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Oil blow by at Filler Cap and Distributor

  
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Oil blow by at Filler Cap and Distributor

 
68SSConv. 68SSConv.
I love my Chevy Chevette! | Posts: 14 | Joined: 08/07
Posted: 07/19/09
06:12 PM

I am having a problem with oil filling up the filler cap and blowing out of the bottom of the filler cap and when I put a rag between the filler cap and valve cover it builds up enough pressure to come up thru the distributor and out the weep hole beneath the distributor. I've changed the valve covers and put on tall ones, I've checked the compression of all the cylinders to see if maybe I had a broken compression ring letting it blow back in the crank case and build up pressure but there is less the 20lbs pressure difference between any of the cylinders. The motor is a 350 with a mild cam, nothing radical, and 4 spd., at 65 mph I am turning 2500 rpms and running about 50lbs of oil pressure. It really seems worse whern I go thru the gears at high rpms. Anyone else experienced this problem or have any suggestions on how to stop it? I appreciate your help.  

kentnova kentnova
I love my Chevy Chevette! | Posts: 5 | Joined: 07/09
Posted: 07/20/09
05:34 AM

I had the same problem with my 70 Chevelle. Most stock valve covers have a baffle inside to let the pressure out and keep the oil in. The 50psi oil pressure and high RPM's will have the oil flying around the top end and likely be blown out. I added 4" breather extensions bolterd to the valve covers and it helped but I eventually purchased valve covers that had an internal baffle already built in and added a PVC valve to also draw off some of the pressure. hope this helps.

Kentnova  

waynep712 waynep712
I have an SS396 tatoo | Posts: 358 | Joined: 12/07
Posted: 07/20/09
07:35 AM

every motor has blowby... where some gasses pass the piston rings..  this puts pressure in the crankcase and valve covers...

it has to get out... or it can build up a lot of pressure...  it has fuel vapors, oil vapors, some burned combustion gasses..

the fuel and oil vapors are combustible...    the PCV system pulls these excess gasses into the intake to be burned again...

increased fuel mileage is a result ... less oil leaks.. cleaner air...  are all results...

but... if you only put a PCV valve... and not a breather filter on the other side of the motor... at idle and light throttle  you can create 20 inches of vacuum in the pan and valve covers...  this vacuum in the pan can pull the pan upwards and block the oil pick up screen...  


under load... there is more blowby created than the pcv can extract...  so you will get crankcase pressure... expanding the pan and valve covers...


a proper PCV system has the pcv on one valve cover..  a filtered breather on the other..  both sides with baffles to prevent oil spray from exiting the motor through those ....

why a filter on the far side...     the pcv continuously pulls crankcase vapors from the motor...   most of the time.. air is pulled in via the filtered breather ...   without a filter... you are pulling in unfiltered air... including dirt and dust... right into your valve cover.. to get washed into the pan by the oil flowing past the valves...


there is a problem...   pcv valves have to be properly sized...  too much and you dilute the fuel mixture in the motor and cause excess flow from the crankcase.. this can result in burning oil at about 400 miles per quart...    too small a pcv flow... and you don't pull enough vapors out and get oily breathers...

a company called RIMAC used to sell a PCV flow tester.. you would put over the breather hole with the engine idleing...  i have only seen a few in my life and have never gotten one for my self...  

i have a friend with a honda drag racer... he hooked up a vacuum sump set up... it pulled the rear main seal into the motor... causing a rear main seal leak...   when he replaced it.. it pulled the cam seals in...  when he put in a proper size breather.. he was able to get 0 pressure at idle.. and some vacuum at race engine speeds to reduce the amount of air the pistons have to push around..   so proper selection after a full understanding of how it all works can increase your driving pleasure..   driving pleasure on this thread includes not having to wipe down oil spills from your clean motor...


questions.. do ask .. i stop by here almost every day...  

