Thread: My 350 sbc is smoking

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Originally posted by bgrd
Could someone post a link to a chart ,which has all the torque specs. for a 350 sbc... TIA

is this what you need?

http://www.hotrodshack.com/torque_settings.htm

Originally posted by tpiini
Maybe I'm the dummy here, so feel free to ignore me. But wouldn't a 20-point difference in wet & dry compression tests tell you that your rings are exactly the problem?

these # are high but the the dif. from dry and wet is ok.

Ready to Test Compression
Connect a compression gauge to the engine—Screw the compression gauge fitting into the spark plug hole. You don't have to worry about torque here. As long as the rubber O-ring on the compression gauge gets compressed, you'll get accurate readings. See photo at right.

Crank the engine over five or six times—And...

Note the readings on the gauge—If you're doing the test by yourself, that's the best you can do. Crank the engine five or six times and read the gauge. If you have a helper, though, have him (or her) crank the engine while you watch the gauge. It's best if you can see what the compression reading is on each turn of the engine, to get an idea of how quickly it comes up to its maximum reading. Then...

Repeat for the other four cylinders—This will give you a set of measurements of your engine's ability to compress the air/fuel mixture.

What's It Mean?

The compression specifications for a Vigor engine are...

...at 250 rpm (cranking speed) and wide open throttle (that's why we blocked the throttle plate open) ...

206 psi (nominal)
135 psi (minimum)
28 psi (maximum variation)



Note: All pressure values in this article are given in pounds per square inch. That's because the author is a typically arrogant and lazy American. If your compression gauge reads only in kilo Pascals, click here. A converter will open in a new window.
See? He's not that lazy!


This means that a new (or near new) engine should have 206 psi of compression. There should not be more than 28 psi difference between the highest and lowest cylinder. All cylinders should have more than 135 psi of compression.

A low reading on the first stroke followed by gradually increasing readings on successive strokes usually indicates worn rings. That's why it's sometimes helpful to be able to watch the gauge while the engine is being cranked.

Probably the most important consideration is the difference between the highest and lowest cylinders. Let's say you've got readings of 169, 165, 135, 168, and 171. Hmmm. One cylinder is significantly lower than the others. That tells us there's a compression problem in that cylinder—but that's all that it tells us.

Let's back off here for a minute. If the readings were 169, 125, 131, 168, and 171, we could make an immediate deduction. If any two adjacent cylinders have a significantly low reading, that usually indicates a blown head gasket—the gasket has broken down between the two cylinders and they're leaking into one another.

But what if only one cylinder has a low reading? We can assume for the moment that the head gasket is probably okay, so the most likely culprit is a different leak, either at a valve or at the rings. We'll have to do another check to narrow it down. This is the time to do a...

Wet Compression Test

This involves squirting a few teaspoons of oil into the spark plug hole and then re-testing the compression of the suspect cylinder. The oil will (temporarily) coat and seal the compression rings. NOTE: do NOT squirt too much oil into the cylinder, or you'll get false results. With excessive oil in the cylinder, compression readings will go up even if the rings are in good condition.

If the new compression readings are significantly higher, then that indicates the compression rings (or the cylinder walls) are worn and need replacement and/or repair. It's time for new rings or cylinder service. Cylinder service entails either boring the cylinders to a larger diameter (with corresponding oversized rings and/or pistons) or re-sleeving the cylinder to its original geometry. Either way, you may as well do all the cylinders.

If the wet compression readings don't change appreciably, then that cylinder's valves aren't sealing properly, or the head gasket has a leak. Either way, it's time to pull the head and see what's going on. Most likely, it'll be a bad (burned) valve or a bad valve seal or valve seat. In other words, it's time for a valve job.

Variation vs. Absolute Results

The variation of one (or two) cylinders from the others tells us there's a definite problem with a head gasket or with one cylinder's valves or rings. But what if the absolute numbers are all on the low side?

That depends on how low the numbers are. It tells us that the engine is wearing out. But it's wearing out evenly. In other words, the engine is getting old, but there's no real problem unless they're all near or below the minimum of 135 psi.

Bottom line—as long as the numbers are above 135 and within 28 psi of each other, don't worry about it. You've probably got plenty of other things to worry about. Give them your attention instead.


these # are a little on the high side, 135 is good compression on a st. motor. it shouldnt be using a qt. of oil every 100 miles no way. that much oil cant get by the rings without oil being blown all over everything.

lt1s10 quote:
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Originally posted by bgrd
Could someone post a link to a chart ,which has all the torque specs. for a 350 sbc... TIA
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is this what you need?

http://www.hotrodshack.com/torque_settings.htm

Thanks lt1s10, for the settings and the oil usage was coming from the valve seals...

Originally posted by bgrd
lt1s10 quote:
--------------------------------------------------------------------------------
Originally posted by bgrd
Could someone post a link to a chart ,which has all the torque specs. for a 350 sbc... TIA
--------------------------------------------------------------------------------




is this what you need?

http://www.hotrodshack.com/torque_settings.htm

Thanks lt1s10, for the settings and the oil usage was coming from the valve seals...

never thought it was the rings and thats a lot of oil going by the valves, but all that counts is you got it fixed.