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68 Mustang No Compression In 3 Cylinders

Tiny
JFARRELL305
  • MEMBER
  • 1968 FORD MUSTANG
Evening,

First let me preface this by saying that I am at best a very amateur mechanic so I apologize if my terminology is incorrect and my question hard to follow.

I have a 1968 Mustang with the original 200ci 6 cylinder motor. The problem I am having is that I have very little compression on 3 of the cylinders and the other 3 are fine. Numbers 3 4 and 5 are the low ones and 1 2 and 6 are good. So of course the engine won't idle and runs very rough when given a lot of gas.

I thought that for sure it was a bad head gasket so I pulled the head. But the gasket looks fine. As does everything else. No visible cracks or holes anywhere. Everything moves appropriately when I manually turn it.

I am hoping someone may be able to shed some insight into what the problem may be because I am completely stumped. What could cause me to have no compression on 3 adjacent cylinders?

Thanks very much for your time,
Joseph~
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Sunday, April 8th, 2007 AT 5:31 PM

9 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Sounds like a worn camshaft-you sure it didn't jump time

Put it back on TDC compression stroke on No.1-check the chain and sprockets alignment. If its Ok-mike the camshaft lobed-one messed-up reading change it.
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Sunday, April 8th, 2007 AT 6:36 PM
Tiny
RASMATAZ
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Sounds like a worn camshaft-you sure it didn't jump time

Put it back on TDC compression stroke on No.1-check the chain and sprockets alignment. If its Ok-mike the camshaft lobed-one messed-up reading change it

BTW what is it- 289 or 302 whatever?

.[/Quote:ea5e8602f1]
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Sunday, April 8th, 2007 AT 6:37 PM
Tiny
JFARRELL305
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  • 5 POSTS
Its 6 cylinder 200 cubic inch
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Monday, April 9th, 2007 AT 12:30 AM
Tiny
JFARRELL305
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First let me thank you for your response. Second I don't understand this part of it:

What exactly does that mean?

Thanks again,
Joseph
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Monday, April 9th, 2007 AT 1:21 AM
Tiny
RASMATAZ
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Look at the book it will tell you the spec's for the camshaft lobes-use a micrometer and measure it from heel to toe the lobes should be all the same and in spec's if not replace it.

Also inspect for bent valves and push rods.
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Monday, April 9th, 2007 AT 3:23 AM
Tiny
JFARRELL305
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Thanks for clearing that up for me, I get what you're saying now. My only question is would one bad lobe on the cam shaft effect 3 cylinders?

Thanks again for your time and expertise,
Joseph
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Monday, April 9th, 2007 AT 4:13 AM
Tiny
RASMATAZ
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Joe

I overlook something here-okay When you pull the head did you change the H/gasket those cyls is in the middle adjacent to each other-am hinting on blown gasket/warped head and no am not ready to say crack block.

Check for bent push rod/collapsed lifters-as for the cam no one bad lobe will not take out 2 more cyls.

Comeback and tell me what's happening.
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Monday, April 9th, 2007 AT 5:42 AM
Tiny
JFARRELL305
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I checked the push rods and lifters as according to my Chiltons's and everything seems ok with them. The old gasket does not appear to be blown though I do have a new one ready to install when I get back to that point.

As for the warped head, I think I would need to take it to a machine shop to verify that. But if a warped head were causing my problem wouldn't at least part of the gasket be blown out?

I was thinking about installing the new gasket and putting the motor back together just enough to do another compression test. But I fear this may just be wishful thinking on my part. Think it's worth a shot?
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Tuesday, April 10th, 2007 AT 1:54 AM
Tiny
RASMATAZ
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I checked the push rods and lifters as according to my Chiltons's and everything seems ok with them. The old gasket does not appear to be blown though I do have a new one ready to install when I get back to that point.

As for the warped head, I think I would need to take it to a machine shop to verify that. But if a warped head were causing my problem wouldn't at least part of the gasket be blown out?

I was thinking about installing the new gasket and putting the motor back together just enough to do another compression test. But I fear this may just be wishful thinking on my part. Think it's worth a shot?[/Quote:7de62a7af7]

Go for it-you only die once- it is not neccessary for the gasket to burn thru. Its expansion that's doing it.
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Tuesday, April 10th, 2007 AT 2:53 AM

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