1977 Chevy 350 Smokes till Warms up, then quits?

[LBJ]

On my 1977 Chevy Bonanza with 350 and automatic tranny, engine miles estimated to be around 75K to 90K miles with nothing major done (disconnected the speedo in 1980 until 2007 because it was making a big racket) it will smoke out the tail pipes until it reaches the operating temp setting on the gauge, which corresponds to the thermostat opening. If I start up and just start driving, it is usually warmed up in a few minutes and quits smoking. But, even sitting in the drive and letting it run to charge the battery after sitting for weeks, it will smoke and then magically quit. And, more, if I drive it regularly every day, as opposed to sitting for weeks between drives, it won't smoke even when dead cold. Now, what could be the cause of this? If it was rings, it would never quit smoking. Valves? Maybe valve guides are worn, but that's about all I can think of. Any ideas? It's not a problem worth tearing down the engine or pulling the heads, but I'd like to know why the heck it does this. Ha. Thanks for any tips. LBJ

[mattfranklin]

Can you tell if it is smoke or steam?

My first worry, but a less likely problem, would be head gaskets leaking water into the engine. When the parts warm up they expand and seal the gasket again. But when cold it repeats the slow leak. There is a risk of hydro-ing the engine if it gets worse.

A less serious and more likely problem might be valve guide seals.

Let's see what the others say.

[LBJ]

Hi Matt, I also need to say it's been doing this almost from new in 1977. So, not sure how that figures into the equation. But, valve guide seals might be close. Also, the left side dual exhaust seems to smoke more than the right side. And, if she blows, she blows (hydro-ing)! Guess i'd have to get a new crate engine then.

[mattfranklin]

Interesting! I remember reading a Smokey Yunick column in Popular Science years ago (maybe mid-1970s???) on the BBC and how it used a lot of oil from new because of looser valve guide seals. Dealers told them that 1 qt per 400 miles was "normal." Smokey was not buying that BS story and thought they should get new seals. Not sure if the SBC had the same seal designers or suppliers at the time.

[68gmsee]

Worn guides, in my experience, start off with a slight puff of bluish smoke after engine has been sitting for some time and stop or diminish after engine warms up. It may be that it has been doing it for so long that you consider the oil usage as normal usage. I had a 77 in my 69 truck and heads were not GMs best.

One thing you need to do is to determine what the smoke is. If it's white it's more than likely moisture of some kind. Either condensation or internal leak. If it has a blue hue to it, it could be oil and you would notice that when checking the oil. If it is more of a dark gray to black color than it's a rich fuel mixture and engine may be getting extra fuel in exhaust until the engine warms up.

[LBJ]

Well, it's been running rich for a long time. I have black residue on both the chrome exhaust tips. Smoke is grey color. I noticed on at least one side (right side above the exhaust pipe connection) of the exhaust headers, there is a device with coil spring that apparently opens and/or closes upon temp increase/decrease. Could this be a factor if it's not working correctly?

[YoungPup1977]

If this engine has done this since 1977 why are you worried about it now. Sounds like you don’t drive it Dailey but if you did it won’t smoke. Unless you are really bored and have money to burn. Open up the engine and find nothing wrong but valve seals need replaced with new technology seals. Getter done.......
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[LBJ]

I'm not concerned about it, just want to know why it does what it does. There HAS to be a reason. Whether I can fix it or want to fix it depends on what the cause is. Runs fine other than that, for a 41 year old engine. If I could get out of paying property taxes and home/auto insurance for JUST ONE YEAR, I could buy a brand new crate engine or have this one rebuilt! Haha. But, sadly, taxes, death, and insurance payments remain constant. ha

[YoungPup1977]

Well take the plates back to dmv and drop the insurance on the truck. We can wait a year or more and assist you on replacing the engine with a crate engine and help you spend your money on the RIGhT crate engine. I bet you can get lots of reply’s on what crate engine to buy.
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[LBJ]

I wish it were that easy! Ha. But, property taxes and home insurance are the real killers ($4500). The amount I saved on letting the 77 remain undriven for a year would be almost nothing. In fact, it would likely make rates on the 2004 go UP due to dropping the multiple vehicle discount! haha.

Guys just like to fix things, if possible. Especially Gear Head Guys! I always say that fixing something is easy, figuring out what needs fixin' is hard!

[cadillac_al]

It's probably a combination of not being driven enough and a mis-adjusted choke. You shouldn't need much choke at all in TX.

[LBJ]

Hi Caddy Al, yes, maybe the choke needs backing off a bit. Been a while since I looked at the choke setup. Have to take a look at that.

[Dead Parrot]

It's Texas and Summer. Just take the choke plate off and see if the smoke goes away. If it is a Q-Jet, two screws and you are done.

If it is the valve seals, I think there is a gizmo that let's you change them without pulling the heads.

[68gmsee]

Originally Posted by LBJ

.... there is a device with coil spring that apparently opens and/or closes upon temp increase/decrease. Could this be a factor if it's not working correctly?

Sorry, LBJ, I missed this question.

The part you are referring to is called a heat riser. It's there to speed up warming of the engine carb. I still have one in my 68 six cylinder but only cause it came with the replacement manifold and still works well. A lot of people just wire them open or get rid of them completely.

Here's a writeup and explanation on it's purpose.
https://www.hemmings.com/magazine/hm...e/3744251.html

[68gmsee]

Originally Posted by Dead Parrot

It's Texas and Summer. Just take the choke plate off and see if the smoke goes away. If it is a Q-Jet, two screws and you are done.

If it is the valve seals, I think there is a gizmo that let's you change them without pulling the heads.

It's called a spark plug adapter or valve holder. I use mine with a small air compressor. It prevents the valves from dropping down when removing the valve spring and retainers. Some people just use a thin nylon rope inserted in the cylinder and then rotate the engine so piston is up in to keep the valves from falling down.
https://images-na.ssl-images-amazon....IL._SY550_.jpg

[LBJ]

Today I pulled the 77 out of the garage and wired open the choke. Still smoked. 1 idea down. Replacing the valve seals might not be too major a task. I saw Wheeler Dealers do it on one show. Time consuming for sure.

[68gmsee]

Originally Posted by LBJ

Today I pulled the 77 out of the garage and wired open the choke. Still smoked. 1 idea down. Replacing the valve seals might not be too major a task. I saw Wheeler Dealers do it on one show. Time consuming for sure.

Shouldn't be more than a half day's leisurely work or as my brother in law measures time -about three, four cans of favorite refreshment.

If you don't have a valve spring compressing tool you should be able to rent one for free at Autozone or O'reilly's. Also, remove all the spark plugs to make it easier to rotate the engine and plug the oil return openings on top of the head. This keeps retainers from accidentally falling in and maybe even buy a small pencil style magnet to make it easier to remove and/or retrieve retainers.