Would like some ideas on installing a PVC on my 261chevy engine. it has a crankcase blow by tube. No ventilation in the valve cover. It's a aftermarket finned aluminum cover. It's a new (just rebuilt) engine and was leaking oil from the back corner. I removed the cover, found it was warped. So I had it machined back flat.So I'd like to put a PVC valve either in the cover or insert a freeze plug, drilled out for the PVC in place of the blow-by tube?
Ignore the advice about using a freeze plug in the road draft tube hole unless you own a lot of stock in an oil company. The factory original PCV valve was in a standpipe at approximately the height of the lip of the valve cover to prevent splashed oil from being drawn into the valve and burned by the engine. Use an oil filler cap with a vent to admit fresh air into the engine for ventilation if you choose not to use the factory method of plumbing air from the "clean" side of the air filter into the rear of the valve cover near the back of the driver's side. That system was used on delivery trucks, step vans like bread trucks, and others which seldom got up to 30 MPH where the road draft starts to work properly. Jerry
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The factory 261 can be found on eBay but it takes patience. Original used PVCV valves need to be checked and cleaned. Apparently there is a small spring inside that may break or seize up.
There are only 3 data points needed to adjust the PCV design to a specific engine (in addition to the fittings). 1. ID of the high vacuum orifice 2. ID of the low vacuum orifice 3. spring tension which determines where 1 or 2 is correct. The PCV from a similar-sized L6 in mild tune is a good substitute.
If you work the truck and use a vented oil-filler cap, bear in mind that at 0 vacuum there will be fumes coming out of the filler cap. On my truck I can smell it and that reminds me to ease up a bit and hold about 2" vacuum. That eliminates the problem and probably forestalls others arising from running WOT for extended time. Sometimes I drop a gear netting about +400RPM and a bit better vacuum; maybe even better fuel consumption.
1951 3800 1-ton "Earning its keep from the get-go" In the DITY Gallery 1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.
