Light white smoke and backfire at high RPM or under load

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

DoubleDingo

Full Access Member
Joined
Jul 3, 2012
Posts
11,325
Reaction score
17,373
Location
Right where I am
First Name
Bagoomba
Truck Year
1981
Truck Model
81-C20 Silverado Camper Special-TH400-4.10s
Engine Size
Carb'ed Vortec 350
Some like to stir the pot, and some want to spend your money. It's your project, your build, your money, glean the good info, ignore the bs, and report back with your progress.
 

RanchWelder

Full Access Member
Joined
Jan 14, 2023
Posts
802
Reaction score
1,154
Location
Earth
First Name
--------
Truck Year
87
Truck Model
Blazer
Engine Size
355ci
In any event, my initial perception, you are trying to build a "simple restoration on a budget"; seems like it might have been spot on?
 
Last edited:

WFO

Full Access Member
Joined
Jan 6, 2017
Posts
3,717
Reaction score
5,110
Location
Texas Panhandle
First Name
Dan
Truck Year
1986
Truck Model
K20
Engine Size
350
Gents, I appreciate the concern about my old 350 being behind from a technology perspective. But, I'll probably only put a couple thousand miles a year on it once I get it restored. Perhaps if it were going to be my daily driver and see a lot of miles, I'd go with the roller cams. Others have also suggested to drop in an LS or at least switch to an HEI distributor. Frankly, I kind of want to get this truck running the way it was originally. I know it is old school. I'm not ignoring your suggestions. I just don't want to go there yet. Yeah, I'll be giving up performance, some fuel economy, and some longevity, but that's okay.
I'm with you there too, except for the HEI. I've only had one fail in 45 years, and it turned out to be an aftermarket module a previous owner had put in.

I've had plenty of points style distributors, including a duel point 440 Cuda.
The thing with points is that we usually don't address them until the engine seems to be running a little off, which ends up causing more carbon buildup and less longevity for the spark plugs.
 

iflyfisher

Full Access Member
Joined
Oct 22, 2023
Posts
105
Reaction score
213
Location
So Utah
First Name
Ken
Truck Year
1973
Truck Model
K20
Engine Size
350
@DoubleDingo, Yep, she's my truck! Warts and all!
@RanchWelder, I'm not sure on a budget and simple are words my wife would agree with! And I haven't even started replacing or fixing rusted panels or worn interior! This restoration will go well beyond getting it running. But it isn't going to be frame off, bring up to modern standards resto.
@WFO, very true re the points. That is exactly how it was with my old motorcycle. I'll have to be a little more proactive with the truck. They aren't hard to change. Just need to do it.

Lots of parts showing up at the house. Given family gatherings and weddings, I probably won't get back to the truck for another week or so.
 

iflyfisher

Full Access Member
Joined
Oct 22, 2023
Posts
105
Reaction score
213
Location
So Utah
First Name
Ken
Truck Year
1973
Truck Model
K20
Engine Size
350
Circling back to close the loop on this thread. Even though I haven't updated for over a month, I have been working on the engine. The heads had one intake and one exhaust valve that were leaking. The machine shop replaced all guides, 9 seats, and ground and seated all valves. I got the heads back a few weeks ago and have been slowly getting the engine back together. Because I had a lifter that wasn't rotating, I installed a new cam and lifters. The timing chain was very sloppy, so I installed a new chain and set of gears. I also installed a new oil pump, water pump, thermostat, belts, and radiator hoses. The old single exhaust was rusty and had holes, so I installed a new dual exhaust. I got everything buttoned up yesterday. Despite the nerves, I decided to start up the engine. I primed the fuel bowl with fuel and hit the ignition. The ol' 350 lit up immediately! I quickly set the timing, check the oil pressure, looked for leaks, then ran the engine at 2K for a half an hour, monitoring oil pressure and temp. Once the thermostat opened, I topped off the coolant and burped the hoses. After 30 mins, I shut down the engine and changed the oil filter and oil. Whew...pretty stressful for a first timer! But I couldn't have been happier to hear that engine run!

I took the truck out for a run today, and no smoke, no backfires, and no missing! The issues I was having I'm sure were due to the leaking valves. The sloppy timing chain likely wasn't helping either. Here is a pic of the engine with the new top end. I painted new parts and cleaned and painted old parts as I worked through the engine. Thanks again everyone for the input!

You must be registered for see images
 

Ricko1966

Full Access Member
Joined
Apr 11, 2017
Posts
5,610
Reaction score
9,152
Location
kansas
First Name
Rick
Truck Year
1975
Truck Model
c20
Engine Size
350
Okay sir, camshaft turns 1/2 crank speed cam bearings aren't usually a problem. Rod bearings are the last bearings oiled and the only bearings that see a rhythmic up and down motion as well as bearing the brunt of most preignition damage so they see the most abuse. Drop some rod caps,look for copper on the shells, look inside the big ends of the rod and make sure the cross hatch is still there.You will see 100 rod bearing failures to every main bearing failure,and 1000 rod bearing failures before you see a cam bearing fail. An oil pump more than what chevrolet put in it new,is not an advantage in most cases. And in some can actually be a negative. It takes more power to turn a bigger pump,a bigger pump has more potential for pumping the pan dry,and excessive oil pressure erodes bearing shells.
 
Last edited:

iflyfisher

Full Access Member
Joined
Oct 22, 2023
Posts
105
Reaction score
213
Location
So Utah
First Name
Ken
Truck Year
1973
Truck Model
K20
Engine Size
350
Thanks Rick. At this point, I have the engine all buttoned back up and running. I had pulled the oil pan when I removed the timing chain cover. I did not remove any of the rod caps. Perhaps I should have. I guess that will have to wait until a future oil change. The oil pump I put in was a Melling stock replacement. I replaced the pump shaft that uses the nylon sleeve with a shaft using a metal sleeve. Oil pressure is good.
 

Forum statistics

Threads
44,425
Posts
957,613
Members
36,779
Latest member
The Dirty Burb
Top