That was fun! I love learning new stuff.

[keithb7]

I decided to invest in a cylinder bore gauge. I have 4 Mopar flathead engines to deal with at some point. It makes sense to me, to know the wear condition of the blocks. Or at least have fun learning how to blue-print a block. 

 

For home hacks, do we need a proper bore gauge? That’s certainly questionable.  A Starret or Mitutoyo brand would have been nice. A new Fowler (currently made in China) will suit my needs fine.  Measures down to .0005”
 

My new tool arrived today. A spare 1949 Canadian 218 block lays-in-waiting out behind the shed. This evening I spent a little time learning how to use the tool, also brushing up on my math. 
 

Stock bore Canadian 218 is 3.375”.  A snap T-gauge test told me this block has been bored .040” over.  Setting the 3-4” caliper at 3.415”, then zero-ing the bore gauge in the caliper gets me bang-on. (Well close enough, for an old flathead)
 

By now its getting dark outside. I headed out behind the shed with a flashlight. Hmm. Bore seems to be about 0.0015” larger than when it was last rebuilt.  That seems reasonable. On the thrust side the bore is about .0004” larger.  The cylinder being 0.0025” out of round. Spec in the 1949 Chrysler manual reads “max allowable out of round , 0.002”. Ok, so early indications are we have a tired block that likely needs full machining services. 
 

I’ll practice more measuring in the daylight. I’ll measure each cylinder for taper too. Exciting stuff!

 

Edited September 18, 2020 by keithb7

[kencombs]

Very handy tool!  Makes short work of measuring bores, compared to snap gauge and OD mics, over and over and over, to get top, mid and bottom.  Then in both fore/aft and side/side.

 

If it were mine, and only  had a .0005 deviation from spec, it would get a sizing hone job and rings.  Would last as long as I need it to and save the cost of machining and pistons.

 

edit: sizing hone:  hard stones used for final hone after boring vs a 'normal' rering hone.  Helps to minimize wear 'ripples' in used bores.  My theory at least.

Edited September 18, 2020 by kencombs