The Ford Barn

Norm M · 05-09-2019, 10:00 AM

I am looking for a reference on the proper way to test a Model A engine for compression and what the results should be with a standard, 5.5 to 1 and 6.0 to 1 head. Any help would be appreciated.

katy · 05-09-2019, 10:49 AM

Engine at operating temperature.
Remove all spark plugs.
Block throttle wide open.
Connect compression gauge for one cylinder.
Spin engine over 5 or 6 or more times, you will hear it grunt on each compression stroke.
Write the reading down.
Repeat for each cylinder.

30 Closed Cab PU · 05-09-2019, 12:46 PM

Add a squirt or 2 of oil to each cylinder? Think I saw this mentioned somewhere but am unsure if it is the correct way to do it.

Synchro909 · 05-09-2019, 06:42 PM

Quote:

Originally Posted by 30 Closed Cab PU

Add a squirt or 2 of oil to each cylinder? Think I saw this mentioned somewhere but am unsure if it is the correct way to do it.

The correct way? The short answer is "Yes and no"!

The first compression test should be done dry. To check for worn rings, a little oil down the bore, then repeat the test will tell you. The second reading would be higher.

chap52 · 05-10-2019, 07:30 AM

I recall reading that compression with stock head= 60#, 5.5 head= 75-80# Do not remember the source.
BUT, also see from my file folder scribbling some different numbers???
Standard-60#
Police-70-75#
5.5, 6.1 90-100#
PLEASE, anyone have the correct numbers? Chap

Railcarmover · 05-10-2019, 07:38 AM

Sponsored Links (Register now to hide all advertisements)

wet dry testing..compression low,squirt oil,if it goes up rings are bad,if it stays the same valves are bad..leak down test more accurate.

dansluck · 05-10-2019, 07:53 AM

Norm, Great Question. Looking forward to answers.

Patrick L. · 05-10-2019, 10:44 AM

So now you know how to perform the test [ as Katy said].
Try it dry and then wet and see what you get. Let us know.
Rather than expect certain readings, difference between cylinders is the important part. Some of these old monsters will show low readings but run just fine. A compression test does not give any indication of condition of the oil rings.

redmodelt · 05-10-2019, 09:01 PM

Don't forget cold hot. While you can open the throttle, it really does not make much difference open or closed on a Model A engine.

05-09-2019, 10:00 AM	#1
Norm M Junior Member Join Date: Jan 2014 Posts: 28	Compression Testing I am looking for a reference on the proper way to test a Model A engine for compression and what the results should be with a standard, 5.5 to 1 and 6.0 to 1 head. Any help would be appreciated.

05-09-2019, 10:49 AM	#2
katy Senior Member Join Date: Jun 2015 Location: Red Deer, Alberta Posts: 5,042	Re: Compression Testing Engine at operating temperature. Remove all spark plugs. Block throttle wide open. Connect compression gauge for one cylinder. Spin engine over 5 or 6 or more times, you will hear it grunt on each compression stroke. Write the reading down. Repeat for each cylinder. __________________ If you don't hear a rumor by 10 AM, start one!. Got my education out behind the barn!

05-09-2019, 12:46 PM	#3
30 Closed Cab PU Senior Member Join Date: Aug 2018 Posts: 2,332	Re: Compression Testing Add a squirt or 2 of oil to each cylinder? Think I saw this mentioned somewhere but am unsure if it is the correct way to do it.

05-10-2019, 07:30 AM	#5
chap52 Senior Member Join Date: Jun 2013 Location: Marana Arizona Posts: 1,776	Re: Compression Testing I recall reading that compression with stock head= 60#, 5.5 head= 75-80# Do not remember the source. BUT, also see from my file folder scribbling some different numbers??? Standard-60# Police-70-75# 5.5, 6.1 90-100# PLEASE, anyone have the correct numbers? Chap

05-10-2019, 07:38 AM	#6
Railcarmover BANNED Join Date: Apr 2017 Location: Sacramento Posts: 1,262	Re: Compression Testing Sponsored Links (Register now to hide all advertisements) wet dry testing..compression low,squirt oil,if it goes up rings are bad,if it stays the same valves are bad..leak down test more accurate.

05-10-2019, 07:53 AM	#7
dansluck Senior Member Join Date: Dec 2014 Location: Nevada Posts: 217	Re: Compression Testing Norm, Great Question. Looking forward to answers.

05-10-2019, 10:44 AM	#8
Patrick L. Senior Member Join Date: May 2010 Location: Largo Florida Posts: 7,225	Re: Compression Testing So now you know how to perform the test [ as Katy said]. Try it dry and then wet and see what you get. Let us know. Rather than expect certain readings, difference between cylinders is the important part. Some of these old monsters will show low readings but run just fine. A compression test does not give any indication of condition of the oil rings.

05-10-2019, 09:01 PM	#9
redmodelt Senior Member Join Date: May 2010 Location: Portland OR Posts: 6,340	Re: Compression Testing Don't forget cold hot. While you can open the throttle, it really does not make much difference open or closed on a Model A engine. __________________ I know the voices aren't real but damn they have some good ideas!