Been learning to operate an EDM (electronic discharge machine) at my friend's machine shop. Been splitting 7 inch 4130 swage dies into thirds - with a .012 thick brass wire. As watching the machine cut is as exciting as watching submarine races my mind wandered. So i says to my self " Self, you have a half dozen Triumph cylinders that need boring. Why don't you use the EDM?" The surface finish of the cut is variable from fine to smooth as glass. I can hold the accuracy of the bore to a half of a tenth - .oooo5 inch. I can control the taper to a tenth (.ooo1) over the seven or so inches. Any thoughts on the subject? Cooper
I should of stated the machine is accurate to half of a tenth - the operator may not be. Will be honing the finished bore - just haven't decided which hone - dingle ball or rigid stone. Will probably start with the dingle ball. Cooper
A torque plate to simulate cylinder distortion caused by tightening the head bolts and a fixed-blade hone is best.The cylinder will go out-of round when the bolts are tightened.The fixed hone will cut it back to round.
Allow for the extra tension on head-bolts caused by cylinder head expansion on a hot engine.
Unfortunately David, that is the World we live in today.
Our engines were built where cylinders were measured in thousandths of an inch. Crankshafts weren't square to the bore. Crankcase mouths were neither square to the bore, and were often stepped from one half to another, Factories, let alone dealers did not use, or have, torque wrenches. Watch a Hughie Hancox video. It was a time where 150 grit honing stones were considered Finishing stones. The apprentices were taught that if you couldn't scratch a match to light on the bore after honing it was too smooth. And grey cast iron rings lapped themselves round during break-in to a bore that was neither round, straight or true. It worked, but these engines would never pass the crudest of emissions tests and had a short life expectancy. It also must be looked at as a package. For example: Put a grey cast iron ring in a cylinder finished honed with a 280 grit stone, or finer and the rings will not seat. Worse, do that using a modern oil designed to give better fuel mileage.
The bores of modern engines are routinely measured in one or two ten thousandths of an inch. Where cylinders are bored with main bearing caps in place and torque plates mounted, often the engine casting is pre-warmed and the honing done with hot lubricant, Ductile iron or steel rings are pre-lapped and coated to prevent wear (you cannot "break" them in as such), and pistons are made from Hyper-Eutectic low expansion alloys. These engines are as near perfect as one could emagine and require little, IF ANY break-in.
Problems exist when people try to mix modern technology, with engines built on machines and with technology and metalurgy that pre-dates WWII without an understanding of what they are doing. It can be done, and is done by guys building race bikes today, but it is with an understanding of what they are doing and what is required.
I see to often a cylinder finished with 400 or 600 grit stones and the owner with a package of grey cast iron rings in his hand. I see oil and water....
John, It is refreshing to hear from someone that knows how it was and how it is now. I get very frustrated trying to explain things to modern machinists when working on old stuff. In many instances modern techniques like clearences and such cannot be used on old equipment because of the changes in metalurgy etc. Many of them have been to school and were taught the modern way and they believe that is the only way.Thanks for your input.
Update - EDM worked great - exact size , no taper. However, it took about 70 minutes a side taking off .010. Not very cost effective. After wiring, mapped the cylinder dimensions with a bore gauge (plus/minus .0005). perfect! I then bolted and torqued my cylinder head to the barrels and remeasured. No dicernable change. I then bolted the base flange to my boring bar fixture (2 inches of tool steel) and repeated measurements. No discernable change. Your results may vary. Will be using the old tried and true boring bar as the EDM is way more time due to setup and cutting speed.
Cooper, most interesting results regarding measurements after torquing head and base down, with no changes. I would guess it may depend on cyl. construction, bolt to bore spacing etc. I have a question regarding EDM, in another post we were discussing modifying an early 5 sp. tranny (Triumph)camplate to match the outer contour of the later model camplate & I was wondering if EDM wouldn't be an easy way to do this. Could you explain the procedure to accomplish this? Cost effective? Do I find a local EDM guy and go in with a template? If you have time an explanation would be great...Mark