2000 Mazda 626 compression question!!!

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  #1  
Old 08-11-05, 05:36 PM
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2000 Mazda 626 compression question!!!

I just did a head gasket job for a friend on his 2000 626, 2.5 DOHC V6. The problem is that it wont hardly start. the compression reads around 90- 120 on most cylinders. I have checked the timing belt timing marks they are right on. The book calls for minimum of 142 psi.If you get it running it will run ok, but it wont idle too good.I had the head resurfaced and used new gaskets. He did not want to replace the head bolts like i recommended, said that he seen no reason to. I did torque the bolts like specified. What could cause the compression to be so low. I think he run the car very hot, i was wondering could the rings be stuck or damaged? I made sure all the lifters went back in there original spots and everything. Probably no help out there for thjis problem but any would VERY VERY appreciated!!!
 
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Old 08-12-05, 07:14 AM
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try removing all plugs and disabling ignition and squirting some oil in each spark plug hole and cranking engine over for about 10 seconds and then recheck compression on each cylinder if compression still low suspect valvetrain problem.
if compression is now ok start engine and run for several minutes and recheck compression if low readings return suspect ring problem.
a leak down test on each cylinder will also help determine what is causing the compression loss.
 
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Old 08-12-05, 09:05 AM
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Thanx bejay ive tried the oil in cylinder trick it didnt help. Would 90-120 psi be enough to run the car? It`s hard to start and doesnt idle too good. the book calls for a min. compression of 142psi - max.203psi. Could not using new head bolts pose a problem, or is it more likely in the rings? I did have the head surfaced. The guy who owns the car is (Old School) and thinks 90- 120psi is plenty of compression and thinks it should be enough to run the car fine, but i keep telling him that todays auto`s have alot different specs. to run properly. I think if it were the head bolts it would act like a blown head gasket.
 
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Old 08-12-05, 09:58 AM
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it would not run very good at lower rpm and would be hard to start and may not even start up at all at times such as when the engine is cold or in cooler weather. while it doesnt need to have 142 psi it should be 130 or better for the car to atleast start up good and idle ok at low rpm if the compression comes up significantly with oil in the cylinder it usually indicates a ring problem.
if the head bolts wasn't stretched they can usually be reused even though most manufacturers recomend replacing them, a stretched bolt is usually obvious in appearnace as the threaded portion of the bolt will appear to be wavy or different diameter at any point where the bolt has stretched.
 
  #5  
Old 08-12-05, 05:56 PM
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It does sound like the possibility of the timing belt being off a tooth or so..I did read that You'd checked them..But having a hard time starting and idling, but runs "ok" sounds like maybe a tooth off? and as you accelerate, the timing comes into range?
 
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