Worn pistons and rings

[Curlymurt]

I've known my KEC 340 had done unknowns. Prior to today, I had 3 leaking gaskets and the pistons had some scratches, though I didn't know the extent. I finally tore the entire engine apart to rebuild it. Disclaimer: I've never been this deep into any engine before so I'm not entirely sure what I'm doing, though I've consulted the manuals and Google.

I've found piston damage so I'm trying to figure out the best solution. The compression was still good, though one cylinder had lost a little if I remember correctly.

My dilemma is whether I should buy some 340 pistons and rings and install those, or is this a good chance to upgrade for more power? I know I'll have to bore the cylinders, which is where I'm afraid I'll spend the most money on this rebuild. It seems there was a KEC 400 that used similar parts to the 340.. maybe just a different cylinders/pistons. I'm not sure if the stator, or carb would need to change. I know the 440 would be an entirely different engine, though that'd be awesome to have.

Correct me if I'm wrong, but I believe the 340 has 58mm pistons, the 400 and 440 have 65mm?

[Curlymurt]

If these were yours, what would you do?

The sled is a rider... Not a show piece or restoration.

[Steven Rempel]

I would replace, with new pistons to match cylinders that have being freshened up. I am not a pro but those look really bad to me.

[Matt]

Those pistons are shot, and your cylinders are probably damaged too. This is a piston-port style engine. Deere did not have a 400cc version of this engine. You could swap it to 440cc just fine, but the 440 piston-port style pistons are getting hard to find. Oversized 340 pistons may also be tricky if you end up needing to bore the cylinders out, which you probably will.

[Curlymurt]

Yeah, that's what I've been worried about. I have searched and called machine shops for two days and I can't find any machine shops locally that are willing/able to bore or hone something this small. One cylinder head feels smooth, so it might be ok, unless it's worn a little larger than it should. I can feel a slight groove in the other, which I'm guessing is the side that had lower compression.

I've also tried finding the correct pistons and I'm striking out on that, too. There's so many variations of a 60mm 60mm that maybe I'm just missing them. I've also tried to find a pair that are oversized so I know how much I can have a shop take off.

[WinnipegStPaul9]

If you're a smoker they'd make great ashtrays.

DA

[snowkat79]

Correct me if I am wrong, but if you bore them.... ....dont they have to be replated too? Nikasil plated cylinders arent they? The pistons are shot. If the cylinders arent too bad, you may be able to get away with a light honing. Judging by the pistons, that is most likely not the case.

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[Curlymurt]

Haha, I'm not a smoker but the engineer will be... With the struggle of finding a small engine hone and pistons, I'm just going to run it into the ground and upgrade to a more powerful engine. It's back together and ready to go in. I think I've got the timing figured out using the flashlight method. I'll do a compression test once it's bolted to the chassis to see where I'm at.

One cylinder was good... One has a light gouge that would need bored, but that's a great question about replating them. I assumed it depended on how much came off, and then just rehoned.

[Matt]

Kioritz bores are not plated, I believe only the Kawasakis were.

[snowkat79]

Kioritz bores are not plated, I believe only the Kawasakis were.

Do they have steel sleeves or something? I am only familiar with the Kaw engines. I am assuming the cylinders are not just aluminum, they couldnt stand the wear of the rings.

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[400brian]

The Kioritz engine cylinders have a cast in place steel bore. There are 3 options; 1) replace with NOS jugs which will be specific to that model engine, and new standard pistons. 2) Have the jugs bored and Nicasil plated back to standard bore. Millenium Technologies in Wisconsin can do that, requires new standard pistons. 3) Have the jugs bored and re-sleeved. Most expensive option and requires new standard pistons. Any of these really require the crank to be freshened up for the best chance of success.

Or, you can clean things up and run it until it dies, it shouldn't take too long. To run 40 year old sleds requires a significant financial commitment, especially as parts are pretty much in the hands of collectors.

[jep_800]

Cylinder hones are easy.... You should be able to get them at Harbor Freight, Grainger, or a number of other places, like engine part websites. I got mine at Harbor Freight. I like the 3 stone medium to fine grit hones that operate on three spring loaded arms.

You said you can't find pistons? What about just putting some new rings on your pistons? If you honed the cylinders and put on new rings, it may last even longer. Could be worth a try if it makes it the rest of this season... do that work in your offseason.

[Curlymurt]

Interesting options here. I certainly thought about trying to wait and look around for NOS pains, but I won't treat them right... It's not a worthwhile and collectible sled and won't be.

I actually didn't even know trying to hone cylinders "at home" was even an option. I know what I'll be researching tonight...

[400brian]

One word of caution. By the looks of the pistons, you no doubt also have aluminum smeared on the steel bore of the cylinders. This needs to be removed. Muriatic acid ( a pool chemical ) is often used. Do not breathe the stuff, apply it carefully, like with a Q-tip, and neutralize it with baking soda and water. Lots of info on-line on the subject. If you do not get the aluminum off, the pistons will likely gall in the bores, and you will be back where you started.