85_trans_am 85_trans_am
I have an SS396 tatoo | Posts: 252 | Joined: 05/09
Posted: 07/20/09
03:11 PM

I had that same problem. I had installed an evac kit and it didn't work. At high RPMs it would just blow the valve cover gaskets out. you need to look at getting a freash air PCV system in and make sure there are baffles in the valve covers.

the system consist of a pcv valve on one valve cover with a 3/8 hose going to the carb vacume port and on the other valve cover a filter. This should take care of you problem.  

68SSConv. 68SSConv.
I love my Chevy Chevette! | Posts: 14 | Joined: 08/07
Posted: 07/20/09
03:27 PM

Thanks Kentnova,  I did replace the stock height valve covers with some tall ones for that very reason. To raise the opening in hopes that it would stop the oil from being pushed out, but even with baffles, not internal baffles, just baffles at the openings, it is still filling up the oil filler breather and letting it run out. I do have a PVC valve in the other valve cover but it may not be the correct size. Thanks again.  

68SSConv. 68SSConv.
I love my Chevy Chevette! | Posts: 14 | Joined: 08/07
Posted: 07/20/09
03:46 PM

Thanks Waynep712,  I do have a PVC valve in one valve cover and a filtered breather on the other valve cover but it seems that instead of pulling air in thru the filtered breather it's blowing oil up into it and when I wrap a paper towel or cloth towel around the bottom of the filtered breather then it pushes it up the distributor and out the weep hole in the bottom. I did replace the stock height valve covers with a set of tall valve covers, that are baffled where the opening is for the PVC and flitered breather are. I may have the wrong size PVC. I'll check and see. I do appreciate your help with this I've never had a motor make so much pressure that it is trying to push it out where ever it can. Thanks again.  

68SSConv. 68SSConv.
I love my Chevy Chevette! | Posts: 14 | Joined: 08/07
Posted: 07/20/09
03:55 PM

Thanks 85 Trans Am,I haven't blown out my valve cover gaskets yet, and I do have a PVC valve with a vacume line going to the carb. and a filtered oil filler cap. I also installed tall valve covers with baffles in them where the PVC and filtered filler cap go in to try and raise it up enough to keep it from blowing oil into it but it hasn't helped. When I wrap a paper towel or cloth towel arond the bottom of the filtered filler cap the pressure forces the oil up the distributor and out the weep hole beneath it. I may have the wrong size PVC valve, I am going to check that and see if it will eliminate or at least cut down on the problem. TRhanks again for your help.  

85_trans_am 85_trans_am
I have an SS396 tatoo | Posts: 252 | Joined: 05/09
Posted: 07/20/09
07:13 PM

ok then the pcv valve is probly to small. I have a 383 and I installed a pcv valve from a pontiac 400 motor, I had to cut off the bottom nipple so it could fit. And being that you have a freash air breather you can get away with a higher flow pcv valve.
one more thing. Make sure you have the proper amount of vacume on the card side.

best of luck  

68SSConv. 68SSConv.
I love my Chevy Chevette! | Posts: 14 | Joined: 08/07
Posted: 07/21/09
04:42 AM

Thanks again, I'll try that and see if that works.  

chevelle83 chevelle83
I have an SS396 tatoo | Posts: 442 | Joined: 10/08
Posted: 07/25/09
06:41 PM

wow! this is more common than I thought. Me and my brother had this issue and the problem was the breather cap, it was new out of the box. The problem was the material inside was too restrictive but it took minimal effort to blow through it but it was still too much so we installed a tube straight from the valve cover to the air cleaner with no trouble since.  

68SSConv. 68SSConv.
I love my Chevy Chevette! | Posts: 14 | Joined: 08/07
Posted: 07/26/09
09:39 AM

I guess there is some comfort in that I am not the only one having that problem. I have repalced a couple of filler caps but after a while they fill up too. I have seen filler caps with a outlet to run a line to another line like the PVC line to the carb and thought about trying that, and now I may! Maybe along with a little larger PVC valve and this additional line I can solve this problem. Thanks alot guys for your help.