|
Sponsored Links (Register now to hide all advertisements) |
|
|
Thread Tools | Display Modes |
06-30-2021, 06:45 PM | #1 |
Junior Member
Join Date: Jun 2021
Posts: 9
|
No compression but starts and drives???
Hi everyone. I'm new to the forum and very new to the Model A world. I'm a long time gear head however. I recently acquired a 1930 A sedan and have been tinkering with it to get it on the road. I quickly discovered Mike-A-Fordables and have been ordering all kinds of goodies from him to get the job done. Most recently was a much needed downdraft carb assembly and low PSI fuel pump. The car now starts and idles really nice, but here is my dilemma. The engine has pretty much 0 compression on all 4 cylinders. The needle on my gauge just twitches as the engine is cranking but won't build pressure. I've driven the car even, up and down the road and the power seems reasonable but I don't have a benchmark to compare it to. My mechanical experience says that this shouldn't be possible. Has anyone encountered something similar before? And yes in case anyone is thinking it, I triple checked my gauge function. Am I missing something? I've got the brass washer under the adapter and the O-ring on my tester is in place and in good shape. I also had the throttle wide open and tried it both cold and warmed up.
|
06-30-2021, 07:01 PM | #2 |
Senior Member
Join Date: Jan 2012
Location: Western North Carolina
Posts: 3,897
|
Re: No compression but starts and drives???
Hi Frank,
Welcome. Being a gear head you should be able to figure out where the compression is going. Try putting a little oil in the cylinders before another compression check. If it improves then you need new rings. Do you have the hand crank? If so you can hand crank the engine over while listening at the crankcase breather tube, the intake manifold, and the exhaust manifold or exhaust pipe with a helper. You will get a hissing sound that will indicate where the compression loss is coming from. The Model A is a simple engine. In the old days a person in your position would grind the valves and throw in new piston rings while the engine was in the car. My preference is to work on the engine out of the car on an engine stand, just because it is easier for me. While you are in there check the bearings. You should have 0.001 to 0.0015 clearance. Get the mechanics books to advise you. An excellent book is the Model A Ford Mechanics Handbook, Vol. I, A Complete Guide For Service and Maintenance by Les Andrews, available at the suppliers.
__________________
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. Last edited by nkaminar; 06-30-2021 at 07:08 PM. |
Sponsored Links (Register now to hide all advertisements) |
|
06-30-2021, 10:40 PM | #3 |
Senior Member
Join Date: May 2010
Location: So Cal
Posts: 8,747
|
Re: No compression but starts and drives???
Is the Schrader valve working in your compression gauge ??
|
06-30-2021, 10:45 PM | #4 |
Senior Member
Join Date: May 2010
Location: Anaheim California
Posts: 551
|
Re: No compression but starts and drives???
Sounds like gauge problem. It certainly won't run with 0 compression and the power sounds reasonable. Don't start tearing it apart. Drive it and borrow someone's gauge.
|
06-30-2021, 11:08 PM | #5 |
Senior Member
Join Date: Jun 2017
Location: Walla Walla, WA
Posts: 1,045
|
Re: No compression but starts and drives???
If it starts and drives, there is combustion and so there must be compression of some sort. I also would suspect the gauge, not the engine.
|
07-01-2021, 03:27 AM | #6 |
Senior Member
Join Date: Feb 2011
Location: NNNNNNNNJJJJJJJJJJ
Posts: 6,785
|
Re: No compression but starts and drives???
Sponsored Links (Register now to hide all advertisements)
|
07-01-2021, 05:13 AM | #7 |
Senior Member
|
Re: No compression but starts and drives???
Do the old thumb trick. Take a plug out, stick your thumb in the hole and turn the engine over. Probably your gage. Have fun with that car.
|
07-01-2021, 05:26 AM | #8 |
Senior Member
Join Date: May 2010
Location: Largo Florida
Posts: 7,225
|
Re: No compression but starts and drives???
Yep, what the fellas said ! Try the gauge on another engine and stick your finger over the hole and crank it over. These monsters don't have or need a whole lot of compression, but, they do need some.
|
07-01-2021, 06:30 AM | #9 |
Senior Member
Join Date: Mar 2017
Location: Connecticut Shoreline
Posts: 1,821
|
Re: No compression but starts and drives???
