Question about Mazda MAZDA5
If the model that you have is OHC with cam working directly onto valves via lifters and you have nil compression in these two cylinders then remove the valve cover and turn over until the camshaft lobes for each cylinder in turn are pointing up,slide a feeler gauge under the heel of the cam lobe between it and the tappet,should only be .1-.3mm,especially if a hydraulic lifter(cam follower).If the gap is large the valve are bent.Similar way to test if the head has rocker arms,but essentially when the valve is closed ther should be only the slightest hint of clearance between rocker arm and valve tip.
Another test we do here is as above turn until both lobes point up on OHC.Valves for this cylinder should now be closed.I knock the centre out of an old sparkplug and fit a airline to it.scew it into the cylinder to be tested and fire the air into it.If air heard out of exhaust,the exhaust valve is problem,if out of inlet area then it is inlet valve,if heard in sump and out of dipstick tube then rings/piston at fault.Having a badly leaking inlet manifold gasket can give a similar run fault but compression will be ok.I hope this helps otherwise get back to me with your findings.
Posted on Apr 01, 2011
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Posted on Jan 02, 2017
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