All around Chevy C20 care (1986)

[MathewC]

I bought a C20 off of my brother a couple of weeks ago. I am not extremely car-savvy unless it comes to general car care like suspension and general maintenance. A little car info, my dad just did the timing belt, replaced the transmission not too long ago, the truck is said to need a new carb, and needs new tires. Now I really don't trust my dad to work on cars at all. So I am wondering how a timing belt and timing chain are different and how I can tell if the timing needs fixed. If so, what would be the worst case scenario if it is off. I also heard that the manufacturer timing is bad and should be altered, like the manufacturer timing is wrong. Any input? Anyhow, would a bad carb and bad timing have similar symptoms? Finally, these tires are some screwed up sizes and are way too narrow. Something like 7.50 R16 or something like that. So I am wondering what options I have for tires sizes. Not what they would tell you at Wal-Mart if I were to go in and ask, but ones that would work. I don't want these super narrow tires because they perform extremely poorly in bad weather.

Sorry if this post does not go here and if it is a little long.
Any additional input on what to look out for is very much appreciated. I will take any advice into consideration. I will read anything posted on here no matter how long the message is or what the advice is in regards to, as far as the car goes.

 

[MathewC]

I would also like to add that I am not going to be driving this truck until I figure this out. Not trying to ruin it now.

 

[Johnny2Bad]

86 C-20? It has a timing chain, not a timing belt. Timing Belts are usually only found on Overhead Valve engines, not pushrod V-8's like your Chevy.

Almost nothing needs a new carb although often the carb can be tuned properly. You can buy a kit for these carbs for like $20, versus a new carb for like $300. Although it is not trivial to install one, I did my first one with no prior experience on my kitchen table just by following the included directions. You might want to buy a HP Books manual for the carb. It will tell you more than you want to know about how to set it up properly.

Not sure what you are talking about with regard to incorrect timing. You can adjust the timing somewhat for either better economy or better power, but not both. The factory setting is usually economy based. I would check it with a timing light, and if it meets the specs for your motor, leave it at that.

Double check the tire size; the C-20's I owned used the 16.5 size tire. They are not interchangeable with 16's. They are a true truck tire and there is nothing wrong with 7.50's. Stop thinking bling and start thinking proper load range for what you intend to carry in the truck. Narrower tires are better in snow, mud, and gravel, and work just fine on pavement.

Those vehicles (73~86 GM/Chevy trucks) are super simple and quite reliable. Keep the oil changed, carry a spare fan/alternator belt, and run her. End of story.

 

[Johnny2Bad]

If the timing chain was not properly installed, there are two dots on the gears that have to be lined up. Easy to remedy if wrong, just get a little dirty. Buy a repair manual for the truck.

If the timing is off due to improper timing chain installation, you will know it (backfiring, very poor running). If it fires up and idles smoothly, that's not the problem.

The C-20 has heavy duty brakes, a thicker steel in the frame, and heavier suspension compared to a half ton (C/K-10, C/K-15). Good vehicles overall.

 

[ragtoplvr]

The engine has a timing chain. It will run one tooth off, but poorly. requires tools above your level to check that.

Timing can be set with a timing light and a wrench to take the hold down loose. The spark advance is controlled by computer. If harness is disconnected it goes into limp home. This may have a feedback carb with mixture control. If so then that is above your current level.

You need to buy a motor manual for it, and read it before working on it further. It is a simple thing and easy to fix if you have the basic knowledge, your post indicates you lack. Get some. If the computer fails most change them back to normal carb and normal distributer, and the run fine.

However if emissions tests exist in your area then that may not be allowed.

10 to 12 MPG is normal.

Rod

 

[CharBaby]

Right, timing chain!
Maybe your dad replaced the serpentine belt(thinking/confusing it for the timing belt).

 

[supton]

Carb can likely be rebuilt; last I knew, most rebuilt carbs (from a parts store) were junk / poorly redone. That said, it can be a fair amount of work to do a Quadrajet, esp if the throttle bushings are worn. Might not be the job for a novice.

Not sure on the tires; but those should be easy to change to something more modern.

I'd get a manual and start reading up. Old carb motor like this, and you'll be the best mechanic for it. They are simple beasts, mostly mechanical.

 

[mk378]

Does the truck run OK? If not, what are the symptoms?

