28Q29U Plymouth Forum

General Category => General Discussion => Topic started by: Rodney on August 15, 2009, 05:39:42 AM

Title: Compression test
Post by: Rodney on August 15, 2009, 05:39:42 AM
Hi all,

I've just preformed a cylinders compression test dry & wet. Does anyone know what the manufactures pressure should be? All my measurements for the four are between 50-60 psi.

Many thanks
Rodney
Title: Re: Compression test
Post by: chetbrz on August 16, 2009, 07:35:14 PM

Rodney,

I don't know what the spec sheet calls for but 50 to 60 from a cold crank seems OK to me.  This is what my car will also produce.  The main thing is that it is relatively even across all cylinders.  The range you stated is good in my book.

Chet...
Title: Re: Compression test
Post by: Rodney on August 16, 2009, 10:44:33 PM
Hi Chet

I understand that the compression is low on the Plymouth; I might have a go at work it out using a compression calculator.

I've dropped and cleaned the sump made a new gasket and the Plymouth is back on the road ready for it next weekend away in September, this time it's only a short 340mile trip. I took it out for a drive on the weekend and all going well.

Many thanks, Rodney
:)
Title: Re: Compression test
Post by: 29 doUg on August 18, 2009, 12:17:40 AM
Around 55 psi for me.

Swapping plugs out, what are the new ones to be gapped at?
Title: Re: Compression test
Post by: chetbrz on August 18, 2009, 08:35:20 AM
Doug,

From the Plymouth instruction manual: see link on this site:  http://www.1948plymouth.info/28Q29U/index.php?topic=122.0 (http://www.1948plymouth.info/28Q29U/index.php?topic=122.0)

"Spark Plugs

The gap between the spark plug points must be .027" to .030". Too wide a gap will cause misfire, especially at high speeds and when laboring with open throttle, while a small gap causes poor idling. Dirty or fouled spark plugs should be washed in gasoline. Uniform gap setting insures evenness of engine firing."

Chet...



Title: Re: Compression test
Post by: 29 doUg on August 18, 2009, 05:59:24 PM
Thanks Chet! I lost my reading glasses and cant read my manual. (New glasses Friday)

Title: Re: Compression test
Post by: Rodney on August 18, 2009, 07:11:11 PM
With the type of gas we use down here (98 octane) I set my gap at 030".
With clean plugs it runs fine at idle & at high speed.

Rodney