The Ford Barn

FrankB · 08-25-2021, 11:22 AM

A bit of background. I'm seeing lot of blowback through the carb from idle to about 3/4 throttle. It blows air/fuel mixture back out the carb until the engine revs really climb, then it pulls it all in. It's bad enough that it won't go beyond idle with the air filter installed. All that fuel mist builds up in the filter and just chokes it out.

So I went and bought a new compression tester and my readings on all 4 pots are in the 32-35 psi range. Obviously low but consistent across all cylinders. My initial thought is a failing head gasket. It starts and idles nice and drives reasonable with the air filter off.
Maybe sticking valves, but across the board? Seems too odd for that IMO.

Any thoughts?

alexiskai · 08-25-2021, 11:27 AM

Is this a new car, where it's been doing this as long as you've had it, or a car you've had for a while that just started doing this?

FrankB · 08-25-2021, 11:30 AM

Car is new to me. I acquired it recently from an estate. Was not running when I got it. I'm unsure how long it's been parked

FrankB · 08-25-2021, 11:32 AM

I have some ATF soaking in the cylinders right now.

katy · 08-25-2021, 11:39 AM

Quote:

Originally Posted by FrankB

I have some ATF soaking in the cylinders right now.

That should produce lots of white smoke next time you start it.

FrankB · 08-25-2021, 11:43 AM

Sponsored Links (Register now to hide all advertisements)

Yup! Lol

alexiskai · 08-25-2021, 11:45 AM

Blowing FAM back through the intake manifold suggests that the intake valves are not closing at the end of the intake stroke (because of sticking, bad springs, bad cam, who knows what else).

LeonardS · 08-25-2021, 12:17 PM

Might be a good idea to check the lifter adjustment.

jayvee34 · 08-25-2021, 12:25 PM

IMHO, Put some MMO in each cylinder and in in the gas, also, maybe some SeaFoam, drive it awhile, see if the sticky valves loosen up. Worth a try before tearing into the engine.

bbrocksr · 08-25-2021, 12:31 PM

Quote:

Originally Posted by FrankB

A bit of background. I'm seeing lot of blowback through the carb from idle to about 3/4 throttle. It blows air/fuel mixture back out the carb until the engine revs really climb, then it pulls it all in. It's bad enough that it won't go beyond idle with the air filter installed. All that fuel mist builds up in the filter and just chokes it out.

So I went and bought a new compression tester and my readings on all 4 pots are in the 32-35 psi range. Obviously low but consistent across all cylinders. My initial thought is a failing head gasket. It starts and idles nice and drives reasonable with the air filter off.
Maybe sticking valves, but across the board? Seems too odd for that IMO.

Any thoughts?

Timing gear!
Bill

Ernie Vitucci · 08-25-2021, 12:33 PM

Good Morning...The Model A carburetor was not designed to be used with an air filter. The amount of extra sucking the engine must due to get fuel causes it to run rich...too much fuel and not enough air...I just use a small piece of screen door mesh over the inlet of my 'B' carburetor. If you are using old gas that came with the car...drain it out and put in fresh...old gas can really mess with your valve guides and make the valves stick...change the oil in the engine and transmission. Lube all 31 zerk fittings, check to make sure the rear end is full. Clean the plugs and gap them. Clean the points and make sure they are set properly. Check the head torque...55 pounds feet is enough... Perhaps a new condenser and coil...run her around at slow cruising speed 30-35 for a 100 or so miles and I think she will surprise you...Ernie in Arizona

bbrocksr · 08-25-2021, 12:33 PM

Quote:

Originally Posted by FrankB

A bit of background. I'm seeing lot of blowback through the carb from idle to about 3/4 throttle. It blows air/fuel mixture back out the carb until the engine revs really climb, then it pulls it all in. It's bad enough that it won't go beyond idle with the air filter installed. All that fuel mist builds up in the filter and just chokes it out.

So I went and bought a new compression tester and my readings on all 4 pots are in the 32-35 psi range. Obviously low but consistent across all cylinders. My initial thought is a failing head gasket. It starts and idles nice and drives reasonable with the air filter off.
Maybe sticking valves, but across the board? Seems too odd for that IMO.

Any thoughts?

