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-   -   Blow by and engine rattle (https://www.hotrodders.com/forum/blow-engine-rattle-517973.html)

Tony miller 11-02-2018 12:53 AM

Blow by and engine rattle
 
I have a sbc 350 it smokes at idle and leak oil out the breather filler and PCs valve I also have a rattle when I’m on the gas petal obove 45 mile an hour can someone help me

302 Z28 11-02-2018 08:18 AM

What year and how many miles on the engine?

36 sedan 11-02-2018 08:18 AM

Unfortunately, usually rattling motor noise when you’re accelerating is a sign of detonation (bad for the motor), a few of the common causes of detonation (but not limited to) are too much total ignition timing, low octane gas, too much compression for the gas available.
Prolonged detonation can cause serious engine problems, piston and ring damage is one, which leads to severe blowby, such as you describe.
IMHO, I would check timing and compression. Occasionally, denonation can cause blowby and backing the timing down eliminate it, if too much damage has not occurred. A compression test will give you an idea if there is any damage in the cylinders.
Good luck

Tony miller 11-02-2018 10:31 AM

Don’t know much about the engine Klm or how old it is etc it had thick oil in it when I bought it 3weeks ago had nothing but trouble with it since I got the car I have turned the timing clock wise which did retard it but it runs like ****

Tony miller 11-02-2018 10:32 AM

Was told it had done 8000 ks but I think his was full of ****

techinspector1 11-02-2018 11:29 AM

Tony, you need to perform a cylinder compression test on the motor.

1. Either buy or rent (yes, from a rental store), a cylinder compression tester.

2. Run the motor until it gets up to operating temperature on the gauge.

3. Remove air filter assembly.

4. Remove + electrical line that goes to the ignition coil, to prevent a fire.

5. Remove all spark plugs so that the starter can turn the crankshaft easily.

6. Use wire or strong string to hold the primary throttle blades wide open so the motor can breathe.

7. Choose the proper spark plug adapter to screw into the spark plug holes.

8. Let the starter pull the motor through at least 5 full "chuffs" for each cylinder. Each time the piston comes up on its compression stroke, you will see the indicator needle on the gauge go higher, until it reaches full pressure after about 5 chuffs.

9. Have pencil and paper there to record the max pressure of each cylinder.

Here's Eric the Car Guy doing a little 4-cylinder motor....
.

BogiesAnnex1 11-02-2018 12:47 PM

Quote:

Originally Posted by Tony miller (Post 4631865)
I have a sbc 350 it smokes at idle and leak oil out the breather filler and PCs valve I also have a rattle when Iím on the gas petal obove 45 mile an hour can someone help me

Not a good sign, this can be from serious but fixable to a rebuild or replacement.

Given that it has high blow by and is speed limited with rattle which might be detonation or an indication of bearing failure which you would see on an oil pressure gauge if it has one.

But your description seems to fit a cam drive failure taking the ignition timing with it since that drives off the cam. Typical here is the timing set is worn out this consists of stretch of the chain and or failure of the cam gear teeth which if factory are nylon, noise being a bigger factor in Detroit think than service life.

- Start by checking and resetting the ignition timing to what is correct for that year and model.
- Then with a timing light on number 1 plug wire bring the revs up to 2000-3000 RPM and slam the throttle shut while observing the timing marks if they wander up and down from your setting more than a couple three degrees either way this is a good sign the timing set is worn out. Detonation and/or blow by are common events that come with cam drive near failures. Pressing the cam drive to failure will result in pistons meeting valves, that converts a hundred dollar repair into a thousands of dollar repair or replacement.

For engine rattles you need to figure out whether this is detonation, or bearing, or piston failure. this takes more of a trained ear but in general connecting rod bearing, piston pin, or piston skirt failures make a double knock each with it's own tone which is hard to describe to someone that hasn't hear them. Crank mains make a single and very heavy sound when they are gone. Rod and main bearing failures reduce to eliminate oil pressure so with a gauge you can see that. Piston pin just makes noise in a double rattle, piston skirt also makes a double rattle neither of these affect oil pressure but the piston skirt can affect blow by if it has damaged the ring lands or is so busted it lets the piston rock in the bore which upsets ring seal.



Bogie

MouseFink 11-02-2018 04:23 PM

The engine is worn out and needs a complete rebuild.

The excessive blow by is a sign of worn cylinders and rings. The blow by is contaminating and lowering the octane of the incoming fuel in the combustion chambers and is causing detonation.

64nailhead 11-03-2018 01:48 PM

Done, put a fork in it. If you're blowing oil out as you described, then the damage is already complete.

Follow Tech's instruction to determine where all of the damage is. And it sounds like you'll be in need of a set of pistons, rings, bearings and gasket set.

The upside is that if the motor is fresh and built to correct specs, then you'll easily get by with a hone job and the parts I described above. But before you start it up and run the snot of the repaired motor, you need to fix the tune that caused all of the destruction (yes, the tune up that's on it now is what caused the issue.)

Tony miller 11-03-2018 02:18 PM

Yes I have had the engine tuned up and dyno done runs great from zero to 45 mile.from 45 mile and up when your foot is on the gas it’s got engine rattle but if I retard the timing anymore than it is it runs cough and back fires can’t get a happy medium mate

BogiesAnnex1 11-04-2018 11:05 PM

Quote:

Originally Posted by Tony miller (Post 4632297)
Yes I have had the engine tuned up and dyno done runs great from zero to 45 mile.from 45 mile and up when your foot is on the gas itís got engine rattle but if I retard the timing anymore than it is it runs cough and back fires canít get a happy medium mate

That's a good sign the timing set, gears and chain, are toast.

Bogie


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