340 piston question
#516121
11/04/09 07:22 PM
11/04/09 07:22 PM
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Joined: Aug 2005
Posts: 403 30 miles west of EuroDisney
fbernard
OP
mopar
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OP
mopar
Joined: Aug 2005
Posts: 403
30 miles west of EuroDisney
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Hi all. I helped a friend take apart his 340 last sunday, adn I was a bit surprised at the piston shape and size (see pic). That was my first small-block experience by the way, I only have big-blocks myself. Pistons are free-floating (as stock) .40 over (now could that be stock?). Four identical valve reliefs with a small indentation towards the front. only external marking is the .40 stamped on the top. Underside, the area between the pin bosses is checkered, and I can see what looks like a 'D' (Diamond?). On the inside of the piston skirt is what could be a casting date : 80 12 75. the piston is also really deep in the hole (.100), although I've read it should not be the case with small-blocks (pistons popping out and requiring open-chamber heads). The piston skirts are only attached to the piston top by the pin boss area, and they're completely cut away from the ring land almost all around the piston. I've sen one picture of such a piston in 'How to Rebuild SB Mopar Engines', but no description about this.
This is a 1970 block, with 1972 heads, so at one time this engine was rebuilt, I just don't know to what extent. I hope the block will clear out OK at .40 over, since I wouldn't like having to bore it further.
What I'd like to do is have an idea of the approximate date at which this engine was rebuilt. Did it happen eons ago (as I'm tempted to think with the '75' part of what seems to be the casting date, although the engine itself was pretty clean, with honing marks still visible on the cylinder bores).
Any thoughts?
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Re: 340 piston question
[Re: RapidRobert]
#516124
11/04/09 07:47 PM
11/04/09 07:47 PM
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Joined: Mar 2003
Posts: 18,688 Fresno, CA
Jim_Lusk
I Live Here
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I Live Here
Joined: Mar 2003
Posts: 18,688
Fresno, CA
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Quote:
Quote:
Any thoughts?
that # would not be a mfr'd date and the last 340 yr was the early 70's ('73 iirc).
No, but they were still making pistons for them in '75 (not saying that's a date, though). And yes, 73 was the last year for a production car to leave the plant with a 340, but I believe blocks were still cast after that time.
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Re: 340 piston question
[Re: fbernard]
#516131
11/06/09 10:36 AM
11/06/09 10:36 AM
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Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
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yes 20 under & 2130CP is a modern era sealed power/federal mogul part #. I just stripped a 1974 400 BB & the rod bearings said 1973. So we know yours has been rebuilt at some point. Good luck.
live every 24 hour block of time like it's your last day on earth
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