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Oil breather cap blowby??
#1
Hey guys, I was wondering if anyone else has had any trouble with a small amount of oil coming out of the filler/breather cap on the valve pan cover?? It doesnt do this very much, but gets worse when i really run the motor. Only a drop or two on valve pan cover once in a while but enough to dirty it up. I also noticed that my dipstick pops up when i run the hell outta the motor. I am running a pcv valve hooked to vaccum on the other valve pan cover. Could it be going bad causing this?? Its not a really big deal but it get my mototr dirty. I was gonna wrap a rag around the breather cap and zip tie it. The motor is fresh from a complete rebuild about 2 years ago with probably less than 5000 miles on it. Let me know what you guys think.
Thanks Kevin
[Image: x3fm8w.png]

Kevin

1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]




                                                                                             
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#2
I have the same issue with mine, it's blowby. It is likely the rings, or some of them, did not seat properly. As far as a fix goes I think putting a rag on the breather may help with the leaking oil. A cylinder leak down test will show which cylinder and how much. Below 15% is a pretty tight engine, up to 20% is acceptable in a street engine.

Jeff T.

Low buck, touring style, '73 Convertible "rolling restoration", 351c, 2v heads with a shave and a haircut, Performer intake, Holley 650(ish), roller rockers, screw in studs, guideplates, stainless valves, Duraspark / Motorsports MSD, T-5 conversion. 1-1/8" front, 3/4" rear swaybars KYB shocks and some home brewed subframe connectors. Future plans; JGC steering box, Cobra brakes and... paint, interior, etc.

When I die I want to die like grandpa, peacefully in my sleep... not screaming, like his passenger.

[Image: 1_12_09_14_10_15_11.png]
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#3
Excessive pressure in the crankcase, caused by too much blow-by, will force the dipstick up and force oil out of the filler cap. If you're not burning a lot of oil it may not be a problem with your rings, but as you said, a bad pvc valve that is either plugged up or has a bad spring in it. I'd start with replacing the pvc valve, and make sure the tube to the intake or base of carburetor is not kinked or plugged. If that doesn't stop it the next step would be a compression check to see if you have some bad rings. Worn guides on the exhaust valves can also create too much pressure in the crankcase.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#4
I really wouldnt think it would be the rings or valve guides in a brand new motor... at least i pray it isnt. This thing runs like hell. Hard to keep your foot out of the loud pedal!! I will try the pcv valve and go from there. Hopefully thats all it is. Like i said its not a really bad amount of oil. And the motor doesnt use any noticeable amount between changes. Just wondering if it was a common thing on these clevelands. Thankd for the input guys!

Kevin

1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]




                                                                                             
  Reply
#5
Does the breather cap have a provision to run a hose to the air cleaner? If not I would try one that does.

73 conv. 460, D0VE large valve heads, Performer RPM manifold, Voodoo 227/233 cam, Holley 950 HP carb, C6 trans, 3.25 trak-loc.
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#6
TommyK;64464 Wrote:Does the breather cap have a provision to run a hose to the air cleaner? If not I would try one that does.

Turtle- All good advice from others do those items first but to me it sounds like possibly that the rings didnt seat right especially if you drive with a heavy foot from the beginning. Improper break in, did that myself when I was a bit younger. A leak down test will be the answer! Good Luck
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