Popping, Backfiring, Catching on Fire, Need Helppp
03-21-2003, 12:50 AM
#22
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Miguel-
You probably have a simple problem and are overlooking it.
You have compression, fuel, and spark- so you have got to verify cam, ignition timing and valve operation. It is not hard to do. You will need a dial indicator and a degree wheel.
Another concern with backfires is to make sure that you don't have a bad exhaust lobe. spin the motor and watch the exhaust rockers real good....
First check to make sure the timing mark on the balancer is correct- my brother has a late 350 balancer that has TDC straight up at TDC, and the older style pointer that is about 30 degrees towards #1. Ran like crap until we went through the verification procedure.
If you know the cam number, find out the intake lobe centerline degree point. This will be about 10 degrees AFTER top dead center and is the point at which the intake is fully open. This method eliminates any concern over a mis-marked timing mark- it directly ensures the cam is where it is supposed to be.
Next, make SURE the ignition timing is right. I rotate the engine until the exhaust is closing and intake is opening on #6 cylinder, at Top dead center. At this point, #1 cylinder will be at TDC on the firing stroke. Then check plug wires for firing order, 1-8-4-3-6-5-7-2, clockwise at the distributor top.
Next, I would check the valve lash.
Solid- use feeler gauges.
Hydraulic- Start at #1, TDC by looking at the distributor rotor. loosen valve adjusters on #1 in & ex valves. tighten adjusters until the slack just disappears, and go 1/4 turn more. Rotate the engine to #8 cylinder and repeat lash procedure. Continue through the firing order.
Some people rotate the pushrod betwwen the thumb and index finger to feel when the slack disappears- I also know of a guy that uses a thin feeler gage and then goes 1/2 turn more.
gotta go
Bulldog
You probably have a simple problem and are overlooking it.
You have compression, fuel, and spark- so you have got to verify cam, ignition timing and valve operation. It is not hard to do. You will need a dial indicator and a degree wheel.
Another concern with backfires is to make sure that you don't have a bad exhaust lobe. spin the motor and watch the exhaust rockers real good....
First check to make sure the timing mark on the balancer is correct- my brother has a late 350 balancer that has TDC straight up at TDC, and the older style pointer that is about 30 degrees towards #1. Ran like crap until we went through the verification procedure.
If you know the cam number, find out the intake lobe centerline degree point. This will be about 10 degrees AFTER top dead center and is the point at which the intake is fully open. This method eliminates any concern over a mis-marked timing mark- it directly ensures the cam is where it is supposed to be.
Next, make SURE the ignition timing is right. I rotate the engine until the exhaust is closing and intake is opening on #6 cylinder, at Top dead center. At this point, #1 cylinder will be at TDC on the firing stroke. Then check plug wires for firing order, 1-8-4-3-6-5-7-2, clockwise at the distributor top.
Next, I would check the valve lash.
Solid- use feeler gauges.
Hydraulic- Start at #1, TDC by looking at the distributor rotor. loosen valve adjusters on #1 in & ex valves. tighten adjusters until the slack just disappears, and go 1/4 turn more. Rotate the engine to #8 cylinder and repeat lash procedure. Continue through the firing order.
Some people rotate the pushrod betwwen the thumb and index finger to feel when the slack disappears- I also know of a guy that uses a thin feeler gage and then goes 1/2 turn more.
gotta go
Bulldog
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03-21-2003, 08:19 AM
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I just don't see how you can get a exact reading of when the valve is opening with the heads off, you can get close with a reading off the lifter but if your going to bother to deg. the cam don't you want it exact. I have built a lot of motors and read a lot of books on it and have never seen it done with out the heads on. With rockers at different ratio's it sure seems to me it would be a lot easier with the heads on. But I see what you are talking about.
Last edited by Lapse of Reason; 03-21-2003 at 08:21 AM.
03-21-2003, 08:57 AM
#25
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what were your cam timing numbers when you dialed it in?? and do not forget to run the numers on more than one hole....i do 4, that way i know for sure. I also use a very large degree wheel. dig those numbers up for us! your timing should have been set to a ballpark at the very least when the wheel was still on.
bulldog had some really good points!...
LoR is correct
i just skimmmed over the posts...sorry if i repeated something.
bulldog had some really good points!...
LoR is correct
i just skimmmed over the posts...sorry if i repeated something.
03-21-2003, 09:03 AM
#27
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bulldog is 1000% correct!! "Miguel-
You probably have a simple problem and are overlooking it.
You have compression, fuel, and spark- so you have got to verify cam, ignition timing and valve operation. It is not hard to do. You will need a dial indicator and a degree wheel. "
remember this procedure IS NOT FOR DIAGNOSTICS! it is a 100% must for building an engine...if you put this engine together and installed with out doing this one BASIC thing...you are not only asking for problems but will have no data to support ANY future diagnostics.
You probably have a simple problem and are overlooking it.
You have compression, fuel, and spark- so you have got to verify cam, ignition timing and valve operation. It is not hard to do. You will need a dial indicator and a degree wheel. "
remember this procedure IS NOT FOR DIAGNOSTICS! it is a 100% must for building an engine...if you put this engine together and installed with out doing this one BASIC thing...you are not only asking for problems but will have no data to support ANY future diagnostics.
03-21-2003, 09:11 AM
#28
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turbojack is also correct...it is done both ways and there are benefits for both...i prefer to do mine after the heads...i can then see valve terrain geometry and play with racker ratio and PR length.
03-21-2003, 10:29 AM
#29
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This so simple I felt really stupid when I screw it up one time. Make sure you have the correct side of the engine for your #1 cylinder. On International gas engines it is backwards from Ford and GM. I could get the engine to idle reasonable well but it had no power. Even had some very good mechanics look at it that didn't check something so simple. I ended up replacing a perfectly good engine. (duh)
03-25-2003, 12:56 AM
#30
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I had a similar problem and it turned out to be the microprocessor in the distributor arcing across to a wire which had been replaced recently. Check the little wire running out the lower external aspect if the cap.
