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Old 08-18-2003, 09:38 PM   #1
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valve seals gone bad or piston blow by?

can anyone list symptoms that would separate bad valve seals/guides from leaky piston rings?

ive searched, but the stuff is a little foggy.., thanks for the help

on an LG4/SBC by the way.
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Old 08-18-2003, 10:36 PM   #2
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A pretty easy way to determine which is leaking is to remove the valve covers. Next, use a leak down tester or something to pressurize the combustion chamber. Then, spray some soapy water around the valve seal. Sometimes you can hear it leak if its pretty bad. If you do this and you find no leak at the valve seal and the cylinders ARE leaking, you know its not the valve seals. Not the most scientific method I'm sure, but it works...
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Old 08-18-2003, 10:44 PM   #3
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Pressurizing the cylinder would help you find a valve seat leak, not a valve seal leak.
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Old 08-18-2003, 11:06 PM   #4
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Quote:
Originally posted by rustybluebird
Pressurizing the cylinder would help you find a valve seat leak, not a valve seal leak.
huh?
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Old 08-18-2003, 11:50 PM   #5
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Quote:
Originally posted by Makaveli
huh?
That makes total sense.

If you pressurize the cylinder and you hear air near the valves, that means the compressed air is getting past the valve seats.

The valve seals keep oil from getting into the intake and exhaust ports. They don't keep the cylinder pressurized.

So scratch that method.

The easiest way to tell is to observe WHEN the engine burns oil (i.e. blue smoke).

If it does it only at start up, it's more than likely the seals. Oil slips past the seals, rolls down the stems, and into the combustion chamber. There it's burned making blue smoke.

If the engine constantly burns blue smoke through the tail pipe (if you have a PCV hooked up), or breathers (if you don't have PCV hooked up), then it's likely the rings.

It doesn't take a lot of money to replace the seals. If you do it and you still have problems, at least you didn't replace the rings first and find out it was only the valve seals.
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Old 08-19-2003, 12:12 AM   #6
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oohhh yea i read that, and didnt notice the difference between valve seaL and seaT. i thought they both said seal, so i was thinking wat the he11 does that mean haha. i read too fast, its too late dammit haha

that makes sense though, thanks for the info guys.

it was definately on start up, but after that we floored it and it let out a lot of smoke too.. so it might be the rings..

would you only need to rebuild the short block, or would you need basically the whole long block rebuilt? whats it cost to rebuild a short block.. factory specs etc? ballpark figure? we remove it from the car and bring it to a shop sort of thing.

thanks!
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Old 08-19-2003, 07:36 AM   #7
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Reguardless a leak down test should be performed. Id rather find out it's not the rings before I touched an engine. Usually guide seals smoke heavy on start up and clear out as the engine is warmed. Rings tent to smoke all the time.
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Old 08-19-2003, 11:25 AM   #8
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mine used to do that, you probably have a combination of both valve seals/guides/and or rings, if you floor it after its been running and it throws smoke it's your rings, that what mine did, i have a 5 speed when going down a hill riding the gear that sucker would cloud your vision i rebuilt the short block and it went away
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Old 08-19-2003, 01:11 PM   #9
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ah that sounds a little scary haha how much did it cost to rebuild your short block?
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Old 08-19-2003, 02:31 PM   #10
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uhm to bore it .20 over dip/magnafluxed, new cam bearings and freeze plugs was around 450 plus having the crank turned .10 under was 100 and pistons and the rods installed i think was close to 200 and i put it together, bearings were 100.00, and rings were around 30
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Old 08-19-2003, 05:15 PM   #11
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The way you tell if a car is burning oil from the seals or rings is to do a compression test. Bad rings usually show up as low compression on one or all cylinders. The final test is to squirt oil in the cylinder through the spark plug, then retest the compression. If the compression jumps up pretty good, that means worn rings. If the compression is normal and the oil does not change the readings, the cylinder is good. My 88IROC has a 305 which are notorious for bad valve seals. Another sign of bad seals: puff of blue smoke when starting up cold. If you are able to do the compression test yourself, then you should be able to do the valve seals. You need an air compressor and a valve spring compressor. Some people use the piston top. That scares me.
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Old 08-19-2003, 05:21 PM   #12
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Missed that one about the smoke when you floored it. If the intake seals are leaking, you are sucking in oil when you floored it.
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Old 08-19-2003, 05:21 PM
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