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Old 05-17-2013, 11:12 PM
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ton of blowby that smells like raw gas

hey guys I have a 350 chevy bored .60 over with an xe 274h comp cam, ported 601 heads with new valve seals, compression is about 10:1, performer eps in take with a 600 cfm edelbtrock carb, 1405 stock jets

the engine runs great, i just have a boat load of blowby even with my pcv valve sucking

it's a high pressure stream of blowby that smells like gas coming out of my breather hole

anybody know what it might be ?

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Old 05-17-2013, 11:18 PM
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I forgot to mention, what's kind of incredible is that my oil isn't diluted with oil

well at least not enough that it's noticeable
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Old 05-18-2013, 12:13 AM
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the engine doesn't knock or tick, it has good power too

the cam is new basically less than 1200 miles on the engine since it was rebuilt

I dont want to jump to conclusions and say piston rings because the engine runs amazing except for the crap load of blowby I'm getting
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Old 05-18-2013, 08:49 AM
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Do a compression test first and see if you find a cylinder with a low PSI figure and you'll have the blowby issue figured out.
Also, pull the oil dipstick out and back away from the vehicle, put a lighter to the oil on the end of the dipstick and see if it flames up, if so fuel is in the oil and if that's the case you either have a ruptured fuel pump or a hole in a piston.
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Old 05-20-2013, 12:49 PM
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Quote:
Originally Posted by xzero117 View Post
the engine doesn't knock or tick, it has good power too

the cam is new basically less than 1200 miles on the engine since it was rebuilt

I dont want to jump to conclusions and say piston rings because the engine runs amazing except for the crap load of blowby I'm getting
Blow by only comes from compression getting past the rings or from damage to the piston or cylinderwall.

- Excess skirt clearance will allow the piston to rock in the bore causing the rings to break seal with their lands and the cylinder wall.

- A ring was broken on assembly.

- A ring is inverted, more likley a top ring with blow by, possibly a second ring though that usually also puts a lot of oil into the combustion chamber.

- Excessive ring gap, while on that subject insufficient ring gap can result in the loss of seal at the least and a busted ring at the most.

- A failure of the piston crown, detonation/preignition, a simply bad part let go, a valve has hit a piston.

- An inclusion, scratch, gouge, failure, of machine error in a cylinder wall.

- Wall finish incompatible with the ring type, a smooth wall will have a hard time sealing with a chrome ring for example. Chrome likes some tooth in the wall, moly or simple cast iron does not.

I'd say run a leak down test first to see if the cylinders hold compression and if there is a reason associated with a piston or bore, you will hear it in the crankcase as pressure bleeds past the problem.

Bogie
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Old 05-21-2013, 02:23 PM
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Seeing its .060 over which makes for weak cylinders, Plate honing is a must with a good hone and proper abrasives.

A leak down test with the piston just below TDC will show poor ring seal.

[quote
This is a pic of a 454 block that has come in for some work as it only has about 3200 miles on it since the rebuild and it was making some lower end noises. We line honed it and squared and decked it flat and bored it and we blued up the 2 center cylinders installed the gasket and torque plate and went in for 6 strokes on each cylinder as you can see the results and look at the piston as it has blowby right to the oil control rings as we could measure .003 distortion on the cylinders.







SBC pics


[/quote]][/QUOTE]
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Old 05-21-2013, 02:56 PM
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the cylinder walls looked real smooth when I assembled the engine

it doesn't have many miles since I first started it up so perhaps I just have to give it a long drive ? I have no idea what the ring material was

any who I've put 2 pcv valves on it for now until I do something about this
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