Ok.. I recently purchased a scat boring tool to try to accomplish my task of making a 1914cc engine for my bug. I realize that all of my other plans, or backyard DIY boring scemes without tools, was just not going to work. I have practiced on some very old cases, using a drill press to power the scat boring too. I test fit each cylinder spiggot on the case, with a 94mm cylinder and it worked fine. I set the scat blade with a digital caliber measurement from my 94mm cylinder. My drill press must be garbage because it takes hours, and I think it broke. I fortuneately have a hand held milwauki angle drill that completed the task in minutes.
My first case, I believe would have been useable. My second case, one cylinder spiggot was off centered, and I don't think I could use it. Being that the head would be off on the spread between cylinders?
Does anyone know how to precisely mount a scat boring tool to a case?? I have another bar with the tool that doesn't hold a cutter blade? Is this to center? I just don't know how to use it. Please if anyone has experience with a scat cutter, please help me out. I am scared to bore a good case, incase I am off center again.
Unfortuneately, my tool doesn't open enough to deck a case. It wont bore a head for 94mm eighter.. maybe I should be considering for
90.5mm instead? That way the tool can do more for me?
Maybe not a Scat tool. But the following method(s) worked okay for the tools made by Gene Berg, BMG and a couple of others.
But you probably won't like it :-) Because the first step has nothing to do with the tool. It has to do with the drill press.
Is it bolted to the floor? If not, make it so. Then make a pair of diagonal braces in the form of struts. Most buys used sections of straight exhaust tubing but some used solid bars. You weld a tang on each end to accept a bolt then drill I tap the table of the drill press. The table is positioned at the correct height for the tool & the crankcase half -- and of whatever fixture you're using to support the left-hand case-half (ie, the one with the studs). Some guys used plywood, other drilled & tapped aluminum plate, some welded up a steel fixture... then spend several years truing it up :-) But there you are, finally, with the table at the proper height and a collar or other stop to re-position the table in the future. The struts are bolted to the table and the tang on the floor-end of the strut is used to mark the concrete. Then you remove the struts, whip out your hammer-drill and shoot a couple of holes in the concrete to accept steel inserts threaded for 3/8" or 1/2" bolts... whatever diameter matches your struts.
NOW you get to bolt everything together and with a bit of luck, your cutter will produce a hole that is not only round but square, which one of those Machinist Jokes, which means you don't have to smile unless you wanna.
As for positioning the cutter on the case... Didja notice that the case ALREADY has some holes for pistons? Well, most of them anyway. Didja figger out that the REAL job is simply making the EXISITING holes bigger? Okay then, because the next step is plain old-fashioned Common Sense. You make up a plug out of aluminum plate that is a light press fit in the hole in the crankcase. You do that on a lathe and you want to hold to +/- a thou OR LESS, which means you've got to take the temperature into account. It gets tricky because it isn't a CIRCULAR plug, it's rectangular, having one dimension narrow enough to fit between the legs of the tool, the other being long enough to span the diameter of the spigot-bore in the case. The tricky-bit comes from this being an 'interrupted cut' during turning, meaning it's going 'thumpity thumpity thumptiy virbrating the hell out of the lathe and knocking your tool bit out of alignment while you're trying to hold to plus or minus a thou and not even coming close, but there it is.
Did I mention that the center of your plug is drilled & tapped to match the thread of your tool? No? Well, never mind... Make sure the threaded bore is perfectly SQUARE with our plug. In fact, you may wanna do the one before the other. Even to machining a threaded spud for the nose of your lathe's spindle and screwing the plug to that. (It's a MACHINE TOOL fer crysakes! It's SUPPOSED to be rigid, accurate, expensive and a pain in the ass to make.)
To align the tool to the case you simply install the plug in the hole and torque down the fasteners in an easy-X pattern, rotating the tool by hand to ensure it doesn't bind at any point. Now you can remove the plug, install the cutter and make your FIRST CUT of the THREE you must make.
Easy, eh? In fact, if you DON'T do all that stuff the odds are you'll simply ruin the crankcase. Oh, it'll be good enough for the Kiddie Trade -- that's why they made the things! But if you don't have a RIGID fixture to support the crankcase half, and don't have a RIGID surface under the fixture, and don't a method of aligning the cutter to the true center of the existing spigot-bore -- you really don't have much of a tool.
Which isn't to say the engine won't run. Slap some chrome on it, noisy exhaust system, you're an Instant Expert. The Bad News is what happens a couple years down the road. But by then the Kiddies will have gotten through their Volkswagen Phase and nobody really cares if the engine was a total piece of shit because the NEXT Kiddie is already planning to build himself a new engine that will be like totally awesome. And kewl, too. Or some damn thing.
Now, I'm sure a few folks will detect a hint of negativity in this message but to give credit where due I DID tell you how to do it. And if you wanna do it RIGHT I'll even tell you that too: Use a milling machine.
Thanks Bob! I never thought of making a plug to center with. That is a great idea.
Haha, the negativity... it's hard trying to learn how to build an engine. I'd assume it just takes practice, and learning from mistakes. That's all I am trying to do. I know my engine wont be near perfect. Neighter were the last couple I've attempted. To be quite honest with you, I broke down last night and bought an allready bored for
90.5-92mm case, full flowed, and stroker clearenced.
I found a nice list of 90.5 stroker configurations:
90.5 X 90.5 X 69 =3D 1776cc
90.5 X 90.5 X 78 =3D 2007cc
Longer rod engines (a little more money)
90.5 X 90.5 X 82 =3D 2110cc
90.5 X 90.5 X 84 =3D 2161cc
90.5 X 90.5 X 86 =3D 2212cc
I'm planning on using the 78mm crank, due to rod length. I know I am going to get bashed for this consideration, but can you tell me what CC it would be with 92 P&C's, rather than the 90.5 shown above.
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