Beware of aftermarket pistons

[Muggman]

So the question is why didn't you go oem the first time?

I could get the aftermarket cheaper, easier and quicker. It all come back to haunt me.

 

[Muggman]

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.

Years ago we would put $12 each pistons in small block Chevrolet and turn them till the valves floated or the hydraulic lifters quit pumping up. They probably lasted about the equivalent of 2500 miles if that.

 

[TheOldHokie]

Do you know what crankshaft bobweight is?

I do. Do you know that 1.2% of the US population suffers from some form of OCD? Strangely enough certain forms can be alleviated with a die grinder.

Dan

 

[North Idaho Wolfman]

Do you know what crankshaft bobweight is?

Yes, and really not relevant to these engines due to in part their short stroke and low RPM.
I personally never just change out one piston, my main reason is if one failed the others might be right behind them!

 

[Dieseldonato]

Years ago we would put $12 each pistons in small block Chevrolet and turn them till the valves floated or the hydraulic lifters quit pumping up. They probably lasted about the equivalent of 2500 miles if that.

So you abused the engine and the pistons failed. You do realize your working on a low speed diesel engine, right?

 

[Dieseldonato]

I could get the aftermarket cheaper, easier and quicker. It all come back to haunt me.

No, nothing has come back to haunt you. You should be replacing all the pistons as wolf man has said. You have no idea what this batch of pistons weigh from the oem. What are you going to do when they are off from the originals? Start a thread and bash kubota pistons? Metallurgy changes and with those changes weight can be effected as well. Just like no 2 batches of pistons made are exactly the same. Not a race engine. Just a little diesel.

 

[TheOldHokie]

No, nothing has come back to haunt you. You should be replacing all the pistons as wolf man has said. You have no idea what this batch of pistons weigh from the oem. What are you going to do when they are off from the originals? Start a thread and bash kubota pistons? Metallurgy changes and with those changes weight can be effected as well. Just like no 2 batches of pistons made are exactly the same. Not a race engine. Just a little diesel.

If you are building a F1 engine matching crankshaft bobweight to new pistons and rods is critically important. But many thousands of everyday car, truck, and tractor engines are professionally rebuilt using after market pistons without rebalancing the crankshaft. Everyday engines and expecially low revving tractor engines don't really care.

Dan

 

[Muggman]

So you abused the engine and the pistons failed. You do realize your working on a low speed diesel engine, right?

Yep, correct, but if I use the aftermarket pistons I would have to rebushing all the rods, for the same money I could have just bought the bota pistons. I purchased the tractor at a parts tractor price. It has alot of leaks also. If it was a mint tractor I would have rebuilt the entire engine. I started the thread to let others be aware of there options, that's all. I KNOW as for as I've got it down it would beto smart to put new pistons and rings in. Over er 400lb compression on the other 2 cyl holding me back. It's a 100 degrees in my shop now don't help matters.

 

[hagrid]

I know what a bobwhite is.






Chirp.

 

[Muggman]

If you are building a F1 engine matching crankshaft bobweight to new pistons and rods is critically important. But many thousands of everyday car, truck, and tractor engines are professionally rebuilt using after market pistons without rebalancing the crankshaft. Everyday engines and expecially low revving tractor engines don't really care.

Dan

Totally off topic and not asking for comments. Just a old story from my past as a teenager. We got to racing Go-Karts but didn't have the money to be competitive but it was still the same amount of fun. I took a old tiller engine and had the carb. bored larger all the way thru. used a penny I think for the throttle blade. Welded up the pushrods to make them longer which was common. Took the original cam ground the thing on homemade cam grinder. Bought a aftermarket rod. The first time out it turned so many rpm, it siezed the crankshaft down in the sideplate. Went home, beat the side plate off, sanded the aluminum off the crankshaft. I got another used sideplate drilled the oilsupply hole larger and funnel ported everything to the oil hole. I took a hacksaw blade and cut a groove in the nonload side of the crankshaft bushing for oil. Neverhad a problem after. Now days you can buy a better engine at harbor tool. It sound like a two stroke. They never protested me because I didn't win, but I had a heap of fun

