I'm finally getting around to ordering the pistons for the twin turbo 400 buildup. I had the Dart Little M hot honed to the minimum it would clean up. The machine shop (Billy The Kid, in Torrington, CT, builds many of the Busch North engines around here) wrote 4.1215" on the spec sheet. Tonight I verified the bores lengthwise, and across the deck at the top, middle, and bottom positions in the cylinder. Measurements were averaging around -5 tenths (i.e. 4.1210"), with a +- of about 6 tenths on some cylinders.

How much distortion would one expect from the torque plate, and having the block pressurized at 25 psi and at 220 degrees with hot coolant flowing through? They hone/measure under those conditions, while I'm measuring the naked block w/o a torque plate, and at room temperature. I'd like some reassurance before I have JE make $1200 custom pistons that aren't returnable.

 

I read an article on torque plates a long time ago that did an experiment. They bored and honed a SBC with torque plates, then took the plates off, sprayed some paint down one of the bores and let it dry. Then without the torque plates, ran a hone down the cylinder, and it was quickly seen where the hone took off the high spots, and the low spots still had the paint. Not sure what the measurement differences were, but I'm sure it is in fact a measurable difference FWIW.

Mike

 

Z28,

Not many machine shops around the country can hot-hone a block, and the ones that do usually know what they are doing. It would amaze you how much a block can move around when heated from room temperature to 220 degrees. I had a block that would fould a plug on #6 hole after about 3-4 1/4 mile passes. Took the engine out, miked the block and everything looked fine. Heated the block to 220, and #6 was egg-shaped. I honed it at 220, put it back together, and it never used any oil, even though at room temperature the bore seemed egg-shaped.

I guess my point is, trust your machine shop. It sounds like they know their ****. If he says 4.1215, then it's 4.1215, and that's what you need to tell JE. I find it odd, however, that you bored and honed your block without pistons, but I guess if JE is going to make custom pistons, they can make them to the OD you need.

Good luck.

Shane

www.freewebs.com/81zmouse

 

Thanks for the responses, guys. I wanted to have the bore at the smallest diameter possible, to leave room for future bore/hones when the inevitable happens, so I had the machine shop hone it till it was fully cleaned up. The JE techs wanted to make the pistons to the bore as well, so I went with their experience. Time to fire up that platinum card. (I really should get an air miles credit card...)

Andris

 

Interesting discussion. I really like this section of the board. Thanks for educating me

Rich Krause