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#1 |
Registered User
Join Date: Sep 2011
Location: United States
Posts: 19
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Excessive Blowby Advice
I'm trying to resurrect my old 77 Chevy C10 Long bed 350/350. I finally got it to a mechanic to repair the rear-main seal and he said it has "Excessive Blow-by, and the aftermarket blow-by filter was plugged. He advised me that the new seals and gaskets may blow again, so my parts and labor doing so may be wasted.
Should I go ahead and have the Rear main seal replaced knowing there is excessive blow by, or should I just put that money toward a motor? The motor was pulled from a running vehicle and was supposed to be good and running. It's not looking like that was the case. |
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#2 |
Registered User
Join Date: Jan 2010
Location: Louisiana
Posts: 127
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Re: Excessive Blowby Advice
If you have excessive blow by, you are probably wasting your money on the rear main seal.You need more than just a rear seal. Question: Is your PCV valve working properly? This might be some of your problem.
__________________
79 C-20 Scottsdale 350/400 3:73 gears 9 leafs and a headache rack (I speak English, thank you) |
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#3 |
Registered User
Join Date: Jan 2010
Location: Roanoke, Tx.
Posts: 1,561
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Re: Excessive Blowby Advice
What is a blow by filter?
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#4 |
Registered User
Join Date: Sep 2011
Location: United States
Posts: 19
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Re: Excessive Blowby Advice
I"ll ask about the PCV Valve. I do think he's going to replace it. The blow-by filter (Maybe I'm using the wrong term) goes in the valve cover gasket. Where it would normally go into the factory air filter, it has an aftermarket filter instead.
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#5 |
Just here to tinker
![]() Join Date: Jun 2008
Location: Holland, MI
Posts: 3,692
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Re: Excessive Blowby Advice
That is not called a blow by filter. That is just a breather tube that vents the crankcase into the air cleaner. The PCV valve is probably on the other valve cover and that needs to be connected to a vacuum source, usually the bottom of the carb. The mechanic should know about that.
If he is saying there is blow-by then I would ask what the results are from the compression tests he did to verify it is blow-by causing the gaskets to fail. And if he did a compression test, ask if he put oil in the cylinder and re-did the test to see whether or not it is the rings that is causing the blow-by. Sorry if that seems like a lot but it is necessary to determine what is the proper place your money should be spent.
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78 C10 SWB Diesel #1 (wrecked)http://67-72chevytrucks.com/vboard/s...1978+silverado 78 C10 SWB Diesel #2 (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=650751 60 GMC Suburban (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=445526 60 GMC 1000 (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=298235 67 GMC 1500 (sold) http://67-72chevytrucks.com/vboard/s...d.php?t=803695 86 Suburban(summer unit) http://67-72chevytrucks.com/vboard/s...d.php?t=810697 88 Suburban 4x4(winter unit)https://67-72chevytrucks.com/vboard/...25#post8900725 |
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#6 |
Registered User
Join Date: Sep 2011
Location: United States
Posts: 19
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Re: Excessive Blowby Advice
Thanks for the info Corts. Those questions will be a huge help.
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#7 |
Registered User
Join Date: Sep 2011
Location: United States
Posts: 19
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Re: Excessive Blowby Advice
Thanks for all of the info. I went ahead and took the truck away from that shop. He was doing the right thing by letting me know that the blow-by might cause the Seals to pop again. But I don't think he was willing or able to help me figure out what was causing the blow by. Looking for a new shop in the Central Arkansas Area.
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#8 |
Registered User
Join Date: Dec 2009
Location: Annapolis Royal Nova Scotia
Posts: 56
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Re: Excessive Blowby Advice
if ita got blow by and been sitting for that long i would also think a broke/stuck ring. i had a 74 350 interceptor that had terrible blow by to the point it spewed oil out the breather tube. turns out the top ring on every piston was broke.
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#9 |
Registered User
![]() Join Date: Apr 2009
Location: New Freedom Pa.
Posts: 1,335
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Re: Excessive Blowby Advice
Just so you know , a small block Chevy "rear main seal" CANNOT be pushed out by blow by. The purpose of the rear main seal is to keep oil pressure to the rear thrust bearing from leaking externally. that's all.
All the other seal can be pushed out with excess crankcase pressure, oil pan gasket , valve cover gaskets , timing cover gasket. Desert |
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