# Can these pistons be repaired?



## waterant (2 mo ago)

hi guys,

we removed and cleaned the pistons from Yanmar 6LY and they look pretty good on all sides except the top


















3 of the pistons have nasty pitting in the piston bowl, which i found after cleaning a lot of carbon on top of them.
Below is the worse of them. One has very small pits and another one has one large crater ~ 1/4" in dia and 1/8" deep.




  









Do you know if this is from the rust (the engine got water into the cylinders at some point) or was this caused by melting because of an incorrect injector spray pattern?
If this is from the rust, strange why those were covered by a layer of very strong carbon, which took a few days to remove in different chemicals.

Can this be repaired by aluminum welding and sending or those are junk? 
Each piston is $670 USD and this, so far, will be the biggest expense in the whole rebuild.

Thank you


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## BinVa (Sep 21, 2020)

Personally I'm a it's either 'good or gone' guy. The 1 piston shows the ring groove is compromised and subject to failure. Any balance and equal compression is lost due to the surface irregularities. It sounds like an expensive rebuild but the benefits of engine longevity may be worth the money. You have it torn down, so that time is already invested. Only you can answer whether the cost is worth it. When I rebuild I prefer to replace anything questionable for a 1 and done result. What do the cylinder walls look like? Are there any pitting or hot spots? To me it appears there has been dirty fuel/water in it. Tho I'm no expert, only someone who maintains/repairs' their own equipment. B.


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## waterant (2 mo ago)

I guess you are right. If a piston will fail on me, the whole engine will probably be junked.

This engine has cylinder sleeves and the rings got rusted to the sleeves so those will have to be replaced for sure. I was hopping to reuse the pistons at least.


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## BinVa (Sep 21, 2020)

Not familiar with that particular engine, but depending on the extent of rust and general condition on the sleeve walls..a light hone may clean them up. B.


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## Vigo (Oct 8, 2021)

I personally would run those on my own equipment. Doesnt look structural and the ring grooves are not involved although i see something at the top edge that made me think there was a ring groove there at first so i can understand that thought. The damage on the top is not really much different from the punch marks on the bottom in terms of expecting it to eventually cause a piston to fail (it wont). Id be more concerned about whether any ring grooves were way out of spec, than what the top looks like. Just my .02.


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## bmaverick (Feb 20, 2014)

waterant said:


> I guess you are right. If a piston will fail on me, the whole engine will probably be junked.
> 
> This engine has cylinder sleeves and the rings got rusted to the sleeves so those will have to be replaced for sure. I was hopping to reuse the pistons at least.


Since the engine is used on a marine vessel and not a tractor, being stranded out at sea is far worse than a machine out in the field. 

Glad your engine has sleeeeeeeeevvvvvvveeeeeeessss. Not all Yanmar engines have this. Un-sleeved engines with wear or scratches on the cylinder walls or bad bearings on the cam can lead to egg shaped cylinders. Not so much with sleeves. 

There are a few YT vids on how to replace sleeves. I've only done the keep the, block cold and the sleeves in the freezer for 72 hours. Then placing the new cold ones into the block becomes super easy. 

BTW, did you dimple the backs of the pistons for what cylinder the came out of or did Yanmar? 

Do you have pixs of how the rings were stacked on the pistons too? Some of these engines require a certain placement for each ring to allow oil at one level and air pressure thru the others. Some are staggered and others not. Depends on the engine manufacture.


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## Longbow (Apr 28, 2016)

Did I notice where you said replacement pistons were $670 each? Wow! Have you considered trying to locate a used engine? There are several farm equipment salvage yards throughout the country. A search on the web can reveal names, location, and toll-free phone numbers. You might be surprised at reasonable prices for used engines. Many times, the seller will know the hours on the tractor and most offer a guarantee. I've had good luck with used tractor parts. Sure hope all works out for you.


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## Busted Tractor (May 22, 2018)

Those pits were probably caused by water. Any water in the cylinder during combustion turns to steam, then it attacks the cylinder head and pistons. I have seen some heads and pitons that have been peppered with pits. Fixed the water problem and put them back together.
If you notice that part of the piston is thick, it would take a lot to burn thru. Personally I would be more concerned with the ring lands and ring fit than those pits. But would be sure timing and injector pattern is correct. I overhauled a 3208 cat that had a bad injector that had burned thru the top of the piston, and the top of the piston had broken off with only the skirt of the piston moving.


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## bmaverick (Feb 20, 2014)

waterant said:


> Can this be repaired by aluminum welding and sending or those are junk?
> Each piston is $670 USD and this, so far, will be the biggest expense in the whole rebuild.


Before reworking the piston heads, it would be best to take measurements of the piston and contact the parts network for Yanmar Ag products for a matching piston. 

For an entire Yanmar engine rebuild kit we pay around $750. This includes the pistons, rings, gaskets, bearings, etc. 
Yanmar 3T80J Engine Rebuilt / Overhaul Kit - 0 - John Deere Compact Tractor Parts 

IF the marine Yanmar engine has the same pistons, then just double the price of the kit for all six cylinders. Weavers has several kits to compare and review. 

For the Ag Yanmar engines, it's neat to find the info.
Example is a 3T80
3 = number of cylinders
T = engine family
80 = piston diameter 

It's a start for you to find replacements at a reasonable cost.


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