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#1
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Sanborn - need balancing and crank weight removal advice
1) Where can I safely remove weight from a 360 crankshaft?
2) When balancing the rods is it best to equalize the big end weights(by cutting pad from big end), and then equalize overall weight by taking weight from small end OR.... equalize big ends and then equalize small ends? 3) How thin can the piston combustion surface be (cast piston)? plan to remove material from underside of head 4) Can the ID of the piston pin be increased slightly? 5) Will I be able to neutral balance the crank? From reading an old posting, I understand you were in the balancing business. I am starting to build a lightweight bottom end for my 360 (will go in my street stock). The engine won't see over 6000 rpm. We also have a $1000 engine claim rule so I want to keep the costs down. I plan to use a 360 magnum block and crank and use some 340 rods. Using one rod as a test I have removed approx 50 grams from it. And will look at the pistons and pins which I suspect a few grams can be trimmed off of them too. I will balance the rods, and equalize the pistons and pins prior to going to the balance shop. My biggest concern is the crank, I don't want the balancing shop to have to add weight to the crank because I cut too much off in the wrong place. Sorry for the pile of questions but I would really appreciate your advice. |
#2
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Right in the wrong direction
If you are only going to twist the engine to 6 grand and you have a $1000 engine claim, why do you want to take weight off your crank? Just balance the stock crank. If you take weight off the crank, you will just have to add it back. Lightweight cranks are high dollar, because you need trick lightweight pistons, skinny rings, lightweight wrist pins, etc. to get an internal balance without adding heavy metal. If you want a cheap, claimer engine just use a stock crank, and spend your time cleaning and prepping the block with suggestions from Sanborn's small block build up. Most of his modifications require hand work you can do yourself (like drilling and taping holes in the block) and not a lot of money.
Good luck on your project. |
#3
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I hope I can help.
First, I don't think you can internal balance a 360 crank with standard rods, pins, and pistons. About all you can do is reduce the amount of heavy metal needed. A standard 360 crank weighs about 58 lbs. First deburr the entire crankshaft, remove any casting slag fom it. Then, grind the crank smooth on all counterweights. At this point you really haven't removed weight. When it comes time to remove weight, the only weight you can really remove is on the connecting rod journal side of the crankshaft. On the center two crank journals try to remove the same amount on both. You can round the front and rear counterweight on the end adjacent to the center two journals. You might consider using 318 rods on a low RPM application. As I recall they are about 50-60 grams lighter to start with. On the pistons, don't go thinner than .200" on the flat of the piston. Remember, the cast pisons are designed for street(3000 or less). Don't try to bore the ID of the pin unless you have lots of time and good carbide tooling. Now, there is another alternative (if you have a little$ to spend). You can use a 327 Chev piston, bush a 360 rod (or 318 that wasn't bushed to begin with), ream it to .927 Chev pin size. this would save you some pin weight and a little piston weight also. You would have to recut the valve reliefs(and I recall remove a little off the top around the perimeter of the piston). This would allow the piston to protrude out of the block a few thousands of an inch(don't remember how much). Don't know about your area but around here you must win to be claimed, then only by a top five car AND, the claimed engine must bolt in without alterations. This pretty much eliminates anyone not running a Mopar. I wouldn't worry about claiming too much. It's a cost of racing! |
#4
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Our claim rules are: top four finishers can be claimed by a car finishing on the same lap as the fourth place car. I am the only mopar, but any one can claim it as it does not have to fit their car. Although if I continue winning as I have been, I may tick the chevy boys off enough to claim me.
For pistons, I was going to use std bore 72-73 340 pistons and cut the top to get the compression I desire and massage the skirt etc to clear the counterweights. The 340 piston is heavy, but alot of material is removed which will put it close to a 360 piston. But the 327 pistons may be a better deal so I will work the math on those. What about the rod balancing method, which is best? (see question 2 of my original posting). Thanks for all the advice |
#5
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You balance each end of the rod individually, first the big end, then the small end. Try to get each end of each rod within 1 gram of each other.
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#6
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Excuse my ignorance on the subject, but I am balancing rods and I was wondering the best method for weighing a single end of the rod. Do I need special equipment??
Thanks in advance. |
#7
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If you were going to do it for a business; yeah, you would need a special fixture. But, if you are going to do it for yourself then you can Rube Goldberg(hope no one is offended) something up to work. All you want to do is suspend the small end in order to weigh the big end, and vice versa. You can actually tie a string through the small end, tie it to a nail somewhere so that the rod is HORIZONTAL and the big end is on the center of the scale. Just make sure you suspend and weigh all the rods exactly the same way. Then, repeat the procedure to weigh the small end. Then finally, check yourself by adding the small end weight and large end weight together. It should equal the weight of the rod on the scale.
Hope I didn't confuse you! If you have any questions-get back! |
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