45 Piston Rings Clearance

[Paps]

Cotten...You checking all TIRS when you set one up ? All ring grooves running true, all diameters dialed in, wrist pin on center to diameter, piston face running out ? We are talking about conventional machine tooling, not 95% contact precision collect production machine tooling where an operator needs only to load and unload parts.

Three jaw chucks are for roughing or don't mean much parts. Great for polishing at best. Never saw a true running three jaw. Close to true, give or take a thousandths, but never true. What do you do when a part moves a tiny bit on ya ? Change it to a four jaw, that's what. Might as well have setup the four jaw in the first place. Four jaw is the only way to go when finishing critical works. Holding power is better and more reliable than any three jaw. Never trust a three jaw for precision work. You can't dial it back in like you can a four jaw. Three jaws have a tendency to spin loose around a part too. Try chasing threads with a three jaw. If the chuck spins loose from the part or the part moves, try picking the thread back up on it. That is a nightmare enough with a four jaw, but at least it can be done. Paps

[Paps]

Scaring is a lack of softjaw usage, over tightening, under tightening, or a combination of some or all. Paps

[T. Cotten]

For Gawd's sake,...No jaws!!!

Just draw it up onto a faceplate.
(Using a drawbar through the headstock with an eye to pull on the wristpin.)

The bottom of the piston is cut square to the ring lands. A dial indicator and a small wooden mallet will true it quite close to its original axis with little patience at all, and the drawbar will secure it most firmly.


...Cotten

[Kojack]

Hey guys, let’s not come to blows about this. I’m sure there are many methods. Cotton’s method is common. I’ve never seen it done on a face plate though. If the bottom of the skirt is square, and it should be, that should work fine. I’ve seen it done with a flat plate that holds the piston the same way and is then held in a chuck. The plate and piston unit can then be easily adjusted to run very true. If I knew I was going to be doing pistons on a regular basis I’d definitely make one up. Cotton, The shop I worked in had over a dozen engine lathes from 6” to 96” (plus CNCs) but not one face plate. Some of the chucks had t-slots that we’d use for some setups, but that was mainly on the big verticals. Maybe if I’d had a chance to live with one I’d like it but I think I can do anything with a chuck that can be done with a faceplate. When I started my apprecticeship the shop used to re-cut the ring grooves oversize for Alco diesel pistons. We used a four jaw chuck. We’d chuck on the head of the piston with the top ring groove just past the chuck jaws. The head is thick enough that it won’t deform. We put small pieces of copper between the jaws and the pistons to prevent dents. We had a counterbored plate that fit on the skirt end to allow us to run a live center for more support plus it aided in holding the piston in place against the chuck during setup. If you’re thinking you needed three hands to do all this you’re about right, but we managed and with time you got pretty good at it. A 45.piston head doesn’t have as much room to chuck on as an Alco but there’s enough and it can be done the same way. The piston is light and you wouldn’t need to support the skirt end. You’re just skinning the grooves, not roughing. I don’t think chucking on the skirt is a good idea. It’s too easily deformed. Besides, I’m not sure but aren’t 45 piston skirts slotted? Paps, I agree with everything you say about three jaw chucks. Fours are better 95% of the time. I don’t work in a shop anymore. I have a friend with a 9” South Bend and all he has is a three jaw chuck. If that’s all you have, you use it. The depth of the ring groove isn’t critical. If I can get the side of the groove running true and the bottom is running out a thousandth or so, I’ll cut it. By the way, when I worked in our die shop I got to spend a lot of time with a Kellenberger grinder. It only had a three jaw chuck. It could be fine tuned with four adjustment screws. Very slick. Much easier to control jaw pressure and still fine set the job.

[charlie frey]

We've come a long way from burnin' our fingerprints off from rubbing rings on sandpaper, eh?

[Kojack]

If the rings are held properly the fingerprints will stay intact.

[T. Cotten]

I'm bein friendly, honest....

Sanding rings has the disadvantage of removing the Parkerizing. Take that away, and you remove not only corrosion protection, but start-up lube as well.

....Cotten

[Paps]

Cotten and I never throw right crosses at each other. Maybe a left jab here and there but never a right cross.

You just have to replace the parkerizing Cotten.

Yeah, I have seen those adjustable three jaws. Never used one though.

I mentioned TIRS because having all those dialed in, represents the original machining proceedure. When you have it all dialed in, you know exactly where the lands stand in relationship to the rest of the machine work. Hopefully they all run true enough to each other. Can't tell you how many times I have found otherwise on parts throughout my life span. This provides you with stock options such as what land to skin cut. how much to skin each land, and where the cut will be at the bottom of each land.

Kojack.... ever use a cathead ? We used to make these up for the tailstock end when re machining old roll shafts who's centers were either never put in or were beyond use from damage. They are hollowed out round stock [like unto a cap] with a center in the un opened end. The center was used with a live center in the tailstock. The other end of the cathead [cap] wall was drilled and tapped in eight equally spaced places around the circumference. The drilled and tapped holes held adjustment bolts for indicating the tailstock end of the roll shaft in. Used mainly for bearing journal work and many times body work as well. The combination of the cathead and a four jaw allowed you to dial a roll shaft in any which way you needed or wanted to. Paps

[Kojack]

Used a lot of catheads and always wondered how they got the name. Someone must have had a really ugly cat. I also made up a few "spiders" that would adjust to fit inside a thin walled job and allow you to chuck it with squashing it out of round. One of my regular assignments was making ladle car axles, kind of like a 20' long railroad car axle. I'd use a cathead to set the stock (which was always bowed) and cut spots for the two steady rests I had, then drill centers. Then I'd start roughing, turn the job around, rough some more, then have to re-cut the spots. The stock would bow in a different direction as it was cut and the stresses changed. Sometimes it would cause the bed of the lathe to start flexing as it changed. Usually took me 5-6 shifts to do one in the CNC lathe I ran. Of course none of this has anything to do with 45 pistons. Maybe we ought to start a "Dumb Machinists' Tips" section in the forum.

[Paps]

Dumb machinists topic.........great idea Kojack ! Should be fun, informative and interesting, to say the least. What do you think Cotten ? We could all learn a lot from each other experiences, such as, tricks of the trade, short cuts, eventful moments doing such work, even shoot the bull stuff. Share photos too ! Please do ! Paps

Used spiders too. Man Bro !! You bring back memories for me ! Your last reply reminded me of numerous such times. How does that song go ??? "THOSE WERE THE DAYS "

[T. Cotten]

I'm not a machinist, I'm a metal butcher.

So 'dumb machinist's tips' is right up my dumpster alley.

...Cotten

[exeric]

I worked for a race engine builder many years ago and Cotten's method of holding pistons is very similar to what we did. However, instead of a face plate, I used a lump of Aluminum with a hole through the center for the draw bar. I chucked on the lump and would take a light face cut with each new job so I knew the face was true. Even though I learned a lot of useful car stuff at that place, it cured me of ever wanting a hot rod or doing anything more than changing spark plugs or oil on a car. It's funny how car people and motorcycle people really don't mix. A philosophical loggerhead.

[Paps]

Great tool Eric ! Along with lathe chucking and face plate usage. we now have three methods of doing the job of ring groove cutting.

Metal Butcher...... Boy do I have stories on that !! Paps