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Al

Cylinder and rod clearances and tools

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Al
Hi, What follows is an e-mail I send to tobskee today regarding some Brs cleanances. Tobin, The new spec on the rod/crank clearance is .0011 to .0013 and as close as I can remember I think the cylinder skirt to wall clearance is about .0035 to 0004. Briggs spec is bore to size and the clearance is ground in the piston. The skirt is measured at right angles to the wrist pin and at the bottom of the skirt normally. These pistons are cam ground and the skirts are always wider at 90 degrees than when parallel to the wrist pin. On some other RARE grinds, the piston skirt may be wider right under the oil ring than at the bottom of the piston. Usually these pistons have a T slot in the skirt accross and down the skirt to control expansion. Regardless of the grind, the widest point determines the clearance. I took some pics of one of our rigid hones and an old taper guage that I will post on the Simple Tractors site hopefully tonight.. Note: The numbers are to tenths not thousandths. Am attaching some pics. The first is a spring scale and a taper guage. This guage is broken, the needle is ruined.


The top unit is a spring and feeler gauges are attached to it. Typically one would put 3 .001 strips on the scale and would slide the piston in the cylinder with the strips between the wide part of the piston skirt and the cylinder after the cylinder was to finished size. Then you would pull them out and see how many lbs. it took to pull it out. If the 3 only took less than a lb, you might remove an .001 and add a .015 and repeat. If this came out about 3 to 4 lbs, you were very close to on at .0035. We used to do this all the time after cylinders were finished to do a final verification. Any more with the new manufacturing capabilities, pistons are more uniform and we just bore and finish to the plus +.0005 -.0005 factory tolerances and go. We mike the cylinders and check the ring end gap on every ring to be sure at sometime someone hasn't opened a pack and mixed a ring from another set etc. (cheap insurance) The bottom item is a taper gauge built by Zim manufacturing, This one is probably 60 years old. It was adjustable to go in the bore and zero it and then slide it down the bore and you could read the taper. This was in the days when cars needed new rings after 30 or 40 thousand miles. Rings were soft and cylinders often had a couple of ring jobs before being rebored.


