Big Block Chrysler CNC

[Groucho57]

I've been a lurker for a while, this is my first post... Anyway, I'm a student at Northwest Technical College in Bemidji MN. I'm in the high performance engine machinist program and I'm working on my advanced engine project. It's going to be a 4.25" stroke in a 440 block. I've got it on the CNC right now and there's just enough core shift that it won't clean up at .030 over if I bore to blueprint locations but it will if I bore to probe locations. Otherwise I could go to .055 over at blueprint locations and be fine. I'm going to use a 440 Source rotating assembly because I'm in college and I need to keep the cost down plus I've heard good things about them and they only offer their 17cc dish piston in .030 or .055 over so those are my choices considering the 10.5:1 compression ratio I'm going for. I'm going to post pictures of the probe readouts from the RMC V30 we have here. One is probed .35" in the bore above the ring wear and the other is 2.5" in the bore and the wear. Is it worth giving up future rebuilds to bore to blueprint? Any input would be appreciated.
- Dan

[Walter R. Malik]

I've been a lurker for a while, this is my first post... Anyway, I'm a student at Northwest Technical College in Bemidji MN. I'm in the high performance engine machinist program and I'm working on my advanced engine project. It's going to be a 4.25" stroke in a 440 block. I've got it on the CNC right now and there's just enough core shift that it won't clean up at .030 over if I bore to blueprint locations but it will if I bore to probe locations. Otherwise I could go to .055 over at blueprint locations and be fine. I'm going to use a 440 Source rotating assembly because I'm in college and I need to keep the cost down plus I've heard good things about them and they only offer their 17cc dish piston in .030 or .055 over so those are my choices considering the 10.5:1 compression ratio I'm going for. I'm going to post pictures of the probe readouts from the RMC V30 we have here. One is probed .35" in the bore above the ring wear and the other is 2.5" in the bore and the wear. Is it worth giving up future rebuilds to bore to blueprint? Any input would be appreciated.
- Dan

Personally ... if I was only wanting to go .030" I would offset the bores slightly from print to be able to get there.

[Groucho57]

Thanks. I think that's what I'll end up doing.

- Dan

[Charliesauto]

You have some strange stuff going on. Your rear deck heights don't make sense. Deck 1 looks pretty good front and middle, then the rear is .026" out? Deck 2 is out .010" front and middle but close on the rear? No way the decks are twisted that bad.
A couple of things I do on blocks like this is cheat the A-axis 0 to help all the Y- axis numbers. Also look like this is an older machine(centurion 6 control) so it probably has the Haas rotary which is going to have some backlash, newer ones have a Nikken rotary, supposed to be 0 backlash. This may be causing some of your Y axis location issue.
Also you can manually edit the probed numbers to get a little closer to blueprint locations, but still use the probed locations boring program. Basically split the difference between blueprint and probed.

Good Luck

[Groucho57]

About the decks, for some reason the program has the probe hitting just barely on the edges of a couple coolant passages, just enough to throw off some of the readings. It is a haas and I have noticed the backlash. I'll have to look into editing the probed locations, that's a really good idea.

[Charliesauto]

About the decks, for some reason the program has the probe hitting just barely on the edges of a couple coolant passages, just enough to throw off some of the readings. It is a haas and I have noticed the backlash. I'll have to look into editing the probed locations, that's a really good idea.

You may want to probe it again, maybe .500" down or whatever it takes to get just below the ridge if one exist. Your 2.500" and .350" probes have almost identical bore diameters and X locations which means you have no wear at 2.500 down(normal). If you have a ridge worn in the cylinders it will usually be more pronounced at the front of the most forward cylinder of each bank(1 & 5). Your Y numbers are different at .350" and 2.500" because the cylinders are not perfectly vertical.

As you can see, machining an existing OEM block usually requires some compromising.

[Charliesauto]

About the decks, for some reason the program has the probe hitting just barely on the edges of a couple coolant passages, just enough to throw off some of the readings. It is a haas and I have noticed the backlash. I'll have to look into editing the probed locations, that's a really good idea.

You may want to probe it again, maybe .500" down or whatever it takes to get just below the ridge if one exist. Your 2.500" and .350" probes have almost identical bore diameters and X locations which means you have no wear at 2.500 down(normal). If you have a ridge worn in the cylinders it will usually be more pronounced at the front of the most forward cylinder of each bank(1 & 5). Your Y numbers are different at .350" and 2.500" because the cylinders are not perfectly vertical.

As you can see, machining an existing OEM block usually requires some compromising.

Sorry, should be cylinders 1 & 2 on the Mopar ( we do a lot of Fords).