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What would cause this (photos attached)? The engine powers a 15 year old zero turn that gets worked pretty hard 3 months out of the year.

I'd like to understand the failure mechanism here so I can avoid (or delay) it with the new engine I'll have to put into this machine.

I've never seen that, i would say lack of lubrication and overheating due to lack of airflow

Scrubcadet10 said:

I've never seen that, i would say lack of lubrication and overheating due to lack of airflow

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Yea, the fact that both cylinders experienced delamination of the nikasil cylinder wall coating suggests either or both overheating and lubrication failure.

I'm trying to decide between a short block or a complete engine. Heads looks good, but they are 15 years old, like everything else on the engine. Given the likelihood of prolonged overheating and/or lubrication failure(s), maybe complete engine is the way to go despite the steep price.

Riddler said:

both cylinders experienced delamination of the nikasil cylinder wall coating suggests either or both overheating and lubrication failure.

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Wow !! I don't see what else could explain that..

Riddler said:

Yea, the fact that both cylinders experienced delamination of the nikasil cylinder wall coating suggests either or both overheating and lubrication failure.

I'm trying to decide between a short block or a complete engine. Heads looks good, but they are 15 years old, like everything else on the engine. Given the likelihood of prolonged overheating and/or lubrication failure(s), maybe complete engine is the way to go despite the steep price.

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I am betting on overheating, but after 15 years who knows. Could of been just time and the coating started delaminating. Anyway. Here is something to consider Short block is a 90 day warranty whereas a new Kohler Command is a 3 year warranty.

ILENGINE said:

I am betting on overheating, but after 15 years who knows. Could of been just time and the coating started delaminating. Anyway. Here is something to consider Short block is a 90 day warranty whereas a new Kohler Command is a 3 year warranty.

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The engine powers a MTD PRO Z 2560 zero turn mower. The complete engine for that machine is discontinued. For that reason, I'm thinking I have no choice but to find a short
block that works and go from there. I figure a
complete replacement engine designed for another machine won't interface correctly with this make and model. Is that a correct assumption?

The main concern when replacing engine is crankshaft diameter and length. If staying within the same series of engine say going kohler command to kohler command then things are fairly simply. Changing brands or series can get interesting but in most cases can be doable. I was trying to see what was available in that size engine and looks like almost al the engines in the range are set up with the cyclonic HD air cleaner not like your more pancake style filter but if room permits isn't really a big deal either.

Looks like you have found a short block used on your current engine. My distributor doesn't show any in stock so may be hard to track one down

ILENGINE said:

The main concern when replacing engine is crankshaft diameter and length. If staying within the same series of engine say going kohler command to kohler command then things are fairly simply. Changing brands or series can get interesting but in most cases can be doable. I was trying to see what was available in that size engine and looks like almost al the engines in the range are set up with the cyclonic HD air cleaner not like your more pancake style filter but if room permits isn't really a big deal either.

Looks like you have found a short block used on your current engine. My distributor doesn't show any in stock so may be hard to track one down

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If you have time, source a good used suitable replacement.

ILENGINE said:

The main concern when replacing engine is crankshaft diameter and length. If staying within the same series of engine say going kohler command to kohler command then things are fairly simply. Changing brands or series can get interesting but in most cases can be doable. I was trying to see what was available in that size engine and looks like almost al the engines in the range are set up with the cyclonic HD air cleaner not like your more pancake style filter but if room permits isn't really a big deal either.

Looks like you have found a short block used on your current engine. My distributor doesn't show any in stock so may be hard to track one down

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I'm willing to go with a complete engine if it won't present problems hooking up to the existing cables or wiring harness. When I research availabilty, complete CV-730 engines (which I understand replaced the CV-725 I have) seem tied to make and model of mower. The complete engine for my mower shows as "discontinued." What would be the trick to ordering a complete engine that I would have the least (if any) modifications to install?

Tiger Small Engine said:

If you have time, source a good used suitable replacement.

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I have checked on that currently. No luck. I wouldn't mind picking up the whole mower if it has low hours. Having a 2nd for parts would be nice. Saw I missed out on a really nice machine out-of-state that sold last April. I realize now that I should have been more proactive being on the look out for a 2nd unit.

CV25 with nickasil cylinder liners? Never saw a CV25 with that all I have ever seen have cast iron liners.

hlw49 said:

CV25 with nickasil cylinder liners? Never saw a CV25 with that all I have ever seen have cast iron liners.

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I was surprised to, but that's why posted the photos. The delamination is interesting, to
say the least.

FWIW, I found this from a Kohler publication:

"Some CH25-26 engines feature POWER- BORE™ cylinders a special patented nickel- silicone plating process for increased power, superior oil control, reduced exhaust
emission, and virtually permanent cylinder life. POWER-BORE™ cylinders cannot be resized or honed as described in the following procedure. If a plated cylinder bore is damaged or out of specification, use a new
miniblock or short block to repair the engine."

Riddler said:

I'm willing to go with a complete engine if it won't present problems hooking up to the existing cables or wiring harness. When I research availabilty, complete CV-730 engines (which I understand replaced the CV-725 I have) seem tied to make and model of mower. The complete engine for my mower shows as "discontinued." What would be the trick to ordering a complete engine that I would have the least (if any) modifications to install?

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The CV732-3014 or CV742-3022 which are both spec'd for Scag. so may need to do a little more research. Looks like crank dimensions are correct. 6 pin wiring harness should be the same connections.

