Skip the auto shop - Our mechanics make house calls

Q: Why am I losing compression on cylinder #4 on my 2006 Mazda 6

asked by on

I bought a block that needed a piston,the block honed and resurfaced after hitting a valve in the cylinder head. I had all of that work done as well as getting all of the bearings and piston rings replaced. I used another head that was warped,had it resurfaced, a three angle valve job and had the valve stem seals replaced from the same machine shop. Replaced all gaskets including the head gasket and timing components. After reassembling the engine using torque specs the engine has a very hard time starting and shuts off after a few seconds. During start up you can hear and feel air being pushed out from the front right of the engine near the intake manifold. A compression test confirmed a leak in cylinder four. There is no oil leaking from the head gasket at all where the sound of the air/compression leak is coming from. If not the intake, could that great amount of compression still be lost between the head and block without oil and after being machined and checked as good to go?

Hi there. If you are feeling air pressure coming out of the engine in this area then you have a problem with warpage or a crack that is not seen. Once everything is put together and torqued then you should not get any air. It is possible that you got a bad head or you may have a valve issue if the pressure is coming from the intake. You need to get some assistance from a certified mechanic, like one from YourMechanic, that can come to you to [diagnose why there is a loss of compression] https://www.yourmechanic.com/services/noise-from-engine-or-exhaust-inspection

Was this answer helpful?

It is possible for the engine to lose compression due to a head gasket leak without loosing any oil due to the head gasket. It is also a definate possibility that the intake manifiold is causing the compression loss. The possible causes of this issue are faulty gaskets, incorrect installation of certain parts, or that the shop that did all of the machine work made a mistake. I would recommend checking all of these things in order to determine where the compression loss is coming from.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: MPV is over heating - replaced the thermostat and Radiator cooling fans. no leaks at all and plenty of water in reservior

Overheating can be caused by a number of issues. You have addressed a couple of them by replacing the thermostat and the cooling fans. Are the fans coming on as they should ? The fans rely on other components like...

Q: At light on and car stalling

The AT Light is indicating a fault with your transmission. The transmission in your particular vehicle has its own computer that can self diagnose issues it may be having. A qualified technician, like one from YourMechanic, could retrieve any stored...

Q: 2003 Chrysler seabring, was a pop then black and grey smoke rpm gauge went crazy and the car cut out. Power went completely and sh

Without knowing exact cause of the oil leak since it sounds severe there would not be any way to tell you what happened. If you leaked oil onto the belts of the alternator then it may slip and cause no...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...