The Ford Barn

mll1446 · 10-16-2012, 04:49 PM

I read where you can put a plastic bag over oil filler to determine engine damage by if bag fills with air or flutters would determine possible internal engine damage. What if bag was sucked in to oil filler what does that mean?

PC/SR · 10-16-2012, 05:25 PM

Big trouble.

Special Coupe Frank · 10-16-2012, 05:53 PM

Um, any other symptoms that would suggest trouble?

Usually, if the bag inflates and stays that way, that suggests lots of blow-by due to worn rings... in which case, keep the filler / breather clear, and let it blow. If you try to stop-it up, you could wind-up blowing the oil out through the rear main, running the crankcase dry, and burning the babbit out of the bearings.

I'm not sure I know of any condition that would cause an A to create vacuum on the crankcase...

mll1446 · 10-16-2012, 06:23 PM

Does it matter what speed engine is at when
Put bag on filler tube?

I have a knock just trying to pinpoint what it is?

mll1446 · 10-16-2012, 06:25 PM

Quote:

Originally Posted by Special Coupe Frank

Um, any other symptoms that would suggest trouble?

Usually, if the bag inflates and stays that way, that suggests lots of blow-by due to worn rings... in which case, keep the filler / breather clear, and let it blow. If you try to stop-it up, you could wind-up blowing the oil out through the rear main, running the crankcase dry, and burning the babbit out of the bearings.

I'm not sure I know of any condition that would cause an A to create vacuum on the crankcase...

mll1446
Member

Join Date: May 2010
Location: Palatine il
Posts: 70
Re: Oil filler question engine damage?
Does it matter what speed engine is at when
Put bag on filler tube?

I have a knock just trying to pinpoint what it is?

700rpm · 10-16-2012, 06:29 PM

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Quote:

Originally Posted by mll1446

Does it matter what speed engine is at when
Put bag on filler tube?

I have a knock just trying to pinpoint what it is?

Try listening with a broom handle or long screwdriver placed at various locations on the block and head and held to your ear. That will help narrow the possibilities.

Special Coupe Frank · 10-16-2012, 07:12 PM

I think the "bag test" is more for blow-by ( bad rings ) than anything else. I don't think it will aid in diagnosing knocks... although an engine with lots of blow-by will probably have piston-slap...

700 RPM described the classic "Stethascope" test for locating mechanical noises.

When trying to pin-down a knock, generally one starts with the engine idling, spark retarded. A connecting rod knock is generally characterized as a "hollow" / metallic knocking sound, in rhythm with the cylinders firing. When driving the car, a loose rod(s) generally rattle when letting off the accelerator to up-shift.

If you take a screw-driver and short each spark-plug to the cylinder head, one at a time, while listening to the knock, if you find a cylinder where shorting the plug lessens or eliminates the knock, that is probably going to be the cylinder where the problem is.

Main bearing knocks are generally a "dull thud" in comparison, and are generally heard on a steady "pull"...

Piston slap is generally heard at idle with a cold engine, and lessens or disappears as the engine comes-up to operating temperature.

Another very common Model A knock comes from the cam-shaft: often , the thrust plunger is either seized or the spring is broken, allowing the cam to "walk" back and forth in the block, each time it "bottoms", a knock is produced. Sounds like a rod knocking. Easy test: remove the timing plug from the timing cover, and turn it around, so that the rounded end is pointing towards the engine. With the engine idling ( and knocking), insert the timing plug into its hole on the cover, and press it gently, but firmly against the cam gear - if the knocking changes or goes away, this indicates a failed cam plunger or spring. Remove the side timing cover ( two 5/8" bolt heads from the side, two 1/2" bolt heads from underneath (oil pan rail), and observe the cam gear with the engine idling... if plunger is bad, you will see the cam gear moving fore and aft in the timing case.

Just be careful around the spinning fan and energized spark-plug connector strips while working in a running engine !

Good luck !

SC Frank

10-16-2012, 04:49 PM	#1
mll1446 Senior Member Join Date: May 2010 Location: Palatine il Posts: 320	Oil filler question engine damage? I read where you can put a plastic bag over oil filler to determine engine damage by if bag fills with air or flutters would determine possible internal engine damage. What if bag was sucked in to oil filler what does that mean?

10-16-2012, 05:25 PM	#2
PC/SR Senior Member Join Date: May 2010 Location: Santa Rosa, CA Posts: 1,279	Re: Oil filler question engine damage? Big trouble.

10-16-2012, 05:53 PM	#3
Special Coupe Frank Senior Member Join Date: May 2010 Location: Northeast Penna Posts: 2,108	Re: Oil filler question engine damage? Um, any other symptoms that would suggest trouble? Usually, if the bag inflates and stays that way, that suggests lots of blow-by due to worn rings... in which case, keep the filler / breather clear, and let it blow. If you try to stop-it up, you could wind-up blowing the oil out through the rear main, running the crankcase dry, and burning the babbit out of the bearings. I'm not sure I know of any condition that would cause an A to create vacuum on the crankcase...

10-16-2012, 06:23 PM	#4
mll1446 Senior Member Join Date: May 2010 Location: Palatine il Posts: 320	Re: Oil filler question engine damage? Does it matter what speed engine is at when Put bag on filler tube? I have a knock just trying to pinpoint what it is?

10-16-2012, 07:12 PM	#7
Special Coupe Frank Senior Member Join Date: May 2010 Location: Northeast Penna Posts: 2,108	Re: Oil filler question engine damage? I think the "bag test" is more for blow-by ( bad rings ) than anything else. I don't think it will aid in diagnosing knocks... although an engine with lots of blow-by will probably have piston-slap... 700 RPM described the classic "Stethascope" test for locating mechanical noises. When trying to pin-down a knock, generally one starts with the engine idling, spark retarded. A connecting rod knock is generally characterized as a "hollow" / metallic knocking sound, in rhythm with the cylinders firing. When driving the car, a loose rod(s) generally rattle when letting off the accelerator to up-shift. If you take a screw-driver and short each spark-plug to the cylinder head, one at a time, while listening to the knock, if you find a cylinder where shorting the plug lessens or eliminates the knock, that is probably going to be the cylinder where the problem is. Main bearing knocks are generally a "dull thud" in comparison, and are generally heard on a steady "pull"... Piston slap is generally heard at idle with a cold engine, and lessens or disappears as the engine comes-up to operating temperature. Another very common Model A knock comes from the cam-shaft: often , the thrust plunger is either seized or the spring is broken, allowing the cam to "walk" back and forth in the block, each time it "bottoms", a knock is produced. Sounds like a rod knocking. Easy test: remove the timing plug from the timing cover, and turn it around, so that the rounded end is pointing towards the engine. With the engine idling ( and knocking), insert the timing plug into its hole on the cover, and press it gently, but firmly against the cam gear - if the knocking changes or goes away, this indicates a failed cam plunger or spring. Remove the side timing cover ( two 5/8" bolt heads from the side, two 1/2" bolt heads from underneath (oil pan rail), and observe the cam gear with the engine idling... if plunger is bad, you will see the cam gear moving fore and aft in the timing case. Just be careful around the spinning fan and energized spark-plug connector strips while working in a running engine ! Good luck ! SC Frank