Above is one of our Sunnen rigid hones. These can be used to oversize cylinders. The frames are rigid and as the stones and aluminum guides come out they are parallel. It is shown nearly retracted. I rarely use a hone to do an engine. I used to have a Quick Way boring bar and a clamp table for small engines. I did all my boring in house. I only ever had one employee that I was able to teach to bore and not have to watch over. (Most mechanics with this ability get jobs in machine shops.) A you need to be sure the deck or top of the block is flat and smooth and clean. If not you will bore at an angle instead of straight. Sometimes you have to have the block decked in a milling machine to get the flat surface you need. Next you have to use the bottom of the bore where there is little or no wear to center the bar. When the bore is completed you pull the bit or cutter and using the bottom angle bore about a .005 45 degree angle on the top to help with the ring installation. You bore to within .0015 of finish and then put the block in a honing tank and use 300 grit stone in the Sunnen hone and hone the .0015 out to size using oil flow on the hone. At this point you switch to 500 grit stones and PLATEAU the finish. The 500s knock the peaks off the 300 peaks and make them like little hills with the tops scraped and a smaller shallow surface on the peaks. This finish makes the rings seat more quickly and lube the cylinder better. If you do a total 500 finish you will have problems with ring seating and the crosshatch be too shallow. All the while you have to keep running the hone all the way up and down in the cylinder at a rate to maintain a 35 to 40 degree crosshatch pattern in the cylinder wall. When finish is done, remove the block and do the MOST IMPORTANT thing. Scrub the cylinder walls and block with hot soap and water, scrub not just rinse. Then rinse and swab, blow dry, wipe and oil. If you use solvent, it will actually cause the honing grit to imbed in the cylinder. Soap floats this out. If you have ever washed something out in solvent or gas (no-no) when the can is emptied you will see the dirt stuck to the bottom of the can. Same principal. If you are going to sleeve, you bore to .001 of the sleeve OD, leaving a 1/8in lip or shoulder in the bottom of the cylinder. Next freeze the sleeve try to get it below 0. Heat the cylinder, coat with sleeve seal and get the cold sleeve and press it in so it hits the lip at the bottom of the cylinder. Give it an hour or more to normalize. Remount the boring bar and run the bit (cutter out so the flat bottom is out to the point where the cutter angle changes to 45 degrees is at the outside edge of the sleeve. Then start the bar and bore the top off the sleeve until it is flush with the top of the block. Next set the bar and bore the sleeve out like a regular block. Side note: Back in 1960, Ford came out with a "thinwall casting process to run cooler and weigh less. I bored a sleeved a cylinder in a 390 block out of late model stock car. When I made the final cut, for the sleeve, I shined a light through the (core) freeze plug and the inside of the block had pinholes all the way around looked like twinkle twinkle little star all the way around. I had never seen such accurate casting. You can resize a cylinder with a Sunnen or Ammoco rigid hone. Anchor the block solid and put 80 or 100 grit stones in. You will HAVE to have a heavy duty 1/2 inch drill with 2 handles minimum. Put the hone in the block to the bottom of the cylinder and run the stones out to the point the drill will barely turn the hone. Start the up and down motion in the bottom of the cylinder. As the motor speeds up, apply more stone pressure. then stroke to the top of the cylinder every other stroke. Keep pressure on the stones and keep stroking. NOTE: If you do not constantly keep stroking the stones up and down the stones will wear unevenly and you will end up with a wavy cylinder. The bottom of the cylinder will be stock bore, no wear below the rings. This is where the hone starts and works up into the taper area. The worst wear will be in the area where the piston is when the crank is in the 1 to 2 oclock area in the crankshaft down,(power) stroke. As you resize from the bottom you will work through the worn area, where the worn side will be on the power stroke area where the piston has the most side thrust. Ultimately you will get the worn area cleaned up and stroking from the bottom to the top you will hear the drill motor pulling the same from the bottom to the top. One you are at .0015 then finish as with a bored hole. It seamed as if every time I need a golf car cylinder bored or a block, I was buried in other things. I decided to sell my boring bar to my first employee in this business, who quit and for a while became my competitor. He now owns Recreational Motorsports and builds about 300 junior snowmobile racing engines plus a lot more. He has 4 boring bars, and developes and grinds his own racing cams etc. I hired him at 17 years old when we added Simplicity, gave him the check book and said run it. I was at Rockwell as an electronics tech and came in and worked nights and Sats and Sundays. When I need to do some quick engine dyno work I run over there and steal some dyno time. He now does all of my boring as I have to focus on repower. He researches and develops his own racing cams plus a ton more. You may see my old boring bar on his site www.recmotor.com

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larry8200
Thanks for an excellent write up! I have a good rigid hone and have achieved excellent results, but takes hours to remove 0.005" If I was rebuilding more than 1 or 2 a year, I think I'd have a machine shop do the work. Nobody does it as well as the people who do it every day.

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powerking_one
Al, Very interesting pictures of the old Sunnen "Cylinder Grinder". When my grandfather past away in 1970, my brother and I took the family station wagon up to his house/shop in Cooperstown, NY and hauled away the most desireable "goodies" including one of these Sunnen hones. I used it twice since (was 11 at the time) and this 2nd use was to try a poor man's bore job on my 3314H Briggs. I must say that it was pretty impressive how well it worked boring from STD to .010" oversize and how precise the results were. After fine finish honing, the ring gap did not vary more than .001" from top to bottom of the bore. I don't know the age of the hone, but gramp's was in the business from the 1920's through 1960. I bet it was manufactured in the 1930's. The whole operation with me holding the block and checking bore measurements and my brother running the 1/2" drill/hone took about 1 hour, but we were being carefull, not knowing how this would turn out or go "bad". By the way, mine is identical in your picture of the Sunnen Rigid Hone. Tom (PK)

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Al
Hi, I forgot to mention you need to keep quite a bit of pressure on the stones to keep the cylinder straight and round. As you move the drill up and down it will speed up at the top and slow down at the bottom. Keep the pressure on and the bottom with the least ware will cut faster. When the dril does not change tone or speed all the way up and down you are starting to get a straight cylinder. When it is straight and round it will pull evenly and you can feel it. Just hone and measure and hone some more etc. Al Eden

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