Ad Radar
Item Posts    Sort Order

need help finding cause for blowby

 
71chevyc10454
I love my Chevy Chevette!
Posts: 3
Joined: 09/10
Posted: 09/29/10 10:40 AM

ok,my buddy just got a 71 c10 with a 454 crate motor,when he got the truck,the drivers side valve cover was leaking so we decided just to change out both gaskets,now we have blowby coming out the passenger side valve cover.

as far as i know,it's properly ventilated with a pcv valve on the driver side and a breather cap on the passenger side,the valve covers are aftermarket,non baffled aluminum,we have replaced the valv cover gaskets twice now thinking maybe the first set was bad,we are at a loss as to what could be causing the problem.  

Post Reply
waynep7122
Everything in my driveway’s a Chevy
Posts: 556
Joined: 08/09
Posted: 09/29/10 01:22 PM

lets test the system  ...

with the engine idling...    unplug the PCV valve from the vacuum hose into the intake manifold...

the engine should change RPMs     (usually stall on smaller motors the engine will stall)

this verifies that there is enough vacuum to properly operate the PCV valve...


there are multiple sizes of pcv valves... turn it over and look up the big end.. see the washer that changes the amount of flow possible..   to big is bad.. to small is bad...
~~~~~~~~~~~~~~~~~~~~

plug the pcv back in...     go to the breather ... take it out... with the engine idling..  place your palm over the opening...    when you start feeling suction.. after about 10 seconds .. pull your hand off.. it should make a popping sound..     then verify that the breather actually flows...    and is NOT bottomed out hard against the baffle.. seen that happen...

i have seen engines were the PCV hose at the intake was filled with carbon.. and blocked... so there was NO suction...  

i have run across cars that had the PCV working...  but the breather was blocked... so during cruise and idle.. there was massive build up of vacuum inside the crankcase....   but under load...  the excess blowby built up tremendous crankcase pressures...   this vacuum and pressure can blow out the gaskets and seals around the motor...


one thing... i have also run into problems with valve cover gaskets not sealing properly to the cylinder heads..

did the areas where the bolts go through get flattened with a small hammer used on the gasket side with the gasket removed..    load spreaders are  available also... big long ones for big blocks...

i have taken to after cleaning , scraping the gaskets.. hammering the flanges flat...   then using black super weather strip adhesive.. to stick the gasket to the valve cover.. pull it apart for a minute then carefully stick it back together...  after 5 minutes its usually set firm enough to reinstall the valve cover.. try not to wait to long...  you don't want the glue to dry without the pressure of the head against it..

a very thin wipe of ultra grey silicone between the gasket and the head will glue it down...

normally silicone is applied.. the gasket installed .. snugged.. but not the final tightness.. the silicone allowed to dry.. then the gasket gets tightened the last of the way.. so the silicone does not just squeeze out.....

do not used silicone on rubber gaskets.. they will just push out...  there are also several different thicknesses of valve cover gaskets available through various manufacturers and most speed shops...  

Post Reply
71chevyc10454
I love my Chevy Chevette!
Posts: 3
Joined: 09/10
Posted: 09/30/10 07:03 AM

thanx,i'll try these today,hopefully i will beable to find the cause,one other question, the brake booster and the pcv valve are one one vac hose going to the base of the carb,not the intake (it's an edelbrock victor jr),would that be hindering the pcv valve in anyway  

Post Reply
idrivejunk
My first time was in a Chevy
Posts: 128
Joined: 04/10
Posted: 09/30/10 10:28 AM

Yes. You don't want PCV and brake hoses connected together. The PCV hose carries oil vapor. It would be best to connect the PCV to the carb base and the brake hose to a fitting on the intake.

Nice post, wayne  
idrivejunk

Post Reply
71chevyc10454
I love my Chevy Chevette!
Posts: 3
Joined: 09/10
Posted: 09/30/10 02:37 PM

unfortunately,the intake has no fitting for the brake hose,according to edelbrock,it should have been drilled out,tapped and a fitting installed before it was put on the car and the owner doesn't want to go to that trouble,the intake is for race engine,with manual brakes

i tested the pcv valve and breather cap today,the idle changed when i unplugged the pcv valve and there was suction on the breather,we are thinking that the valve cover on the passenger side is warped,as that is the only side that is leaking  

Post Reply
TO TOP