Timing gear!
Bill

FrankB · 08-25-2021, 12:40 PM

I will try and check all of the above before I tear into it. Thanks everyone.

Is the valve cover/plate as easy to remove for inspection as it appears? Seems straightforward.

JayJay · 08-25-2021, 12:45 PM

Quote:

Originally Posted by FrankB

I will try and check all of the above before I tear into it. Thanks everyone.

Is the valve cover/plate as easy to remove for inspection as it appears? Seems straightforward.

Yup, it's easy peasy. Just don't forget the new gasket.

JayJay

nkaminar · 08-25-2021, 12:51 PM

In 1937 a mechanic would tell you that it is time for a valve and ring job.

JayJay · 08-25-2021, 12:53 PM

The thing that jumps out at me is the consistent low readings. If you have ATF in the cylinders then you could repeat the compression test with the cylinders wet. A consistent increase with wet cylinders would tend to indicate worn rings (you might need something a bit heavier like 30wt oil, several squirts before the compression test). I don't see head gasket with the consistent low readings you're seeing, more like ring wear. If it was valves you will not see much increase in compression, but that backfire does point in that direction. No reason it could not be both rings and valves - a just plain worn out engine.

I agree that an air filter, especially one clogged with backfire crud, doesn't help.

JayJay

PC/SR · 08-25-2021, 02:01 PM

Checking the obvious first, were the plugs out and throttle fully open when checking compression? Timing checked and checked again. Since it drives "reasonable" with the filter off, not sure what more you want. Filter is marginal use anyway. If the compression numbers are accurate it just seems the engine is tired.

Patrick L. · 08-25-2021, 02:50 PM

Drive it for awhile. Adding some oil to each cylinder and letting it set for awhile is good.

Mine has had 45# compression for 45 years and runs fine.

Bob C · 08-25-2021, 02:54 PM

Was the throttle wide open when to took the compression readings??

Big hammer · 08-25-2021, 04:02 PM

A couple of more things to check, probably not the cause of low compression but good to check with an A that's be sitting! Oil fill cap clogged or on to far, and that the muffler is not clogged by Mr & Mrs mouse !

08-25-2021, 11:22 AM	#1
FrankB Junior Member Join Date: Jun 2021 Posts: 9	Low compression, all holes A bit of background. I'm seeing lot of blowback through the carb from idle to about 3/4 throttle. It blows air/fuel mixture back out the carb until the engine revs really climb, then it pulls it all in. It's bad enough that it won't go beyond idle with the air filter installed. All that fuel mist builds up in the filter and just chokes it out. So I went and bought a new compression tester and my readings on all 4 pots are in the 32-35 psi range. Obviously low but consistent across all cylinders. My initial thought is a failing head gasket. It starts and idles nice and drives reasonable with the air filter off. Maybe sticking valves, but across the board? Seems too odd for that IMO. Any thoughts?

08-25-2021, 11:27 AM	#2
alexiskai Senior Member Join Date: Apr 2018 Location: Mebane NC Posts: 2,350	Re: Low compression, all holes Is this a new car, where it's been doing this as long as you've had it, or a car you've had for a while that just started doing this?

08-25-2021, 11:30 AM	#3
FrankB Junior Member Join Date: Jun 2021 Posts: 9	Re: Low compression, all holes Car is new to me. I acquired it recently from an estate. Was not running when I got it. I'm unsure how long it's been parked

08-25-2021, 11:32 AM	#4
FrankB Junior Member Join Date: Jun 2021 Posts: 9	Re: Low compression, all holes I have some ATF soaking in the cylinders right now.

08-25-2021, 11:43 AM	#6
FrankB Junior Member Join Date: Jun 2021 Posts: 9	Re: Low compression, all holes Sponsored Links (Register now to hide all advertisements) Yup! Lol

08-25-2021, 11:45 AM	#7
alexiskai Senior Member Join Date: Apr 2018 Location: Mebane NC Posts: 2,350	Re: Low compression, all holes Blowing FAM back through the intake manifold suggests that the intake valves are not closing at the end of the intake stroke (because of sticking, bad springs, bad cam, who knows what else).