 

[TheOldHokie]

Totally off topic and not asking for comments. Just a old story from my past as a teenager. We got to racing Go-Karts but didn't have the money to be competitive but it was still the same amount of fun. I took a old tiller engine and had the carb. bored larger all the way thru. used a penny I think for the throttle blade. Welded up the pushrods to make them longer which was common. Took the original cam ground the thing on homemade cam grinder. Bought a aftermarket rod. The first time out it turned so many rpm, it siezed the crankshaft down in the sideplate. Went home, beat the side plate off, sanded the aluminum off the crankshaft. I got another used sideplate drilled the oilsupply hole larger and funnel ported everything to the oil hole. I took a hacksaw blade and cut a groove in the nonload side of the crankshaft bushing for oil. Neverhad a problem after. Now days you can buy a better engine at harbor tool. It sound like a two stroke. They never protested me because I didn't win, but I had a heap of fun

So in summary you know what needs to be done and how to do it but you would rather complain about inconsequential differences in perfectly good aftermarket parts.

Dan

 

[Dieseldonato]

So in summary you know what needs to be done and how to do it but you would rather complain about inconsequential differences in perfectly good aftermarket parts.

Dan

BINGO!

 

[Muggman]

I

So in summary you know what needs to be done and how to do it but you would rather complain about inconsequential differences in perfectly good aftermarket parts.

Dan

If you go back and read the original post., you will see I never made a negative comment. I just stated what the facts were. Anything remotely negative came from other people. Only posted for information purposes. Nobody does everything right. I just finished some nice running boards with harbor tool non slip material and would like to post pics. I'm threw with this post. If anyone can contact the moderator they can delete my post and/or account(they have my permission). All I've got since joining is a verbal handjob instead of a welcome to the forum. If I want drama i'll watch TV. Also, got the bota piston in today. Thanks for the input everyone.

 

[Dieseldonato]

I

If you go back and read the original post., you will see I never made a negative comment. I just stated what the facts were. Anything remotely negative came from other people. Only posted for information purposes. Nobody does everything right. I just finished some nice running boards with harbor tool non slip material and would like to post pics. I'm threw with this post. If anyone can contact the moderator they can delete my post and/or account(they have my permission). All I've got since joining is a verbal handjob instead of a welcome to the forum. If I want drama i'll watch TV. Also, got the bota piston in today. Thanks for the input everyone.

Did you weigh it?

 

[GreensvilleJay]

Hay Muggman, I APPRECIATE your post ! I would have done the same as you, buy the aftermarket piece and if it fits proper, pat myself for saving a few bucks and getting the machine 'up and running'. I do wonder ifsome(most, any ?) of the posters have torn THEIR engine completely apart and rebuilt using ONLY Kubota parts ? It's one thing to be an 'armchair mechanic' another to actually turn wrenches.
What I get out of this is that for really CRITICAL parts, it's 'probably' best to use OEM parts. Course that opens up a huge can of worms ,like 'is an air filter 'critical' part' ?
The only thing keeping me from rebuilding the Buda diesel in my forklift is not KNOWING which ring sets to buy. There's a 3pc set AND a 4pc set !!! Since oil and diesel are still 'kinda' cheap,I'll just keep running it 'asis'.
BTW WELCOME to the Forum !!!

Jay

 

[hagrid]

Hay Muggman, I APPRECIATE your post ! I would have done the same as you, buy the aftermarket piece and if it fits proper, pat myself for saving a few bucks and getting the machine 'up and running'. I do wonder ifsome(most, any ?) of the posters have torn THEIR engine completely apart and rebuilt using ONLY Kubota parts ? It's one thing to be an 'armchair mechanic' another to actually turn wrenches.

I belong in the "completely dismantled and rebuild" population.

What I egg-spect from OEM parts is stringent quality assurance so I dont have to wonder the imponderables.

Such hits as:
- is the part in tolerance?
- does the part contain internal defects from melt/hot work excursions?
- will I have support if I use OEM but something unforeseen arises?

