Hi,(again!) i've lost compresion on one cylinder,it's at 100psi,the others are 175psi. I was wondering if theres a way of finding out why without taking the head off? It's a new 2.5 block thats only done 1400 miles. I lost the compresion when i started running a bit more boost(1 bar),is it possbile the head has lifted and may need re-tightening? (Yeah a long shot!)

Thanks,Tim

 

did you check compression in the spark plug hole. could be a few things. Lifted head is one. Head gasket could do it. Stuck valve or damaged valve seat especially the exhaust side or a broken compression ring or rings.
Appart from checking the torque of the head bolts then im afraid its not gonna be easy!

 

add a smidgen of oil to that cylinder and recheck the compression, if it temprarily goes up then the rings are wearing, if not it could be a valve seat problem.

Next check would be a leak down test (special equipment whereby you add compressed air to the cylinder on it's power stroke and listen to see where the hiss is coming from (crancase = rings, inlet manifold = inlet valve, exhaust = exhaust valve and bubbling water = head gasket etc)

Andy

 

hopefully you were cranking the engine with all the plugs out and the throttle fully open.. this puts less strain on the battery whilst cranking and keeps the results more accurate.

Andy

 

Yeah all plugs were out/throttle open,also disconnected the injectors. The car runs better once warm,which kind of points to a gasket problem,getting better as things expand . Think ill take the cams out and check the torque and lifters,i used arp studs with the moly lube.Im not loosing oil or water,if you take the oil cap off when running theres not loads of pressure,also if you take the water cap off when starting from cold theres no bubbles.

Tim