chevy 350 Valve Calibration admission and escape

[Yanqui84@gmail.com]

Hello Everybody,

As most of you know that my 57 President have a chevy 350 in it.

I finally took it for a ride around the block after a tune-up and the car is still back firing and even through the carburetor. My father thinks is that the the valves are too tight. Any of you smart guys out there can help me with the actual calibration specification, my father told me there are leafs and they have a number depending what the engine valves take, am thinking he is referring to the gap same thing you do to spark plugs. what they need to be set to? I Google it and everybody talks how to adjust them and don't see what my father is referring to. Please correct me if i dont make sense as im learning more everyday about cars,im a computer technician lol...

we replace:
Spark Plugs
Spark Plug Wire
Distributor Cap
Distributor Rotor
Change Oil
Change Oil Filter
Flush Radiator and put new fluids in there.

[bige]

If your Chevy is a stock 350 with hydraulic lifters the adjustment is done with the engine warm and running. Back each rocker nut out until it begins to tap. Slowly tighten the nut until the noise goes away. Then slowly tighten one more full turn by turning the nut 1/4 turn at a time. The engine will stumble a little on each turn just wait until it smooths out before you turn the next 1/4 turn.

It's messy but you can buy rocker clips to control the oil flow.

ErnieR


R2 R5388 @ Macungie 2006________________ 1988 "Beater" Avanti

[bams50]

If they're solid lifters, you set them with a feeler gauge. Most likely you have hydraulic lifters.

For hydraulics, here's how I do it:

1. With the engine off, find the pushrods that are all the way down (shortest).

2. Snug the nut down until it has no play, but no tension

3. Start engine; listen to the rockers and find the ones clacking and slowly tighten until they quiet down

4. When none are clacking, slowly tighten each another 1/4 turn. Pause after each to allow the lifter to settle. When you've done them all, go around again and give each one more quarter turn, following the same procedure.

5. Reinstall covers.

You'll have an oily, stinky mess, but it works[:I] If you have an extra set of covers, you could split them lengthwise and bolt the bottom halves on while you adjust the valves. Saves a lot of mess.

Robert (Bob) Andrews- on the IoMT (Island of Misfit Toys)
Parish, central NY 13131

GOD BLESS AMERICA

[Dick Steinkamp]

Adjust per how Ernie and Bob outlinned, but....Chevy hydraulic lifters rarely, if ever, need adjustment unless some work was done to the heads and they were not adjusted afterwards.

I'd look for timing off, wrong dwell (if a points type distributor), burned valves (check compression), bad carb or misadjusted carb, vacuum leak.

Dick Steinkamp
Bellingham, WA

[Yanqui84@gmail.com]

Ok now it makes sense why i could not find what my father is talking about because my car have hydraulic lifters. Is a 1993 Chevrolet Caprice LTZ 5.7 motor. Thank you all we will try your suggestions and hopefully stops backfiring. I got scare because the carburetor caught fire for a few seconds and that wasn't nice to my eyes.

[bige]

1993 5.7 would have started life as a computer controlled engine. If you could tell us the parts that are on it now ie. distributor, carburetor, intake manifold it would help with the diagnosis.

ErnieR


R2 R5388 @ Macungie 2006________________ 1988 "Beater" Avanti

[Yanqui84@gmail.com]

Well the engine is complete except the breather that goes on top of the valve cover that is not connected to the air filter and the actual air filter is not on the carb yet, but i dont think that being off can cause such backfiring through the muffler and carb. Sounds more like what you guys have mention bad valve calibration, or possible burnt valve. I hope is nothing worst. Even in this videos you can hear the backfiring:

http://s33.photobucket.com/albums/d53/yanquiel/?action=view&current=IMG_0309.flv

http://s33.photobucket.com/albums/d53/yanquiel/?action=view&current=IMG_0308.flv

[sweetolbob]

Yanqui

Bige has the right idea. Your motor( 93 LTZ) is a full computer controlled engine. Please take a couple of shots with the air cleaner off.

That will at least give us a starting point as to what we are talking about. Your motor must have been converted to a carb in the past. That entails a lot of modifications. Pictures will at least show us what type carb setup and distributor you have.

The back firing in the video could be a valve but also the dist off a tooth or two . It does not like being under load so something is off.

Bob

,

[bige]

Have you double checked the firing order, right wires on the right plugs in the right order. Burned valves are rare in the newer V8's and normally only cause a miss and subtle popping sound. You have what sounds like a cylinder firing on the intake stroke.

Timing that's severely off could cause that also but if it was off that much I think you would have a harder time starting the car. Extended crank for too far retarted and labored crank for too far advanced. Your car lights off quickly.

Check the plug wires for proper firing order but let us see what distributor and carb you are running.

BTW, how's the new Camaro?

ErnieR


R2 R5388 @ Macungie 2006________________ 1988 "Beater" Avanti

[laughinlark]

Like Ernie said. I'd check the firing order. I had a 65 Commander 283 do that. I had #5 & #7 crossed. Couldn't here it at idle. On the throttle it would pop back through the carb. They are next to each other on the dist cap & firing order.

Gordon

[rodnutrandy]

Might mention another reason to back fire. My truck was running great and I changed valve covers. truck missed badly after changing covers. First thought, crossed wires, nope, I went nuts for over a week chasing miss. it was water in my gas! Have no idea how it got that much moisture that quick, but 2 cans of dry gas fixed the miss.

Randy Wilkin
1946 M5 Streetrod
Hillsboro,Ohio 45133

[tim87114]

FYI on CHEVY 350's. They are notorious for the stud mount backing out of the block that the rocker arm bolts to. Feel the push rods and see if any are loose. Follow what the guys above said but if you find that a pushrod is still very loose after adjustment check the height on each rocker arm mount. You may find one has backed out. They need to be pressed back in. It's not the worst thing in the world but just a poor design by GM that stumps alot of people.