Chainsaw Repair

Chain - Grinders - Filing - Wood Milling - Tools - Welding - Machinist - Mowers - Tillers => Chain - Bars - Grinders - Filing => Topic started by: Midpines on July 31, 2019, 12:11:28 am

Title: Yosmitesam's Grinding, Filing, and Tools Thread
Post by: Midpines on July 31, 2019, 12:11:28 am
Midpines CA is where I live, Yosemite Sam is who I am.  I can see El Capitan and Half Dome from my up stairs bedroom window.

This is my workbench thread.  Anyone can say what they want, but it is my thread.    ;D

Today I'm going to explain how to hone a chainsaw cylinder for a tool cost of about $ 1.50 cents.  Beer backwash is a necessary ingredient but I haven't cost it into that $1.50 cent cost factor.

To begin I need to have the cylinder one needs honed in hand while I'm rooting through my junk pile.  Looking for a pipe which will fit into the cylinder with at least 0.035 clearance, but no more than 0.125. PVC is preferable but Aluminum and Copper are OK too.

Once I've found my pipe I take it to the table saw and with the sliding square I saw it into a foot long chunk.  Then I set the fence for ripping at half the diameter of the pipe, set the blade low so it just cuts through the bottom of the pipe, and I rip a slot from end to end. 

Today I wanted to hone three cylinders, a 47mm, a 49mm, and a 50mm.  I used a 1 1/2 i.d plastic electrical conduit tube, it could have just as easily have been a sec 40 pvc drain pipe.  What I made was a tool.  A tool which will span all three of those cylinders.  Before applying the paper and cloth I take a knife tip and drag it up and down the slot to form it around, easing the sharp edge on both sides of the slot.

Then I measure the depth of the deepest cylinder and cut a strip of 400 grit wet or dry sandpaper, and a strip of Crocus Cloth about a half inch longer than that.  I feed one end of the paper into the slot with the paper overhanging the end to the pipe by about a quarter inch. Form it around the slot edges and use super glue on the inside of the pipe to glue that end of the paper down.  Then I stretch the paper tight and insert the other end after trimming away the excess all but the amount I need to glue down to the other side of the slot. 

Then I switch to the other end, gluing the Crocus Cloth down. Crocus Cloth is like a medium oil stone hone ground up and impregnated into a cloth with binder. That is why i'm saying I'm honing the cylinder.

Once I've got the paper and cloth glued to both ends, I strike off the quarter inch excess off the end of the pipe using a sharp knife. It leaves a nice square end which will reach all the way into the cylinder to remove the worn lip where the piston ring travels. If one doesn't remove that excess right at the end of travel the new piston ring will hit if, and that will cause the ring to go dull. 

Piston rings come sharp, it's a bad thing if they go dull.

This tool allows me to bear down on that upper end and grind it off with the 400 grit end of the tool.  Once I've got the top lip dealt with I can then apply the pressure to the whole cylinder to smooth out the walls if there are scratches. I do all of that dry.

As soon as most of the scratches are dealt with I switch ends to use the Crocus Cloth.  I like to wet it with beer backwash, if you don't have that use a bit of water.   ;)

On the two best cylinders I had today I used the Crocus Cloth from start to finish. The worst one I sanded on for about a half hour, then switched to the Crocus Cloth end for an additional 15 minutes.  The worst one took 3/4 of an hour, and the two best ones took 15 minutes each.

I had to drink a whole six pack to get enough backwash to wet that cloth. That's something.   ;D

Tomorrow I will explain how to sharpen old piston rings using a pocket hone, the piston the rings go on, two rubber bands, and a few bits of note book paper.   (The bits of note book paper are used to set up the angle the rings ought to be sharpened too).

Title: Re: Yosmitesam's Grinding, Filing, and Tools Thread
Post by: Midpines on August 01, 2019, 07:33:32 pm
I didn't get here tomorrow, today is the day after tomarrow, but I did hone the piston rings I needed to sharpen on tomarow.  Two of the three cylinders are getting new rings, the ones I'm reusing are the two in the Poulan 245.  They're angled face rings, I can see the angle but I didn't know what angle it is.  They're widest at the top. 

What I did was coat the surfaces with blue layout fluid.  Then I cut a strip of paper from a Right Aid cash register ribbon.  It is very tough thin paper, 0.002 inches thick.  It's ideal.  I cut a two inch long by 3/4 inch wide.  Then for the first trial I folded one end on itself 1/8 wide. I placed that upside with respect to the fold down on the hone.  The hone I used is a medium oil stone, a six inch long stick, one inch wide shaped like a wedge with a 1/8 radius on one edge, a 1/4 inch radius on the other. I'm using the flat so a rectangular four or six inch pocket hone will work fine, use the fine side. 

I laid that fold in the paper down on a spot which looked smooth and flat, the area just beyond the fold is the part of the hone which will be used.  The piston was set on the paper with the ring grove just overhanging that 1/8 inch wide end which has been folded over.  the skirt of the piston was resting on a single layer of paper.  The piston is set at a slight angle due to that.  0.002 rise over approximately 1.000 run, that is 0.11 degrees.

Then I held it down and rotated the rings around once.  My first guess was good enough, the blue dye was wiped away all the way across the edge surface of the ring.  To test that I reapplied the dye and laid the piston down on another strip of paper without a fold. It only removed the dye from the top edge of the piston ring edge.   Then I folded it's end twice and it only removed the dye from the bottom edge of the piston ring edge. So one fold, 0.11 degrees is the correct angle.

I returned the one fold strip of paper to the hone, set the piston ring down and used rubber bands to lash it in place.  This is a good time to mention that I placed the piston ring pin in the side of the piston which keeps the rings from turning to the top so that the rings when expanded would pass over it without hanging up. 

The piston holds the rings at the correct angle while I grasp the rings with my finger tips and rotate them around and around. Some practice is necessary the rings have to be held round.  round with most of that gap still open to where it springs out too when the piston is pulled out of the cylinder.  Once one develops that knack, it goes smoothly and well.

From start to finish it took me a half hour.  Those rings look nice and they have no nicks left on their edges.  That's sharp.