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Old 12-12-2003, 09:24 PM
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leak down test results

Hello, recently had my 350 sbc rebuilt. Used moly rings. Am using alot of oil, say 1 qt. to 200-250 miles. Have got about 1000 miles on the rebuild now. Today had my mech do a compression and leak down test. Here are the results- cyl. #1 150lbs with 8% leakdown, cyl. #2 155lbs with 7% leakdown, cyl. #3 145lbs with 9%, cyl. #4 with 9%, cyl. #5 150lbs with 11%, cyl. #6 145lbs with 9%, cyl. #7 145lbs with 6%, and cyl. #8 145lbs with 14%. The leakdown is alittle higher in cylinders 5 and 8. Was wondering what is considered good leakdown %'s. My mechanic thinks possibly that since we installed moly rings that it might be possible they still haven't seated?? What do ya think!! Thanks!!

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Old 12-12-2003, 09:30 PM
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I have said this 1000's times " There are a 1000's ways of rebuilding an engine But only 1 correct way. You sir have created a piece of junk just like the other 1000's. Next time buy a crate engine and be done with it. Only morons rebuild engines these days especially you amerikans Dam you can buy crate engines for less then an old rotten rebuilt one. The only rule that I follow in rebuilding an engine is if you are restoring a rare car car with an original engine. Latter

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Old 12-12-2003, 09:35 PM
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Who did the rebuild?
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Old 12-12-2003, 09:36 PM
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it has been my experience that molley rings seat faster than cast iron. mine seemed to seat in less than five minutes if even that long.
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Old 12-12-2003, 09:39 PM
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GOD, please let me reach through my computer screen tonight! Father, even just one hand! Yeah, I know your Commandments, but you have seen the HORROR that we are putting up with! Ok, Ok, if it's patience that I need it's patience I'll pray for, AMEN!!!!!

P.S. I'm a little slow, two posts got in where this was meant to go!
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Old 12-12-2003, 09:40 PM
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there`s a little test you can do, remove the PCV valve, run without it for a short while and see if the oil usage goes away, my car used a quart a week, I placed a piece of a foam lawn mower air filter in the baffle, oil usage stopped cold.
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Old 12-12-2003, 10:32 PM
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Doublevision, thanks I'll try that idea. OddRodder, I'm lost with your reply!! The guy that rebuilt the motor is a machanist, dirt tracker that has been doing this kinda work for about 20 years. Rebuilt ALOT of motors!! He's more then willing to tear back into the motor and replace rings or whatever seems to be the problem. Again, what are good leakdown % numbers for a 350 chevy?? The thing runs like a top, just a real thirsty one. Thanks!!
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Old 12-13-2003, 07:10 AM
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5% is an acceptable figure. 10% is pushin it. I would look at the valves for leakage first before pulling the motor.
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Old 12-13-2003, 07:41 AM
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Along the lines of what 4 Jaw is saying. When you did the leakdown test where did you hear the air escaping from on each cylinder? 3-5% is fairly common with stock type rings, 14% is kinda high. Do you see any oil smoke out the exhaust or is it just kind of disappearing?
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Old 12-13-2003, 08:12 AM
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last rebuild I did on my motor before the one now, had plasma moly rings. the guy at my machine shop gave me the wrong gap specs for KB dome hypers. in less than 2 months I had 15% leakdown in 4 cylinders.
Went ahead and ran the smoking beast for 3 more months. When I took the motor apart I had 6 cylinders with the endgaps aligned. and they were gapped to big so it was like sucking oil thru a straw.
Oh I ended up doing the rebuild when I did because the officials at my track checked for oildown after every pass I was making. LOL
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Old 12-13-2003, 09:30 AM
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Two things come to mind that I haven't seen mentioned yet:

1. Bore finish too rough for the moly rings. This doesn't happem very often any more, but I still see it occaisonally.

2. Second compression ring installed upside-down. This will scrape oil into the cumbustion chamber, rather than down to the oil ring.

Good Luck.
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Old 12-13-2003, 09:42 AM
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Thanks to everyone that has replyed so far. Man this is really frustrating after all the time and money spent. As for where the air leakage was, I'll have to ask my mech. I wasn't able to be there unfortunately! The car doesn't seem to be smoking, and when the mech pulled the plugs he said they all were alittle gassy. We put new Dart heads on this motor with the 2.02 valves. The machanist pulled the heads all apart and checked them then lapped them in. It's running the 2 valve relief .030 hypereutetic speed pro pistons with speed pro sealed power moly rings. It's running a weiand 8004 intake. I installed the fel pro 1256 intake gasket. So if 5% is good, and 10% pushing it, would two cylinders running 11% and 14% be enough to cause the oil usage I've got?? Thanks again, and keep the replys coming!!
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Old 12-13-2003, 03:58 PM
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Auto-part it might be a good idea to not say anything at all if you have no valid input
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Old 12-13-2003, 04:02 PM
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Sorry Tim! My reply was meant for a very ignorant member that should really JUST GO AWAY!!!! His reply to your problem was about the last straw for me. Tom, Chuck, and DV all are dependable members! Again, SORRY
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Old 12-13-2003, 04:04 PM
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Quote:
Originally posted by OddRodder
Sorry Tim! My reply was meant for a very ignorant member that should really JUST GO AWAY!!!! His reply to your problem was about the last straw for me. Tom, Chuck, and DV all are dependable members! Again, SORRY

We are all hero's in our own mines. Latter
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