No compression on 2004 MSM BP4W rebuild
Hey guys,
Would appreciate some public input on why I am having compression issues on my rebuilt engine before I start rebuilding the head. Here are the specs: 2004 MSM BP4W, engine out of a NB with a rear collision. Swapped into my NA6, never seen the engine run. Did not check compression on engine before rebuilding as it's oil had been drained. -JE 83.5mm pistons, rings staggered properly and brand new -Manley H-beam conrods -ACL main and rod bearings -ARP head studs and main journal studs -Completely stock cylinder head including new OEM valve stem seals but reused springs, valves, cams and SOB lifters -All seals and gaskets are new -Borg Warner efr6258 Machine work: -Block decked, bored and honed -Head decked -Rotating mass balanced -Valves lapped in respective seats I might be forgetting some stuff; my suspicion lies on the valve springs being tired and installed incorrectly. I remember when reinstalling the valves, some valves wouldn't seat completely unless a nudged them in a bit. I chalked it up to dry valve stem seals but in hindsight I shouldn't have been so quick to overlook it. I vividly remember putting in the valve springs in their correct orientation (tight end of coil down) but is it possible I accidentally reversed it and this is causing my issue of no compression on all cylinders? Or are these stock springs just tired. Thanks in advance. |
The valve clearances where set/shimmed correctly?
I mean, if you have too thick a shim, it may be in constant contact with the cam lobe and potentially keep the valve open a teeny weeny bit? |
Timing set correctly? An open valve during compression stroke could be the issue.
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Triple check cam timing.
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Do any of the cylinders make compression? What numbers are you seeing? If it’s all 4 down/no comp I’d wager cam timing is your culprit. If just one or two are low it could be valves stuck open from improper shim heights. |
Originally Posted by psyber_0ptix
(Post 1494124)
The valve clearances where set/shimmed correctly?
I mean, if you have too thick a shim, it may be in constant contact with the cam lobe and potentially keep the valve open a teeny weeny bit? |
Originally Posted by karter74
(Post 1494128)
Timing set correctly? An open valve during compression stroke could be the issue.
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Originally Posted by themonkeyman
(Post 1494195)
Do any of the cylinders make compression? What numbers are you seeing? If it’s all 4 down/no comp I’d wager cam timing is your culprit. If just one or two are low it could be valves stuck open from improper shim heights. |
Originally Posted by Slayata
(Post 1494278)
Mechanical timing is bang on, that was the first thing I checked.
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50 or 60 pounds of Seat pressure should definitely cause the valve to be closed without any additional help. Something is very wrong. Imagine two bags of cat litter pushing that one valve closed. That's how much weight were talking.
2 things. You should have used light double valve springs from supertech if you went to the trouble to build your bottom end. And you should have tested the the setup up you did use for proper tension (and usually bind) once installed. I would throw away 20 year old springs and would definitely not use them on a turbo motor that would see boost trying to hold the intake valves open every time they close. Did they replace the valve guides or check them for play? They're a common wear item. |
Also, are you using the crank notch for TDC/timing or the marks on the damper? |
Issue ended up being machinist error. Sorry for late reply; thanks lads. :)
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Originally Posted by Slayata
(Post 1527563)
Issue ended up being machinist error. Sorry for late reply; thanks lads. :)
hell, even if he left the rings out I’d think it would make some compression. |
Originally Posted by Stealth97
(Post 1527634)
what kind of machinist error causes 0 compression? Did he forget to put valves in?
hell, even if he left the rings out I’d think it would make some compression. |
That would do it!
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