If it runs good, doesn’t smoke, doesn’t make crazy noises, and most important, the car stops.
DRIVE IT! |
07-01-2021, 07:05 AM | #10 |
Senior Member
Join Date: Sep 2019
Location: Fort Gratiot, Michigan
Posts: 2,296
|
Re: No compression but starts and drives???
Ask for a new gauge for Christmas or any other holiday.
|
07-01-2021, 08:21 AM | #11 |
Senior Member
Join Date: Apr 2021
Location: St. Augustine, Fl.
Posts: 437
|
Re: No compression but starts and drives???
Shouldn't have to wait to long, 4th of July is Sunday.
__________________
IN GOD WE TRUST - SEMPER FIDELIS John |
07-01-2021, 09:24 AM | #12 |
Senior Member
Join Date: Jun 2014
Location: Land of Lincoln
Posts: 3,129
|
Re: No compression but starts and drives???
X-2 Go for a nice drive and learn your new to you car, enjoy the drive!
__________________
Don't force it with a little hammer tap, tap, tap get a bigger hammer tap done |
07-01-2021, 09:32 AM | #13 |
Senior Member
Join Date: Jan 2012
Location: Western North Carolina
Posts: 3,897
|
Re: No compression but starts and drives???
Frank stated that he tested the gauge. But it would be an easy matter to test it on another car, even a modern one, or replace the Schrader valve.
__________________
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. |
07-01-2021, 10:26 AM | #14 |
Junior Member
Join Date: Jun 2021
Posts: 9
|
Re: No compression but starts and drives???
Thank you for the reply. All great ideas. My intention is to next remove the head and the valve cover/plate and to inspect and clean everything. I was wondering however if this is normal for these cars to run on such little compression? Is this simply because the nature of this already low compression design? This of course is assuming my gauge is fine. Again I tested the gauge and it works fine on straight shop air and on my other engines.
I did the thumb test and it's got some compression but it's not a strong push on my thumb. I can almost hold it down when being cranked. It should blow my thumb out of the way really hard no?? |
07-01-2021, 10:38 AM | #15 |
Junior Member
Join Date: Jun 2021
Posts: 9
|
Re: No compression but starts and drives???
I think I'll put another gauge assembly on it just to try. Always good to eliminate variables. Thinking more about it maybe my gauge has a fault below a certain pressure. All my check were 100psi and higher. I'll check this and report back. Thanks guys.
|
07-01-2021, 11:00 AM | #16 |
Senior Member
Join Date: Apr 2018
Location: Mebane NC
Posts: 2,353
|
Re: No compression but starts and drives???
Normal compression on a stock system is ~60. 45psi would indicate some problems but likely still drivable. Below that you get backfires, misfires, exhaust in the engine bay, oil on the plugs, etc.
|
07-01-2021, 11:57 AM | #17 |
Senior Member
Join Date: Oct 2016
Location: harpursville ny
Posts: 1,040
|
Re: No compression but starts and drives???
I once pulled the heads on a 39 truck due to low readings on gauge. You guessed it, gauge was bad.( intermittly) was nothing wrong with engine.
|
07-01-2021, 12:26 PM | #18 |
Senior Member
Join Date: May 2010
Location: Largo Florida
Posts: 7,225
|
Re: No compression but starts and drives???
If you're new to the car and want to check things over, fine. take the side cover off and check the lash. If the lash is good and nothing hanging up, drive it. Taking off a head can be a real task at times.
Mine has had 45# compression since I bought it in 1975 and hasn't changed. It doesn't burn or leak a thing. I drive it every day day I can. |
07-01-2021, 01:52 PM | #19 | |
Senior Member
Join Date: Mar 2017
Location: Connecticut Shoreline
Posts: 1,821
|
Re: No compression but starts and drives???
Quote:
Please don’t start taking things apart before you know if there is something wrong. “Drive the car”!!! When you go to the doctors office. He just doesn’t start surgery. They check you out first. See how you walk, talk, and breath. Do the same. Enjoy. |
|
07-01-2021, 04:38 PM | #20 |
Senior Member
Join Date: May 2010
Location: Wa.
Posts: 5,408
|
Re: No compression but starts and drives???
You still haven't said if you put oil in the plug holes and tried a test.
|
|
|
Sponsored Links (Register now to hide all advertisements) |
|