is completely aftermarket with headers. I didn't think it would work with different heads but I had someone say it was okay so I went with it. The smoke clears up when it's warm and I'm driving but it comes back when I stop driving and let it idle after driving for like 20 minutes then it starts to smoke out the one side

 

[4WDKC]

I'll check the exhaust later today and get back. But I put the exhaust in and it looked like it was clearing everything. I've never heard of a squish test but I'll look into it. Yea it's got 2 different heads on it but a guy I know who has built several cars said it was okay. I should also add that it only makes the noise after it gets warmed up. Before it gets warm it's fine.
I'll look more into it as soon as I can.

The exhaust is completely aftermarket with headers. I didn't think it would work with different heads but I had someone say it was okay so I went with it. The smoke clears up when it's warm and I'm driving but it comes back when I stop driving and let it idle after driving for like 20 minutes then it starts to smoke out the one side

does the smoke come out the same side as the 305 head?

It sounds to me like someone rebuilt the engine found it had a bad matching head and had a 305 head laying around they put on it thinking it wouldnt matter. If that engine was rebuilt to be 9:1 with a 350 head with the 305 that side maybe 10:1..Id look at swapping them if it were mine.

 

[Michael Nielsen]

does the smoke come out the same side as the 305 head?

It sounds to me like someone rebuilt the engine found it had a bad matching head and had a 305 head laying around they put on it thinking it wouldnt matter. If that engine was rebuilt to be 9:1 with a 350 head with the 305 that side maybe 10:1..Id look at swapping them if it were mine.

I can't remember what side it was on. I put the engine in over the summer last year. If I end up swapping it I'll probably just rebuild the 4 bolt main I blew that came out of the truck. I can get a set of rebuilt 350 heads for 250 bucks from a shop close to me

 

[4WDKC]

I can't remember what side it was on. I put the engine in over the summer last year. If I end up swapping it I'll probably just rebuild the 4 bolt main I blew that came out of the truck. I can get a set of rebuilt 350 heads for 250 bucks from a shop close to me

spend the extra money if needed and get a good set of heads, they all arent the same some 76cc smog heads arent good for power and make the swap almost pointless when for that same amount you may be able to get a set of vortec heads a customer dropped off and never returned for.

 

[Michael Nielsen]

spend the extra money if needed and get a good set of heads, they all arent the same some 76cc smog heads arent good for power and make the swap almost pointless when for that same amount you may be able to get a set of vortec heads a customer dropped off and never returned for.

I'm still in the process of learning but I didn't know it was possible to get a set of vortec heads for a pre 86 350.

 

[Dutch Rutter]

Before pulling anything apart. Try running some higher octane gas in it if you are not already. Only reason for saying this is I just had the same noise and it was due to running low octane gas which was causing a fuel ping. Plus its a quick, easy and cheap thing to check before digging into other possibilities. Could be the builder has it at a higher compression which wouldn't like lower octane fuels.

Now I'll actually read through the other posts and put my foot in my mouth

The white smoke out of the one pipe could be moisture or condensation built up in the one pipe somewhere from header back. This would explain why only one is spitting it out and not both. Or like has been said above and its due to the odd head.

 

[Michael Nielsen]

Before pulling anything apart. Try running some higher octane gas in it if you are not already. Only reason for saying this is I just had the same noise and it was due to running low octane gas which was causing a fuel ping. Plus its a quick, easy and cheap thing to check before digging into other possibilities. Could be the builder has it at a higher compression which wouldn't like lower octane fuels.

Now I'll actually read through the other posts and put my foot in my mouth

I was actually thinking about doing that because I've read a lot and that was one of the possibilities.

 

[Dutch Rutter]

I was actually thinking about doing that because I've read a lot and that was one of the possibilities.

Like @1987 GMC Jimmy said. Detonation which is what low octane causes doesn't normally get described like a marble but mine was. Sort of a low metallic rattle. Mine only would do it at 1/4 throttle cruising and then slowly rolling on the throttle. Yet it would disappear when no load on the motor (in Neutral) and would also disappear when hammering the throttle and the trans would downshift. Or I just couldn't hear it over the carb and pipes. Also it seemed rather sluggish but not slow or like a misfire.

 

[Dutch Rutter]

@Michael Nielsen I have a video of my sound I'll try and post up for you.

 

[Michael Nielsen]

Like @1987 GMC Jimmy said. Detonation which is what low octane causes doesn't normally get described like a marble but mine was. Sort of a low metallic rattle. Mine only would do it at 1/4 throttle cruising and then slowly rolling on the throttle. Yet it would disappear when no load on the motor (in Neutral) and would also disappear when hammering the throttle and the trans would downshift. Or I just couldn't hear it over the carb and pipes. Also it seemed rather sluggish but not slow or like a misfire.

That's pretty much what mine is doing. It's starting to drive me crazy. I have to get it figured out. I'm gonna start with the higher octane fuel and go from there. But if worse comes to worse I will end up doing a ton of research on either rebuilind one of the blocks I have with vortec heads or just swapping on a set of vortec heads. If anybody has any good info on doing a vortec swap let me know

 

[Michael Nielsen]

@Michael Nielsen I have a video of my sound I'll try and post up for you.

I would appreciate that

 

[Dutch Rutter]

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Here you go. Might be kind of tough to hear, But it was louder in the cab plus I was driving about 55-70 here so there is some wind and road noise. Its the rattling towards the beginning of the video. The louder at the end I think is my keys.

Also even if it is a fuel issue, Its still a good idea to get a set of matching heads.