Feedback carb systems from the end of the carb era (ca 1986) are incredibly complicated to get and keep running properly. To the point that I would not buy a vehicle that has one.

It is possible though that it is one of GM's early fuel injection systems and your dad and brother just don't know what they are talking about. The "timing belt" thing is a clue to that.

 

[eljefino]

A one ton truck will have more conservative emissions goals to meet. I doubt it even has a feedback carb, "but maybe". If there's an oxygen sensor in the exhaust then yes it does.

If it'll go highway speeds I bet the timing chain is just fine. A lot of carb issues show up as trouble starting, idling, and stumbling getting on the gas. But they generally go at half throttle good when warmed up.

 

[TooManyWheels]

I still have an 86 Chevy half ton truck in my garage, and I have had many similar technology GM vehicles in the past. The carburetor on mine is not a feedback one, although it does have an additional electrically controlled accelerator pump. One thing to note is that modern gasoline has not been good for the normal, non-electric accelerator pump cup, so a rebuild may be in order on that score alone. Supton has a good point about the throttle shaft bushings possibly needing to be redone, and as he says, it takes some tools and aptitude to do it, not to mention a source for the drill and bushings. These used to be commonly available, it might take some research to find them now.

Theoretically, the fuel injection systems did not start until the 87 model year. Similarly, the distributor is not computer controlled, although it does have a circuit that retards timing due to a knock sensor. Sometimes that can give trouble, and the easiest fix is to wire around it.

In my experience, old school small block Chevy's need the timing chain replaced about every hundred thousand miles. They will run longer of course, but at some point the stretch will cause problems.

Probably the first thing to do is go over it carefully for deteriorated or badly connected vacuum lines.

 

[supton]

Depending upon emissions laws, miles per year and budget, I'd be tempted to go to a new carb, sans electronics. EFI is great but may not justify itself. Holley used to be good for power but IIRC Edelbrock has Quadrajet-like performance (could get mpg and power, albeit with more things that need adjustment).

All depends upon the engine. Might want to start with a compression test, check oil pressure, make sure the bottom end is in good shape. Then work the way outward.

 

[bubbatime]

I'm going to be 100% honest here. That kind of car is a hobbiest car and requires a pretty good understanding of old school mechanics to keep it tuned up properly. It will nickle and dime you to keep it running. I had an 86 K2500 a few years ago and I was dumping several hundred dollars into every couple of months just to keep it on the road.

My honest, best advice, is to sell it to someone that wants that style of truck, and get yourself something more modern, with fuel injection. Remember, they stopped installing carburetors on cars about 30 years ago, and most of the good technicians that know how to work on them are long retired. I bet that 75%+ of the technicians at your local Chevy/gmc dealership have never even rebuilt a carburetor in their working career.

 

[artificialist]

Originally Posted By: supton
Carb can likely be rebuilt; last I knew, most rebuilt carbs (from a parts store) were junk / poorly redone. That said, it can be a fair amount of work to do a Quadrajet, esp if the throttle bushings are worn. Might not be the job for a novice.

Not sure on the tires; but those should be easy to change to something more modern.

I'd get a manual and start reading up. Old carb motor like this, and you'll be the best mechanic for it. They are simple beasts, mostly mechanical.

This is why people should search their phone books for a local carb rebuilder. They can get the job done correctly, and usually for less money.

Another thing to consider is that the oxygen sensor should be replaced. After 1981, nearly all cars sold in the USA had an oxygen sensor in the exhaust, no matter if it used a carb, EFI, or even mechanical injection. On the old carb and TBI engines which were very smoggy, the old sensor would more quickly get covered with soot and lose accuracy. Having a properly functioning O2 sensor is critical to make the computerized carb function properly. Fortunately, O2 sensors for those engines are usually not expensive.

Another thing to keep in mind with the 1980s carb engine is that there are probably mazes of vacuum hoses to operate the smog devices. They probably are failing, but every plastic part they are connected to is brittle and may crack easily. The engine probably has an EGR valve, and if the engine has problems with knock and high NOX emissions, you would need to clean the EGR valve and clean all the passages which direct exhaust gasses into the intake. Sometimes you can't clean an EGR valve, and replacement is the only option.

These computerized carbs can trigger a check engine light if certain problems occur. Know how to scan for codes. Code readers for old GM engines aren't expensive. Sometimes people will remove the check engine light bulb rather than properly repair their vehicle.

