no compression on 6 help!!!

[rascalman]

Ok,

I have a 98 chvey silverado pickup 5.7 vortec and a compression check was
done on it. All that was said to me was there is absolutely no compression on number six, you need a new motor.......Ok what can cause no compression on one cylinder, and what other options do I have to find out about it. I have already been taken to the cleaners for a timing chain and gears water pump four injectors fuel regulator and if this is indeed the problem is no compression on six, then I would prefer to fix sell the pickup and move on.

Please help with options as to what this might be.

Thanks,

Rascalman

[maxwedge]

Next step is to have a cylinder leak down test done, this will determine if the problem is a hole in the piston, bad intake or exhaust valve, then a better decision can be made.

[tykrz]

If you just have compression tester, first do a normal compression test and note the reading. Then squirt some oil into the spark plug hole and do another compression test. If the readings go way up the problem is in the piston rings. If they stay the same it's likely the valves. Also pull the valve cover and make sure the the camshaft is lifting the valve. As for a hole in the piston, I haven't seen one yet after 15 years of twisting wrenches.

[sreve]

remove pass. side valve cover inspect valve springs on #6 third from front. if no trouble found back off the rocker arms and instead of hooking up the compression gauge put shop air to the cylinder. w\no compression massive amounts of air should come from somewhere ie: throttle body-intake valve:exhaust pipe-exhaust valve :oil fill cap (gotta lay the valve cover back on) piston .

[06Z71]

Could be the worst broken connecting rod but it is probaly a valve issue. Do you run cheap gas like walmart gas if so the carbon build up on the head could cause a valve to stick. I would pull off the valve cover to make sure you didn't drop a valve. that could also be the promblem

[rascalman]

Ok,

Lest see if I have this right, you are saying with the oil in the spark plug whole will act as a temporarey seal in place of the ring, which in turn will tell if the piston ring is bad or not..........Is this correct. Wow you must have allot of happy customers if you can do a test like that without pulling the heads and looking in................Thanks for the useful info we are trying this very soon............Rascalman

Originally Posted by tykrz

If you just have compression tester, first do a normal compression test and note the reading. Then squirt some oil into the spark plug hole and do another compression test. If the readings go way up the problem is in the piston rings. If they stay the same it's likely the valves. Also pull the valve cover and make sure the the camshaft is lifting the valve. As for a hole in the piston, I haven't seen one yet after 15 years of twisting wrenches.

[Mork]

If you have no compression at all on an indiviual cylinder it is a valve issue. Even bad rings will allow some compression. Most likely the cause of your problem is a severly burned valve or some reason for one of the valves in the effected piston to remain stuck open. This could be a s simple as a bent push rod to a damaged rocker arm assembly.
And yes the rings can be checked by applying oil to the clylinder and re-running the compression test, but only if the valve issue has been rulled out.