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Engine breathing/leaks

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radibob

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I have a 67 Sprite with a 1275 in it. The 1275 has a breather "port" on the front of the engine on the timing chain cover. It also has a vented cap on the rocker arm cover and a tube for a vent on the rocker arm cover. I am thinking too many vents and one reason why the engine leaks. Should I get a non vented cap. and run the vacuum tube from the front carb to either the vent on the rocker cover or the one on the timing chain cover and block the other vent.Which would be the better vent to use as the suction point?

Thanks for any help. It would be nice to at least slow down the engine oil leaks.
 
Gerard

Gerard

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Depends on the carbs you have. Illustrations below should guide you or you can post pictures.

Best results will be with a PCV, but depending on your engine condition, vacuum may or may not help. Success depends largely on the tolerance at the rear main to be wishing limits, and those limits are pretty small. The other option of that fails is rebuilding the engine to restore tolerances or adding an actual rear main seal.

https://gerardsgarage.com/Garage/Tech/SealKit/SealKit.htm

Crankcase Emission Control.pngScreen Shot 2016-Emission valve.png
 
Pythias

Pythias

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Let it breath. .. I've added an extra breather into the rocker cover and it's been recommended that I add another. Racers have told me that some of the reason for excessive leaking (more than the normal) is too much crankcase pressure -and whatever can be done to relieve it will lower the leakage.
 
Boink

Boink

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I'm back to letting it breath (with my 1275)... with the front oil separator having a hose up to a simple breather. My rocker cover has no breather though.
I did use the PCV that Bill (above) gave me and tried it per Gerard's second drawing; but what I found was that the suction from the intake was a tad bit too strong and I'd gulp some oil, and would produce brief smoke. One time it gulped so much I had thick smoke for 5 minutes... so I'm back to the sump simply breathing.

Bill, if you want that PCV back, it's yours. :eek:
 
Gerard

Gerard

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That can be regulated by reducing the size of the orifice. Technically, it should be a 9/64" aperture. Were you using a vented or non-vented cap?

Boink said:
I'm back to letting it breath (with my 1275)... with the front oil separator having a hose up to a simple breather. My rocker cover has no breather though.
I did use the PCV that Bill (above) gave me and tried it per Gerard's second drawing; but what I found was that the suction from the intake was a tad bit too strong and I'd gulp some oil, and would produce brief smoke. One time it gulped so much I had thick smoke for 5 minutes... so I'm back to the sump simply breathing.

Bill, if you want that PCV back, it's yours. :eek:
Click to expand...
 
N

nomad

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Gerard said:
That can be regulated by reducing the size of the orifice. Technically, it should be a 9/64" aperture. Were you using a vented or non-vented cap?
Click to expand...

Also by how much air you let into the engine as well. IE through the valve cover vent. With a PCV system there is normally a suction on the crankcase until it is overwhelmed by blow by under hard acceleration or load and then the crankcase vent's through the valve cover. Least that's my understanding of it.:smile:

Kurt.
 
Boink

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Yoda
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Still meaning to try that. I think the orifice was a bit too large.
Can't even remember if the cap is vented!

I guess I got lazy and just decided to vent.
 
1974MGMidget

1974MGMidget

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My anecdotal experience is that I don't think you can have too much venting. My 1275 has "active" neg. pressure as in Gerard's first picture, along with vented cap and small breather in the valve cover. (Its an aftermarket unit with no vent tube attached). I tried just putting a breather on the oil separator - no connection to carb or manifold - and it leaked a lot more. With the active breathing it leaks very little. (Also, the rest of the emission control system has been removed.)
 
Boink

Boink

Yoda
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I have a line that runs from the oil separator to a breather that is up at the top of the engine. Any oil that spurts up that way seems to go right down (and nothing has emerged at the aftermarket filter). Seems to work well (in the "let it breath" camp).
 
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