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Old 03-25-2006, 09:43 PM
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is it gonna explode now, or later?

engine: chevy 350

Compression test: carb open, all plugs out, engine hot(it burned me), 3 hits on the gauge to max pressure. All cylinders have 120 + or - 1 except for cylinder #6 it had 100 PSI. I tried adding oil and it only upped compression to 105 PSI at the most.

Did a leak down test and could hear it ever so faintly from the exhaust pipe. This engine runs great and all of the plugs look exactly the same and all of the threads on these plugs had a little bit of oil on them. I checked all fluids for contamination and they were good. no bubbles in the rad.(i'm hoping is't a head gasket).

I tested compression about a year and a half ago and all cylinders were good.
Then i went to the drag strip and floated the valves 2 times, opps. this motor is all stock and the cam on the level of a rv cam so no huge lift. After this I stored it for the rest of summer and this winter so it has been stored for close to year. I just tested compression today and i got the results listed above.

Since it runs the same as it did before i floated the valves will it be ok until i build another engine during the next winter if i only drive it in summer or is this gonna go downhill fast.

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Old 03-25-2006, 09:51 PM
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How does it run? I can tell you 120 psi isn't very high even for a worn stock 350. Are you sure of your gauge condition? If you added oil and compression didn't jump, that means the valves or valve is leaking. Might try running top engine cleaner threw it may just be crud on the valve seats. If it doesn't miss I wouldn't tear it down.
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Old 03-25-2006, 10:19 PM
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No misses at all, runs smooth as ever. ya i also agree that the compression is low anyway but the motor was in the truck when i bought it. I also ran some crud remover through it today and compression stayed the same. Maybe some drivin will fix it.
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Old 03-25-2006, 11:18 PM
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Probably, I wouldnt give it a second thought. Drive it till it gets worse, may run forever.
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Old 03-26-2006, 03:57 AM
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Have you reset the tappets? Valve recession can hold a valve off seat.
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Old 03-27-2006, 10:50 AM
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when you say valve recession do you mean that the valve seat sinks deeper into the head then causing the valve to be held open at what was previously proper ajustment? This is what i believe you mean.

I figured that if anything the valves would become looser over time considering the compression was 120 PSI in all cylinders a year ago but i had never ever thought of valve recession. i will check the valves on that cylinder as soon as i can.

Last edited by Scrumgees; 03-27-2006 at 11:03 AM.
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Old 03-27-2006, 12:52 PM
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Quote:
Originally Posted by IanRiordan
Have you reset the tappets? Valve recession can hold a valve off seat.

Not with hydraulic lifters. They automatically ajust for this.
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Old 03-28-2006, 02:00 AM
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Recession is when the seats pound out and the spring pulls the valve up, thereby increasing its installed height.
At 1 turn on a 5/16 unf thread you get approx 40 thou per turn (similar to an 8x1mm thread). One half turn at the rocker stud gives approx 20 thou lifter preload. If the valve recesses 40 or 50 thou the lifter can't compensate, Crane and others make rocker pedestal shims in varying thicknesses to solve this on 302/351c's and others with non adjustable rockers - cheaper than adjustable pushrods.
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