Motor work on a 1916 H-D

[exeric]

The depth of the finished bore about 6.81" with about 1/8" to 3/16" of relief before the domed head. From the edge of the spigot to the top of the dome head is about 7.4".

aug29cyl.jpg

[BigLakeBob]

Thanks Eric! I know how you like to do things yourself and I thought of a different approach that you could do, but that is deeper then the process I was going to suggest that you could do with your equipment.

[exeric]

A good friend said, 'don't ruin a good cylinder, by boring out a non-replaceable cylinder to fit a piston'. Okay, that's the ethos I have been working towards as an alternative to the proper (expensive) route of getting the cylinders bored and honed for new pistons. I am going the 'depression era' route of attempting to make what I have work. I have a number of cast iron J era pistons and a pile of fat J rings so I have to think that some combination of pistons and rings will give this motor enough compression to fulfill the suck, spark, blow trilogy that makes an engine run. Attached are pictures of the fixture I am using to turn a piston down to a usable diameter.

Years ago, I had a "lay-off" job that paid the bills before I got called back to my good job. The lay-off job was at a race shop that built high quality, big horsepower racing engines from NASCAR, to Saturday night mayhem racers. The owner was Bo Law who was a NHRA champion from the '60s and whose business is still going. Brilliant motor builder, but not fun to work for. He had this piston fixture to do motor-head stuff to pistons that I didn't understand, but I admired how well it worked and how well it located and centered a piston. So, that is what I am doing to make a piston fit a cylinder bore. . . Low tech in my universe but I just want it to run.

sept2pistona2.jpg sept2pistonb2.jpg

[T. Cotten]

Looks a lot like my draw bar, Eric.

If you figure out how to cam-grind pistons, I'll send you an oversized Chief blank to practice upon.

....Cotten

[chuckthebeatertruck]

Generally, cast iron pistons are not "cam ground" in the same fashion as alloy pistons.

Most cast iron pistons have at most .002 ovality and most cast iron pistons are fit at .001 on the skirt bottom and .0015 on the top of the skirt. This is not per inch - -this is for any bore 1 to 4 inches in diameter.

So, if you have a motor where you have concern the pin may cause a differential expansion you can easily reduce and blend that side of the piston with a fine cut file. You simply "relieve" and blend the area about 3/4 of an inch on either side of the pin and about half the pin diameter above and below. Viola -- "cam grinding" on cast iron.

For your turning, Eric, I almost always use tail stock pressure on piston crowns to ensure no slip. There's no need for a draw bar and the resultant internal pressure from "pulling" the casting. If you have a ten thou test indicator - you will see the piston "spring" when you release the draw bar pressure.

Cast iron pistons are not like alloys -- and they last forever.