 

[clinebarger]

Originally Posted By: artificialist
Originally Posted By: supton
Carb can likely be rebuilt; last I knew, most rebuilt carbs (from a parts store) were junk / poorly redone. That said, it can be a fair amount of work to do a Quadrajet, esp if the throttle bushings are worn. Might not be the job for a novice.

Not sure on the tires; but those should be easy to change to something more modern.

I'd get a manual and start reading up. Old carb motor like this, and you'll be the best mechanic for it. They are simple beasts, mostly mechanical.

This is why people should search their phone books for a local carb rebuilder. They can get the job done correctly, and usually for less money.

Another thing to consider is that the oxygen sensor should be replaced. After 1981, nearly all cars sold in the USA had an oxygen sensor in the exhaust, no matter if it used a carb, EFI, or even mechanical injection. On the old carb and TBI engines which were very smoggy, the old sensor would more quickly get covered with soot and lose accuracy. Having a properly functioning O2 sensor is critical to make the computerized carb function properly. Fortunately, O2 sensors for those engines are usually not expensive.

Another thing to keep in mind with the 1980s carb engine is that there are probably mazes of vacuum hoses to operate the smog devices. They probably are failing, but every plastic part they are connected to is brittle and may crack easily. The engine probably has an EGR valve, and if the engine has problems with knock and high NOX emissions, you would need to clean the EGR valve and clean all the passages which direct exhaust gasses into the intake. Sometimes you can't clean an EGR valve, and replacement is the only option.

These computerized carbs can trigger a check engine light if certain problems occur. Know how to scan for codes. Code readers for old GM engines aren't expensive. Sometimes people will remove the check engine light bulb rather than properly repair their vehicle.


8,600 GVW & up GM Carbureted trucks didn't have a O2 sensor, Mixture Control Solenoid, Electronic Spark Control & all that jazz.

My '85 C20 Suburban (8,600 GVW) could run Leaded Fuel, No "Unleaded Fuel Only" anywhere on the truck, & it had a Diesel filler neck.....No Catalytic Converter, & Dual Exhaust from the factory, The only emissions equipment was a EGR Valve & Dual Smog Pumps. And no it wasn't a Mexican Market truck....Bought new from Bruce Lowrie Chevrolet in Ft. Worth Texas.

 

[clinebarger]

2000 & up GM Forged Aluminum wheels fit these trucks perfectly, Then you can run a wider tire like 265/75/16.

My Suburban with 2004 wheels & 265/75/16's circa 2011.

 

[MathewC]

One of the problems with these tires is that they are really hard to find used. I personally hate buying new tires because I can find treads like new for my Accord anywhere. I won't really be hauling anything in the truck to worry about load capacity. The mention of vacuum hoses is a good point. Though I believe that it is the timing belt. It kinds of sputters funny while in park and when you turn the truck off. It kind of idles even after you shut it off. Like a sputtering idle. Though I am not sure what that is about. The truck does kind of seem to struggle getting above 40mph. Like I said, I am not trying to run it if anything substantial is wrong with it. I changed the oil and used the advice of many people on hereand put in 15w40 Rotella with a Wix filter.

 

[TooManyWheels]

I would suspect retarded distributor timing and/or a bad vacuum advance cannister on the distributor.

 

[MathewC]

About the timing chain, that is why I asked what the difference is between a belt and chain. My dad said it was a chain. All I know is, doing the timing belt on my Honda was a pain and it also has an auto shutoff. I am sure that a truck like this won't have one though. In regards to the tires, my brother said that they don't perform well on snow, rain, and that he got stuck in mud before. I will personally not be driving it in mud or gravel at all. Biggest concern will be rain, snow, and price and availability. I am trying to be practical with this truck. Not going to be looking for lift kits, stacks, or shiny new rims. lol This is more or less going to be a little project and secondary car for when I am working on my other car. Not to mention it was my grandfather's truck.

 

[TooManyWheels]

After reading back through your statements I have to ask, Do you know the difference between ignition (distributor) timing and cam timing, and how they are related? Either one could be off, but the ignition timing is easier to check. If we are losing you on this it might be time for you to seek out someone in person who is more experienced.

Also, there is no question that it is a timing chain.

 

[mk378]

How many miles are on this truck?

OP you have to realize that you have an antique collector / enthusiast truck, not a practical daily driver. It's going to eat you alive with its mechanical needs.