No compression-next move?

-

RockinRobin

Well-Known Member
Joined
May 15, 2013
Messages
1,241
Reaction score
867
Location
Corsicana, Tx
I know this is a Gen3 Hemi, but it should be the same for all motors:
Car was idling in the garage, suddenly died. Not electrical or fuel. Removed valve covers, everything is moving. Zero compression on all cylinders. Does this sound like chain or sprocket slipped?

It's a ***** to take off the front cover on this motor because it has a motor plate so I have to support the motor with a cherry picker. Sounds like the front cover needs to come off though.

Once again, the cam is turning but the valve timing seems suddenly way off.
 
Interesting! If cam is turning then valves are opening and closing. If crank is turning then pistons are going up and down. I would think you would have to have compression even if the chain has slipped.
 
I would bring #1 up to TDC and check valves on that cylinder first.
Before you pull everything off.
I have a wooden dowel that I can stick in the spark plug hole and get me pretty close. What exactly am I checking for? To confirm that piston timing and cam timing are suddenly off from each other?
 
I have a wooden dowel that I can stick in the spark plug hole and get me pretty close. What exactly am I checking for? To confirm that piston timing and cam timing are suddenly off from each other?
Piston at tdc valves should both be seated, no pressure on pushrod holding valves open slightly.
 
I'm not familiar with the gen 3 hemi, but I assume it has timing Mark's some where. Line them at 0 degrees #1 piston should be at tdc, check with your dowel to make sure. Valves for #1 cylinder should be seated at that point.
 
Does it have those dumbass bleed down lifters that cancel the cylinders out?
 
I'm not familiar with the gen 3 hemi, but I assume it has timing Mark's some where. Line them at 0 degrees #1 piston should be at tdc, check with your dowel to make sure. Valves for #1 cylinder should be seated at that point.
No timing marks. Will have to figure that out some other way. Damper is marked every degree from 0 to 360, but there is no reference mark on the front cover.
Does it have those dumbass bleed down lifters that cancel the cylinders out?
No, this is a non MDS motor and non VVT.
 
Yup, dowel in cylinder, and watch valves as you roll it over. Both valves should be closed when piston reaches top.
 
If you don't want to pull the cover right away. Just pull the valve covers and see if any of the push rods flop up and down if so just pull the engine because most likely there is also valve damage as well
 
New build?

The gen 3 cam goes in with the dot at 12 and the crank at 12. They dont line up.

Wonder if you bent all the valves?
 
No timing marks. Will have to figure that out some other way. Damper is marked every degree from 0 to 360, but there is no reference mark on the front cover.

No, this is a non MDS motor and non VVT.

Then you "gotta problem".
 
It's an easy mistake to make. I'll give you one guess as to why I know that.....

:BangHead::mad:
 
try another gauge?
If the valves are moving, and split overlap is close, I have never seen zero psi

If you stick anything in the hole, be aware what can happen if the valves begin to open.
I use a different method. I take the gauge off the compression tester (Quick disconnect),and screw the hose back into the plughole. Then I stick the other end in my mouth, but do not make the mistake of sealing it hard and cranking it with the starter; you could blow your eardrums out!!.No, instead, gently motor the engine by hand. You will be able to find TDC compression pretty close........ if everything is as it should be; certainly close enough if the damper is marked.
 
Last edited:
try another gauge?
If the valves are moving, and split overlap is close, I have never seen zero psi

If you stick anything in the hole, be aware what can happen if the valves begin to open.
And what could happen on a gen3 hemi where the plug holes are in the top of the head?
 
are you sure the gauge is good? hard to believe they're all flat and you didn't hear something destroy it's self
 
Timing chain, cant see it jumping if valves are still moving.
Recheck the compression tester...
 
-
Back
Top