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Notching pistons for oil squirters after assembly has been balanced
I’m hoping to get the opinions and thoughts from some of you that have run into this specific situation yourself. I’m doing a new TSP balanced rotating assembly for my LT1. I already received everything from TSP and while speaking to WIseco about something else, I asked them why they were not notching the pistons to clear the oil‘s squirters. As it turns out, they’ve change the design and are now notching the pistons effective late July 2018. My pistons were originally shipped to me in June 2018 so they don’t have the updated design.
Wiseco has generously offered to take the pistons back and notch them for me on the CNC machine and then send them back my way, but my question has to do with the engine balancing. Because the assembly has already been balanced by TSP before the pistons were notched, how much will this notching offset the balance? Because they are taking off the same amount from each of the pistons equally will they be OK the way it is to assemble? Or will I need to pull the crank back out of the block and have everything rebalanced again?
How big are the notches... how much material gets removed? I don't know the answer but my mental image of a notch is small so even if they aren't exactly the same (but with CNC they should be) the differences would have to be tiny.
I would at minimum put the pistons on a scale before considering installing them. If they are not exact, I would make them exact. CNC is great, but every time a human comes close variation exists. Tools wear, material density can vary. Nope, I would not do it without checking.
I don't know that the rest of the assembly needs to re balanced. I tend to think if the rest was in balance, and the pistons were balanced, you should be good to go with new balanced pistons, but I would love to learn something about balancing a rotating assembly here.
And if they all are within a tolerance you can WOT with more confidence.
How big are the notches... how much material gets removed? I don't know the answer but my mental image of a notch is small so even if they aren't exactly the same (but with CNC they should be) the differences would have to be tiny.
Typically pretty big. I haven’t gotten them back yet but I believe they will look like this:
Originally Posted by The Chev
I would at minimum put the pistons on a scale before considering installing them. If they are not exact, I would make them exact. CNC is great, but every time a human comes close variation exists. Tools wear, material density can vary. Nope, I would not do it without checking.
I don't know that the rest of the assembly needs to re balanced. I tend to think if the rest was in balance, and the pistons were balanced, you should be good to go with new balanced pistons, but I would love to learn something about balancing a rotating assembly here.
And if they all are within a tolerance you can WOT with more confidence.
I’m not as concerned with the piston vs other piston variation. I’m concerned with if that affects the weight thats added/removed from the crank enough to matter. If you google engine balancing there are youtube vids to show you how they do it and you’ll see what I mean.
I've never balanced an engine but it still seems to me that any differences in the notches between pistons would be very small if any at all. And the notches, while bigger than I had envisioned, are still only a few % of the overall piston. So a tiny % difference in a few % is basically zilch and probably nothing to worry about. Just IMHO. But too bad you didn't get the new ones in the first place. Just bad luck.
Edit: I missed the other part about the crank. Man, I don't know. I guess that the crank counterweights could be varied to balance things out but not sure that removing that amount would matter. I bet Wiseco could tell you how many grams come off. That might be good data for someone knowledgeable to get to the answer.
Originally Posted by FYREANT
Typically pretty big. I haven’t gotten them back yet but I believe they will look like this:
I’m not as concerned with the piston vs other piston variation. I’m concerned with if that affects the weight thats added/removed from the crank enough to matter. If you google engine balancing there are youtube vids to show you how they do it and you’ll see what I mean.
I've never balanced an engine but it still seems to me that any differences in the notches between pistons would be very small if any at all. And the notches, while bigger than I had envisioned, are still only a few % of the overall piston. So a tiny % difference in a few % is basically zilch and probably nothing to worry about. Just IMHO. But too bad you didn't get the new ones in the first place. Just bad luck.
Edit: I missed the other part about the crank. Man, I don't know. I guess that the crank counterweights could be varied to balance things out but not sure that removing that amount would matter. I bet Wiseco could tell you how many grams come off. That might be good data for someone knowledgeable to get to the answer.
I wouldn’t take the chance at all especially at your power goal. No way in hell. Spend the money, time or both or you may have bad dreams every time someone bumps this thread lol
I wouldn’t take the chance at all especially at your power goal. No way in hell. Spend the money, time or both or you may have bad dreams every time someone bumps this thread lol
I agree are at least get up with them like you have said & see what they tell you on it.
Rotating assembly balancing is the crankshaft counter weights to piston weights delta, which should be zero, so removing mass/weight from the pistons throws the whole thing out of balance if the crank counter weights are not equally attended to. I would get it all re-balanced at a good machine shop as it doesn't cost all that much really. Good luck with it all and I hope it turns out to be a great build.
Rotating assembly balancing is the crankshaft counter weights to piston weights delta, which should be zero, so removing mass/weight from the pistons throws the whole thing out of balance if the crank counter weights are not equally attended to. I would get it all re-balanced at a good machine shop as it doesn't cost all that much really. Good luck with it all and I hope it turns out to be a great build.
Agreed. A good rotating assembly is balanced to less than one gram. No way you should take that much out of a set of pistons without rechecking the balance.
Rotating assembly balancing is the crankshaft counter weights to piston weights delta, which should be zero, so removing mass/weight from the pistons throws the whole thing out of balance if the crank counter weights are not equally attended to. I would get it all re-balanced at a good machine shop as it doesn't cost all that much really. Good luck with it all and I hope it turns out to be a great build.
I've been watching some videos under your suggestion FYREANT and based on what I am seeing, the bob weight has changed and therefore the entire balance is now off. How far off depends on the level of balance. We're they adjusting to grams, or tenths of grams?
I've been watching some videos under your suggestion FYREANT and based on what I am seeing, the bob weight has changed and therefore the entire balance is now off. How far off depends on the level of balance. We're they adjusting to grams, or tenths of grams?
Pretty sure to tenths of a gram. I’m thinking I am probably going to have it rebalanced. Unless Wiseco comes back and says they are certain its fine. Which I doubt..
10-18-2018, 04:46 PM
Notching pistons for oil squirters after assembly has been balanced
