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blow-bye and breathers

PostPosted: September 30th, 2014, 1:14 pm
by grumpyvette
36firerat wrote: I have stock 305 that builds crankcase pressure. I started with a breather on each valve cover, had issues with pressure, switched to a pcv still have issues. The issue is inconsistent though, one day a short drive will push oil, the next time it might be all day before i have an issue. I might go 3-4 days and no issue.

pressure in the crank case, you see as blow-bye out the breathers on valve covers is the result of cylinder combustion pressure, or to a far lower degree compression, getting past the ring to bore wall seal,the obvious best answer to reducing it is better ring seal.
now doing a ring and bearing refresh/and rebuild is just a weekend deal if your set up with the tools and have a place to work, but of course you may need a re-bore and new pistons, if the bores worn. and if thats true it will take longer and get more expensive due to the labor and machine shop costs and parts required, intermittent blow by is frequently the result of minimal ring damage due to detonation

if the edges of the piston lands look rounded off slightly and FROSTED that's the results of detonation, the rough stuff it micro sized bits of molten piston aluminum , that got transferred to the combustion chamber and exhaust port surfaces. do a leak down test,and try it at both TDC and BDC on each cylinder, it will help point to the cause
you can cure the problem at its source









or you can deal with the results




Re: blow-bye, and breathers

PostPosted: February 16th, 2015, 9:06 am
by grumpyvette
LUVmachine wrote:So finally get my first test drive in my LUV truck yesterday. After the drive I opened the hood and noticed the valve cover breathers dripping a small amount of oil and it happens to end up on the exhaust. Is there something that can be done to these old offenhauser type breathers to keep the oil in and let them keep breathing? I plan on eventually switching these valve covers out and using more of a updated style breather but for now this is what I have to work with. Overall for the first time out I'm happy with it. Not to mention it shreds the tires with zero effort.

just a point of interest, breathers are designed to be located on the UPPER edge of the valve cover , NEVER the lower edge as shown ABOVE here
and and no your not alone in having the breather located in the wrong location,or alone having purchased valve covers with breathers having previously been mounted that way then sold, off as a result! all fluids tend to drain to the lower areas and oil in an engine tends to flow back and accumulate in the lower areas of the heads and valve covers, at higher rpms there can be a quart or more in the valve covers and lifter gallery areas
I see it frequently....with similar results as a result. I see it frequently....with similar results as a result.


Re: blow-bye and breathers

PostPosted: February 16th, 2015, 11:28 am
by philly
those breather tubes with the crossover lok really trick, but wont those get in the way of the filter assembly / water neck/ distributor, etc? i cant picture where on what motor you can mount those excapt on the back of a SBF with a tall intake manifold