08-25-2021, 12:17 PM	#8
LeonardS Senior Member Join Date: May 2010 Location: Jamestown, ND Posts: 657	Re: Low compression, all holes Might be a good idea to check the lifter adjustment.

08-25-2021, 12:25 PM	#9
jayvee34 Senior Member Join Date: Apr 2021 Location: St. Augustine, Fl. Posts: 437	Re: Low compression, all holes IMHO, Put some MMO in each cylinder and in in the gas, also, maybe some SeaFoam, drive it awhile, see if the sticky valves loosen up. Worth a try before tearing into the engine. __________________ IN GOD WE TRUST - SEMPER FIDELIS John

08-25-2021, 12:33 PM	#11
Ernie Vitucci Senior Member Join Date: May 2016 Location: Scottsdale, Arizona Posts: 611	Re: Low compression, all holes Good Morning...The Model A carburetor was not designed to be used with an air filter. The amount of extra sucking the engine must due to get fuel causes it to run rich...too much fuel and not enough air...I just use a small piece of screen door mesh over the inlet of my 'B' carburetor. If you are using old gas that came with the car...drain it out and put in fresh...old gas can really mess with your valve guides and make the valves stick...change the oil in the engine and transmission. Lube all 31 zerk fittings, check to make sure the rear end is full. Clean the plugs and gap them. Clean the points and make sure they are set properly. Check the head torque...55 pounds feet is enough... Perhaps a new condenser and coil...run her around at slow cruising speed 30-35 for a 100 or so miles and I think she will surprise you...Ernie in Arizona

08-25-2021, 12:40 PM	#13
FrankB Junior Member Join Date: Jun 2021 Posts: 9	Re: Low compression, all holes I will try and check all of the above before I tear into it. Thanks everyone. Is the valve cover/plate as easy to remove for inspection as it appears? Seems straightforward.

08-25-2021, 12:51 PM	#15
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 3,898	Re: Low compression, all holes In 1937 a mechanic would tell you that it is time for a valve and ring job. __________________ A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past.

08-25-2021, 12:53 PM	#16
JayJay Senior Member Join Date: Jan 2020 Location: SF Bay Area Posts: 1,068	Re: Low compression, all holes The thing that jumps out at me is the consistent low readings. If you have ATF in the cylinders then you could repeat the compression test with the cylinders wet. A consistent increase with wet cylinders would tend to indicate worn rings (you might need something a bit heavier like 30wt oil, several squirts before the compression test). I don't see head gasket with the consistent low readings you're seeing, more like ring wear. If it was valves you will not see much increase in compression, but that backfire does point in that direction. No reason it could not be both rings and valves - a just plain worn out engine. I agree that an air filter, especially one clogged with backfire crud, doesn't help. JayJay __________________ JayJay San Francisco Bay Area ------------------------ 1930 Murray Town Sedan 1931 Briggs S/W Town Sedan

08-25-2021, 02:01 PM	#17
PC/SR Senior Member Join Date: May 2010 Location: Santa Rosa, CA Posts: 1,278	Re: Low compression, all holes Checking the obvious first, were the plugs out and throttle fully open when checking compression? Timing checked and checked again. Since it drives "reasonable" with the filter off, not sure what more you want. Filter is marginal use anyway. If the compression numbers are accurate it just seems the engine is tired.

08-25-2021, 02:50 PM	#18
Patrick L. Senior Member Join Date: May 2010 Location: Largo Florida Posts: 7,225	Re: Low compression, all holes Drive it for awhile. Adding some oil to each cylinder and letting it set for awhile is good. Mine has had 45# compression for 45 years and runs fine.

08-25-2021, 02:54 PM	#19
Bob C Senior Member Join Date: May 2010 Location: So Cal Posts: 8,741	Re: Low compression, all holes Was the throttle wide open when to took the compression readings??

08-25-2021, 04:02 PM	#20
Big hammer Senior Member Join Date: Jun 2014 Location: Land of Lincoln Posts: 3,127	Re: Low compression, all holes A couple of more things to check, probably not the cause of low compression but good to check with an A that's be sitting! Oil fill cap clogged or on to far, and that the muffler is not clogged by Mr & Mrs mouse ! __________________ Don't force it with a little hammer tap, tap, tap get a bigger hammer tap done