2014 pro rmk 800 cylinder wear marks

[05rmksteve]

What would cause these rings at the top of the cylinder bore on both sides bad plating? This cylinder was re-plated about 3-400 miles ago. I've worked on quite a few of these motors and this is the first 1 that I recall having these rings at the top of the bore. This is on my sons boosted 2014 pro rmk 800 that seized on him this season, upon tearing it down I found a broke piston skirt. When I rebuilt this motor back in 2019 I had the cylinder re-plated, rebuilt crank, and did a fix kit with spacer plate. I ran it for about 100-150 miles then installed the turbo. This was my spare/loaner sled so it didn't get used much, then my son bought it from me and only got a couple rides on it before it went down. I did run a hone through them to clean them up a little.

 

[Sheetmetalfab]

Looks like that's how far up the piston rings go before returning downward.

 

[05rmksteve]

That's what it looks little to me also. But why is it wore so bad? Excessive side load at or towards TDC? I have 4 other cylinders with a lot more miles on them that don't have any wear marks like this one does at the top.

 

[Sheetmetalfab]

That's what it looks little to me also. But why is it wore so bad? Excessive side load at or towards TDC? I have 4 other cylinders with a lot more miles on them that don't have any wear marks like this one does at the top.

If the piston skirts are collapsed the piston rock could make those marks.

Can you catch them with a fingernail?

 

[05rmksteve]

I need to measure the 1 good piston to see if its collapsed. You can definitely feel that there's a difference. Can't catch them with finger nail but can feel the grove.

 

[Lawnmower]

Water intrusion from intake or coolant getting into cylinder?

 

[RHODESIE]

Definately piston rock. I’ve seen those pistons collapsed over .008”.

 

[05rmksteve]

I used a different brand of fix kit than I usually use. I usually install the bikeman durability kit on theses but on this 1 I tried a different brand that uses spi pistons. Lesson learned! Sense it's going to be boosted again ill probably ditch the fix kit and go with oem pistons. If I knew it was going to be boosted from the get go I wouldn't have done the fix kit.

 

[ditch1000]

I picked up a 2014 Pro last fall in a farmers field find; it had a grenaded engine. I picked up a good bottom end for cheap and got a fix kit from Georgian Bay Motorsports in Ontario; they used the Pro-X M8 pistons. That sled pulls like an absolute train!!
I’ve made pulls on that sled that I did not try on my old 2012 Pro Rmk with the RK TEK kit with a high compression head, 3” track, etc; and that sled ran awesome!!
I am very impressed and pleased with the kit!!

 

[BeartoothBaron]

Huh, I've wondered about SPI's fix kit. I've got SPI hyperdrive pistons on my long-rod 800, and it's run strong for at least 300 miles now. I haven't peeked into the bores lately; I need to do that, I suppose. What version of SPI pistons were you running on that? Hyperdrive is a different alloy - maybe hypereutectic? But a lot of cast pistons are actually hypereutectic these days - I think including most OE two-stroke pistons. All I can find is "HyperDrive Piston line is made from a space-age aluminum alloy which maintains it's high tensile strength up to 7000F (3800C), 50% higher than a conventional cast piston." I'm not sure how it maintains its strength at 4500F over the highest melting point of ANY aluminum alloy, so that statement is pretty useless other than (hopefully) meaning it is a stronger alloy.

After seeing marring to the freshly-plated bores from forged pistons (Wossner - I've heard it's not uncommon, and "not a problem," but if the cast pistons hold up and don't do it, that's a no-brainer), I'm sticking with cast, and preferably OE. That's what's going in my 600 when I get a chance - those are still Elko, made in Austria, and if that's the case with the OE 800 pistons, I'd say it's worth the money on a fresh build (long-rod, if cost is no object). I just didn't want to spend twice as much for OE pistons with already-marred bores, that's why I swapped to the SPIs. There's a bit of "what I've got is best" in that, I'll admit, but it seems the fix kits are a band-aid - they reduce piston excessive piston rock that wouldn't be there to begin with using longer rods. Anyway, just my thoughts on it; you know more about it than me, Steve. I do think OE pistons are the best quality, but fix kit pistons might last longer, plus it's a harder choice to spend that money when the bores aren't pristine and they might not last any longer because of that.

 

[05rmksteve]

I dont recall who I got the kit from. Might have been from Utah crankshaft or MCB. I've ran the hyperdrive pistons in other sleds before and have had good luck with them. I've decided I'm going to ditch the fix kit and run wossner oe style pistons since it's still going to be boosted. Going to send the cylinder out to get re-plated and have them take a look at it to make sure its not an issue with the cylinder or coating from the last time it was re-plated. With the cost of re-plating now I want to make sure everything is good and this won't happen again.