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Old 06-27-2010, 08:35 AM
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Crankcase pressure in new 429

I bought a 429 Cobra Jet that was built 6 years ago, but never started. After we got it installed in a '90 model fox body, it had some blow by. We thought it needed time for the rings to seat in, but it started blowing out the rear main and dipstick. Lots of pressure in the crankcase. Any suggestions or tips to seat rings??

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Old 06-27-2010, 09:23 AM
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Wow... that's a LOT of blow-by!

I'm wondering if it may have been badly tapered, and honed rather than bored? Or perhaps it was assembled with all of the ring end gaps lined up?

Rusted frozen rings? 6 years is a long time.

I don't know what your exact circumstances are, but it's the pits buying a "rebuilt" motor from "some guy" in the newspaper or e-bay. You just have no idea what you're getting.

I made the mistake of buying a Ford 390 from a machine shop on an "as is" basis. It was explained to me that the guy that owned it just wanted it "patched up" ... and then never returned to pick it up. I installed it in my 68 "Battlestar Galactica" and it wasn't long before I picked up on piston slap.
It eventually it became a $400 boat-anchor, but it lasted long enough to have the original 390 rebuilt properly.
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Old 06-27-2010, 11:10 AM
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Quote:
Originally Posted by timcourtney
I bought a 429 Cobra Jet that was built 6 years ago, but never started. After we got it installed in a '90 model fox body, it had some blow by. We thought it needed time for the rings to seat in, but it started blowing out the rear main and dipstick. Lots of pressure in the crankcase. Any suggestions or tips to seat rings??
First step would be to run a compression test to see if you have a cylinder issue or a whole engine issue. If the compression test doesnt show anything I would then run a leak down test.

Did you do anything to prep this engine for its first startup. 6 years is a long time for a new engine to sit. If it was never ran, it also may never have been primed so you could basically have raw cast iron that sat for 6 years with no protective oil coating. The cylinder walls could be pitted, could have broken a ring etc. The compression test should tell a story.

If you have or can get ahold of one of those bore scopes, it may be worth looking in a cylinder or two.

I am always leery of something that was "rebuilt" and never used. Usually there is a reason.
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Old 06-27-2010, 08:10 PM
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thanks!!

Thanks for the advice! I really appreciate your input & look forward to trying your tips to get this car down the strip!
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Old 06-28-2010, 06:55 PM
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Quote:
Originally Posted by timcourtney
I bought a 429 Cobra Jet that was built 6 years ago, but never started. After we got it installed in a '90 model fox body, it had some blow by. We thought it needed time for the rings to seat in, but it started blowing out the rear main and dipstick. Lots of pressure in the crankcase. Any suggestions or tips to seat rings??
For blow by to be causing the dipstick and rear seal to be loosing pressure/blowing out oil, the rings would have to be well and truly stuck or broken or the ring lands broken- that sort of thing.

If this is the case, the engine will be smoking from the tail pipes/headers/whatever, too- not just from the dip stick tube. The breather and PCV grommet- if either or both are used- would be blowing smoke, too. Plugs will be oil fouled or on there way to becoming fouled.

If all these things aren't happening, you may have overfilled the engine w/oil. Had a time where I filled a Ford 351W engine and then my "helper" came along and he, too filled the engine. 8 quarts in a 5 quart pan. What a mess!
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Old 06-28-2010, 07:05 PM
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What are you using for a breather set up?
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