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Need help with mystery compression readings

bmoss1457

New member
Joined
May 5, 2019
Messages
3
Location
Oklahoma
Corvette
2003 Z06
I have a 2003 Z06, 140k miles with no previous issues. While moderately driving I suddenly lost significant power, feeling like I lost at least two cylinders. I limped 5 more mile to home.
No unusual noises excepts what sounded like compression bursts from passenger side somewhere. Fuel check good, spark good, plugs good. It got interesting with compression check.
#1, 2. 4 and 8 only had 25-35psi and the rest had non. on second round little to no compression on any. On third round #1,2,4 and 8 again had very low reading. Timing chain has considerable slack but no jump and marks are fairly aligned. Crank feels really hard to turn by hand at points, enough that I was forced to bump the starter to continue. Any opinions where to look next? Would excessive slack in the timing chain cause timing to be off that bad?
How much slack or deflection with the timing chain can be tolerated before potential damage to valves?
 
Last edited:

LLC5

Well-known member
Joined
Sep 28, 2004
Messages
2,299
Location
Wa.
Corvette
98 black 6spd convert.
LS's are interference engines. Do a cylinder leak down and or pull the valve covers for valve/push rod damage.
 

bmoss1457

New member
Joined
May 5, 2019
Messages
3
Location
Oklahoma
Corvette
2003 Z06
I actually didn't know the difference until you mentioned that. Thank you. I have he front cover off, etc ready to pull the chain and sprockets. I guess I'll just plan on pulling the heads and look for damage there too.
 

bmoss1457

New member
Joined
May 5, 2019
Messages
3
Location
Oklahoma
Corvette
2003 Z06
Can you tell me how much slack or deflection with the timing chain can be tolerated before damage to valves or pistons?
 

LLC5

Well-known member
Joined
Sep 28, 2004
Messages
2,299
Location
Wa.
Corvette
98 black 6spd convert.
Back in the old days if you could rock the damper pulley 8* of ignition timing (distributer rotor) side to side it needed to be replaced. With modern engines chains are usually considered "lifetime" by most manufactures and will usually make slapping noises or set CEL's with corresponding codes.

I you already have the timing cover off I would put a new chain on and do another compression test, you never know luck could be on your side.
 

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