Purchased a d722 aftermarket replacement piston online. I decided to weigh the parts to see if they were the same. It turns out that the new piston was about 20 grams lighter. The weight of 2 us quarters difference. Mostly in the wrist pin. I was going to use my old wrist pin and it would have got me within 3 grams, acceptable to me. It happened to be almost 1 thousandths larger than the new pin. I went ahead and ordered a new kubota piston. Had I have used the aftermarket piston and pin I would have been a little loose at the rod end.
Beware of aftermarket pistons
- Thread starter Muggman
- Start date
Make sure you do the same thing with the kubota parts. Don't assume the weights will be the same. really 20 grams isn't much in the big picture not at the low rpm these engines spin. I'd be more concerned with the pin end.
Good catch on the iffy piston! There's a very short list of sources I'd buy Kubota parts from online, Messick's being one of them.
I'd stay well away from the jungle place and their third-party merchants.
I'd stay well away from the jungle place and their third-party merchants.
I ordered 1 from messicks before I posted. They didn't have one in stock. Cost $30 extra dollars to have it drop shipped to me from bota.
Ugh. Well better than having to do the job twice. Or having a questionable piston come apart at full load....
Would you care to share the name of the business you bought the original piston from? I can't see that doing so would open you up to liability and it could save adventurous other members from trying their luck with that supplier. Maybe someone will discover a good supplier?
A friend who works for a global quality assurance complany recently returned from China, and says that generally, aftermarket goods from there are either very good quality, or very poor, there's no in-between.
A friend who works for a global quality assurance complany recently returned from China, and says that generally, aftermarket goods from there are either very good quality, or very poor, there's no in-between.
Short story, my uncle has a G4200. Bought it with oit seeing it run. Needles to say it would start but had zero power. After doing several checks we found it was rather low on compression on one cylinder. Pulled it apart, broken ring muffed up the cylinder. Found out kubota at one time offered over sized pistons but for some reason the dealer couldn't come up with a good number for them. Ended up getting an aftermarket rebuild kit. Came with pretty much everything you needed, you let them know the over size for pistons and bearings. Got the kit, I was fairly suspect of it. Bored the cylinders slapped it together. Not really thinking it would last. The company we (he) got the kit from didn't even bother to hide it was made in China. It's been several years since we rebuilt it. Never bothered to weigh the pistons, the pin bore was within allowable tolerances, so we're the rod and main bearings. Still going strong. I'm no professor of aftermarket parts but they arnt all junk and factory parts can and do vary with production runs.
I think that all the d722 pistons on ebay are made by the same supplier and just packaged differently. Atleast the all look the same.
TheOldHokie
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What am I missing here? I believe that piston and rod is full float design. You would normally replace the rod small end bushing along with the piston and pin and hone the new bushing to fit the new pin.
Dan
After looking at the WSM for that engine I see the factory tolerance on the pin OD is +/- .0005 and the max factory rod clearance is .0015. Assuming worst case tolerance stackup the aftermarket pin would give you .00025 rod clearance which is less than half the allowable max of .0059. Assuming best case stackup the clearance comes out very close to the factory max of .0015. It might not be quite as good as OEM but its well within the acceptable range
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My engine had 54 lb of oil pressure. It HD 2 broke ring lands on the number 1 piston. Compression was 160 to 200. The other 2 had over 400lb. I just wanted to fix the engine and not rebuild,because I don't have history of how it was treated. Started to buy a used piston because it would have matched the other 2. I believe it sit up and stuck. When the starter was hit it broke the ring lan
The engine doesn't have alot of wear. I don't have tools to replace a almost perfect bushing. If I did, it would still be out of balance on that 1 cylinder with the new parts. (The weight of 2 us quarters.) That's unacceptable to me, is what you're missing. Would it run, yeah.
The math side is. I gave $60 dollars for a aftermarket piston to save $40. I ended up giving $100 for a bota piston and $30 to have it dropped shipped. Unless I get my money back for aftermarket piston I will have spent $190 for a piston that I could have had 2 weeks ago and no bs, and still had the $90. I'm just trying to helpsomeone else weigh their options
You do realize at the max rpm of this engine 20 grams will never matter? Don't get me wrong it's your engine, do whatever you want but it's not a high rev engine. But don't go saying you tried to be cheap and the aftermarket piston you bought it garbage. There's no reason other then your overly picky that it won't work.
TheOldHokie
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Not to mention you can lighten the piston-rod assembly. Engine builders do it every day.
My point was you need to look at clearances not just individual dimensions. The allowable variance on a factory pin is almost a thousandth and i would guess pins and pistons are selective fit.
Dan
Yep... we balanced rotating assemblies at the machine shop, very cool thing to be part of. Never did it myself but got to help with it a few times. Was actually interesting to see what mfg did and didn't worry about balance wise.
That's the same thing the Taiwanian technician said. Just saying for $40 more i could have done it right the first time. Maybe there's more people out there like me.
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North Idaho Wolfman
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