Friday, April 3, 2015

235 Rocker Oiling Evolution


1953-57 full pressure 235’s (full pressure started in 1953 in the Powerglide cars) had a 1/16” oil restrictor fitting which screwed into the block at the beginning of the rocker oil supply tube under the side cover.


They also used a rocker connector that looped over the top and then dumped excess oil back on the head. The shafts were only supplied with gravity oil pressure with this design.(picture of early and late design)


 Starting in 1958 the tube under the side cover was discontinued and the engines now had a 1/16" orifice in a cast in the block galley. This received oil directly from the center of the lifter oil galley.
 Starting in 1959 the orifice size was increased to 11/32", see picture.(this was scanned from a 1960 manual, but stayed the same through 1962).

This larger orifice offered almost no oil flow restriction.
At the same time the overflow tube on the rocker connector was pinched off. This pressurized the shafts.
Sample of the three styles used
 At the same time the groove inside each rocker was offset 1/4" so it did not line up with the supply hole at each rocker. This prevented oil from squirting out of the vent hole on each rocker.

If you use 1958 or earlier rockers on a 1959-62 engine you will have the best luck preventing oil flooding to the top end if you restrict the oil supply to the rockers. Chev did this on replacement short blocks by selling you a plug to put in the block to block the original oil path and a special drilled head bolt drilled with a 1/16" hole for the oil to pass through.
 I have experimented with several designs, if a plug and drilled head bolt was not available. This orifice I designed drops in the head right below the connector supply tube and seems to work well.



 The orifice I make is 5/16" OD, .400" long, with a 1/16" hole drilled through the center. It is installed in the head under where the rocker supply tube fits in the head. I then use a rocker connector with the overflow tube.

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