Ideas for sanding (cutting) the base, no lathe.

[ANewSawyer]

So the idea of sanding the base of a flat bottom cylinder has been kicked around and done quite well: http://opeforum.com/threads/machining-base-without-a-lathe.3989/ So why couldn't it been done with some patience, a piece of glass, DS tape and wet/dry sandpaper? I don't see why the glass wouldn't be flat enough. But that still means you can't easily do a flanged cylinder. Then I remembered that I have seen diamond hole saws. Hmmm. Now we are getting somewhere. Just need a really good straight edge. Anybody, thinking along the same lines?

 

[dbittle]

I have recently done this, for a 346 cylinder with the protruding flange. I took four pieces of steel, 3/4" thick and 6" square, that I borrowed from work. I put them on the concrete floor in the garage and arranged them in a pinwheel pattern with a gap in the middle big enough to fit the cylinder flange through. I had bought some spray adhesive and 60 grit coated sandpaper and crocus cloth. I had good results from the sandpaper and fairly poor results from the crocus cloth. I just sat there and twisted the cylinder around back and forth and slowly took off metal. I took off about .020" off and called it good. I started with the crocus cloth and had to change it half a dozen times because it wore out really fast. I switched to the coated sandpaper and only had to change it once or twice. It probably did most of the sanding also. The same sandpaper routine with the spray adhesive on top of an old piston worked great on the squish band. I worked the squish band until a .020" circular piece of cardboard on top of the new piston would cycle through without interference.

 

[drf256]

I'm all for DIY, but I'd just send it to someone here with a lathe and get it cut.

Your talking less than it will cost you in supplies and it will be done right.

I know you asked how to do without a lathe. Yeah, I'm that Dick that replies it's not worth it.

 

[angelo c]

 

[Chainsaw Jim]

It takes some pretty good skill to do it by hand. One piece of advise I can offer is to bevel the inside bottom edge of plating away before flat sanding the base or it will not be flat and you'll snap the corners off the base when torquing it down. The flat surface will take the aluminum faster than the chrome ringed center.

 

[ANewSawyer]

It takes some pretty good skill to do it by hand. One piece of advise I can offer is to bevel the inside bottom edge of plating away before flat sanding the base or it will not be flat and you'll snap the corners off the base when torquing it down. The flat surface will take the aluminum faster than the chrome ringed center.

. I will be honest, I have no clue what you are talking about. Is the base partially chrome plated?

 

[mdavlee]

Once you start taking the base down the plating from the cylinder bore is being sanded off

 

[Backtroller]

Not a Dick, just a giant member

 

[dbittle]

I'm all for DIY, but I'd just send it to someone here with a lathe and get it cut.

Your talking less than it will cost you in supplies and it will be done right.

I know you asked how to do without a lathe. Yeah, I'm that Dick that replies it's not worth it.

But where's the fun in that?

My flanged cylinder base sanded down without issue. I was completely happy with the base sanding and squish cutting result. On the other hand, I knew before I started that I could replace the cylinder for a hundred bucks if the job went bad, so I didn't feel a lot of pressure about experimenting.

 

[A.E.E.llc]

Sanding a base flat is one thing. Guaranteeing the base is perpendicular to the bore is another.

 

[drf256]

Sanding a base flat is one thing. Guaranteeing the base is perpendicular to the bore is another.

Exactly.

This is one area where it wont be known to be incorrect for a while, but the results of doing it wrong will be quite significant.

Being off by .001 on either side will load the piston. It could conceivably make the top of the band by the jug out by a significant amount.

 

[A.E.E.llc]

Exactly.

This is one area where it wont be known to be incorrect for a while, but the results of doing it wrong will be quite significant.

Being off by .001 on either side will load the piston. It could conceivably make the top of the band by the jug out by a significant amount.

Skewed load would be hard on bearings. IMO

 

[Stump Shot]

Would first have to rule out that there was not a machine shop in my local that could do this for a reasonable charge or send it off to one of the many good builders here to have done. I'm all about DIY, also doing it right the first time. Sometimes dollars spent in the beginning are more than worth it, in an overall picture kinda way. These are just my thoughts.

While not apples to apples, I just did a crankcase cover swap for a Briggs & Stratton that needed the end thrust play of the crank turned down. I could have took a short file to it to take off a few thousandths, but when an engine shop had a tiny boring bar that did the job perfectly, seemed like a no brainer to me, even if I am pretty darn handy with a file. Would I be happy later with a worn out crank because I was a couple thousandths out of square and lost oil retention, probably not.

 

[junkman]

 

[dbittle]

Exactly.

This is one area where it wont be known to be incorrect for a while, but the results of doing it wrong will be quite significant.

Being off by .001 on either side will load the piston. It could conceivably make the top of the band by the jug out by a significant amount.

Hmmm. Anybody work the math on that? The distance across the cylinder extension flanges on the 346NE is 1.925", which we can round to 2". The height of the cylinder is, roughly anyway, 6". So then, at the top of the stroke, the piston is off its perfect theoretical path by .003". Your mileage may vary....

 

[ANewSawyer]

Exactly.

This is one area where it wont be known to be incorrect for a while, but the results of doing it wrong will be quite significant.

Being off by .001 on either side will load the piston. It could conceivably make the top of the band by the jug out by a significant amount.

. I assume before people start cutting they measure bore to flange for squareness, what is the method for checking that? Also, what about checking the bore against itself to makes sure it doesn't change angles slightly, or make sure it is an even width all the way to the top. What is the typical method for checking those?

 

[Metals406]

I did a dolly 117 with a file and sandpaper. . . Got within .004" between ears. Close enough to run just fine.

 

[ANewSawyer]

Once you start taking the base down the plating from the cylinder bore is being sanded off

I should have just left this one alone to begin with since it's something that really cannot be taught over the phone. There's quite a few guys around here that'll do it for you at a cost of around $50 plus shipping.

No, you are fine. I know next to zero about engines as you can tell from my posts. I though mdavlee's explanation adaquate. I am surprised to see approximate cost be around $50. I was expecting $100+ since I believe a full porting job is a multi hundred dollars proposition. But I have never priced a full port job, so I may be wrong.

 

[mdavlee]

I cut base and squish for $50.

 

[Al Smith]

If you already have the set up it doesn't take long to carve off a base in a lathe .With the type arbor I have maybe 20 minutes tops .1/2 hour of machine time at whatever ever they charge .Any machinest they knows anything could do it .Besides that unless the guy is a total douce the base will be dead nuts 90 degrees from the bore .Sandpaper most likely not so close .