I understand and participate in thrift but there are limits.

 

[Muggman]

Hay Muggman, I APPRECIATE your post ! I would have done the same as you, buy the aftermarket piece and if it fits proper, pat myself for saving a few bucks and getting the machine 'up and running'. I do wonder ifsome(most, any ?) of the posters have torn THEIR engine completely apart and rebuilt using ONLY Kubota parts ? It's one thing to be an 'armchair mechanic' another to actually turn wrenches.
What I get out of this is that for really CRITICAL parts, it's 'probably' best to use OEM parts. Course that opens up a huge can of worms ,like 'is an air filter 'critical' part' ?
The only thing keeping me from rebuilding the Buda diesel in my forklift is not KNOWING which ring sets to buy. There's a 3pc set AND a 4pc set !!! Since oil and diesel are still 'kinda' cheap,I'll just keep running it 'asis'.
BTW WELCOME to the Forum !!!

Jay

THANKS, That's what a reply should look like.

 

[Dieseldonato]

Hay Muggman, I APPRECIATE your post ! I would have done the same as you, buy the aftermarket piece and if it fits proper, pat myself for saving a few bucks and getting the machine 'up and running'. I do wonder ifsome(most, any ?) of the posters have torn THEIR engine completely apart and rebuilt using ONLY Kubota parts ? It's one thing to be an 'armchair mechanic' another to actually turn wrenches.
What I get out of this is that for really CRITICAL parts, it's 'probably' best to use OEM parts. Course that opens up a huge can of worms ,like 'is an air filter 'critical' part' ?
The only thing keeping me from rebuilding the Buda diesel in my forklift is not KNOWING which ring sets to buy. There's a 3pc set AND a 4pc set !!! Since oil and diesel are still 'kinda' cheap,I'll just keep running it 'asis'.
BTW WELCOME to the Forum !!!

Jay

There's way more aftermarket parts in heavy duty diesels then you can shake a stick at. Quality aftermarket parts. You go back to the dealer everytime you need something for your vehicle? Guessed you missed the cat 3500 exhaust valve issues years ago, the bad oem rods from Detroit, clearance issues on dt466e liners. C-16 pistons with the bad coating in the pin bore. The list is actually exhaustive, and normally goes unnoticed unless your the one dealing with the aftermath. And guess what, the oem has the same crappy parts warranty most aftermarket companies have. 6 month (if that) however many hours or miles. I've built tons of engines, both with oem and aftermarket. But I guess you also buy everything for your vehicles from the dealer as well. Good on you.

 

[Muggman]

There's way more aftermarket parts in heavy duty diesels then you can shake a stick at. Quality aftermarket parts. You go back to the dealer everytime you need something for your vehicle? Guessed you missed the cat 3500 exhaust valve issues years ago, the bad oem rods from Detroit, clearance issues on dt466e liners. C-16 pistons with the bad coating in the pin bore. The list is actually exhaustive, and normally goes unnoticed unless your the one dealing with the aftermath. And guess what, the oem has the same crappy parts warranty most aftermarket companies have. 6 month (if that) however many hours or miles. I've built tons of engines, both with oem and aftermarket. But I guess you also buy everything for your vehicles from the dealer as well. Good on you.

It's 89 degrees in my house right now. I tight aced enough to pick up a brand new 12,000 btu window unit today at dinner. It was probably 120f in my shop. U always got to know the other guys pain. I'll address the a/c later. It wasn't the deal breaker on a complete overhaul but a small point.

 

[Muggman]

Did you weigh it?

Used broke kubota-242.56 grams
New kabota oem-239.89
New aftermarket-234.68
Used kubota pin-86.35
*New aftermarket pin-70.83
Oem piston pin combo-328.91
New oem combo-325.24
Aftermarket combo-305.51
1 US quarter-5.68 = 4 quarters difference almost.
I tried to be very fair and put the smallest pop rivet in with the broke piston, to account for the small piece of missing ring land. Most of the difference was due to wrist pin weight. But the pins are different diameters.