how to test compression?
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Senior User
Joined: Jun 2009
Posts: 278
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how to test compression?
how to check compression? I think the rings in my 300 are SHOT lots of blow by from the breather and the dipstick hole.
1. what would cause this?
2. how to tell if I need
A. Rings
B. sleaved cylinders
c. just a new head/valve job
2. Thinking about just buying a remanufactured motor...heck one company offers a 7/70 warranty on long block for 1350.00
1. what would cause this?
2. how to tell if I need
A. Rings
B. sleaved cylinders
c. just a new head/valve job
2. Thinking about just buying a remanufactured motor...heck one company offers a 7/70 warranty on long block for 1350.00
Posting Guru
Joined: Jun 2002
Posts: 2,091
Likes: 3
From: Suffolk, VA USA
There are compression testing tools that screw into the spark plug holes that will give you readings for each individual cylinders. Generally, if you're getting enough pressure into the crankcase to blow oil out of the dispstick tube its likely your rings. I onwed a 300 that did just that, and when during a rebuild I pulled the the pistons, the rings literally fell off.
Post Fiend
Joined: Jan 2005
Posts: 8,402
Likes: 10
What he says.
Remove all spark plugs, fit pressure gauge into first plug hole and spin engine over on the starter until the gauge no longer climbs. Make a note of cylinder number and the pressure reading. Repeat for all cylinders.
You may be able to hire a gauge.
Remove all spark plugs, fit pressure gauge into first plug hole and spin engine over on the starter until the gauge no longer climbs. Make a note of cylinder number and the pressure reading. Repeat for all cylinders.
You may be able to hire a gauge.
Freshman User
Joined: Aug 2005
Posts: 47
Likes: 0
From: S.W. Florida
Also make sure you have the carb or throttle body wide open for the test to be accurate.
It's also better to test the motor when its warmed up too.
If you have a low cylinder, squirt some oil in the cylinder and re-test.
It's also better to test the motor when its warmed up too.
If you have a low cylinder, squirt some oil in the cylinder and re-test.
Posting Guru
Joined: Sep 2006
Posts: 1,781
Likes: 1
If it is rings, when you put some oil into the cylinder it should bump the compression up a little.
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Senior User
Joined: Jun 2009
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yup read that in my haynes manual. you guys rock. still thinking about a new motor though as i just know what i got then.
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Cargo Master
Joined: Sep 2006
Posts: 2,119
Likes: 390
From: Evansville, Indiana
Rebuilding the head has put added pressure on the rings. Replaceing the rings at this point would put added pressure on the bearings. And so on.
My 302 is blowing too. I'm saving up for a thorough rebuild.
My 302 is blowing too. I'm saving up for a thorough rebuild.
Tuned
Joined: Jun 2006
Posts: 363
Likes: 3
From: Graham WA
Good Call
300/6 Freak
You made a good call going re-man long block (as long as it comes from a reputable builder and with some sort of warranty). Especially if time is a factor for you.
Deciding to rebuild yours really all depends on whether you have connections to a good machine shop and can trust your machinist to do justice. You need to go in with some knowledge about builds and the condition of your engine. Know what to ask for and also know when you are getting skinned unnecessarily (Doing unnecessary work or not getting the work you paid for). Some shops will take advantage, if you know what I mean.
The forum had some real good points about only doing rings also. I bet those thoughts played into your decision.
Tom
You made a good call going re-man long block (as long as it comes from a reputable builder and with some sort of warranty). Especially if time is a factor for you.
Deciding to rebuild yours really all depends on whether you have connections to a good machine shop and can trust your machinist to do justice. You need to go in with some knowledge about builds and the condition of your engine. Know what to ask for and also know when you are getting skinned unnecessarily (Doing unnecessary work or not getting the work you paid for). Some shops will take advantage, if you know what I mean.
The forum had some real good points about only doing rings also. I bet those thoughts played into your decision.
Tom
