Time 4 a rebuild
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Joined: Apr 2005
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Time 4 a rebuild
My '70 350/350 has 107k and looks like it's never been yanked out of the car. The pan has been dropped and the top was painted half-youknowwhat.
It's using a ton of oil: 1 qt/ 300 miles highway driving!
Here's what I don't get: that much oil ought to smoke at start up or at speed, and while it smells rich, you can't see anything.
Also, I just finished a leak-down test on it.
ALL cylinders had between 15-20% leakage, which according to the gauge I used, is acceptable. All of the leaking air sounded like it was coming from the crankcase, indicating worn rings. No sound was heard through the carb or exhaust pipes, so valve guides and seals appear not to be the problem.
Finally, I replaced the spark plugs about 100 miles ago, and they're already very oily. Rings, right?
So how come the leak down doesn't show a higher percentage? I did calibrate the tester and followed the directions.
Would a compression test tell me anything more or different, or is that inferior to the leak-down test?
Thanks -
Mark
It's using a ton of oil: 1 qt/ 300 miles highway driving!
Here's what I don't get: that much oil ought to smoke at start up or at speed, and while it smells rich, you can't see anything.
Also, I just finished a leak-down test on it.
ALL cylinders had between 15-20% leakage, which according to the gauge I used, is acceptable. All of the leaking air sounded like it was coming from the crankcase, indicating worn rings. No sound was heard through the carb or exhaust pipes, so valve guides and seals appear not to be the problem.
Finally, I replaced the spark plugs about 100 miles ago, and they're already very oily. Rings, right?
So how come the leak down doesn't show a higher percentage? I did calibrate the tester and followed the directions.
Would a compression test tell me anything more or different, or is that inferior to the leak-down test?
Thanks -
Mark
Burning Brakes
Joined: Nov 2005
Posts: 1,143
Likes: 0
From: Leander Texas
Originally Posted by AirTrafficController
My '70 350/350 has 107k and looks like it's never been yanked out of the car. The pan has been dropped and the top was painted half-youknowwhat.
It's using a ton of oil: 1 qt/ 300 miles highway driving!
Here's what I don't get: that much oil ought to smoke at start up or at speed, and while it smells rich, you can't see anything.
Also, I just finished a leak-down test on it.
ALL cylinders had between 15-20% leakage, which according to the gauge I used, is acceptable. All of the leaking air sounded like it was coming from the crankcase, indicating worn rings. No sound was heard through the carb or exhaust pipes, so valve guides and seals appear not to be the problem.
Finally, I replaced the spark plugs about 100 miles ago, and they're already very oily. Rings, right?
So how come the leak down doesn't show a higher percentage? I did calibrate the tester and followed the directions.
Would a compression test tell me anything more or different, or is that inferior to the leak-down test?
Thanks -
Mark
It's using a ton of oil: 1 qt/ 300 miles highway driving!
Here's what I don't get: that much oil ought to smoke at start up or at speed, and while it smells rich, you can't see anything.
Also, I just finished a leak-down test on it.
ALL cylinders had between 15-20% leakage, which according to the gauge I used, is acceptable. All of the leaking air sounded like it was coming from the crankcase, indicating worn rings. No sound was heard through the carb or exhaust pipes, so valve guides and seals appear not to be the problem.
Finally, I replaced the spark plugs about 100 miles ago, and they're already very oily. Rings, right?
So how come the leak down doesn't show a higher percentage? I did calibrate the tester and followed the directions.
Would a compression test tell me anything more or different, or is that inferior to the leak-down test?
Thanks -
Mark
Just a suggestion.
DR. Jay
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Joined: Apr 2005
Posts: 618
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Originally Posted by DR.Jay
I think with that much oil on the plugs it's time for a rebuild. Do you have more oil fouling on one plug than the others? (#7)Cylinder? I have found that a bad PCV valve or some types of valve covers can cause oil consumption with fouling on all plugs. Oil is drafted through the non baffled valve cover into the PCV valve right into the intake.
Just a suggestion.
DR. Jay
Just a suggestion.
DR. Jay
The plug fouling is not even. But here's the twist: the old plugs I took out had #'s 1,4,and 5 as the oiliest. The new plugs I put in 100 miles ago show #'s 2,6, and 8 as the worst. #1 actually looks pretty clean on the new one. The valve cover does have a baffle underneath the PCV hole. The PCV valve still rattles, if that's any indicator? My assumption is that the motor has never been completely torn down. Only the oil pan shows signs of newness. That said, with 107k, I think it's a given.
Thread Starter
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Joined: Apr 2005
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Originally Posted by MotorHead
Was the intake ever changed on that motor ?
I don't know for sure either way. Looking at it, someone painted the intake on the motor, as all of the intake bolts and one bracket show signs of Chevy Orange. The water pump and timing chain covers have newer paint as well, but it looks like it was sprayed in place - probably a quick engine degreasing and some orange to spruce it up. I would think if they had pulled it, they would have done a better job painting it. The lower front of it isn't newly painted.
Le Mans Master
Joined: Dec 2003
Posts: 5,727
Likes: 38
From: Fremont CA
Chevy used someof the worst valve guide oil seals ever invented on all its engines. My guess is they are all gone on your motor now. The 350/350 has rather high compression so it would show strongly on a compression test. The leakdown figures look OK even excellent for your mileage. I would rebuild with modern forged flat-top pistons (if it is a "real" 350/350 you have high compression domed pistons.) Your heads were never designed to use unleaded fuel, the descion process now begings on whether to use the factory heads (quite good cylinder heads until you fit the exhaust valve seats with hardened inserts for unleaded fuel) or invest the $$ into aftermarket cylinder heads during the rebuild.
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