OK, 2004 R53, just completed a minor strip of the engine, pan gasket, timing chain and guides, new valves guides, valve job, supercharger rebuild, etc, etc, etc. Engine ran fine before except for for 110 psi compression in cylinders 1 & 4, 2 & 3 were at 160+. Anyways all back together and 0 psi on #4, timing chain is good and turned over by hand and primed oil pressure prior to start up. No unusual mechanical noises, no leaks just 0 psi in cylinder 4 (I mean nothing not even a puff) almost like valves are held slightly open. Pulled rocker cover and all looks good, original cam, I did replace one exhaust valve on cylinder #4 with a new one. Before I pull the head would like some input just to be sure I am not having a brain fart.

 

did you try a wet compression test? teaspoon of oil in the cylinder, via spark plug whole. then do the comp test again


only way to know where its going is with a leak down test. similar setup to a compression test just that you are pumping air in through the spark plug hole. and turning the enigne over very slowly by hand to see if its rings. valves, or head gasket. but sense you just did a head job i dont think i should be valves or gasket. but you never know.

 

OK so performed a wet test on #4 and compression reads 20 psi. Prior to tear down the compression on #4 was 110 (dry) and 130 (wet), this led me to pull the head and replace the guides and regrind the valves. Now compression is 0, what am I missing? I will pick up a leak down test kit today and see what that test yields.

 

i dont know if you know what your looking for when doing a leak down test. but there are good videos on it. but sense your compresssion went up with a wet test it could be your rings.

you need to have that cylinder at TDC then hook up your gauge and compressor. at TDC open your oil cap on valve cover listen/ look for air. if its there bad rings. if you hear air coming out the intake its the intake valves, and out the exhaust, exhaust valves. you can also take the cap off coolant resivour and look for bubbles or air coming out. if thats it bad head gasket, but at that point you would have oil/coolant mixing.

 

OK, so leak down test complete, here is what I found, these results are with a very cold engine, here in mid Michigan it was again below freezing last night and engine does have 170K miles on her (my daughters car, just wanted to do a minor refresh to keep her going for a couple more years). At TDC 1, 2 & 3 have 35% to 40% leak down (these also have 155 psi compression after 5 or 6 cranks). Cylinder # 4 is where the fun starts, 0 - 5 psi compression (dry) 25 psi (wet) however when at TDC leak down is 70% and most coming from intake valves. So, set engine so all pistons at half stroke and backed off both rocker shafts to where all rockers loose and no load on valves. All cylinders showed approximately 35% leak down including #4. I have a new exhaust rocker and can compress the HLA's against the internal spring yet on the ones on the engine are solid, I cannot compress them at all. Seems that when I tighten the rockers shafts down the HLA's are holding the intake valves on 4 open (maybe also 3).

 

Just a wild guess...
Check the timing? Not sure if you were 180° or close to it if you would see what you are seeing....

 

Timings spot on, new timing chain and all assembled with timing cover off so all checked after guide, rail, chain and tensioner installed. Was just looking at the rocker arms again and the HLA's are locked solid. With the valve regrind it would have moved the valves into the head thus the HLA would need to compress slightly to allow the valve to completely close but obviously with them locked that is not happening, just a theory!

 

Does anyone have a used rocker in their garage they can check to see if the HLA can be depressed by hand? I have the inlet rocker shaft off and all 8 are solid, I will pull the exhaust shaft off in a few and check those. The new one I have was in another engine for a couple minutes but found not to be the solution so was removed, the HLA's in that unit can be compressed by hand.

 

Well it was a great theory but did not pan out as well. Collapsed the HLA's in a press (oil force out of the small hole in the rocker arm) nice spring feel to them and did not break the plastic retainer either. Reassembled and and cranked engine to gain oil pressure, still no compression on #4. Unless someone has any suggestions I guess its off with the head again and re-ring the pistons. The bores are immaculate, no ridge and still see the hone marks. They measure out at stock dimensions, should I replace the the rod bearings while in there and I guess I need to hone the bores to break the glaze?

 

thats really wierd. i huess take the head off again and check the sealing of the valves

one trick i use is to have the valve closed and fill the port with rubbing alcohol, if it leakes you got a leak but if you have a good seal it wont leak , but it may get a little wet looking

 

OK, so pulled intake and exhaust manifolds, and used leak down tester to push air into cylinders. Exhaust valves all sealing well, intakes however are grossly leaking especially cylinder #4. The good news is that when I put my hand over the intake ports I get 15% leak down on all cylinders (cold engine) which I can live with as she has 168K miles on her. So off to the machine shop that rebuilt the head tomorrow, that and purchase another head gasket and head bolt set, there goes a quick $150, could have been worse I guess. Thanks for the insight guys, much appreciated.