"Weight matching" OEM pistons
03-30-2015, 12:12 AM
#27
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So if you take a gram or two off a piston, but the crank is out of balance on a journal by a half ounce, what do you think you gained. You'll never know if the piston was off by even 10 grams. If you balance the crank by that half ounce, but the pressure plate/flywheel assembly that bolted to the rotating crank is off an ounce, you'll never know if the crank is off or not. In actuality, the pistons would be the last thing I would balance as they make the least difference.
And unless you are going to spin it past 7k, the only thing any of this is going to give you is possibly a smoother idle.
And unless you are going to spin it past 7k, the only thing any of this is going to give you is possibly a smoother idle.
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03-30-2015, 08:46 AM
#28
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So if you take a gram or two off a piston, but the crank is out of balance on a journal by a half ounce 15 grams, what do you think you gained. You'll never know if the piston was off by even 10 grams. If you balance the crank by that half ounce 15 grams, but the pressure plate/flywheel assembly that bolted to the rotating crank is off an ounce 30 grams, you'll never know if the crank is off or not. In actuality, the pistons would be the last thing I would balance as they make the least difference.
And unless you are going to spin it past 7k, the only thing any of this is going to give you is possibly a smoother idle.
And unless you are going to spin it past 7k, the only thing any of this is going to give you is possibly a smoother idle.
Michael, thank you for putting it into proper perspective.
Research into crank balancing was quite interesting, especially the additon of journal "bob"s during the operation. *EDIT*
Another thing: Inline 4's are going to have 2X frequency vibration regardless of how perfectly they are balanced (unless there are counter-rotating balance shafts).
Costs to have the system balanced do seem modest.
Last edited by DNMakinson; 03-30-2015 at 09:08 AM. Reason: Updated Bob weight comment
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03-30-2015, 11:29 AM
#29
This thread sucks.
OP wasn't asking to discuss which parts have the biggest effect on balancing and whether or not it's worth the investment to pay to balance the whole assembly.
I'm pretty sure he was never going to pay to have everything balanced...he's doing a pretty simple "rods only" build and trying to keep costs at a minimum.
The original question was how to and where to remove weight from an OEM piston. Not why.
If he wants to take the time to try to balance out the weight of pistons, I say more power to him. Even if it has basically zero impact on the final product.
OP wasn't asking to discuss which parts have the biggest effect on balancing and whether or not it's worth the investment to pay to balance the whole assembly.
I'm pretty sure he was never going to pay to have everything balanced...he's doing a pretty simple "rods only" build and trying to keep costs at a minimum.
The original question was how to and where to remove weight from an OEM piston. Not why.
If he wants to take the time to try to balance out the weight of pistons, I say more power to him. Even if it has basically zero impact on the final product.
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04-12-2015, 02:25 PM
#31
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This thread sucks.
OP wasn't asking to discuss which parts have the biggest effect on balancing and whether or not it's worth the investment to pay to balance the whole assembly.
I'm pretty sure he was never going to pay to have everything balanced...he's doing a pretty simple "rods only" build and trying to keep costs at a minimum.
The original question was how to and where to remove weight from an OEM piston. Not why.
If he wants to take the time to try to balance out the weight of pistons, I say more power to him. Even if it has basically zero impact on the final product.
OP wasn't asking to discuss which parts have the biggest effect on balancing and whether or not it's worth the investment to pay to balance the whole assembly.
I'm pretty sure he was never going to pay to have everything balanced...he's doing a pretty simple "rods only" build and trying to keep costs at a minimum.
The original question was how to and where to remove weight from an OEM piston. Not why.
If he wants to take the time to try to balance out the weight of pistons, I say more power to him. Even if it has basically zero impact on the final product.
Anyways, it's already been done. I'll be putting this motor together shortly and will see what happens. I will also update this thread. If it does nothing it all, it was only a few hours wasted, so whatever.
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04-12-2015, 07:07 PM
#32
IMO it should help. If it's every apart again, you can balance the entire rod/piston/rings/wrist pin/clips/bearings assembly using basically just the scale you're already using and a couple simple fixtures. You can at least make them all match, last step would be to have the crank balanced to them, but to do that you'll have to take it somewhere but if you had all the parts already balanced it would be cheaper to have just the crank done by a machine vs paying them to do everything.
You got pics of what you did? I never balanced my engines when I built them, always wanted to. I'll probably do the next one I build myself. My spare engine I have now was balanced/assembled by a machine shop.
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04-12-2015, 09:07 PM
#33
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Hey guys, I did a bunch of searching before creating this thread but could not find anything definitive, so bear with me.
I have a set of OEM pistons that are going back into this motor, for a "mild" build, aka Vlad style. Anyways, the heaviest piston is some 5-6 grams heavier than the lightest, and I'd like to do some balancing.
All of the rods are almost exactly the same weight (ebay forged), so I can't really match the heaviest rod with lightest piston, etc.
So now I'd like to get these pistons closely matched, but I cannot figure out WHERE I should be taking weight from them. I've read a few different opinions on the matter, and from what i gather there are a few options.
1) take the weight from underneath the top of the piston. IE dril/dremel from underneath and remove material.
2) Remove "casting" marks from the inside of the piston.
3) "shave" the weight from the bottom of the piston skirts with a belt grinder.
4) don't take any material from the pistons themselves, but rather remove material from the inside of the wrist pins.
Whatcha guys think? Want to get rolling on some miata related stuff, and this would be the next step.
Thanks <3
I have a set of OEM pistons that are going back into this motor, for a "mild" build, aka Vlad style. Anyways, the heaviest piston is some 5-6 grams heavier than the lightest, and I'd like to do some balancing.
All of the rods are almost exactly the same weight (ebay forged), so I can't really match the heaviest rod with lightest piston, etc.
So now I'd like to get these pistons closely matched, but I cannot figure out WHERE I should be taking weight from them. I've read a few different opinions on the matter, and from what i gather there are a few options.
1) take the weight from underneath the top of the piston. IE dril/dremel from underneath and remove material.
2) Remove "casting" marks from the inside of the piston.
3) "shave" the weight from the bottom of the piston skirts with a belt grinder.
4) don't take any material from the pistons themselves, but rather remove material from the inside of the wrist pins.
Whatcha guys think? Want to get rolling on some miata related stuff, and this would be the next step.
Thanks <3
Eaton Balancing » Engine Balancing, Part 3
Eaton Balancing » Engine Balancing, Part 4
You should also balance the rods, both big and little ends. You can buy (what I feel is an overly expensive) scale system, or you can make your own pretty easily. Ours consists of a rod with a chain hanging off it. We suspend one end of the rod with the chain and weigh the opposite end on the scale. We had pictures on facebook a while back ago, but it's a pretty simple setup.
You won't spend more than a couple hours balancing both the pistons and rods, and it's pretty fun.
Not everyone has the budget or need for a full spin balancing, though it's great in an ideal world.
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04-12-2015, 09:11 PM
#34
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FYI, I have David Vizard booked to give a presentation at MegaMeet this year. Google him if you don't know who that is, but he literally wrote the book on engine building--actually he wrote A LOT of books on engine building.
MegaSquirt Mega Meet 2015
MegaSquirt Mega Meet 2015
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