Mechanical repairs... Hubby wants to know..... Mazda 626, 1993, 2.5ltr V6.... Right hand cylinder bank (rear)

Question

1993. 2.5ltr V6 Right hand (rear) cylinder head has no compression. He has compression tested the front bank and those three cylinders are 150 psi compression each. The rear three have 0. Has had the heads reconditioned, new timing belt, cams and timing belt cogs are lined up on timing marks. Decoked pistons...checked out ok, so what could I have done wrong as the problems are in 1,3,and 5?

Answer 1

Try taking off that rocker covers and turn the engine by hand (breaker bar and socket on crank bolt) and watch the cam lobes, make sure they are going in correct sequence and valves are opening and closing fully. REF HERE FOR SEQUENCE http://autorepair.about.com/library/firi...

Other than that i would think it would be a head gasket issue or even cracked head, did he get it crack tested when it was machined?

going back to the sequence issue i has a similar situation when the heads were taken off ( by myself ) they were pulled apart valves, cams, everything, sent in for clean, machine and crack tested. when i got them back i trusted a friend to refit the new valves, cams, rockers etc, the cogs and all, when i finished putting everything back togeather the damm thing would`nt start, after alot of swearing and hair pulling i took off the rocker covers and to my suprise the lobes sequence on 1 cam were wrong, my so called friend had fitted one of the cams back to front. errrrr. anyway refitted it the right way and bam she started.

hope this helps.. good luck

Answer 2

do not know motor but i would redo comp test again dry pot then wet with oil if comp goes up its piston&ring problem if no rise in comp get a leak down test kit follow instructions and it will tell you wear compresionis leaking.  i think it sounds like valve train try to insert feeler gauge to check cleance. if it has button disc it is easy to mix up button sizes incorrect button sizeing can hold valves open  

Answer 3

that almost has to be an incorrect cam timing issue, could the cam sprockets have been placed on the wrong cams, allowing the marks to be lined up correctly but the cams in the wring position (assuming a DUAL overhead cam motor), some manufacturers use sprockets that can be turned around to use either side with markings for one cam on one side and markings for the other cam on the other side so a backwards mounted sprocket can put the cam in the wrong position.

other possibilities include seized/dry rings from the head being off for to long, in this event a squirt of oil down each spark plug hole should bring the compression up and get the motor running and the condition should cure itself quickly at that point

last possibility I can think would be misadjusted valves or lifters that haven't pumped up, but the fact that you say the engine is "sucking" well makes doubt this answer, good luck

Answer 4

It cannot be piston rings cause that would likely be only on one cylinder, so the source must be that the head is not sealed on the block.  Either it is not torqued properly or maybe the head gasket was not applied (or applied improperly).