Slayata

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.

psyber_0ptix

iTrader: (4)

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?

karter74

iTrader: (4)

Timing set correctly? An open valve during compression stroke could be the issue.

Stealth97

iTrader: (5)

Triple check cam timing.

themonkeyman

Slayata

Hmm never thought of that; I'll take some clearances. Thanks.

Slayata

Mechanical timing is bang on, that was the first thing I checked.

Slayata

None make compression but the timing is right on the money; although as psyber_0ptix mentioned, I'm going to recheck my shim clearances and report back if they were the issue.

Gee Emm

At the risk of labouring a point, that was TDC compression stroke?

sixshooter

iTrader: (12)

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.

themonkeyman

Slayata

Issue ended up being machinist error. Sorry for late reply; thanks lads.

Stealth97

iTrader: (5)

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.

Slayata

The valves and seats were matched and in doing so, the machinists removed an equal amount of material from the valve stem. After the valve work was done, the head was decked and apparently the exhaust valves were put back into the head in reverse order (exhaust valves in the order of cylinders #1-4 put into the head as #4-1). So the valves weren't seating completely. Fortunately, they were cool about it and reinstalled the valves with new seals and guides no charge.

Stealth97

iTrader: (5)

That would do it!