External Balanced 360 With new parts still Balanced??
- Thread starter 72DMag
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Dartfreak75
Restore it, Dont part it!
That is awesome.
72DMag
Well-Known Member
@nm9stheham If I added the bushings to the connecting rods how much do they weigh? curious that they won't throw things off? Also to hone out the connecting rod what size drill bit would be needed for me to use in my drill press to enlarge them just enough to make the 1.094 pin floating? Thanks
nm9stheham
Well-Known Member
You'll replace the steel with bronze and change the small end weight by about 0.5 to 1 gram. Not a worry.
BUT.... no drill press. You need an interference fit of the bushing of around .002" all around the hole and with a very tight tolerance.... no way you can accomplish that in a drill press. Nor will the hole be straight enough, round enough, or square enough to the axis of the rod. And then you have to finish hone the bushing to a tolerance of something like .0002". It's not a home shop operation.
The shops have special honing machines designed just for this type of work.
BUT.... no drill press. You need an interference fit of the bushing of around .002" all around the hole and with a very tight tolerance.... no way you can accomplish that in a drill press. Nor will the hole be straight enough, round enough, or square enough to the axis of the rod. And then you have to finish hone the bushing to a tolerance of something like .0002". It's not a home shop operation.
The shops have special honing machines designed just for this type of work.
72DMag
Well-Known Member
@nm9stheham Thank you!! good to know bushing weight isnt alot. I thought they made bushings that can be pressed in using the stock connecting pin size that then allow you to run the 990 pin. I was under the impression those bushings are press in at home and go type of thing since I I am going to a smaller pin diameter size.
Marcohotrod
Well-Known Member
360 magnum pin size is .984 - big chevy .990 - big mopar 1.094 - small chevy is .927 . I have had some engines in my solid engine mount car that were factory balance, some race engine shop balanced, and some where I changed to different weight pistons - no noticeable vibrations or problems - some shifting at 7000 . unless u are racing over 7000 rpm
72DMag
Well-Known Member
@Marcohotrod you are right. I'm sorry I was thinking big block there for a second.
@nm9stheham Doing more research and referencing the build in hotrod magazine done by IMM. They used the following icon piston and had no issues and no rebalance but it is much heavier then stock. with external balance how much difference compared to stock bob weight can you get away with?? Looks like the icon piston they used was 38 gram heavier than stock. That seems like a drastic difference to me!
Stock: 474 +136 =610 grams Piston/pin actual weight.
ICON IC741: 530 + 118 = 648 grams from Icon website.
KB107: 524 + 132 = 656 grams From KB website.
https://www.hotrod.com/articles/build-500hp-capable-360-magnum-short-block-cheap/
@nm9stheham Doing more research and referencing the build in hotrod magazine done by IMM. They used the following icon piston and had no issues and no rebalance but it is much heavier then stock. with external balance how much difference compared to stock bob weight can you get away with?? Looks like the icon piston they used was 38 gram heavier than stock. That seems like a drastic difference to me!
Stock: 474 +136 =610 grams Piston/pin actual weight.
ICON IC741: 530 + 118 = 648 grams from Icon website.
KB107: 524 + 132 = 656 grams From KB website.
https://www.hotrod.com/articles/build-500hp-capable-360-magnum-short-block-cheap/
Marcohotrod
Well-Known Member
if those icon and kb pistons r that much heavier it is depressing. and magazine builds do not care about longevity , that is where we may see extra wear. as I said I have run some 340s with different pistons for some years no problem. is the stock pistons only 474 ??
72DMag
Well-Known Member
Yeah the stock piston are a really light cast material meanwhile the KB and icon are forged. I got the 474 from the "How to Build Big Inch Mopar Small Blocks" book by Jim Szilagyi. True the hot rod magazine could be about making big numbers for a short period of time and not actually geared to someone that gonna run it for multiple passes or thousands of miles.
nm9stheham
Well-Known Member
Good observations.... and this got discussed before. (I think I asked Brian of IMM here...) The ring pack is lighter for the ICON's to make up some of that weight difference.... at least that is what I recall off the top of my head was the answer. Ditto for the KB ring pack. My own observations: You can pull 5-8 grams out of the pistons without too much effort, some off of the rod small ends, and there are lighter pins available. The UEMP pin locks add 2 grams back in, but are not used for press fitting.
No one really seems to 100% knows the factory tolerance, but a +/- tolerance of 20 to 30 grams has been cited here, based on measurements and balance work done through the years.
The numbers you list for stock Magnum pistons is very close to my data.
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sireland67
Well-Known Member
I know for a fact, that I took LA 318 rods and pistons out of two engines.
The difference in balance was 240 grams total.
The difference in balance was 240 grams total.
nm9stheham
Well-Known Member
If it was light rod 318 (pre-74 IIRC) versus heavy rod 318, then the light rods are 32 grams lighter apiece on average.... which would be 256 grams across a set of 8 just in the different rods. So we need to know more data for this observation to have any meaning. (But balance is not determined by a full set of pistons/rods anyway.....)
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