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I have a 68 mustang and last summer I was driving and all of a sudden I lost compression and it started to overheat and then started the tacking sound.Its been parked ever since but I do go out and start it and it will start right up but it still makes the tacking sound.I've had people telling me it spun a bearing and others say its the valves because of the lost compression.The motor was supposeably rebuilt right before I bought the car about 4 yrs. ago. Do you think I spun a bearing or hopefully its just the valves.Please help. Thanks Ginger
 
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What do the results of a compression test show.. if a cylinder has no compression, remove the respective valve cover and look at the valve position. It may be stuck open accounting for the noise.
What was the oil pressure? If the results of compression are satisfactory, then you may want to look elsewhere and examine oil pressure.
 
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Since you have a six cylinder, I would have a compression test done, and like someone else said check for obvious, loose spark plug or wire, stuff like that.Could be blown head gasket, they can sometimes be a problem, or a bad lifter not pumping up.How is your oil pressure? Is your oil a good quality/weight etc.

1967 S code GT Deluxe Coupe 65B
1966 Convertible 76B 289 4 speed

Descendent of Francois Seguin dit Laderoute,
Soldier Regiment d' Carignan, New France 1665-1668

<P ID="edit"><FONT SIZE=-1>Edited by kbstang on 04/02/01 11:29 AM (server time).</FONT></P>
 

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My first impression would be a blown head gasket.

Describe the "tacking" sound ....... is this "ticking"?

How do you know it lost compression?



Hal
Love hard, drive fast, wear your seat belt.

PS, that's my 'bird...... My Mustang is too ugly to take pictures of yet........*G*.

http://www.teleport.com/~cosa/bird2.jpg
 
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The subtle difference between a tacking sound, a tapping sound and a ticking sound must
be determined by a qualified professional. It could be something a simple as a loose
spark plug or as complicated as a carpet installer locked in your trunk. Before you loose
any more compression I suggest you get out your phone book and call for help.
jimbo

M.C.A.# 50000
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Discussion Starter #7
An all of a sudden problem like that could be a collapsed lifter. I assume you have a hydraulic cam. If the collapsed lifter is on the intake side, that cylinder will not draw as much air and will have a lower compression. The collapsed lifter opens up the valve lash and causes the ticking sound. I'm assuming the ticking sound is tied to RPM. Vintage lifters are notorious for this in high mileage applications. If the engine was professionally rebuilt, these should have been replaced, if it was just "freshened up" with new rings / gaskets, the P.O. may not have replaced them.
Best of luck!

Red '67 Coupe / 289 bored-stroked to 306 / toploader 4spd / 8" Currie Ent. 3.80:1 rear / lowered front A arms / 620 lb springs / etc..
Used for drive-in nights and open track days!
 

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Still kinda' at a loss here. Is the engine "missing" on a cylinder or shaking? How do you know it's down on compression?

If you are hearing a lifter it will sound like tapping on metal, and might be as simple as a valve adjustment depending on the rocker arms in your particular engine. That, in itself won't affect your compression on a compression test very much.

The overheating is an indicator of other things.

I'd sugest a full compression test and possibly a leak-down test. One simple check would be to look for coolant in the oil, oil in the coolant, and bubbles in the coolant with the radiator cap removed and the engine running.

Hal
Love hard, drive fast, wear your seat belt.

PS, that's my 'bird...... My Mustang is too ugly to take pictures of yet........*G*.

http://www.teleport.com/~cosa/bird2.jpg
 
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If the sound you describe is ticking, I'd start looking in the top end of the engine. If it sounds more like knocking, then the bottom end is more likely the culprit.

If compression on one cylinder is gone, a simple test is to pull off and put back the plug leads on by one with the engine idling. Every time you pull off one lead the rpm should drop a little. If the rpm should refuse to drop on the unplugging of one cylinder, that's the one without compression.
 
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