So my question from last Sunday hasn’t been answered. How far off can 1 piston be if the other 7 and the rest of the rotating parts were originally balanced. This is a street engine stock cam, no headers, etc.. what is your limit light and heavy. still awaiting parts.
If the lone piston is the same brand and design, it should be pretty darn close. Pistons are now made essentially to weigh the same; take a standard bore piston, and a .040 piston that's the same brand/design/part number, and they'll weigh basically the same. You won't notice it. This ain't the old days any more. I am Butch/56sedandelivery.
Thanks Butch. I’m helping a guy who’s waiting for one to show up with the proper rings. Not positive on the brand but it is a cast not forged. The block has some scaring so it will be honed out to new piston size which is just .010” by good luck. I know he can live with 5 grams either way but was wondering what any interest here has ever seen that ran without a problem. Thanks
So, Jimmy, you guys are putting one oversized piston in an engine and you are concerned about it being heavier than the other 7? Is that the problem? Bones
I once had a Harley with one .030 over piston and one .010 over, ran fine, couldn’t tell how smooth it ran, it was a paint shaker either way. Sent from my iPhone using The H.A.M.B. mobile app
I was just downstairs putting a Y block motor together with used pistons and wouldn't you know it, the last piston to go in has a flaw. Now I need ONE 292 .040 over piston, used in good shape would be fine, or a new one. anyone know where I can buy just one piston?
Man have i screwed up a bunch of engines in my life! I bought a re-ring kit when i should've bought a re-piston kit lmao! I'm not "old", but I've probably "rebuilt" 30? Engines and the only time I've bought pistons was when i had to have it bored. I looked everywhere for .030 oversize rings, but never found any lol. I've bought new pistons and threw them on the paint scales for shits and giggles and they weren't balanced. The moral of this bit of my brain is that you should never let your paint guy touch your engine
Chrysler back in the 50s used to sell new cars with some cylinders overbored and cranks throws turned under! This is where the custom of making sure the pistons go back in the same hole started. Not sure by how much. Maybe other cars did it also! I had a nice running 1974 Confederate Special FXE, that I was sure was factory original. Ran smoother than any Shovelhead I had ever ridden. When I tore it down after many miles and years, one cylinder was .010 over! You will never be able to feel .010 over on one cylinder. On a V-8, you probably couldn’t feel .040 over! PS: I still have that bike! Bones
I don't know how the HAstings knurler works, but I believe when knurling a piston skirt it would be better to squeeze the 0.2" thick skirt than grip the piston head lands and foce the knurling tool into skirt OD. Coarse glass bead " peening " just the skirt expands the skirt Ø .001" -.003" or so, and creates a surface that wears very nicely. Cleaning the grit from any blasting process is a non-trivial task, with the potential for real bad outcomes.
I've got one never used. I'll send it in a a postal box if you like. 608 grams and 754 with the pin. Sealed power W1022P 40 with pin and keepers. PM me.
Yes, Bones that's about it. I was wondering how many grams would not be noticeable or at least not cause a problem. I realize that in the past new cast oversize Pistons were kept to what the original weight was if possible so rebuilders didn't need to balance the engine again. All my engines today use custom forgings and aftermarket rods and we balance every thing... This is not one of these.
For an already balanced assembly, the different piston being lighter would be better than being heavier....with that said, in a performance engine they say 15 grams heavier or 40 grams lighter, you and the crank will never even notice it. Oil windage and cling to the crank while running changes the weight felt at each rod journal constantly anyway as the oil is roped and tentacled around the crank in a constantly moving mass. In a street cast piston deal, I would not be afraid of 30 grams heavier and 75 grams lighter assuming you aren't shooting to run up over 6500 rpm with it
Eric. That’s what I’m hoping to hear. The engine in question is still together and running with a problem on one cylinder wall. There’s a stock piston available that’s only .010 over the piston now. After the holidays the head is coming off and I’m 99% sure I can hone it to the correct size, .002-.003” over the skirt at 2.85” down from the top. I have a hone,(not a glaze breaker) a cylinder mic, and can finish with a ball hone if necessary. I also have new cast rings. Thanks I am hoping for a lighter or near to the weight I have now piston.
That’s kinda what I though. What I used to do in a previous century when we were piecing together engines for circle track racing , was to use a “ balance scale” . I borrowed one from my school science class. Take a piston off the rod and weight it against the new one. If the new one is heavier , some material can be removed to make it the same weight. If it’s lighter , well you can’t really add weight easily! This is how I used to “ backyard “ balance our racing engines! lol, poor folks have poor ways. I can’t really help you on the limits of the differences in weight. PS: there is great deal on a really good balance scale on E-Bay right now. $34 for an old quality one! But shipping will be more than the purchase price! Lol Bones
Even if the new replacement piston is heavier, if you have a good scale, you can remove some metal from the bottom of the piston pin boss, match it to the other pistons. The amount you remove, will be negligible. In the old days, I used a balance scale to match my rotating parts, both pistons and rods. The rods were done by matching the small ends to the lightest rod, and then doing the same with the big ends. Poor man's balancing. Bob
My grandfather says when he was working as a taxi cab fleet mechanic after WWII, they would on-car bore single cylinders, and put an oversize piston in just that hole. Balance? What's that. If the car was not moving, it was not making money.
Stock replacement oversize pistons are the same weight as standard size. Here's info from Ford, but is typical of US manufacturers.
Seen some old footage of US v8s being assembled. Guys pulling parts out of a bin and tossing them together. Watched a Ferrari engine put together at the factory.(video) One guy measuring and assembling precise parts. Gm probably assembled a few thousand engine during the time the Ferrari was assembled. what’s the point? I guess US manufactures left enough slop so us backyard builders can keep driving our crap. If ya want to twist up a bunch of RPMs, ya better build it like that Italian guy. Had a f100 that was bought with a slung rod, bought a piston and rod, rehoned, add some rings and bearings. Put a100k on the 6. What’s the moral of the story, don’t ask me to build your Ferrari engine.
Dan if you look at the picture in post #86 you will see some cone shaped pieces beside the unit. The piston is held by a chuck at the ring lands and the cone is held in the upper fixture and is adjusted down to fit inside the skirt to back it up. You need to be careful with slipper skirt pistons.
Gimpys correct, & that was std practice most everywhere from probably the 20's 'till at least the late 60's. This wasn't hi-po building, it was needed maintenance. & the practice worked well for the engines n clientele is served. & that practice led to the bragging about " the block's never been out of the chassis" . Was a big damn deal for a long time. JS, unless the slug is made from lead, it'll be very close to factory balance of the day. Not TODAY's specs, but say, 70's... It'll work well. Marcus...
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