Gents, Your advice please. I've just got a set of .030" over 425 Egge pistons on the way for the 425 dual quad rebuild. The machine shop needs to know exactly what the correct piston:bore clearance needs to be so they can machine the bores accurately - in decimals of an inch please. Can anyone please tell me? Also - what is the desired ring gap please? Many thanks all & have a good weekend best regards Nick
Nick, the piston-to-wall clearance will vary depending on the piston material.....follow the piston manufactures recommendations.... For the stock, cast pistons, Buick specifies: 0.0004" - 0.0010" at the top of the skirt 0.0019" - 0.0035" at the bottom of the skirt 0.034" -0.042" at the ring land Ring gap: #1 and #2 compression: 0.015"-0.025" #3 oil ring: 0.015"-0.055" These specs are from a '66 Buick chassis service manual.....try to get one for your '65!
your machinist should always wait to have the pistons in his posession before trying to hone for final clearance. some times a piston is a bit off and there is no way to know without measuring each one. better to know for sure than to guess and possible get it wrong.
Guys, Many thanks for the info. I haven't got a 425 shop manual [need to get one I know - anyone have a spare?] but I do have a '65 GS Service Manual - mainly a supplement for the 401 engine [not the 425 note!]. It doesn't state the piston to bore clearances but does say the side clearance on the compression rings should be .003" to .005" and side clearance of the oil ring should be .0035" to .0095". Does this match with your experience? It also confirms the end gap of the piston rings as .015". Many thanks once again Nick
