porous casting repair

[Rough Edge racing]

I disagree, this passage feeds the front cam bearing and the rockers. I would try to be as precise as possible. 8 mm is .3150" 5/16 is .3125 that would be a decent interference fit. I would prefer doing it in a mill or a good drill press at the very least.

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  From my vast experience with using hand held drills, it will be difficult to get a round straight hole that will allow the tube to be pressed in properly..And you only have one shot at doing it correctly...I don't have good luck with odd jobs at machines shops. Their time is expensive and and they don't do what I want them to do...So....I would do it myself with a hand held drill and get a light press fit and use an anaerobic sealer or epoxy on the tube...A couple of drills and a short length of gas line tubing is pocket change...

[Chuck in Indiana]

I disagree, this passage feeds the front cam bearing and the rockers. I would try to be as precise as possible. 8 mm is .3150" 5/16 is .3125 that would be a decent interference fit. I would prefer doing it in a mill or a good drill press at the very least.

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Agreed on all points. Drill it 1/64" undersize and ream 5/16." You'll only get one shot at it, so make sure the tubing is straight, and maybe polish a thousanth or so off of it. Freeze the tube, warm the case, and tap it in.

[John A]

That should be a fine repair and if it goes sideways get another block. How are the cam bearings? If it's had chrome cylinders that shed chrome, it gets imbedded in the cam journals that can't be gotten out. It's hard and chews on the cam journals.You need a magnifier and strong light. I use a sharp three corner scraper to get out the big chunks and let the rest be. I'd take that into consideration for a different block.