Riddler said:

I was surprised to, but that's why posted the photos. The delamination is interesting, to
say the least.

FWIW, I found this from a Kohler publication:

"Some CH25-26 engines feature POWER- BORE™ cylinders a special patented nickel- silicone plating process for increased power, superior oil control, reduced exhaust
emission, and virtually permanent cylinder life. POWER-BORE™ cylinders cannot be resized or honed as described in the following procedure. If a plated cylinder bore is damaged or out of specification, use a new
miniblock or short block to repair the engine."

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It says some CH25-26 engines. Those are horizontal shaft engines. Did it also say CVs as well?

Don't know if they do Kohler engines or not you may want to check this out. https://millennium-technologies.com/cylinderrepair/

ILENGINE said:

The main concern when replacing engine is crankshaft diameter and length. If staying within the same series of engine say going kohler command to kohler command then things are fairly simply. Changing brands or series can get interesting but in most cases can be doable. I was trying to see what was available in that size engine and looks like almost al the engines in the range are set up with the cyclonic HD air cleaner not like your more pancake style filter but if room permits isn't really a big deal either.

Looks like you have found a short block used on your current engine. My distributor doesn't show any in stock so may be hard to track one

Click to expand...

hlw49 said:

It says some CH25-26 engines. Those are horizontal shaft engines. Did it also say CVs as well?

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TBH, I can't recall if it mentioned CVs as well. I think I found the statement in a CH repair manual.

Wiki says this in their write up on nikasil:

"The coating was further developed as a replacement for hard-chrome plated cylinder bores for Mercury Marine Racing, and Kohler Engines . . ."

I also came across some mention in an online Q&A with a small engine performance shop that Kohler and others dabbled in plating beginning in 2002. The mower that this CV powers is an early 2000s MTD Pro.

I figure that if Kohler was doing it on the CH, they probably did it on the CV. Regardless, as you can see from the photos that are part of my initial post, the cylinders in this engine are definitely coated, not iron sleeved. The coating in both cylinders has delaminated. I bought the machine new 20 years ago. Full disclosure, I have misused and neglected it since day one (long story). I'm surprised it held up this long, lol. I'm in a better spot these days to care for the equipment, so if and when I get this mower running again, I'll treat it better.

Yes the same comment is in the CV25 service manual.

Kohler only used Nikasil on the early CV and CH 25 engines. The issue you have was typically caused by dirt ingestion. The Nikasil was supposed to stand up better to dirt ingestion but unfortunately it didn't. Kohler changed to cast iron liners on the 25 hp just like the rest of the Command series sometime in the late 90s if my memory serves me correctly.

Riddler said:

The complete engine for my mower shows as "discontinued."

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Do you have the original spec number of the engine? Should be 69XXX. MTD normally used a pretty basic spec engine so finding a replacement shouldn't be too hard. I have an engine comparison spreadsheet I can check if you can post the original engine spec number. The spreadsheet lets me compare everything from type of air filter and crankshaft to the type of charging system and wire harness.

Okay found your spec # in another post you made. This is what I found from my comparison spreadsheet. The big thing is would you have room for the Heavy Duty canister style air filter. It shows your original engine had a WAWB air filter system which stands for Wide Area Walk Behind.

I found a CV742-3016 that looks like a good replacement if you have room for the air filter. Same crankshaft and same wiring harness so should pretty much drop right in. The CV742-3016 is current production and shows in stock at distributors in St. Louis, Memphis and Kansas City.

VegetiveSteam said:

Do you have the original spec number of the engine? Should be 69XXX. MTD normally used a pretty basic spec engine so finding a replacement shouldn't be too hard. I have an engine comparison spreadsheet I can check if you can post the original engine spec number. The spreadsheet lets me compare everything from type of air filter and crankshaft to the type of charging system and wire harness.

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I do. Here is a pic of the engine tag:

I've added some info to my previous post if you want to look at it again.

VegetiveSteam said:

I've added some info to my previous post if you want to look at it again.

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I see what you added. That is terrific. There is no space limit on the air cleaner. I was prepared to make necessary modications to the wiring harness (figured at minimum that the newer engine uses different connectors than the old one), but maybe not (fingers crossed).

It may take me a few weeks to get the swap completed, but I'll report back when I'm done.

Thanks again for the valuable input.

Riddler said:

I see what you added. That is terrific. There is no space limit on the air cleaner. I was prepared to make necessary modications to the wiring harness (figured at minimum that the newer engine uses different connectors than the old one), but maybe not (fingers crossed).

It may take me a few weeks to get the swap completed, but I'll report back when I'm done.

Thanks again for the valuable input.

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Yeah, same wire harness part number so it should plug right in with no modifications. Exhaust will fit fine too.

Is the damage on the bottom? closer to the exhaust valve? Crud packed on the outside from the area?

Same area on both sides?

Fish said:

Is the damage on the bottom? closer to the exhaust valve? Crud packed on the outside from the area?

Same area on both sides?

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Yea, one cylinder has damage to the very bottom of the bore, nearest to the where the exhaust manifold bolts on. In the photos I attached to my original post, it's easy to see.

The other cylinder, however, also has some damage to the lining, but it is located in the upper half of the bore. I posted a picture
of that cylinder too.

VegetiveSteam said:

Yeah, same wire harness part number so it should plug right in with no modifications. Exhaust will fit fine too.

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Thanks to all the helpful input in this thread, I found a new Kohler model that replaced the engine in my 20 year old mower perfectly. Pic below. Machine runs great now.